dnsmasq man page on ElementaryOS

Man page or keyword search:  
man Server   4994 pages
apropos Keyword Search (all sections)
Output format
ElementaryOS logo
[printable version]

DNSMASQ(8)							    DNSMASQ(8)

       dnsmasq - A lightweight DHCP and caching DNS server.

       dnsmasq [OPTION]...

       dnsmasq	is a lightweight DNS, TFTP, PXE, router advertisement and DHCP
       server. It is intended to provide coupled DNS and  DHCP	service	 to  a

       Dnsmasq	accepts	 DNS  queries  and  either  answers them from a small,
       local, cache or forwards them to a  real,  recursive,  DNS  server.  It
       loads  the  contents of /etc/hosts so that local hostnames which do not
       appear in the global DNS can be resolved and also answers  DNS  queries
       for  DHCP  configured  hosts.  It can also act as the authoritative DNS
       server for one or more domains, allowing local names to appear  in  the
       global DNS.

       The  dnsmasq DHCP server supports static address assignments and multi‐
       ple networks. It automatically sends a sensible	default	 set  of  DHCP
       options, and can be configured to send any desired set of DHCP options,
       including vendor-encapsulated options. It includes a secure, read-only,
       TFTP  server  to	 allow	net/PXE	 boot  of DHCP hosts and also supports
       BOOTP. The PXE support is full featured,	 and  includes	a  proxy  mode
       which  supplies	PXE information to clients whilst DHCP address alloca‐
       tion is done by another server.

       The dnsmasq DHCPv6 server provides the same  set	 of  features  as  the
       DHCPv4 server, and in addition, it includes router advertisements and a
       neat feature which allows nameing for  clients  which  use  DHCPv4  and
       stateless  autoconfiguration only for IPv6 configuration. There is sup‐
       port for doing address allocation (both DHCPv6  and  RA)	 from  subnets
       which are dynamically delegated via DHCPv6 prefix delegation.

       Dnsmasq	is  coded with small embedded systems in mind. It aims for the
       smallest possible memory footprint compatible with the supported	 func‐
       tions,	and  allows  uneeded functions to be omitted from the compiled

       Note that in general missing parameters	are  allowed  and  switch  off
       functions,  for	instance  "--pid-file" disables writing a PID file. On
       BSD, unless the GNU getopt library is linked,  the  long	 form  of  the
       options	does  not  work on the command line; it is still recognised in
       the configuration file.

       --test Read and syntax check configuration file(s). Exit with code 0 if
	      all  is  OK,  or a non-zero code otherwise. Do not start up dns‐

       -h, --no-hosts
	      Don't read the hostnames in /etc/hosts.

       -H, --addn-hosts=<file>
	      Additional hosts file.  Read  the	 specified  file  as  well  as
	      /etc/hosts.  If  -h is given, read only the specified file. This
	      option may be repeated for more than one additional hosts	 file.
	      If  a  directory	is given, then read all the files contained in
	      that directory.

       -E, --expand-hosts
	      Add the domain to simple names (without a period) in  /etc/hosts
	      in  the  same way as for DHCP-derived names. Note that this does
	      not apply to domain names in cnames, PTR	records,  TXT  records

       -T, --local-ttl=<time>
	      When  replying  with  information	 from  /etc/hosts  or the DHCP
	      leases file dnsmasq by default sets the  time-to-live  field  to
	      zero,  meaning  that  the	 requester should not itself cache the
	      information. This is the correct thing to do in almost all situ‐
	      ations.  This  option  allows  a time-to-live (in seconds) to be
	      given for these replies. This will reduce the load on the server
	      at  the  expense	of clients using stale data under some circum‐

	      Negative replies from upstream servers normally contain time-to-
	      live  information in SOA records which dnsmasq uses for caching.
	      If the replies from upstream servers omit this information, dns‐
	      masq does not cache the reply. This option gives a default value
	      for time-to-live (in seconds) which dnsmasq uses to cache	 nega‐
	      tive replies even in the absence of an SOA record.

	      Set  a maximum TTL value that will be handed out to clients. The
	      specified maximum TTL will be given to clients  instead  of  the
	      true  TTL	 value	if  it is lower. The true TTL value is however
	      kept in the cache to avoid flooding the upstream DNS servers.

	      Set a maximum TTL value for entries in the cache.

	      Set the TTL value returned in  answers  from  the	 authoritative

       -k, --keep-in-foreground
	      Do  not  go  into the background at startup but otherwise run as
	      normal. This is intended for use when dnsmasq is run under  dae‐
	      montools or launchd.

       -d, --no-daemon
	      Debug  mode:  don't  fork	 to  the background, don't write a pid
	      file, don't change user id, generate a complete  cache  dump  on
	      receipt  on SIGUSR1, log to stderr as well as syslog, don't fork
	      new processes to handle TCP queries. Note that  this  option  is
	      for  use	in debugging only, to stop dnsmasq daemonising in pro‐
	      duction, use -k.

       -q, --log-queries
	      Log the results of DNS queries handled by dnsmasq. Enable a full
	      cache dump on receipt of SIGUSR1.

       -8, --log-facility=<facility>
	      Set the facility to which dnsmasq will send syslog entries, this
	      defaults to DAEMON, and to LOCAL0 when debug mode is  in	opera‐
	      tion. If the facility given contains at least one '/' character,
	      it is taken to be a filename, and	 dnsmasq  logs	to  the	 given
	      file,  instead  of  syslog.  If the facility is '-' then dnsmasq
	      logs to stderr.  (Errors whilst reading configuration will still
	      go  to syslog, but all output from a successful startup, and all
	      output whilst running, will go exclusively to  the  file.)  When
	      logging  to  a file, dnsmasq will close and reopen the file when
	      it receives SIGUSR2. This allows the  log	 file  to  be  rotated
	      without stopping dnsmasq.

	      Enable  asynchronous logging and optionally set the limit on the
	      number of lines which will be queued by dnsmasq when writing  to
	      the syslog is slow.  Dnsmasq can log asynchronously: this allows
	      it to continue functioning without being blocked by syslog,  and
	      allows  syslog  to  use  dnsmasq for DNS queries without risking
	      deadlock.	 If the queue of log-lines becomes full, dnsmasq  will
	      log  the overflow, and the number of messages  lost. The default
	      queue length is 5, a sane value would be	5-25,  and  a  maximum
	      limit of 100 is imposed.

       -x, --pid-file=<path>
	      Specify  an  alternate path for dnsmasq to record its process-id
	      in. Normally /var/run/dnsmasq.pid.

       -u, --user=<username>
	      Specify the userid to which dnsmasq will change  after  startup.
	      Dnsmasq  must normally be started as root, but it will drop root
	      privileges after startup by changing id to  another  user.  Nor‐
	      mally  this  user	 is  "nobody" but that can be over-ridden with
	      this switch.

       -g, --group=<groupname>
	      Specify the group which dnsmasq will run	as.  The  defaults  to
	      "dip",	 if	available,    to    facilitate	  access    to
	      /etc/ppp/resolv.conf which is not normally world readable.

       -v, --version
	      Print the version number.

       -p, --port=<port>
	      Listen on <port> instead of the standard DNS port (53).  Setting
	      this to zero completely disables DNS function, leaving only DHCP
	      and/or TFTP.

       -P, --edns-packet-max=<size>
	      Specify the largest EDNS.0 UDP packet which is supported by  the
	      DNS  forwarder.  Defaults	 to  4096, which is the RFC5625-recom‐
	      mended size.

       -Q, --query-port=<query_port>
	      Send outbound DNS queries from, and listen for their replies on,
	      the  specific  UDP  port	<query_port>  instead  of using random
	      ports. NOTE that using this option will make dnsmasq less secure
	      against  DNS  spoofing attacks but it may be faster and use less
	      resources.  Setting this option to zero makes dnsmasq use a sin‐
	      gle  port allocated to it by the OS: this was the default behav‐
	      iour in versions prior to 2.43.

	      Do not use ports less than that given as source for outbound DNS
	      queries.	Dnsmasq	 picks	random	ports  as  source for outbound
	      queries: when this option is given, the ports used  will	always
	      to  larger  than that specified. Useful for systems behind fire‐

       -i, --interface=<interface name>
	      Listen only on the specified interface(s). Dnsmasq automatically
	      adds the loopback (local) interface to the list of interfaces to
	      use when the --interface option  is used. If no  --interface  or
	      --listen-address options are given dnsmasq listens on all avail‐
	      able interfaces except any given in --except-interface  options.
	      IP  alias	 interfaces (eg "eth1:0") cannot be used with --inter‐
	      face  or	--except-interface   options,	use   --listen-address
	      instead. A simple wildcard, consisting of a trailing '*', can be
	      used in --interface and --except-interface options.

       -I, --except-interface=<interface name>
	      Do not listen on the specified interface. Note that the order of
	      --listen-address --interface and --except-interface options does
	      not matter and that --except-interface options  always  override
	      the others.

	      Enable  DNS authoritative mode for queries arriving at an inter‐
	      face or address. Note that the interface or address need not  be
	      mentioned	 in  --interface  or  --listen-address	configuration,
	      indeed --auth-server will overide these and provide a  different
	      DNS  service  on	the  specified	interface. The <domain> is the
	      "glue record". It should resolve in the global DNS to a A and/or
	      AAAA record which points to the address dnsmasq is listening on.
	      When an interface is specified, it may be qualified with "/4" or
	      "/6"  to specify only the IPv4 or IPv6 addresses associated with
	      the interface.

       -2, --no-dhcp-interface=<interface name>
	      Do not provide DHCP or TFTP on the specified interface,  but  do
	      provide DNS service.

       -a, --listen-address=<ipaddr>
	      Listen  on the given IP address(es). Both --interface and --lis‐
	      ten-address options may be given, in which case the set of  both
	      interfaces  and  addresses  is used. Note that if no --interface
	      option is given, but --listen-address is, dnsmasq will not auto‐
	      matically listen on the loopback interface. To achieve this, its
	      IP address,, must be explicitly given as  a  --listen-
	      address option.

       -z, --bind-interfaces
	      On systems which support it, dnsmasq binds the wildcard address,
	      even when it is listening on only some interfaces. It then  dis‐
	      cards  requests  that it shouldn't reply to. This has the advan‐
	      tage of working even when interfaces  come  and  go  and	change
	      address.	This  option  forces  dnsmasq  to really bind only the
	      interfaces it is listening on. About the only time when this  is
	      useful  is  when running another nameserver (or another instance
	      of dnsmasq) on  the  same	 machine.  Setting  this  option  also
	      enables multiple instances of dnsmasq which provide DHCP service
	      to run in the same machine.

	      Enable a network mode which is a	hybrid	between	 --bind-inter‐
	      faces  and  the default. Dnsmasq binds the address of individual
	      interfaces, allowing multiple  dnsmasq  instances,  but  if  new
	      interfaces  or  addresses	 appear,  it  automatically listens on
	      those (subject to any access-control configuration). This	 makes
	      dynamically  created  interfaces	work  in  the  same way as the
	      default. Implementing this option requires non-standard network‐
	      ing  APIs	 and  it is only available under Linux. On other plat‐
	      forms it falls-back to --bind-interfaces mode.

       -y, --localise-queries
	      Return answers to DNS queries from /etc/hosts  which  depend  on
	      the  interface  over  which the query was received. If a name in
	      /etc/hosts has more than one address associated with it, and  at
	      least one of those addresses is on the same subnet as the inter‐
	      face  to	which  the  query  was	sent,  then  return  only  the
	      address(es)  on  that  subnet. This allows for a server  to have
	      multiple addresses in /etc/hosts corresponding to	 each  of  its
	      interfaces,  and	hosts  will  get  the correct address based on
	      which network they are attached to. Currently this  facility  is
	      limited to IPv4.

