ip-route man page on ElementaryOS

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IP-ROUTE(8)			     Linux			   IP-ROUTE(8)

       ip-route - routing table management

       ip [ ip-OPTIONS ] route	{ COMMAND | help }

       ip route { list | flush } SELECTOR

       ip route save SELECTOR

       ip route restore

       ip route get ADDRESS [ from ADDRESS iif STRING  ] [ oif STRING ] [ tos
	       TOS ]

       ip route { add | del | change | append | replace } ROUTE

       SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table
	       TABLE_ID ] [ proto RTPROTO ] [ type TYPE ] [ scope SCOPE ]


       NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ] [ table TABLE_ID ] [ proto
	       RTPROTO ] [ scope SCOPE ] [ metric METRIC ]

       INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ] ...

       NH := [ via ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS

       OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ rtt TIME ] [ rttvar
	       TIME ] [ reordering NUMBER ] [ window NUMBER ] [ cwnd NUMBER ]
	       [ ssthresh REALM ] [ realms REALM ] [ rto_min TIME ] [ initcwnd
	       NUMBER ] [ initrwnd NUMBER ] [ quickack BOOL ]

       TYPE := [ unicast | local | broadcast | multicast | throw | unreachable
	       | prohibit | blackhole | nat ]

       TABLE_ID := [ local| main | default | all | NUMBER ]

       SCOPE := [ host | link | global | NUMBER ]

       NHFLAGS := [ onlink | pervasive ]

       RTPROTO := [ kernel | boot | static | NUMBER ]

       ip route is used to manipulate entries in the kernel routing tables.

       Route types:

	       unicast - the route entry describes real paths to the destina‐
	       tions covered by the route prefix.

	       unreachable - these destinations are unreachable.  Packets are
	       discarded and the ICMP message host unreachable is generated.
	       The local senders get an EHOSTUNREACH error.

	       blackhole - these destinations are unreachable.	Packets are
	       discarded silently.  The local senders get an EINVAL error.

	       prohibit - these destinations are unreachable.  Packets are
	       discarded and the ICMP message communication administratively
	       prohibited is generated.	 The local senders get an EACCES

	       local - the destinations are assigned to this host.  The pack‐
	       ets are looped back and delivered locally.

	       broadcast - the destinations are broadcast addresses.  The
	       packets are sent as link broadcasts.

	       throw - a special control route used together with policy
	       rules. If such a route is selected, lookup in this table is
	       terminated pretending that no route was found.  Without policy
	       routing it is equivalent to the absence of the route in the
	       routing table.  The packets are dropped and the ICMP message
	       net unreachable is generated.  The local senders get an ENETUN‐
	       REACH error.

	       nat - a special NAT route.  Destinations covered by the prefix
	       are considered to be dummy (or external) addresses which
	       require translation to real (or internal) ones before forward‐
	       ing.  The addresses to translate to are selected with the
	       attribute via.  Warning: Route NAT is no longer supported in
	       Linux 2.6.

	       anycast - not implemented the destinations are anycast
	       addresses assigned to this host.	 They are mainly equivalent to
	       local with one difference: such addresses are invalid when used
	       as the source address of any packet.

	       multicast - a special type used for multicast routing.  It is
	       not present in normal routing tables.

       Route tables: Linux-2.x can pack routes into several routing tables
       identified by a number in the range from 1 to 2^31 or by name from the
       file /etc/iproute2/rt_tables By default all normal routes are inserted
       into the main table (ID 254) and the kernel only uses this table when
       calculating routes.  Values (0, 253, 254, and 255) are reserved for
       built-in use.

       Actually, one other table always exists, which is invisible but even
       more important.	It is the local table (ID 255).	 This table consists
       of routes for local and broadcast addresses.  The kernel maintains this
       table automatically and the administrator usually need not modify it or
       even look at it.

       The multiple routing tables enter the game when policy routing is used.

       ip route add
	      add new route

       ip route change
	      change route

       ip route replace
	      change or add new one

	      to TYPE PREFIX (default)
		     the destination prefix of the route.  If TYPE is omitted,
		     ip assumes type unicast.  Other values of TYPE are listed
		     above.  PREFIX is an IP or IPv6 address optionally fol‐
		     lowed by a slash and the prefix length.  If the length of
		     the prefix is missing, ip assumes a full-length host
		     route.  There is also a special PREFIX default - which is
		     equivalent to IP 0/0 or to IPv6 ::/0.

	      tos TOS

	      dsfield TOS
		     the Type Of Service (TOS) key.  This key has no associ‐
		     ated mask and the longest match is understood as: First,
		     compare the TOS of the route and of the packet.  If they
		     are not equal, then the packet may still match a route
		     with a zero TOS.  TOS is either an 8 bit hexadecimal num‐
		     ber or an identifier from /etc/iproute2/rt_dsfield.

	      metric NUMBER

	      preference NUMBER
		     the preference value of the route.	 NUMBER is an arbi‐
		     trary 32bit number.

