Home : Computers : Linux : Man Pages : ip-route

ip-route


SYNOPSIS

       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 ]

       ROUTE := NODE_SPEC [ INFO_SPEC ]

       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 ] [ features FEATURES ] [ quickack
               BOOL ] [ congctl NAME ] [ expires TIME ]

       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 ]

       FEATURES := [ ecn | ]


DESCRIPTION

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

       Route types:
               prohibit - these destinations are unreachable. Packets are dis-
               carded and the ICMP message communication administratively pro-
               hibited is generated. The local senders get an EACCES error.

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

               broadcast - the destinations are broadcast addresses. The pack-
               ets 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 ENETUNREACH
               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 ta-
       ble automatically and the administrator usually need not modify it or
              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 associated
                     mask and the longest match is understood as: First, com-
                     pare 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 number 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 unicast
                     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-
                     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
                     milliseconds.

              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

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

              congctl NAME (3.20+ only)

              congctl lock NAME (3.20+ only)
                     Sets a specific TCP congestion control algorithm only for
                     a given destination.  If not specified, Linux keeps the
                     current global default TCP congestion control algorithm,
                     or the one set from the application. If the modifier lock
                     is not used, an application may nevertheless overwrite
                     the suggested congestion control algorithm for that des-
                     tination. If the modifier lock is used, then an applica-
                     tion is not allowed to overwrite the specified congestion
                     control algorithm for that destination, thus it will be
                     enforced/guaranteed to use the proposed algorithm.

              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-
                     interpretation.  Namely:

                             redirect - the route was installed due to an ICMP
                             redirect.

                             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
                             protocol.

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

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

       expires TIME (4.4+ only)
              the route will be deleted after the expires time.  Only support
              IPv6 at present.

       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
              fails.

       ip route show
                     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.

              cloned

              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

       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
                     routed.

              connected
                     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

       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.


EXAMPLES

       ip ro
           Show all route entries in the kernel.

       ip route add default via 192.168.1.1 dev eth0
           Adds a default route (for all addresses) via the local gateway
           192.168.1.1 that can be reached on device eth0.


SEE ALSO

       ip(8)


AUTHOR

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


iproute2 13 Dec 2012 IP-ROUTE(8)



Subscribe to us on YouTube