       -b, --bogus-priv
	      Bogus  private  reverse lookups. All reverse lookups for private
	      IP  ranges  (ie  192.168.x.x,  etc)  which  are  not  found   in
	      /etc/hosts  or  the  DHCP leases file are answered with "no such
	      domain" rather than being forwarded upstream.

       -V, --alias=[<old-ip>]|[<start-ip>-<end-ip>],<new-ip>[,<mask>]
	      Modify IPv4 addresses returned from upstream nameservers; old-ip
	      is  replaced  by	new-ip. If the optional mask is given then any
	      address which matches the masked old-ip will be re-written.  So,
	      for   instance  --alias=,,  will  map to and	 to	This  is  what
	      Cisco  PIX  routers call "DNS doctoring". If the old IP is given
	      as range, then only addresses in the range, rather than a	 whole
	      subnet,		   are		    re-written.		    So
	      --alias=,,	  maps> to>

       -B, --bogus-nxdomain=<ipaddr>
	      Transform	 replies  which	 contain the IP address given into "No
	      such domain" replies. This is intended to counteract  a  devious
	      move  made  by  Verisign	in  September  2003  when they started
	      returning the address of an advertising web page in response  to
	      queries  for unregistered names, instead of the correct NXDOMAIN
	      response. This option tells dnsmasq to fake the correct response
	      when  it	sees  this  behaviour.	As at Sept 2003 the IP address
	      being returned by Verisign is

       -f, --filterwin2k
	      Later versions of windows make periodic DNS requests which don't
	      get  sensible answers from the public DNS and can cause problems
	      by triggering dial-on-demand links. This flag turns on an option
	      to filter such requests. The requests blocked are for records of
	      types SOA and SRV, and type ANY where  the  requested  name  has
	      underscores, to catch LDAP requests.

       -r, --resolv-file=<file>
	      Read  the	 IP addresses of the upstream nameservers from <file>,
	      instead of /etc/resolv.conf. For the format  of  this  file  see
	      resolv.conf(5).	The  only  lines relevant to dnsmasq are name‐
	      server  ones.  Dnsmasq  can  be  told  to	 poll  more  than  one
	      resolv.conf  file,  the first file name  specified overrides the
	      default, subsequent ones add to the list. This is	 only  allowed
	      when  polling;  the  file with the currently latest modification
	      time is the one used.

       -R, --no-resolv
	      Don't read /etc/resolv.conf. Get upstream servers only from  the
	      command line or the dnsmasq configuration file.

       -1, --enable-dbus[=<service-name>]
	      Allow dnsmasq configuration to be updated via DBus method calls.
	      The configuration which can be changed is upstream  DNS  servers
	      (and  corresponding domains) and cache clear. Requires that dns‐
	      masq has been built with DBus support. If the  service  name  is
	      given,  dnsmasq  provides	 service at that name, rather than the
	      default which is uk.org.thekelleys.dnsmasq

       -o, --strict-order
	      By default, dnsmasq will send queries to	any  of	 the  upstream
	      servers  it  knows  about	 and  tries to favour servers that are
	      known to be up. Setting this flag forces	dnsmasq	 to  try  each
	      query  with  each	 server	 strictly  in the order they appear in

	      By default, when dnsmasq	has  more  than	 one  upstream	server
	      available, it will send queries to just one server. Setting this
	      flag forces  dnsmasq  to	send  all  queries  to	all  available
	      servers.	The  reply from the server which answers first will be
	      returned to the original requester.

	      Reject (and log) addresses from upstream nameservers  which  are
	      in  the private IP ranges. This blocks an attack where a browser
	      behind a firewall is used to probe machines on  the  local  net‐

	      Exempt from rebinding checks. This address range is
	      returned by realtime black hole servers, so blocking it may dis‐
	      able these services.

	      Do  not detect and block dns-rebind on queries to these domains.
	      The argument may be either a single domain, or multiple  domains
	      surrounded  by  '/',  like  the  --server syntax, eg.  --rebind-

       -n, --no-poll
	      Don't poll /etc/resolv.conf for changes.

	      Whenever /etc/resolv.conf is re-read or the upstream servers are
	      set  via	DBus,  clear  the  DNS cache.  This is useful when new
	      nameservers may have different data than that held in cache.

       -D, --domain-needed
	      Tells dnsmasq to never forward  A	 or  AAAA  queries  for	 plain
	      names, without dots or domain parts, to upstream nameservers. If
	      the name is not known from /etc/hosts or DHCP then a "not found"
	      answer is returned.

       -S,							      --local,
	      Specify  IP  address  of upstream servers directly. Setting this
	      flag does not suppress reading of /etc/resolv.conf, use -R to do
	      that.  If one or more optional domains are given, that server is
	      used only for those domains and they are queried only using  the
	      specified	 server.  This is intended for private nameservers: if
	      you have a nameserver on your network which deals with names  of
	      the form xxx.internal.thekelleys.org.uk at then giv‐
	      ing  the flag  -S	 /internal.thekelleys.org.uk/  will
	      send  all	 queries  for  internal	 machines  to that nameserver,
	      everything else will go to the servers in	 /etc/resolv.conf.  An
	      empty  domain  specification,  //	 has  the  special  meaning of
	      "unqualified names only" ie names without any dots  in  them.  A
	      non-standard  port  may  be  specified as part of the IP address
	      using a # character.  More than one -S  flag  is	allowed,  with
	      repeated domain or ipaddr parts as required.

	      More  specific  domains  take  precendence  over	less  specific
	      domains,		  so:		  --server=/google.com/
	      --server=/www.google.com/	  will	  send	 queries   for
	      *.google.com to, except *www.google.com, which  will  go

	      The   special  server  address  '#'  means,  "use	 the  standard
	      servers",		   so		  --server=/google.com/
	      --server=/www.google.com/# will send queries for *.google.com to, except  *www.google.com	which  will  be	 forwarded  as

	      Also  permitted  is  a  -S  flag	which gives a domain but no IP
	      address; this tells dnsmasq that a domain is local  and  it  may
	      answer  queries from /etc/hosts or DHCP but should never forward
	      queries on that domain to any upstream servers.  local is a syn‐
	      onym  for	 server	 to  make  configuration files clearer in this

	      IPv6  addresses  may   include   a   %interface	scope-id,   eg

	      The  optional  string after the @ character tells dnsmasq how to
	      set the source of the queries to this nameserver. It  should  be
	      an  ip-address, which should belong to the machine on which dns‐
	      masq is running otherwise this server line will  be  logged  and
	      then  ignored,  or  an  interface	 name. If an interface name is
	      given, then queries to the server will be forced via that inter‐
	      face;  if	 an ip-address is given then the source address of the
	      queries will be set to that address.   The  query-port  flag  is
	      ignored  for  any	 servers which have a source address specified
	      but the port may be specified directly as	 part  of  the	source
	      address.	Forcing	 queries to an interface is not implemented on
	      all platforms supported by dnsmasq.

       -A, --address=/<domain>/[domain/]<ipaddr>
	      Specify an IP address to	return	for  any  host	in  the	 given
	      domains.	 Queries in the domains are never forwarded and always
	      replied to with the specified IP address which may  be  IPv4  or
	      IPv6.  To	 give  both  IPv4 and IPv6 addresses for a domain, use
	      repeated -A flags.  Note that /etc/hosts and DHCP	 leases	 over‐
	      ride this for individual names. A common use of this is to redi‐
	      rect the entire doubleclick.net domain to	 some  friendly	 local
	      web  server  to avoid banner ads. The domain specification works
	      in the same was as for --server, with  the  additional  facility
	      that  /#/	 matches  any  domain.	Thus --address=/#/ will
	      always return for any query not answered from /etc/hosts
	      or  DHCP	and  not sent to an upstream nameserver by a more spe‐
	      cific --server directive.

	      Places the resolved IP addresses of queries  for	the  specified
	      domains  in  the specified netfilter ip sets. Domains and subdo‐
	      mains are matched in the same way as --address.  These  ip  sets
	      must already exist. See ipset(8) for more details.

       -m, --mx-host=<mx name>[[,<hostname>],<preference>]
	      Return  an MX record named <mx name> pointing to the given host‐
	      name (if given), or the host specified in the --mx-target switch
	      or,  if  that  switch is not given, the host on which dnsmasq is
	      running. The default is useful for directing mail	 from  systems
	      on  a LAN to a central server. The preference value is optional,
	      and defaults to 1 if not given. More than one MX record  may  be
	      given for a host.

       -t, --mx-target=<hostname>
	      Specify  the  default  target for the MX record returned by dns‐
	      masq. See --mx-host.  If --mx-target is  given,  but  not	 --mx-
	      host,  then dnsmasq returns a MX record containing the MX target
	      for MX queries on the hostname of the machine on	which  dnsmasq
	      is running.

       -e, --selfmx
	      Return  an  MX record pointing to itself for each local machine.
	      Local machines are those in /etc/hosts or with DHCP leases.

       -L, --localmx
	      Return an MX record pointing to the host given by mx-target  (or
	      the machine on which dnsmasq is running) for each local machine.
	      Local machines are those in /etc/hosts or with DHCP leases.

       -W, --srv-host=<_service>.<_prot>.[<domain>],[<target>[,<port>[,<prior‐
	      Return  a	 SRV  DNS record. See RFC2782 for details. If not sup‐
	      plied, the domain defaults  to  that  given  by  --domain.   The
	      default for the target domain is empty, and the default for port
	      is one and the defaults for weight and  priority	are  zero.  Be
	      careful  if  transposing	data  from  BIND zone files: the port,
	      weight and priority numbers are in a different order. More  than
	      one  SRV	record for a given service/domain is allowed, all that
	      match are returned.

	      Add A, AAAA and PTR records to the DNS. This adds	 one  or  more
	      names  to	 the  DNS  with	 associated  IPv4  (A) and IPv6 (AAAA)
	      records. A name may appear in  more  than	 one  host-record  and
	      therefore	 be  assigned  more  than  one address. Only the first
	      address creates a PTR record linking the address	to  the	 name.
	      This  is	the  same  rule as is used reading hosts-files.	 host-
	      record options are considered to be read before host-files, so a
	      name  appearing there inhibits PTR-record creation if it appears
	      in hosts-file also. Unlike hosts-files, names are not  expanded,
	      even  when  expand-hosts	is in effect. Short and long names may
	      appear in the same host-record,  eg.   --host-record=laptop,lap‐

       -Y, --txt-record=<name>[[,<text>],<text>]
	      Return  a	 TXT  DNS  record. The value of TXT record is a set of
	      strings, so  any number may be included,	delimited  by  commas;
	      use  quotes  to  put commas into a string. Note that the maximum
	      length of a single string is 255 characters, longer strings  are
	      split into 255 character chunks.

	      Return a PTR DNS record.

	      Return an NAPTR DNS record, as specified in RFC3403.

	      Return a CNAME record which indicates  that  <cname>  is	really
	      <target>.	 There	are  significant limitations on the target; it
	      must be a DNS name which is known to dnsmasq from /etc/hosts (or
	      additional  hosts	 files),  from	DHCP, from --interface-name or
	      from another --cname.  If the target does not satisfy this  cri‐
	      teria, the whole cname is ignored. The cname must be unique, but
	      it is permissable to have more than one cname  pointing  to  the
	      same target.

