Back to main site | Back to man page index

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 ] [ 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 | ]

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

       Route types:

               unicast - the route entry describes real paths to the destinations covered by the route prefix.

               unreachable - these destinations are unreachable. Packets are discarded and the ICMP message host

               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 equiva‐
               lent 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 forwarding. The addresses to
               translate to are selected with the attribute via.  Warning: Route NAT is no longer supported in Linux

               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 auto‐
       matically 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 followed 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.

                     the preference value of the route.  NUMBER is an arbitrary 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 destinations 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 modifier lock is not used, the MTU may be
                     updated by the kernel due to Path MTU Discovery. If the modifier lock is used, no path MTU dis‐
                     covery will be tried, all packets will be sent without the DF bit in IPv4 case or fragmented to
                     MTU for IPv6.

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

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

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

              initcwnd NUMBER (2.5.70+ only)
                     the initial congestion window size for connections to this destination.  Actual window size is
                     this value multiplied by the MSS (``Maximal Segment Size'') for same connection. The default is
                     zero, meaning to use the values 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.

              features FEATURES (3.18+only)
                     Enable or disable per-route features.  Only available feature at this time is ecn to enable
                     explicit congestion notification when initiating connections to the given destination network.
                     When responding to a connection request from the given network, ecn will also be used even if
                     the net.ipv4.tcp_ecn sysctl is set to 0.

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

              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 speci‐
                     fied, 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 over‐
                     write the suggested congestion control algorithm for that destination. If the modifier lock is
                     used, then an application 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 con‐
                     nections. 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 argument lists:

                             via ADDRESS - is the nexthop router.

              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 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 administrator to override dynamic routing. Rout‐
                             ing daemon will respect them and, probably, even advertise them to its peers.

                             ra - the route was installed by Router Discovery protocol.

                     The rest of the values are not reserved and the administrator 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 inter‐
                     face 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
              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 modi‐
                     fier (root, match or exact) and a prefix.  root PREFIX selects routes with prefixes not shorter

              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

              realms FROMREALM/TOREALM
                     only list routes with these realms.

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

       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

              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.

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

              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 information exactly as it was at the time of the save, so any translation of informa‐
              tion 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.


       Original Manpage by Michail Litvak <[email protected]>

iproute2                                             13 Dec 2012                                          IP-ROUTE(8)