dhcrelay man page on SuSE

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dhcrelay(8)							   dhcrelay(8)

NAME
       dhcrelay - Dynamic Host Configuration Protocol Relay Agent

SYNOPSIS
       dhcrelay	 [ -4 ] [ -dqaD ] [ -p port ] [ -c count ] [ -A length ] [ -pf
       pid-file ] [ --no-pid ] [ -m append | replace | forward | discard  ]  [
       -i interface0 [ ...  -i interfaceN ] ] server0 [ ...serverN ]

       dhcrelay	 -6 [ -dqI ] [ -p port ] [ -c count ] [ -pf pid-file ] [ --no-
       pid ] -l lower0 [ ...  -l lowerN ] -u upper0 [ ...  -u upperN ]

DESCRIPTION
       The Internet Systems Consortium DHCP Relay Agent, dhcrelay, provides  a
       means  for  relaying  DHCP and BOOTP requests from a subnet to which no
       DHCP server is directly connected to one or more DHCP servers on	 other
       subnets.	 It supports both DHCPv4/BOOTP and DHCPv6 protocols.

OPERATION
       The  DHCP Relay Agent listens for DHCPv4 or DHCPv6 queries from clients
       or other relay agents on one or more interfaces, passing them along  to
       ``upstream''  servers or relay agents as specified on the command line.
       When a reply is received from upstream, it is multicast or unicast back
       downstream to the source of the original request.

COMMAND LINE
       Protocol selection options:

       -6     Run  dhcrelay as a DHCPv6 relay agent.  Incompatible with the -4
	      option.

       -4     Run dhcrelay as a DHCPv4/BOOTP relay agent.  This is the default
	      mode  of operation, so the argument is not necessary, but may be
	      specified for clarity.  Incompatible with -6.

       Specifying DHCPv4/BOOTP servers

       In DHCPv4 mode, a list of one or more server addresses must  be	speci‐
       fied  on	 the  command  line,  to  which	 DHCP/BOOTP  queries should be
       relayed.

       Options available for both DHCPv4 and DHCPv6:

       -c COUNT
	      Maximum hop count.  When forwarding packets,  dhcrelay  discards
	      packets which have reached a hop count of COUNT.	Default is 10.
	      Maximum is 255.

       -d     Force dhcrelay to run as a foreground process.  Useful when run‐
	      ning  dhcrelay  under  a	debugger, or running out of inittab on
	      System V systems.

       -p PORT
	      Listen and transmit on port PORT.	 This  is  mostly  useful  for
	      debugging	 purposes.   Default  is  port 67 for DHCPv4/BOOTP, or
	      port 547 for DHCPv6.

       -q     Quiet mode.  Prevents dhcrelay6 from printing its	 network  con‐
	      figuration on startup.

       -pf pid-file
	      Path to alternate pid file.

       --no-pid
	      Option  to  disable  writing  pid files.	By default the program
	      will write a pid file.

       Options available in DHCPv4 mode only:

       -a     Append an agent option field to each request  before  forwarding
	      it  to  the server.   Agent option fields in responses sent from
	      servers to clients  will	be  stripped  before  forwarding  such
	      responses	 back to the client.  The agent option field will con‐
	      tain two agent options: the Circuit ID suboption and the	Remote
	      ID  suboption.   Currently, the Circuit ID will be the printable
	      name of the interface on which the client request was  received.
	      The  client supports inclusion of a Remote ID suboption as well,
	      but this is not used by default.

       -A LENGTH
	      Specify the maximum  packet  size	 to  send  to  a  DHCPv4/BOOTP
	      server.	This might be done to allow sufficient space for addi‐
	      tion of relay agent options while still fitting into the	Ether‐
	      net MTU size.

       -D     Drop  packets  from upstream servers if they contain Relay Agent
	      Information  options  that  indicate  they  were	generated   in
	      response	to  a query that came via a different relay agent.  If
	      this option is not specified, such packets will be relayed  any‐
	      way.

       -i ifname
	      Listen  for  DHCPv4/BOOTP queries on interface ifname.  Multiple
	      interfaces may be specified by using more than  one  -i  option.
	      If  no  interfaces  are  specified on the command line, dhcrelay
	      will identify all network interfaces, eliminating	 non-broadcast
	      interfaces if possible, and attempt to listen on all of them.

       -m append|replace|forward|discard
	      Control  the  handling  of incoming DHCPv4 packets which already
	      contain relay agent options.  If such a  packet  does  not  have
	      giaddr  set  in  its header, the DHCP standard requires that the
	      packet be discarded.  However, if giaddr is set, the relay agent
	      may  handle  the	situation in four ways:	 It may append its own
	      set of relay options to the packet, leaving the supplied	option
	      field intact; it may replace the existing agent option field; it
	      may forward the packet unchanged; or, it may discard it.

	      To use this option you must also enable the -a option.

       Options available in DHCPv6 mode only:

       -I     Force use of the DHCPv6 Interface-ID  option.   This  option  is
	      automatically  sent when there are two or more downstream inter‐
	      faces in use, to	disambiguate  between  them.   The  -I	option
	      causes  dhcrelay	to  send  the option even if there is only one
	      downstream interface.

       -l [address%]ifname[#index]
	      Specifies the ``lower'' network interface for DHCPv6 relay mode:
	      the  interface on which queries will be received from clients or
	      from other relay	agents.	  At  least  one  -l  option  must  be
	      included	in  the command line when running in DHCPv6 mode.  The
	      interface name  ifname  is  a  mandatory	parameter.   The  link
	      address can be specified by address%; if it isn't, dhcrelay will
	      use the first non-link-local address configured  on  the	inter‐
	      face.   The  optional  #index  parameter specifies the interface
	      index.

       -u [address%]ifname
	      Specifies the ``upper'' network interface for DHCPv6 relay mode:
	      the  interface  to  which	 queries  from clients and other relay
	      agents should be forwarded.  At least  one  -u  option  must  be
	      included	in  the command line when running in DHCPv6 mode.  The
	      interface name ifname is a mandatory parameter. The  destination
	      unicast  or  multicast  address can be specified by address%; if
	      not specified, the  relay	 agent	will  forward  to  the	DHCPv6
	      All_DHCP_Relay_Agents_and_Servers multicast address.

       It  is  possible to specify the same interface with different addresses
       more than once, and even, when the system supports it, to use the  same
       interface as both upper and lower interfaces.

SEE ALSO
       dhclient(8), dhcpd(8), RFC3315, RFC2132, RFC2131.

BUGS
       Using the same interface on both upper and lower sides may cause loops,
       so when running this way, the maximum hop count should be set to a  low
       value.

       The loopback interface is not (yet) recognized as a valid interface.

AUTHOR
       dhcrelay(8)  To	learn  more  about  Internet  Systems  Consortium, see
       https://www.isc.org

								   dhcrelay(8)
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