       --dns-rr=<name>,<RR-number>,[<hex data>]
	      Return  an arbitrary DNS Resource Record. The number is the type
	      of the record (which is always in the C_IN class). The value  of
	      the  record  is  given by the hex data, which may be of the form
	      01:23:45 or 01 23 45 or 012345 or any mixture of these.

	      Return a DNS  record  associating	 the  name  with  the  primary
	      address on the given interface. This flag specifies an A or AAAA
	      record for the given name in the same way as an /etc/hosts line,
	      except  that  the	 address  is  not constant, but taken from the
	      given interface. The interface may be followed by "/4"  or  "/6"
	      to  specify  that	 only  IPv4 or IPv6 addresses of the interface
	      should be used. If the interface is down, not configured or non-
	      existent,	 an  empty record is returned. The matching PTR record
	      is also created, mapping the interface address to the name. More
	      than  one	 name  may  be associated with an interface address by
	      repeating the flag; in that case the first instance is used  for
	      the reverse address-to-name mapping.

       --synth-domain=<domain>,<address range>[,<prefix>]
	      Create  artificial  A/AAAA and PTR records for an address range.
	      The records use the address, with periods (or colons  for	 IPv6)
	      replaced with dashes.

	      An  example  should  make	 this clearer.	--synth-domain=thekel‐
	      leys.org.uk,,internal- will result in a query  for
	      internal-192-168-0-56.thekelleys.org.uk  returning
	      and a reverse query vice versa. The same applies	to  IPv6,  but
	      IPv6  addresses may start with '::' but DNS labels may not start
	      with '-' so in this case if no prefix is configured  a  zero  is
	      added in front of the label. ::1 becomes 0--1.

	      The  address  range can be of the form <ip address>,<ip address>
	      or <ip address>/<netmask>

	      Add the MAC address of the requestor to DNS  queries  which  are
	      forwarded	 upstream.  This  may  be used to DNS filtering by the
	      upstream server. The MAC	address	 can  only  be	added  if  the
	      requestor is on the same subnet as the dnsmasq server. Note that
	      the mechanism used to achieve this (an EDNS0 option) is not  yet
	      standardised,  so	 this  should be considered experimental. Also
	      note that exposing MAC addresses in this way may	have  security
	      and  privacy  implications.  The warning about caching given for
	      --add-subnet applies to --add-mac too.

       --add-subnet[[=<IPv4 prefix length>],<IPv6 prefix length>]
	      Add the subnet address of the requestor to the DNS queries which
	      are  forwarded  upstream.	 The  amount  of the address forwarded
	      depends on the prefix length parameter: 32 (128 for  IPv6)  for‐
	      wards  the  whole	 address,  zero	 forwards none of it but still
	      marks the request so that no upstream nameserver will add client
	      address  information  either.  The default is zero for both IPv4
	      and IPv6. Note that upstream nameservers may  be	configured  to
	      return different results based on this information, but the dns‐
	      masq cache does not take account. If a dnsmasq instance is  con‐
	      figured  such that different results may be encountered, caching
	      should be disabled.

       -c, --cache-size=<cachesize>
	      Set the size of dnsmasq's cache. The default is 150 names.  Set‐
	      ting the cache size to zero disables caching.

       -N, --no-negcache
	      Disable  negative	 caching.  Negative  caching allows dnsmasq to
	      remember "no such domain" answers from upstream nameservers  and
	      answer identical queries without forwarding them again.

       -0, --dns-forward-max=<queries>
	      Set  the	maximum	 number of concurrent DNS queries. The default
	      value is 150, which should be fine for  most  setups.  The  only
	      known  situation	where this needs to be increased is when using
	      web-server log file resolvers, which can generate large  numbers
	      of concurrent queries.

	      A	 resolver  on a client machine can do DNSSEC validation in two
	      ways: it can perform the cryptograhic operations on the reply it
	      receives, or it can rely on the upstream recursive nameserver to
	      do the validation and set a bit in the  reply  if	 it  succeeds.
	      Dnsmasq is not a DNSSEC validator, so it cannot perform the val‐
	      idation role of  the  recursive  nameserver,  but	 it  can  pass
	      through  the  validation	results	 from  its  own upstream name‐
	      servers. This option enables this behaviour. You should only  do
	      this  if	you  trust all the configured upstream nameservers and
	      the network between you and them.	 If you use the	 first	DNSSEC
	      mode,  validating	 resolvers  in	clients,  this	option	is not
	      required. Dnsmasq always returns	all  the  data	needed	for  a
	      client to do validation itself.

       --auth-zone=<domain>[,<subnet>[/<prefix	   length>][,<subnet>[/<prefix
	      Define a DNS  zone  for  which  dnsmasq  acts  as	 authoritative
	      server. Locally defined DNS records which are in the domain will
	      be served. If subnet(s) are given, A and AAAA records must be in
	      one of the specified subnets.

	      As alternative to directly specifying the subnets, it's possible
	      to give the name of an interface,	 in  which  case  the  subnets
	      implied  by  that	 interface's  configured  addresses  and  net‐
	      mask/prefix-length are used; this	 is  useful  when  using  con‐
	      structed	DHCP  ranges  as the actual address is dynamic and not
	      known when configuring dnsmasq. The interface addresses  may  be
	      confined	to  only IPv6 addresses using <interface>/6 or to only
	      IPv4 using <interface>/4. This is useful when an	interface  has
	      dynamically determined global IPv6 addresses which should appear
	      in the zone,  but	 RFC1918  IPv4	addresses  which  should  not.
	      Interface-name  and address-literal subnet specifications may be
	      used freely in the same --auth-zone declaration.

	      The subnet(s) are also used to define in-addr.arpa and ipv6.arpa
	      domains  which are served for reverse-DNS queries. If not speci‐
	      fied, the prefix length defaults to 24 for IPv4 and 64 for IPv6.
	      For  IPv4 subnets, the prefix length should be have the value 8,
	      16 or 24 unless you are familiar with RFC 2317 and have arranged
	      the in-addr.arpa delegation accordingly. Note that if no subnets
	      are specified, then no reverse queries are answered.

	      Specify fields in the SOA record associated  with	 authoritative
	      zones.  Note  that  this	is optional, all the values are set to
	      sane defaults.

	      Specify any secondary servers for a zone for  which  dnsmasq  is
	      authoritative. These servers must be configured to get zone data
	      from dnsmasq by zone transfer, and answer queries for  the  same
	      authoritative zones as dnsmasq.

	      Specify  the addresses of secondary servers which are allowed to
	      initiate zone transfer (AXFR) requests for zones for which  dns‐
	      masq  is	authoritative.	If this option is not given, then AXFR
	      requests will be accepted from any secondary.

	      Read the Linux connection track mark  associated	with  incoming
	      DNS queries and set the same mark value on upstream traffic used
	      to answer those queries. This allows traffic generated  by  dns‐
	      masq  to	be  associated with the queries which cause it, useful
	      for bandwidth accounting and firewalling. Dnsmasq must have con‐
	      ntrack  support  compiled	 in and the kernel must have conntrack
	      support included and configured. This option cannot be  combined
	      with --query-port.

       -F,	      --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-
       addr>[,<end-addr>][,<mode>][,<netmask>[,<broadcast>]][,<lease time>]

       -F,	      --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-
       len>][,<lease time>]

	      Enable the DHCP server. Addresses will be	 given	out  from  the
	      range  <start-addr>  to  <end-addr>  and from statically defined
	      addresses given in dhcp-host  options.  If  the  lease  time  is
	      given,  then  leases  will be given for that length of time. The
	      lease time is in seconds, or minutes (eg 45m) or hours  (eg  1h)
	      or "infinite". If not given, the default lease time is one hour.
	      The minimum lease time is two  minutes.  For  IPv6  ranges,  the
	      lease  time maybe "deprecated"; this sets the preferred lifetime
	      sent in a DHCP lease or  router  advertisement  to  zero,	 which
	      causes  clients  to  use	other addresses, if available, for new
	      connections as a prelude to renumbering.

	      This option may be repeated, with different addresses, to enable
	      DHCP  service  to	 more than one network. For directly connected
	      networks (ie, networks on which the machine running dnsmasq  has
	      an interface) the netmask is optional: dnsmasq will determine it
	      from the interface configuration.	 For  networks	which  receive
	      DHCP  service  via  a  relay agent, dnsmasq cannot determine the
	      netmask itself, so it should  be	specified,  otherwise  dnsmasq
	      will  have  to guess, based on the class (A, B or C) of the net‐
	      work address. The broadcast address is always  optional.	It  is
	      always allowed to have more than one dhcp-range in a single sub‐

	      For IPv6, the parameters are slightly different: instead of net‐
	      mask  and	 broadcast address, there is an optional prefix length
	      which must be equal to or larger then the prefix length  on  the
	      local  interface.	 If not given, this defaults to 64. Unlike the
	      IPv4 case, the prefix length is not automatically	 derived  from
	      the  interface  configuration.  The  mimimum  size of the prefix
	      length is 64.

	      IPv6 (only) supports another type of range. In this,  the	 start
	      address  and  optional end address contain only the network part
	      (ie ::1) and they are followed by constructor:<interface>.  This
	      forms  a template which describes how to create ranges, based on
	      the addresses assigned to the interface. For instance


	      will look for addresses on eth0 and then	create	a  range  from
	      <network>::1  to	<network>::400.	 If  the interface is assigned
	      more than one network, then the  corresponding  ranges  will  be
	      automatically  created,  and then deprecated and finally removed
	      again as the address is deprecated and then deleted. The	inter‐
	      face  name  may  have  a	final "*" wildcard. Note that just any
	      address on eth0 will not do: it must not be an autoconfigured or
	      privacy address, or be deprecated.

	      If  a  dhcp-range	 is  only being used for stateless DHCP and/or
	      SLAAC, then the address can be simply ::


	      The optional set:<tag> sets an alphanumeric  label  which	 marks
	      this network so that dhcp options may be specified on a per-net‐
	      work basis.  When it is prefixed with 'tag:' instead,  then  its
	      meaning  changes from setting a tag to matching it. Only one tag
	      may be set, but more than one tag may be matched.

	      The optional <mode> keyword may be static which tells dnsmasq to
	      enable  DHCP  for	 the network specified, but not to dynamically
	      allocate IP addresses: only hosts which  have  static  addresses
	      given  via  dhcp-host  or	 from  /etc/ethers  will  be served. A
	      static-only subnet with address all  zeros  may  be  used	 as  a
	      "catch-all" address to enable replies to all Information-request
	      packets on a subnet which is provided with stateless DHCPv6,  ie

	      For  IPv4,  the  <mode>  may be proxy in which case dnsmasq will
	      provide proxy-DHCP on the specified subnet. (See pxe-prompt  and
	      pxe-service for details.)

	      For  IPv6,  the  mode may be some combination of ra-only, slaac,
	      ra-names, ra-stateless.

	      ra-only tells dnsmasq to offer Router Advertisement only on this
	      subnet, and not DHCP.

	      slaac tells dnsmasq to offer Router Advertisement on this subnet
	      and to set the A bit in the router advertisement,	 so  that  the
	      client  will use SLAAC addresses. When used with a DHCP range or
	      static DHCP address this results in the  client  having  both  a
	      DHCP-assigned and a SLAAC address.

	      ra-stateless  sends  router advertisements with the O and A bits
	      set, and provides a stateless DHCP service. The client will  use
	      a	 SLAAC	address, and use DHCP for other configuration informa‐

	      ra-names enables a mode which  gives  DNS	 names	to  dual-stack
	      hosts  which  do	SLAAC  for  IPv6. Dnsmasq uses the host's IPv4
	      lease to derive the name, network segment and  MAC  address  and
	      assumes  that the host will also have an IPv6 address calculated
	      using the SLAAC algorithm, on  the  same	network	 segment.  The
	      address is pinged, and if a reply is received, an AAAA record is
	      added to the DNS for this IPv6 address. Note that this  is  only
	      happens for directly-connected networks, (not one doing DHCP via
	      a relay) and it will not work if a host is using privacy	exten‐
	      sions.  ra-names can be combined	with ra-stateless and slaac.