	      table TABLEID
		     the table to add this route to.  TABLEID may be a number
		     or a string from the file /etc/iproute2/rt_tables.	 If
		     this parameter is omitted, ip assumes the main table,
		     with the exception of local, broadcast and nat routes,
		     which are put into the local table by default.

	      dev NAME
		     the output device name.

	      via ADDRESS
		     the address of the nexthop router.	 Actually, the sense
		     of this field depends on the route type.  For normal uni‐
		     cast routes it is either the true next hop router or, if
		     it is a direct route installed in BSD compatibility mode,
		     it can be a local address of the interface.  For NAT
		     routes it is the first address of the block of translated
		     IP destinations.

	      src ADDRESS
		     the source address to prefer when sending to the destina‐
		     tions covered by the route prefix.

	      realm REALMID
		     the realm to which this route is assigned.	 REALMID may
		     be a number or a string from the file

	      mtu MTU

	      mtu lock MTU
		     the MTU along the path to the destination.	 If the modi‐
		     fier lock is not used, the MTU may be updated by the ker‐
		     nel due to Path MTU Discovery.  If the modifier lock is
		     used, no path MTU discovery will be tried, all packets
		     will be sent without the DF bit in IPv4 case or frag‐
		     mented to MTU for IPv6.

	      window NUMBER
		     the maximal window for TCP to advertise to these destina‐
		     tions, measured in bytes.	It limits maximal data bursts
		     that our TCP peers are allowed to send to us.

	      rtt TIME
		     the initial RTT ('Round Trip Time') estimate. If no suf‐
		     fix is specified the units are raw values passed directly
		     to the routing code to maintain compatibility with previ‐
		     ous releases.  Otherwise if a suffix of s, sec or secs is
		     used to specify seconds and ms, msec or msecs to specify

	      rttvar TIME (2.3.15+ only)
		     the initial RTT variance estimate. Values are specified
		     as with rtt above.

	      rto_min TIME (2.6.23+ only)
		     the minimum TCP Retransmission TimeOut to use when commu‐
		     nicating with this destination.  Values are specified as
		     with rtt above.

	      ssthresh NUMBER (2.3.15+ only)
		     an estimate for the initial slow start threshold.

	      cwnd NUMBER (2.3.15+ only)
		     the clamp for congestion window.  It is ignored if the
		     lock flag is not used.

	      initcwnd NUMBER (2.5.70+ only)
		     the initial congestion window size for connections to
		     this destination.	Actual window size is this value mul‐
		     tiplied by the MSS (``Maximal Segment Size'') for same
		     connection. The default is zero, meaning to use the val‐
		     ues specified in RFC2414.

	      initrwnd NUMBER (2.6.33+ only)
		     the initial receive window size for connections to this
		     destination.  Actual window size is this value multiplied
		     by the MSS of the connection.  The default value is zero,
		     meaning to use Slow Start value.

	      quickack BOOL (3.11+ only)
		     Enable or disable quick ack for connections to this des‐

	      advmss NUMBER (2.3.15+ only)
		     the MSS ('Maximal Segment Size') to advertise to these
		     destinations when establishing TCP connections.  If it is
		     not given, Linux uses a default value calculated from the
		     first hop device MTU.  (If the path to these destination
		     is asymmetric, this guess may be wrong.)

	      reordering NUMBER (2.3.15+ only)
		     Maximal reordering on the path to this destination.  If
		     it is not given, Linux uses the value selected with
		     sysctl variable net/ipv4/tcp_reordering.

	      nexthop NEXTHOP
		     the nexthop of a multipath route.	NEXTHOP is a complex
		     value with its own syntax similar to the top level argu‐
		     ment lists:

			     via ADDRESS - is the nexthop router.

			     dev NAME - is the output device.

			     weight NUMBER - is a weight for this element of a
			     multipath route reflecting its relative bandwidth
			     or quality.

	      scope SCOPE_VAL
		     the scope of the destinations covered by the route pre‐
		     fix.  SCOPE_VAL may be a number or a string from the file
		     /etc/iproute2/rt_scopes.  If this parameter is omitted,
		     ip assumes scope global for all gatewayed unicast routes,
		     scope link for direct unicast and broadcast routes and
		     scope host for local routes.

	      protocol RTPROTO
		     the routing protocol identifier of this route.  RTPROTO
		     may be a number or a string from the file
		     /etc/iproute2/rt_protos.  If the routing protocol ID is
		     not given, ip assumes protocol boot (i.e. it assumes the
		     route was added by someone who doesn't understand what
		     they are doing).  Several protocol values have a fixed
		     interpretation.  Namely:

			     redirect - the route was installed due to an ICMP

			     kernel - the route was installed by the kernel
			     during autoconfiguration.

			     boot - the route was installed during the bootup
			     sequence.	If a routing daemon starts, it will
			     purge all of them.

			     static - the route was installed by the adminis‐
			     trator to override dynamic routing. Routing dae‐
			     mon will respect them and, probably, even adver‐
			     tise them to its peers.

			     ra - the route was installed by Router Discovery

		     The rest of the values are not reserved and the adminis‐
		     trator is free to assign (or not to assign) protocol

	      onlink pretend that the nexthop is directly attached to this
		     link, even if it does not match any interface prefix.

       ip route delete
	      delete route
	      ip route del has the same arguments as ip route add, but their
	      semantics are a bit different.