       -G,							       --dhcp-
	      Specify  per  host parameters for the DHCP server. This allows a
	      machine with a particular hardware address to  be	 always	 allo‐
	      cated  the  same hostname, IP address and lease time. A hostname
	      specified like this overrides any supplied by the DHCP client on
	      the  machine.  It is also allowable to omit the hardware address
	      and include the hostname, in which case the IP address and lease
	      times  will apply to any machine claiming that name. For example
	      --dhcp-host=00:20:e0:3b:13:af,wap,infinite tells dnsmasq to give
	      the  machine  with  hardware  address 00:20:e0:3b:13:af the name
	      wap, and an infinite DHCP lease.	 --dhcp-host=lap,
	      tells  dnsmasq to always allocate the machine lap the IP address

	      Addresses allocated like this are not constrained to be  in  the
	      range  given by the --dhcp-range option, but they must be in the
	      same subnet as some valid dhcp-range.  For subnets  which	 don't
	      need a pool of dynamically allocated addresses, use the "static"
	      keyword in the dhcp-range declaration.

	      It is allowed to use client identifiers (called client  DUID  in
	      IPv6-land	 rather	 than  hardware addresses to identify hosts by
	      prefixing	 with  'id:'.  Thus:  --dhcp-host=id:01:02:03:04,.....
	      refers  to  the  host  with client identifier 01:02:03:04. It is
	      also allowed to specify  the  client  ID	as  text,  like	 this:

	      A	 single	 dhcp-host  may	 contain  an  IPv4  address or an IPv6
	      address, or both. IPv6 addresses must  be	 bracketed  by	square
	      brackets	thus: --dhcp-host=laptop,[1234::56] IPv6 addresses may
	      contain only the host-identifier part: --dhcp-host=laptop,[::56]
	      in  which case they act as wildcards in constructed dhcp ranges,
	      with the appropriate network part inserted.  Note that  in  IPv6
	      DHCP,  the hardware address may not be available, though it nor‐
	      mally is for direct-connected clients,  or  clients  using  DHCP
	      relays which support RFC 6939.

	      For DHCPv4, the  special option id:* means "ignore any client-id
	      and use MAC addresses  only."  This  is  useful  when  a	client
	      presents a client-id sometimes but not others.

	      If  a  name appears in /etc/hosts, the associated address can be
	      allocated to a DHCP lease, but  only  if	a  --dhcp-host	option
	      specifying  the name also exists. Only one hostname can be given
	      in a dhcp-host option, but aliases are possible by using CNAMEs.
	      (See --cname ).

	      The special keyword "ignore" tells dnsmasq to never offer a DHCP
	      lease to a machine. The machine can  be  specified  by  hardware
	      address,	 client	  ID   or   hostname,	for  instance  --dhcp-
	      host=00:20:e0:3b:13:af,ignore  This  is  useful  when  there  is
	      another  DHCP server on the network which should be used by some

	      The set:<tag> construct sets the	tag  whenever  this  dhcp-host
	      directive	 is  in use. This can be used to selectively send DHCP
	      options just for this host. More than one tag can be  set	 in  a
	      dhcp-host	 directive  (but not in other places where "set:<tag>"
	      is allowed). When a host matches any dhcp-host directive (or one
	      implied  by  /etc/ethers)	 then  the special tag "known" is set.
	      This allows dnsmasq to be configured  to	ignore	requests  from
	      unknown	machines   using   --dhcp-ignore=tag:!known   Ethernet
	      addresses (but not client-ids) may have wildcard bytes,  so  for
	      example  --dhcp-host=00:20:e0:3b:13:*,ignore  will cause dnsmasq
	      to ignore a range of hardware addresses. Note that the "*"  will
	      need  to	be escaped or quoted on a command line, but not in the
	      configuration file.

	      Hardware addresses normally match any network (ARP) type, but it
	      is  possible  to restrict them to a single ARP type by preceding
	      them  with  the  ARP-type	 (in  HEX)   and   "-".	  so   --dhcp-
	      host=06-00:20:e0:3b:13:af,	 will  only match a Token-Ring
	      hardware address, since the ARP-address type for token  ring  is

	      As  a  special  case,  in DHCPv4, it is possible to include more
	      than	one	 hardware      address.	     eg:       --dhcp-
	      host=11:22:33:44:55:66,12:34:56:78:90:12, This allows
	      an IP address to be associated with multiple hardware addresses,
	      and  gives  dnsmasq permission to abandon a DHCP lease to one of
	      the hardware addresses when another one asks for a lease. Beware
	      that this is a dangerous thing to do, it will only work reliably
	      if only one of the hardware addresses is active at any time  and
	      there  is	 no  way  for  dnsmasq	to  enforce  this.  It is, for
	      instance, useful to allocate a stable IP	address	 to  a	laptop
	      which has both wired and wireless interfaces.

	      Read  DHCP host information from the specified file. If a direc‐
	      tory is given, then read all the files contained in that	direc‐
	      tory. The file contains information about one host per line. The
	      format of a line is the same as text to  the  right  of  '='  in
	      --dhcp-host.  The	 advantage of storing DHCP host information in
	      this file is that it can be changed without re-starting dnsmasq:
	      the file will be re-read when dnsmasq receives SIGHUP.

	      Read  DHCP  option  information  from  the specified file.  If a
	      directory is given, then read all the files  contained  in  that
	      directory. The advantage of using this option is the same as for
	      --dhcp-hostsfile: the dhcp-optsfile will be re-read when dnsmasq
	      receives SIGHUP. Note that it is possible to encode the informa‐
	      tion in a --dhcp-boot flag as DHCP options,  using  the  options
	      names  bootfile-name,  server-ip-address	and  tftp-server. This
	      allows these to be included in a dhcp-optsfile.

       -Z, --read-ethers
	      Read /etc/ethers	for  information  about	 hosts	for  the  DHCP
	      server.  The  format  of /etc/ethers is a hardware address, fol‐
	      lowed by either a hostname or dotted-quad IP address. When  read
	      by  dnsmasq  these lines have exactly the same effect as --dhcp-
	      host options containing the same information. /etc/ethers is re-
	      read  when  dnsmasq receives SIGHUP. IPv6 addresses are NOT read
	      from /etc/ethers.

       -O,	      --dhcp-option=[tag:<tag>,[tag:<tag>,]][encap:<opt>,][vi-
	      Specify different or extra options to DHCP clients. By  default,
	      dnsmasq sends some standard options to DHCP clients, the netmask
	      and broadcast address are set to the same as  the	 host  running
	      dnsmasq,	and  the  DNS  server and default route are set to the
	      address of the machine running dnsmasq. (Equivalent rules	 apply
	      for IPv6.) If the domain name option has been set, that is sent.
	      This configuration allows these defaults to  be  overridden,  or
	      other  options specified. The option, to be sent may be given as
	      a decimal number or as "option:<option-name>" The option numbers
	      are specified in RFC2132 and subsequent RFCs. The set of option-
	      names known by dnsmasq can be  discovered	 by  running  "dnsmasq
	      --help  dhcp".   For example, to set the default route option to, do --dhcp-option=3, or  --dhcp-option  =
	      option:router, and to set the time-server address to, do --dhcp-option = 42, or	 --dhcp-option
	      = option:ntp-server, The special address (or
	      [::] for DHCPv6) is taken to mean "the address  of  the  machine
	      running dnsmasq". Data types allowed are comma separated dotted-
	      quad IP addresses, a decimal number, colon-separated hex	digits
	      and  a  text  string.  If	 the optional tags are given then this
	      option is only sent when all the tags are matched.

	      Special processing is done on a text argument for option 119, to
	      conform with RFC 3397. Text or dotted-quad IP addresses as argu‐
	      ments to option 120 are handled as per RFC 3361. Dotted-quad  IP
	      addresses	 which are followed by a slash and then a netmask size
	      are encoded as described in RFC 3442.

	      IPv6 options are specified using the option6: keyword,  followed
	      by  the option number or option name. The IPv6 option name space
	      is disjoint from the IPv4 option name space. IPv6	 addresses  in
	      options  must  be	 bracketed  with square brackets, eg.  --dhcp-

	      Be careful: no checking is done that the correct	type  of  data
	      for  the option number is sent, it is quite possible to persuade
	      dnsmasq to generate illegal DHCP packets with injudicious use of
	      this  flag.  When	 the  value  is a decimal number, dnsmasq must
	      determine how large the data item is. It does this by  examining
	      the  option  number  and/or  the value, but can be overridden by
	      appending a single letter flag as follows: b = one byte, s = two
	      bytes,  i	 = four bytes. This is mainly useful with encapsulated
	      vendor class options (see below) where dnsmasq cannot  determine
	      data  size  from	the  option number. Option data which consists
	      solely of periods and digits will be interpreted by  dnsmasq  as
	      an  IP  address, and inserted into an option as such. To force a
	      literal string, use quotes. For instance when using option 66 to
	      send  a  literal IP address as TFTP server name, it is necessary
	      to do --dhcp-option=66,""

	      Encapsulated Vendor-class options may also  be  specified	 (IPv4
	      only)   using  --dhcp-option:  for  instance  --dhcp-option=ven‐
	      dor:PXEClient,1, sends the encapsulated vendor class-spe‐
	      cific  option "mftp-address=" to any client whose vendor-
	      class matches "PXEClient". The  vendor-class  matching  is  sub‐
	      string  based (see --dhcp-vendorclass for details). If a vendor-
	      class option (number 60) is sent by dnsmasq, then that  is  used
	      for  selecting encapsulated options in preference to any sent by
	      the client. It is possible to omit the  vendorclass  completely;
	      --dhcp-option=vendor:,1,  in  which case the encapsulated
	      option is always sent.

	      Options may be encapsulated (IPv4 only)  within  other  options:
	      for  instance  --dhcp-option=encap:175,  190, iscsi-client0 will
	      send option 175, within which is the  option  190.  If  multiple
	      options  are  given  which are encapsulated with the same option
	      number then they will be correctly combined  into	 one  encapsu‐
	      lated option.  encap: and vendor: are may not both be set in the
	      same dhcp-option.

	      The final variant on encapsulated options is "Vendor-Identifying
	      Vendor  Options" as specified by RFC3925. These are denoted like
	      this: --dhcp-option=vi-encap:2, 10, text The number in  the  vi-
	      encap:  section  is  the IANA enterprise number used to identify
	      this option. This form of encapsulation is supported in IPv6.

	      The address is not  treated  specially  in  encapsulated

	      This works in exactly the same way as --dhcp-option except  that
	      the  option will always be sent, even if the client does not ask
	      for it in the parameter request list. This is sometimes  needed,
	      for example when sending options to PXELinux.

	      (IPv4  only)  Disable re-use of the DHCP servername and filename
	      fields as extra option space. If it can, dnsmasq moves the  boot
	      server  and  filename  information (from dhcp-boot) out of their
	      dedicated fields into DHCP options. This make extra space avail‐
	      able in the DHCP packet for options but can, rarely, confuse old
	      or broken clients. This flag forces "simple and safe"  behaviour
	      to avoid problems in such a case.

       --dhcp-relay=<local address>,<server address>[,<interface]
	      Configure	 dnsmasq  to  do  DHCP	relay. The local address is an
	      address allocated to an interface on the host  running  dnsmasq.
	      All  DHCP requests arriving on that interface will we relayed to
	      a remote DHCP server at the server address. It  is  possible  to
	      relay  from a single local address to multiple remote servers by
	      using multiple dhcp-relay configs with the  same	local  address
	      and  different  server addresses. A server address must be an IP
	      literal address, not a domain name. In the case of  DHCPv6,  the
	      server   address	may  be	 the  ALL_SERVERS  multicast  address,
	      ff05::1:3. In this case the interface  must  be  given,  not  be
	      wildcard,	 and  is  used	to direct the multicast to the correct
	      interface to reach the DHCP server.

	      Access control for DHCP clients has the same rules  as  for  the
	      DHCP  server,  see  --interface,	--except-interface,  etc.  The
	      optional interface name in the dhcp-relay config has a different
	      function:	 it  controls on which interface DHCP replies from the
	      server will be accepted. This  is	 intended  for	configurations
	      which  have  three  interfaces: one being relayed from, a second
	      connecting the DHCP server, and a third untrusted network, typi‐
	      cally  the  wider	 internet.  It avoids the possibility of spoof
	      replies arriving via this third interface.

	      It is allowed to have dnsmasq act as a DHCP server on one set of
	      interfaces  and  relay  from  a disjoint set of interfaces. Note
	      that whilst it is quite possible to write	 configurations	 which
	      appear  to  act  as  a server and a relay on the same interface,
	      this is not supported: the relay function will take precedence.

	      Both DHCPv4 and DHCPv6 relay is supported. It's not possible  to
	      relay DHCPv4 to a DHCPv6 server or vice-versa.

       -U,    --dhcp-vendorclass=set:<tag>,[enterprise:<IANA-enterprise	  num‐
	      Map from a vendor-class string to a tag. Most DHCP clients  pro‐
	      vide  a "vendor class" which represents, in some sense, the type
	      of host. This option maps vendor classes to tags, so  that  DHCP
	      options  may  be	selectively  delivered to different classes of
	      hosts. For example dhcp-vendorclass=set:printers,Hewlett-Packard
	      JetDirect will allow options to be set only for HP printers like
	      so:  --dhcp-option=tag:printers,3,  The  vendor-class
	      string is substring matched against the vendor-class supplied by
	      the client, to allow fuzzy matching. The set: prefix is optional
	      but allowed for consistency.

	      Note  that  in  IPv6  only, vendorclasses are namespaced with an
	      IANA-allocated enterprise number. This is given with enterprise:
	      keyword and specifies that only vendorclasses matching the spec‐
	      ified number should be searched.

       -j, --dhcp-userclass=set:<tag>,<user-class>
	      Map from a user-class string to a tag (with substring  matching,
	      like  vendor  classes). Most DHCP clients provide a "user class"
	      which is configurable. This option maps user classes to tags, so
	      that  DHCP  options  may	be  selectively delivered to different
	      classes of hosts. It is possible, for instance to	 use  this  to
	      set a different printer server for hosts in the class "accounts"
	      than for hosts in the class "engineering".

       -4, --dhcp-mac=set:<tag>,<MAC address>
	      Map from a MAC address to a tag. The  MAC	 address  may  include
	      wildcards.  For  example --dhcp-mac=set:3com,01:34:23:*:*:* will
	      set the tag "3com" for any host whose MAC	 address  matches  the

       --dhcp-circuitid=set:<tag>,<circuit-id>,			       --dhcp-
	      Map from RFC3046 relay agent options to tags. This data  may  be
	      provided	by  DHCP  relay agents. The circuit-id or remote-id is
	      normally given as colon-separated hex, but is also allowed to be
	      a	 simple string. If an exact match is achieved between the cir‐
	      cuit or agent ID and one provided by a relay agent, the  tag  is

	      dhcp-remoteid (but not dhcp-circuitid) is supported in IPv6.

	      (IPv4  and  IPv6)	 Map  from  RFC3993  subscriber-id relay agent
	      options to tags.

       --dhcp-proxy[=<ip addr>]......
	      (IPv4 only) A normal DHCP relay agent is only  used  to  forward
	      the initial parts of a DHCP interaction to the DHCP server. Once
	      a client	is  configured,	 it  communicates  directly  with  the
	      server.  This  is undesirable if the relay agent is adding extra
	      information to the DHCP packets, such as that used by  dhcp-cir‐
	      cuitid  and  dhcp-remoteid.  A full relay implementation can use
	      the RFC 5107 serverid-override option to force the  DHCP	server
	      to  use  the  relay  as  a  full proxy, with all packets passing
	      through it. This flag provides an alternative  method  of	 doing
	      the  same	 thing, for relays which don't support RFC 5107. Given
	      alone, it manipulates the server-id  for	all  interactions  via
	      relays.  If  a  list of IP addresses is given, only interactions
	      via relays at those addresses are affected.

       --dhcp-match=set:<tag>,<option	  number>|option:<option     name>|vi-
	      Without  a  value, set the tag if the client sends a DHCP option
	      of the given number or name. When a value is given, set the  tag
	      only  if the option is sent and matches the value. The value may
	      be of the form "01:ff:*:02" in which case the value  must	 match
	      (apart  from  wildcards)	but the option sent may have unmatched
	      data past the end of the value. The value may  also  be  of  the
	      same  form  as  in  dhcp-option in which case the option sent is
	      treated as an array, and one element must match, so


	      will set the tag "efi-ia32" if the the number 6 appears  in  the
	      list  of architectures sent by the client in option 93. (See RFC
	      4578 for details.)  If the value is a string, substring matching
	      is used.

	      The  special  form  with	vi-encap:<enterprise  number>  matches
	      against vendor-identifying  vendor  classes  for	the  specified
	      enterprise.  Please  see RFC 3925 for more details of these rare
	      and interesting beasts.

	      Perform  boolean	operations  on	tags.  Any  tag	 appearing  as
	      set:<tag>	 is  set if all the tags which appear as tag:<tag> are
	      set, (or unset when tag:!<tag> is used) If no tag:<tag>  appears
	      set:<tag>	 tags are set unconditionally.	Any number of set: and
	      tag: forms may appear, in any order.  Tag-if lines ares executed
	      in  order,  so  if  the tag in tag:<tag> is a tag set by another
	      tag-if, the line which sets the tag must precede the  one	 which
	      tests it.

       -J, --dhcp-ignore=tag:<tag>[,tag:<tag>]
	      When  all	 the  given tags appear in the tag set ignore the host
	      and do not allocate it a DHCP lease.

	      When all the given tags appear in the tag set, ignore any	 host‐
	      name  provided by the host. Note that, unlike dhcp-ignore, it is
	      permissible to supply no tags, in which  case  DHCP-client  sup‐
	      plied  hostnames are always ignored, and DHCP hosts are added to
	      the DNS using only dhcp-host configuration in  dnsmasq  and  the
	      contents of /etc/hosts and /etc/ethers.

	      (IPv4 only) Generate a name for DHCP clients which do not other‐
	      wise have one, using the MAC address expressed in hex, separated
	      by  dashes. Note that if a host provides a name, it will be used
	      by preference to this, unless --dhcp-ignore-names is set.

	      (IPv4 only) When all the given  tags  appear  in	the  tag  set,
	      always  use  broadcast  to  communicate with the host when it is
	      unconfigured. It is permissible to supply no tags, in which case
	      this  is	unconditional.	Most DHCP clients which need broadcast
	      replies set a flag in their requests so that this happens	 auto‐
	      matically, some old BOOTP clients do not.

       -M,	     --dhcp-boot=[tag:<tag>,]<filename>,[<servername>[,<server
	      (IPv4 only) Set BOOTP options to be returned by the DHCP server.
	      Server  name and address are optional: if not provided, the name
	      is left empty, and the address set to the address of the machine
	      running  dnsmasq.	 If  dnsmasq  is providing a TFTP service (see
	      --enable-tftp ) then only	 the  filename	is  required  here  to
	      enable  network booting.	If the optional tag(s) are given, they
	      must match for this configuration to be sent.  Instead of an  IP
	      address,	the  TFTP server address can be given as a domain name
	      which is looked up in /etc/hosts. This name can be associated in
	      /etc/hosts  with	multiple  IP  addresses, which are used round-
	      robin.  This facility can be used to load balance the tftp  load
	      among a set of servers.

	      Dnsmasq  is  designed  to	 choose	 IP addresses for DHCP clients
	      using a hash of the client's MAC address. This normally allows a
	      client's	address to remain stable long-term, even if the client
	      sometimes allows its DHCP lease to expire. In this default  mode
	      IP  addresses  are  distributed  pseudo-randomly over the entire
	      available address range. There are sometimes circumstances (typ‐
	      ically server deployment) where it is more convenient to have IP
	      addresses	 allocated  sequentially,  starting  from  the	lowest
	      available address, and setting this flag enables this mode. Note
	      that in the sequential mode, clients  which  allow  a  lease  to
	      expire  are much more likely to move IP address; for this reason
	      it should not be generally used.

       --pxe-service=[tag:<tag>,]<CSA>,<menu   text>[,<basename>|<bootservice‐
       type>][,<server address>|<server_name>]
	      Most uses of PXE boot-ROMS simply allow the PXE system to obtain
	      an IP address and then download the file specified by  dhcp-boot
	      and  execute  it. However the PXE system is capable of more com‐
	      plex functions when supported by a suitable DHCP server.

	      This specifies a boot option which may  appear  in  a  PXE  boot
	      menu.  <CSA> is client system type, only services of the correct
	      type will appear in a menu. The known  types  are	 x86PC,	 PC98,
	      IA64_EFI,	 Alpha,	 Arc_x86, Intel_Lean_Client, IA32_EFI, BC_EFI,
	      Xscale_EFI and X86-64_EFI; an integer  may  be  used  for	 other
	      types.  The parameter after the menu text may be a file name, in
	      which case dnsmasq acts as a boot server	and  directs  the  PXE
	      client  to  download  the	 file  by  TFTP,  either from itself (
	      enable-tftp must be set for this to work) or another TFTP server
	      if  the  final  server  address/name  is	given.	 Note that the
	      "layer" suffix (normally ".0") is supplied by  PXE,  and	should
	      not  be  added to the basename. If an integer boot service type,
	      rather than a basename is given, then the PXE client will search
	      for  a  suitable boot service for that type on the network. This
	      search may be done by broadcast, or direct to a server if its IP
	      address/name  is	provided.  If no boot service type or filename
	      is provided (or a boot service type of 0 is specified) then  the
	      menu  entry will abort the net boot procedure and continue boot‐
	      ing from local media. The server	address	 can  be  given	 as  a
	      domain  name  which is looked up in /etc/hosts. This name can be
	      associated in /etc/hosts with multiple IP addresses,  which  are
	      used round-robin.

	      Setting  this  provides a prompt to be displayed after PXE boot.
	      If the timeout is given then after the timeout has elapsed  with
	      no keyboard input, the first available menu option will be auto‐
	      matically executed. If the timeout is zero then the first avail‐
	      able  menu  item	will be executed immediately. If pxe-prompt is
	      omitted the system will wait for user input if there are	multi‐
	      ple  items  in  the  menu, but boot immediately if there is only
	      one. See pxe-service for details of menu items.