	      Key values (to, tos, preference and table) select the route to
	      delete.  If optional attributes are present, ip verifies that
	      they coincide with the attributes of the route to delete.	 If no
	      route with the given key and attributes was found, ip route del

       ip route show
	      list routes
	      the command displays the contents of the routing tables or the
	      route(s) selected by some criteria.

	      to SELECTOR (default)
		     only select routes from the given range of destinations.
		     SELECTOR consists of an optional modifier (root, match or
		     exact) and a prefix.  root PREFIX selects routes with
		     prefixes not shorter than PREFIX.	F.e.  root 0/0 selects
		     the entire routing table.	match PREFIX selects routes
		     with prefixes not longer than PREFIX.  F.e.  match
		     10.0/16 selects 10.0/16, 10/8 and 0/0, but it does not
		     select 10.1/16 and 10.0.0/24.  And exact PREFIX (or just
		     PREFIX) selects routes with this exact prefix. If neither
		     of these options are present, ip assumes root 0/0 i.e. it
		     lists the entire table.

	      tos TOS

	      dsfield TOS
		     only select routes with the given TOS.

	      table TABLEID
		     show the routes from this table(s).  The default setting
		     is to show table main.  TABLEID may either be the ID of a
		     real table or one of the special values:

			     all - list all of the tables.

			     cache - dump the routing cache.


	      cached list cloned routes i.e. routes which were dynamically
		     forked from other routes because some route attribute
		     (f.e. MTU) was updated.  Actually, it is equivalent to
		     table cache.

	      from SELECTOR
		     the same syntax as for to, but it binds the source
		     address range rather than destinations.  Note that the
		     from option only works with cloned routes.

	      protocol RTPROTO
		     only list routes of this protocol.

	      scope SCOPE_VAL
		     only list routes with this scope.

	      type TYPE
		     only list routes of this type.

	      dev NAME
		     only list routes going via this device.

	      via PREFIX
		     only list routes going via the nexthop routers selected
		     by PREFIX.

	      src PREFIX
		     only list routes with preferred source addresses selected
		     by PREFIX.

	      realm REALMID

		     only list routes with these realms.

       ip route flush
	      flush routing tables
	      this command flushes routes selected by some criteria.

	      The arguments have the same syntax and semantics as the argu‐
	      ments of ip route show, but routing tables are not listed but
	      purged.  The only difference is the default action: show dumps
	      all the IP main routing table but flush prints the helper page.

	      With the -statistics option, the command becomes verbose. It
	      prints out the number of deleted routes and the number of rounds
	      made to flush the routing table. If the option is given twice,
	      ip route flush also dumps all the deleted routes in the format
	      described in the previous subsection.

       ip route get
	      get a single route
	      this command gets a single route to a destination and prints its
	      contents exactly as the kernel sees it.

	      to ADDRESS (default)
		     the destination address.

	      from ADDRESS
		     the source address.

	      tos TOS

	      dsfield TOS
		     the Type Of Service.

	      iif NAME
		     the device from which this packet is expected to arrive.

	      oif NAME
		     force the output device on which this packet will be

		     if no source address (option from) was given, relookup
		     the route with the source set to the preferred address
		     received from the first lookup.  If policy routing is
		     used, it may be a different route.

	      Note that this operation is not equivalent to ip route show.
	      show shows existing routes.  get resolves them and creates new
	      clones if necessary.  Essentially, get is equivalent to sending
	      a packet along this path.	 If the iif argument is not given, the
	      kernel creates a route to output packets towards the requested
	      destination.  This is equivalent to pinging the destination with
	      a subsequent ip route ls cache, however, no packets are actually
	      sent.  With the iif argument, the kernel pretends that a packet
	      arrived from this interface and searches for a path to forward
	      the packet.

       ip route save
	      save routing table information to stdout
	      This command behaves like ip route show except that the output
	      is raw data suitable for passing to ip route restore.

       ip route restore
	      restore routing table information from stdin
	      This command expects to read a data stream as returned from ip
	      route save.  It will attempt to restore the routing table infor‐
	      mation exactly as it was at the time of the save, so any trans‐
	      lation of information in the stream (such as device indexes)
	      must be done first.  Any existing routes are left unchanged.
	      Any routes specified in the data stream that already exist in
	      the table will be ignored.

       ip ro
	   Show all route entries in the kernel.

       ip route add default via dev eth0
	   Adds a default route (for all addresses) via the local gateway that can be reached on device eth0.


       Original Manpage by Michail Litvak <mci@owl.openwall.com>

iproute2			  13 Dec 2012			   IP-ROUTE(8)

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