	      Dnsmasq supports PXE "proxy-DHCP", in  this  case	 another  DHCP
	      server   on   the	 network  is  responsible  for	allocating  IP
	      addresses, and dnsmasq simply provides the information given  in
	      pxe-prompt  and  pxe-service  to	allow netbooting. This mode is
	      enabled using the proxy keyword in dhcp-range.

       -X, --dhcp-lease-max=<number>
	      Limits dnsmasq to the specified maximum number of	 DHCP  leases.
	      The  default  is 1000. This limit is to prevent DoS attacks from
	      hosts which create thousands of leases and use lots of memory in
	      the dnsmasq process.

       -K, --dhcp-authoritative
	      Should be set when dnsmasq is definitely the only DHCP server on
	      a network.  For DHCPv4, it changes the behaviour from strict RFC
	      compliance  so that DHCP requests on unknown leases from unknown
	      hosts are not ignored. This allows new  hosts  to	 get  a	 lease
	      without  a  tedious  timeout  under  all	circumstances. It also
	      allows dnsmasq to rebuild its lease database without each client
	      needing  to  reacquire  a	 lease,	 if  the database is lost. For
	      DHCPv6 it sets the priority in  replies  to  255	(the  maximum)
	      instead of 0 (the minimum).

       --dhcp-alternate-port[=<server port>[,<client port>]]
	      (IPv4  only) Change the ports used for DHCP from the default. If
	      this option is given alone, without arguments,  it  changes  the
	      ports used for DHCP from 67 and 68 to 1067 and 1068. If a single
	      argument is given, that port number is used for the  server  and
	      the  port number plus one used for the client. Finally, two port
	      numbers allows arbitrary specification of both server and client
	      ports for DHCP.

       -3, --bootp-dynamic[=<network-id>[,<network-id>]]
	      (IPv4  only)  Enable dynamic allocation of IP addresses to BOOTP
	      clients. Use this with care, since each address allocated	 to  a
	      BOOTP  client  is	 leased	 forever, and therefore becomes perma‐
	      nently unavailable for re-use by other hosts. if this  is	 given
	      without  tags,  then  it unconditionally enables dynamic alloca‐
	      tion. With tags, only when the tags  are	all  set.  It  may  be
	      repeated with different tag sets.

       -5, --no-ping
	      (IPv4  only)  By default, the DHCP server will attempt to ensure
	      that an address in not in use before allocating it to a host. It
	      does  this  by  sending an ICMP echo request (aka "ping") to the
	      address in question. If it gets a reply, then the	 address  must
	      already be in use, and another is tried. This flag disables this
	      check. Use with caution.

	      Extra logging for DHCP: log all the options sent to DHCP clients
	      and the tags used to determine them.

       --quiet-dhcp, --quiet-dhcp6, --quiet-ra
	      Suppress	logging	 of  the routine operation of these protocols.
	      Errors and problems  will	 still	be  logged.  --quiet-dhcp  and
	      quiet-dhcp6 are over-ridden by --log-dhcp.

       -l, --dhcp-leasefile=<path>
	      Use the specified file to store DHCP lease information.

	      (IPv6  only)  Specify the server persistent UID which the DHCPv6
	      server will use. This option is not normally required as dnsmasq
	      creates  a  DUID	automatically  when  it	 is first needed. When
	      given, this option provides dnsmasq the data required to	create
	      a	 DUID-EN  type DUID. Note that once set, the DUID is stored in
	      the lease database, so to change between DUID-EN	and  automati‐
	      cally  created  DUIDs  or vice-versa, the lease database must be
	      re-intialised. The enterprise-id is assigned by  IANA,  and  the
	      uid is a string of hex octets unique to a particular device.

       -6 --dhcp-script=<path>
	      Whenever	a  new DHCP lease is created, or an old one destroyed,
	      or a TFTP file transfer completes, the executable	 specified  by
	      this  option  is	run.   <path> must be an absolute pathname, no
	      PATH search occurs.  The arguments to  the  process  are	"add",
	      "old" or "del", the MAC address of the host (or DUID for IPv6) ,
	      the IP address, and the hostname, if known. "add" means a	 lease
	      has  been created, "del" means it has been destroyed, "old" is a
	      notification of an existing  lease  when	dnsmasq	 starts	 or  a
	      change  to  MAC  address or hostname of an existing lease (also,
	      lease length or expiry and client-id, if leasefile-ro  is	 set).
	      If  the  MAC address is from a network type other than ethernet,
	      it    will    have    the	   network    type    prepended,    eg
	      "06-01:23:45:67:89:ab"  for  token  ring.	 The process is run as
	      root (assuming that dnsmasq was originally run as root) even  if
	      dnsmasq is configured to change UID to an unprivileged user.

	      The  environment	is inherited from the invoker of dnsmasq, with
	      some or all of the following variables added

	      For both IPv4 and IPv6:

	      DNSMASQ_DOMAIN if the fully-qualified domain name of the host is
	      known,  this is set to the  domain part. (Note that the hostname
	      passed to the script as an argument is never fully-qualified.)

	      If the client provides a hostname, DNSMASQ_SUPPLIED_HOSTNAME

	      If the client provides  user-classes,  DNSMASQ_USER_CLASS0..DNS‐

	      If dnsmasq was compiled with HAVE_BROKEN_RTC, then the length of
	      the lease (in seconds) is stored in DNSMASQ_LEASE_LENGTH, other‐
	      wise   the   time	  of   lease   expiry	is   stored   in  DNS‐
	      MASQ_LEASE_EXPIRES. The number of seconds until lease expiry  is
	      always stored in DNSMASQ_TIME_REMAINING.

	      If  a  lease used to have a hostname, which is removed, an "old"
	      event is generated with the new state of the lease, ie no	 name,
	      and the former name is provided in the environment variable DNS‐

	      DNSMASQ_INTERFACE stores the name of the interface on which  the
	      request  arrived; this is not set for "old" actions when dnsmasq

	      DNSMASQ_RELAY_ADDRESS is set if the client used a DHCP relay  to
	      contact dnsmasq and the IP address of the relay is known.

	      DNSMASQ_TAGS  contains all the tags set during the DHCP transac‐
	      tion, separated by spaces.

	      DNSMASQ_LOG_DHCP is set if --log-dhcp is in effect.

	      For IPv4 only:

	      DNSMASQ_CLIENT_ID if the host provided a client-id.

	      a DHCP relay-agent added any of these options.

	      If the client provides vendor-class, DNSMASQ_VENDOR_CLASS.

	      For IPv6 only:

	      If  the  client  provides vendor-class, DNSMASQ_VENDOR_CLASS_ID,
	      containing the IANA  enterprise  id  for	the  class,  and  DNS‐

	      DNSMASQ_SERVER_DUID  containing  the DUID of the server: this is
	      the same for every call to the script.

	      DNSMASQ_IAID containing the IAID for the lease. If the lease  is
	      a temporary allocation, this is prefixed to 'T'.

	      DNSMASQ_MAC containing the MAC address of the client, if known.

	      Note  that the supplied hostname, vendorclass and userclass data
	      is only  supplied for "add" actions or "old" actions when a host
	      resumes an existing lease, since these data are not held in dns‐
	      masq's lease database.

	      All file descriptors are closed except stdin, stdout and	stderr
	      which are open to /dev/null (except in debug mode).

	      The  script is not invoked concurrently: at most one instance of
	      the script is ever running (dnsmasq waits	 for  an  instance  of
	      script  to  exit	before running the next). Changes to the lease
	      database are which require the script to be invoked  are	queued
	      awaiting	exit  of  a running instance.  If this queueing allows
	      multiple state changes occur to a single lease before the script
	      can  be  run  then  earlier states are discarded and the current
	      state of that lease is reflected when the script finally runs.

	      At dnsmasq startup, the script will be invoked for all  existing
	      leases as they are read from the lease file. Expired leases will
	      be called	 with  "del"  and  others  with	 "old".	 When  dnsmasq
	      receives	a  HUP signal, the script will be invoked for existing
	      leases with an "old " event.

	      There are two further actions which  may	appear	as  the	 first
	      argument	to the script, "init" and "tftp". More may be added in
	      the future, so scripts  should  be  written  to  ignore  unknown
	      actions.	"init" is described below in --leasefile-ro The "tftp"
	      action is invoked when a TFTP file transfer completes: the argu‐
	      ments  are the file size in bytes, the address to which the file
	      was sent, and the complete pathname of the file.

	      Specify a script written in Lua, to be run when leases are  cre‐
	      ated,  destroyed or changed. To use this option, dnsmasq must be
	      compiled with  the  correct  support.  The  Lua  interpreter  is
	      intialised  once,	 when dnsmasq starts, so that global variables
	      persist between lease events. The Lua code must define  a	 lease
	      function, and may provide init and shutdown functions, which are
	      called, without arguments when dnsmasq starts up and terminates.
	      It may also provide a tftp function.

	      The  lease function receives the information detailed in --dhcp-
	      script.  It gets two arguments, firstly the action, which	 is  a
	      string  containing,  "add", "old" or "del", and secondly a table
	      of tag value pairs. The tags mostly correspond to	 the  environ‐
	      ment  variables  detailed	 above,	 for instance the tag "domain"
	      holds the same data as the environment variable  DNSMASQ_DOMAIN.
	      There are a few extra tags which hold the data supplied as argu‐
	      ments to --dhcp-script.  These are mac_address,  ip_address  and
	      hostname	for IPv4, and client_duid, ip_address and hostname for

	      The tftp function is called in the same way as the  lease	 func‐
	      tion,   and   the	 table	holds  the  tags  destination_address,
	      file_name and file_size.

	      Specify the user as which to run the lease-change script or  Lua
	      script.  This  defaults  to  root, but can be changed to another
	      user using this flag.

       -9, --leasefile-ro
	      Completely suppress use of the lease  database  file.  The  file
	      will not be created, read, or written. Change the way the lease-
	      change script (if one is provided) is called, so that the	 lease
	      database may be maintained in external storage by the script. In
	      addition to the invocations  given in --dhcp-script  the	lease-
	      change  script is called once, at dnsmasq startup, with the sin‐
	      gle argument "init". When called like  this  the	script	should
	      write  the  saved state of the lease database, in dnsmasq lease‐
	      file format, to stdout and exit with  zero  exit	code.  Setting
	      this  option  also forces the leasechange script to be called on
	      changes to the client-id and lease length and expiry time.

	      Treat DHCP request packets arriving at any of the <alias> inter‐
	      faces as if they had arrived at <interface>. This option is nec‐
	      essary when using "old style" bridging on BSD  platforms,	 since
	      packets arrive at tap interfaces which don't have an IP address.

       -s, --domain=<domain>[,<address range>[,local]]
	      Specifies	 DNS  domains  for  the DHCP server. Domains may be be
	      given unconditionally (without the IP range) or for  limited  IP
	      ranges.  This has two effects; firstly it causes the DHCP server
	      to return the domain to any hosts which request it, and secondly
	      it  sets	the domain which it is legal for DHCP-configured hosts
	      to claim. The intention is to constrain  hostnames  so  that  an
	      untrusted	 host on the LAN cannot advertise its name via dhcp as
	      e.g. "microsoft.com" and capture traffic not meant for it. If no
	      domain suffix is specified, then any DHCP hostname with a domain
	      part (ie with a period) will be disallowed and logged. If suffix
	      is  specified,  then  hostnames  with a domain part are allowed,
	      provided the domain part matches the suffix. In addition, when a
	      suffix is set then hostnames without a domain part have the suf‐
	      fix added as an optional domain part. Eg on my network I can set
	      --domain=thekelleys.org.uk  and  have a machine whose DHCP host‐
	      name is "laptop". The IP address for that machine	 is  available
	      from dnsmasq both as "laptop" and "laptop.thekelleys.org.uk". If
	      the domain is given as "#" then the  domain  is  read  from  the
	      first "search" directive in /etc/resolv.conf (or equivalent).

	      The  address  range can be of the form <ip address>,<ip address>
	      or <ip address>/<netmask> or just a  single  <ip	address>.  See
	      --dhcp-fqdn  which  can  change  the  behaviour  of dnsmasq with

	      If the address range is given as ip-address/network-size, then a
	      additional  flag "local" may be supplied which has the effect of
	      adding --local declarations for forward and reverse DNS queries.
	      Eg.   --domain=thekelleys.org.uk,,local is identi‐
	      cal	  to	     --domain=thekelleys.org.uk,
	      --local=/thekelleys.org.uk/ --local=/0.168.192.in-addr.arpa/ The
	      network size must be 8, 16 or 24 for this to be legal.

	      In the default mode, dnsmasq inserts the	unqualified  names  of
	      DHCP  clients  into  the DNS. For this reason, the names must be
	      unique, even if two clients which have the same name are in dif‐
	      ferent  domains.	If  a second DHCP client appears which has the
	      same name as an existing client, the name is transferred to  the
	      new  client.  If --dhcp-fqdn is set, this behaviour changes: the
	      unqualified name is no longer put in the DNS, only the qualified
	      name.  Two  DHCP	clients	 with  the same name may both keep the
	      name, provided that the domain part is different (ie  the	 fully
	      qualified	 names differ.) To ensure that all names have a domain
	      part, there must be at least --domain without an address	speci‐
	      fied when --dhcp-fqdn is set.

	      Normally,	 when  giving  a DHCP lease, dnsmasq sets flags in the
	      FQDN option to tell the client not to attempt a DDNS update with
	      its  name	 and  IP  address. This is because the name-IP pair is
	      automatically added into dnsmasq's  DNS  view.  This  flag  sup‐
	      presses  that  behaviour, this is useful, for instance, to allow
	      Windows clients to update Active Directory servers. See RFC 4702
	      for details.

	      Enable  dnsmasq's	 IPv6  Router  Advertisement  feature.	DHCPv6
	      doesn't handle complete network configuration in the same way as
	      DHCPv4. Router discovery and (possibly) prefix discovery for au‐
	      tonomous address creation are handled by a  different  protocol.
	      When  DHCP  is in use, only a subset of this is needed, and dns‐
	      masq can handle it, using existing DHCP configuration to provide
	      most  data.  When RA is enabled, dnsmasq will advertise a prefix
	      for each dhcp-range,  with  default  router  and	recursive  DNS
	      server as the relevant link-local address on the machine running
	      dnsmasq. By default, he "managed address" bits are set, and  the
	      "use  SLAAC"  bit	 is  reset. This can be changed for individual
	      subnets  with  the  mode	keywords  described  in	 --dhcp-range.
	      RFC6106  DNS  parameters	are included in the advertisements. By
	      default, the relevant link-local address of the machine  running
	      dnsmasq is sent as recursive DNS server. If provided, the DHCPv6
	      options dns-server and domain-search  are	 used  for  RDNSS  and

       --ra-param=<interface>,[high|low],[[<ra-interval>],<router lifetime>]
	      Set  non-default	values	for  router advertisements sent via an
	      interface. The priority field for the router may be altered from
	      the  default of medium with eg --ra-param=eth0,high.  The inter‐
	      val between router advertisements may be set (in	seconds)  with
	      --ra-param=eth0,60.  The lifetime of the route may be changed or
	      set to zero, which allows a router to advertise prefixes but not
	      a route via itself.  --ra-parm=eth0,0,0 (A value of zero for the
	      interval means the default value.) All three parameters  may  be
	      set  at  once.   --ra-param=low,60,1200  The interface field may
	      include a wildcard.

	      Enable the TFTP server function. This is deliberately limited to
	      that  needed  to net-boot a client. Only reading is allowed; the
	      tsize and blksize extensions are supported (tsize is  only  sup‐
	      ported  in octet mode). Without an argument, the TFTP service is
	      provided to the same set of interfaces as DHCP service.  If  the
	      list  of	interfaces  is provided, that defines which interfaces
	      recieve TFTP service.

	      Look for files to transfer using	TFTP  relative	to  the	 given
	      directory.  When	this is set, TFTP paths which include ".." are
	      rejected, to stop clients getting outside	 the  specified	 root.
	      Absolute	paths  (starting with /) are allowed, but they must be
	      within the tftp-root. If	the  optional  interface  argument  is
	      given,  the  directory  is  only used for TFTP requests via that

	      Add the IP address of the TFTP client as a path component on the
	      end  of  the  TFTP-root  (in  standard dotted-quad format). Only
	      valid if a tftp-root  is	set  and  the  directory  exists.  For
	      instance,	 if  tftp-root	is "/tftp" and client requests
	      file   "myfile"	then	the    effective    path    will    be
	      "/tftp/"  if  /tftp/ exists or /tftp/myfile

	      Enable TFTP secure mode: without this, any file which  is	 read‐
	      able  by	the  dnsmasq  process under normal unix access-control
	      rules is available via TFTP.  When  the  --tftp-secure  flag  is
	      given,  only files owned by the user running the dnsmasq process
	      are accessible. If dnsmasq is being run as root, different rules
	      apply:  --tftp-secure  has  no effect, but only files which have
	      the world-readable bit set are accessible. It is not recommended
	      to  run  dnsmasq	as  root  with TFTP enabled, and certainly not
	      without specifying --tftp-root. Doing so can expose  any	world-
	      readable file on the server to any host on the net.

	      Convert  filenames  in  TFTP  requests to all lowercase. This is
	      useful for requests from	Windows	 machines,  which  have	 case-
	      insensitive  filesystems	and  tend  to play fast-and-loose with
	      case in filenames.  Note that dnsmasq's tftp server always  con‐
	      verts "\" to "/" in filenames.

	      Set  the	maximum number of concurrent TFTP connections allowed.
	      This defaults to 50. When serving a large number of TFTP connec‐
	      tions,  per-process  file	 descriptor limits may be encountered.
	      Dnsmasq needs one file descriptor for each concurrent TFTP  con‐
	      nection and one file descriptor per unique file (plus a few oth‐
	      ers). So serving the same file simultaneously to n clients  will
	      use  require  about  n  + 10 file descriptors, serving different
	      files simultaneously to n clients will require about (2*n) +  10
	      descriptors.  If --tftp-port-range is given, that can affect the
	      number of concurrent connections.

	      Stop the TFTP server from	 negotiating  the  "blocksize"	option
	      with  a  client. Some buggy clients request this option but then
	      behave badly when it is granted.

	      A TFTP server listens on a well-known port (69)  for  connection
	      initiation,  but	it  also uses a dynamically-allocated port for
	      each connection. Normally these are allocated  by	 the  OS,  but
	      this  option  specifies  a range of ports for use by TFTP trans‐
	      fers. This can be useful when TFTP has to traverse  a  firewall.
	      The  start of the range cannot be lower than 1025 unless dnsmasq
	      is running as root. The number of concurrent TFTP connections is
	      limited by the size of the port range.

       -C, --conf-file=<file>
	      Specify  a different configuration file. The conf-file option is
	      also allowed in configuration files, to include multiple config‐
	      uration files. A filename of "-" causes dnsmasq to read configu‐
	      ration from stdin.

       -7, --conf-dir=<directory>[,<file-extension>......]
	      Read all the files  in  the  given  directory  as	 configuration
	      files.  If  extension(s) are given, any files which end in those
	      extensions are skipped. Any files whose names end in ~ or	 start
	      with . or start and end with # are always skipped. This flag may
	      be given on the command line or in a configuration file.

       At startup, dnsmasq reads /etc/dnsmasq.conf, if it exists. (On FreeBSD,
       the  file  is  /usr/local/etc/dnsmasq.conf  )  (but  see	 the -C and -7
       options.) The format of this file consists  of  one  option  per	 line,
       exactly as the long options detailed in the OPTIONS section but without
       the leading "--". Lines starting with # are comments and	 ignored.  For
       options	which may only be specified once, the configuration file over‐
       rides the command line.	Quoting is allowed in a config file: between "
       quotes  the special meanings of ,:. and # are removed and the following
       escapes are allowed: \\ \" \t \e \b \r and \n. The later	 corresponding
       to tab, escape, backspace, return and newline.

       When  it	 receives a SIGHUP, dnsmasq clears its cache and then re-loads
       /etc/hosts and /etc/ethers and  any  file  given	 by  --dhcp-hostsfile,
       --dhcp-optsfile	or  --addn-hosts.   The	 dhcp  lease  change script is
       called for all existing DHCP leases. If --no-poll is  set  SIGHUP  also
       re-reads	 /etc/resolv.conf.   SIGHUP does NOT re-read the configuration

       When it receives a SIGUSR1, dnsmasq writes  statistics  to  the	system
       log.  It	 writes	 the cache size, the number of names which have had to
       removed from the cache before they expired in order to  make  room  for
       new  names  and	the total number of names that have been inserted into
       the cache. For each upstream server it  gives  the  number  of  queries
       sent, and the number which resulted in an error. In --no-daemon mode or
       when full logging is enabled (-q), a complete dump of the  contents  of
       the cache is made.

       When it receives SIGUSR2 and it is logging direct to a file (see --log-
       facility ) dnsmasq will close and reopen the log file. Note that during
       this operation, dnsmasq will not be running as root. When it first cre‐
       ates the logfile dnsmasq changes the ownership of the file to the  non-
       root  user  it  will run as. Logrotate should be configured to create a
       new log file with the ownership which matches the existing  one	before
       sending	SIGUSR2.   If TCP DNS queries are in progress, the old logfile
       will remain open in child processes which are handling TCP queries  and
       may  continue  to  be  written.	There is a limit of 150 seconds, after
       which all existing TCP processes will have expired: for this reason, it
       is  not	wise  to configure logfile compression for logfiles which have
       just been rotated. Using logrotate, the required options are create and

       Dnsmasq	is  a  DNS  query  forwarder: it it not capable of recursively
       answering arbitrary queries starting from the root servers but forwards
       such  queries  to  a fully recursive upstream DNS server which is typi‐
       cally provided by an ISP. By default, dnsmasq reads /etc/resolv.conf to
       discover	 the  IP  addresses of the upstream nameservers it should use,
       since the information is typically stored there.	 Unless	 --no-poll  is
       used,  dnsmasq  checks  the  modification  time of /etc/resolv.conf (or
       equivalent if --resolv-file is used) and re-reads  it  if  it  changes.
       This  allows the DNS servers to be set dynamically by PPP or DHCP since
       both protocols provide the information.	Absence of /etc/resolv.conf is
       not an error since it may not have been created before a PPP connection
       exists. Dnsmasq simply keeps checking in case /etc/resolv.conf is  cre‐
       ated  at	 any  time.  Dnsmasq  can  be  told  to	 parse	more  than one
       resolv.conf file. This is useful on a laptop, where both PPP  and  DHCP
       may  be	used: dnsmasq can be set to poll both /etc/ppp/resolv.conf and
       /etc/dhcpc/resolv.conf and will use the contents of  whichever  changed
       last, giving automatic switching between DNS servers.

       Upstream	 servers  may  also be specified on the command line or in the
       configuration file.  These  server  specifications  optionally  take  a
       domain  name  which tells dnsmasq to use that server only to find names
       in that particular domain.

       In order to configure dnsmasq to act as cache for the host on which  it
       is  running,  put  "nameserver" in /etc/resolv.conf to force
       local processes to send queries to dnsmasq.  Then  either  specify  the
       upstream	 servers  directly  to	dnsmasq	 using --server options or put
       their addresses real in another file, say /etc/resolv.dnsmasq  and  run
       dnsmasq	with  the -r /etc/resolv.dnsmasq option. This second technique
       allows for dynamic update of the server addresses by PPP or DHCP.

       Addresses in /etc/hosts will "shadow" different addresses for the  same
       names  in  the  upstream	 DNS, so "mycompany.com" in /etc/hosts
       will ensure that queries for "mycompany.com" always return even
       if  queries  in	the  upstream  DNS  would otherwise return a different
       address. There is one exception to this: if the upstream DNS contains a
       CNAME  which  points  to	 a  shadowed  name,  then looking up the CNAME
       through dnsmasq will result in the unshadowed address  associated  with
       the  target  of	the  CNAME.  To	 work  around  this,  add the CNAME to
       /etc/hosts so that the CNAME is shadowed too.

       The tag system works as follows: For each DHCP  request,	 dnsmasq  col‐
       lects a set of valid tags from active configuration lines which include
       set:<tag>, including one from  the  dhcp-range  used  to	 allocate  the
       address,	 one  from  any matching dhcp-host (and "known" if a dhcp-host
       matches) The tag "bootp" is set for BOOTP requests,  and	 a  tag	 whose
       name  is the name of the interface on which the request arrived is also

       Any configuration lines which include one or more tag:<tag>  constructs
       will  only  be  valid  if  all that tags are matched in the set derived
       above. Typically this is dhcp-option.  dhcp-option which has tags  will
       be  used in preference  to an untagged dhcp-option, provided that _all_
       the tags match somewhere in the set collected as described  above.  The
       prefix  '!' on a tag means 'not' so --dhcp=option=tag:!purple,3,
       sends the option when the tag purple is not in the set of  valid	 tags.
       (If  using  this in a command line rather than a configuration file, be
       sure to escape !, which is a shell metacharacter)

       When selecting dhcp-options, a tag from dhcp-range is second class rel‐
       ative to other tags, to make it easy to override options for individual
       hosts, so dhcp-range=set:interface1,......   dhcp-host=set:myhost,.....
       dhcp-option=tag:interface1,option:nis-domain,"domain1"		 dhcp-
       option=tag:myhost,option:nis-domain,"domain2" will set  the  NIS-domain
       to  domain1  for hosts in the range, but override that to domain2 for a
       particular host.

       Note that for dhcp-range both tag:<tag> and set:<tag> are  allowed,  to
       both select the range in use based on (eg) dhcp-host, and to affect the
       options sent, based on the range selected.

       This system evolved from an earlier, more limited one and for  backward
       compatibility  "net:"  may  be used instead of "tag:" and "set:" may be
       omitted. (Except in dhcp-host, where "net:"  may	 be  used  instead  of
       "set:".)	 For  the same reason, '#' may be used instead of '!' to indi‐
       cate NOT.

       The DHCP server in dnsmasq will function as a BOOTP server  also,  pro‐
       vided that the MAC address and IP address for clients are given, either
       using dhcp-host configurations or in /etc/ethers	 ,  and	 a  dhcp-range
       configuration  option  is present to activate the DHCP server on a par‐
       ticular network. (Setting --bootp-dynamic removes the need  for	static
       address mappings.) The filename parameter in a BOOTP request is used as
       a tag, as is the tag "bootp", allowing some control  over  the  options
       returned to different classes of hosts.

       Configuring  dnsmasq  to	 act as an authoritative DNS server is compli‐
       cated by the fact  that	it  involves  configuration  of	 external  DNS
       servers	to provide delegation. We will walk through three scenarios of
       increasing complexity. Prerequisites for all of these scenarios	are  a
       globally	 accessible  IP	 address, an A or AAAA record pointing to that
       address, and an external DNS server capable of doing delegation of  the
       zone  in question. For the first part of this explanation, we will call
       the A (or AAAA) record for the globally accessible address server.exam‐
       ple.com, and the zone for which dnsmasq is authoritative our.zone.com.

       The  simplest configuration consists of two lines of dnsmasq configura‐
       tion; something like


       and two records in the external DNS

       server.example.com	A
       our.zone.com	       NS    server.example.com

       eth0 is the external network interface on which dnsmasq	is  listening,
       and has (globally accessible) address

       Note that the external IP address may well be dynamic (ie assigned from
       an ISP by DHCP or PPP) If so, the A  record  must  be  linked  to  this
       dynamic assignment by one of the usual dynamic-DNS systems.

       A  more	complex,  but practically useful configuration has the address
       record for the globally accessible IP address residing in the  authori‐
       tative  zone  which  dnsmasq  is serving, typically at the root. Now we


       our.zone.com		A
       our.zone.com	       NS    our.zone.com

       The A record for our.zone.com has now become a glue record,  it	solves
       the chicken-and-egg problem of finding the IP address of the nameserver
       for our.zone.com when the A record is within that zone. Note that  this
       is  the	only role of this record: as dnsmasq is now authoritative from
       our.zone.com it too must provide this record. If the  external  address
       is static, this can be done with an /etc/hosts entry or --host-record.


       If  the	external  address  is  dynamic,	 the  address  associated with
       our.zone.com must be derived from the address of	 the  relevant	inter‐
       face. This is done using interface-name Something like:


       (The  "eth0"  argument  in  auth-zone adds the subnet containing eth0's
       dynamic address to the zone, so that  the  interface-name  returns  the
       address in outside queries.)

       Our final configuration builds on that above, but also adds a secondary
       DNS server. This is another DNS server which learns the	DNS  data  for
       the  zone by doing zones transfer, and acts as a backup should the pri‐
       mary server become inaccessible. The configuration of the secondary  is
       beyond  the scope of this man-page, but the extra configuration of dns‐
       masq is simple:



       our.zone.com	      NS    secondary.myisp.com

       Adding auth-sec-servers enables zone transfer in dnsmasq, to allow  the
       secondary to collect the DNS data. If you wish to restrict this data to
       particular hosts then

       auth-peer=<IP address of secondary>

       will do so.

       Dnsmasq acts as an authoritative server for  in-addr.arpa and ipv6.arpa
       domains associated with the subnets given in auth-zone declarations, so
       reverse (address to name) lookups can be simply configured with a suit‐
       able NS record, for instance in this example, where we allow

	3.2.1.in-addr.arpa  NS	  our.zone.com

       Note that at present, reverse (in-addr.arpa and ip6.arpa) zones are not
       available  in  zone transfers, so there is no point arranging secondary
       servers for reverse lookups.

       When dnsmasq is configured to act as an authoritative server, the  fol‐
       lowing data is used to populate the authoritative zone.

       --mx-host, --srv-host, --dns-rr, --txt-record, --naptr-record , as long
       as the record names are in the authoritative domain.

       --cname as long as the record name is in	 the authoritative domain.  If
       the  target of the CNAME is unqualified, then it	 is qualified with the
       authoritative zone name.

       IPv4 and IPv6 addresses from /etc/hosts (and --addn-hosts ) and --host-
       record  and --interface-name provided the address falls into one of the
       subnets specified in the --auth-zone.

       Addresses of DHCP leases, provided the address falls into  one  of  the
       subnets	specified  in the --auth-zone.	(If contructed DHCP ranges are
       is use, which depend on the address dynamically assigned to  an	inter‐
       face, then the form of --auth-zone which defines subnets by the dynamic
       address of an interface should be used  to  ensure  this	 condition  is

       In  the	default	 mode, where a DHCP lease has an unqualified name, and
       possibly a qualified name constructed using --domain then the  name  in
       the authoritative zone is constructed from the unqualified name and the
       zone's domain. This may or may not equal that  specified	 by  --domain.
       If  --dhcp-fqdn	is set, then the fully qualified names associated with
       DHCP leases are used, and must match the zone's domain.

       0 - Dnsmasq successfully forked into the background, or terminated nor‐
       mally if backgrounding is not enabled.

       1 - A problem with configuration was detected.

       2  - A problem with network access occurred (address in use, attempt to
       use privileged ports without permission).

       3 - A problem occurred with a filesystem operation (missing file/direc‐
       tory, permissions).

       4 - Memory allocation failure.

       5 - Other miscellaneous problem.

       11  or  greater	-  a non zero return code was received from the lease-
       script process "init" call. The exit code from dnsmasq is the  script's
       exit code with 10 added.

       The default values for resource limits in dnsmasq are generally conser‐
       vative, and appropriate for embedded router type devices with slow pro‐
       cessors and limited memory. On more capable hardware, it is possible to
       increase the limits,  and  handle  many	more  clients.	The  following
       applies to dnsmasq-2.37: earlier versions did not scale as well.

       Dnsmasq	is  capable  of	 handling DNS and DHCP for at least a thousand
       clients. The DHCP lease times should not be very short (less  than  one
       hour).  The  value of --dns-forward-max can be increased: start with it
       equal to the number of clients and increase if  DNS  seems  slow.  Note
       that  DNS  performance  depends	too on the performance of the upstream
       nameservers. The size of the DNS cache may be increased: the hard limit
       is  10000  names	 and the default (150) is very low. Sending SIGUSR1 to
       dnsmasq makes it log information which is useful for tuning  the	 cache
       size. See the NOTES section for details.

       The  built-in  TFTP  server is capable of many simultaneous file trans‐
       fers: the absolute limit is  related  to	 the  number  of  file-handles
       allowed	to  a  process	and the ability of the select() system call to
       cope with large numbers of file handles. If the limit is set  too  high
       using  --tftp-max it will be scaled down and the actual limit logged at
       start-up. Note that more transfers are possible when the same  file  is
       being sent than when each transfer sends a different file.

       It  is possible to use dnsmasq to block Web advertising by using a list
       of known banner-ad servers, all resolving to or,  in
       /etc/hosts or an additional hosts file. The list can be very long, dns‐
       masq has been tested successfully with one  million  names.  That  size
       file needs a 1GHz processor and about 60Mb of RAM.

       Dnsmasq	can  be	 compiled to support internationalisation. To do this,
       the make targets "all-i18n" and "install-i18n" should be	 used  instead
       of  the standard targets "all" and "install". When internationalisation
       is compiled in, dnsmasq will produce log messages in the local language
       and  support  internationalised	domain	names  (IDN).  Domain names in
       /etc/hosts, /etc/ethers and /etc/dnsmasq.conf which  contain  non-ASCII
       characters  will be translated to the DNS-internal punycode representa‐
       tion. Note that dnsmasq determines both the language for	 messages  and
       the  assumed  charset for configuration files from the LANG environment
       variable. This should be set to the system default value by the	script
       which  is responsible for starting dnsmasq. When editing the configura‐
       tion files, be careful to do so using only  the	system-default	locale
       and not user-specific one, since dnsmasq has no direct way of determin‐
       ing the charset in use, and must assume that it is the system default.



       /etc/resolv.conf	  /var/run/dnsmasq/resolv.conf	  /etc/ppp/resolv.conf






       hosts(5), resolver(5)

       This manual page was written by Simon Kelley <simon@thekelleys.org.uk>.


List of man pages available for ElementaryOS

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net