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ip-route


SYNOPSIS

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

       ip route { show | flush } SELECTOR

       ip route save SELECTOR

       ip route restore

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

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

       SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table
               TABLE_ID ] [ vrf NAME ] [ 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 := [ encap ENCAP ] [ via [ FAMILY ] ADDRESS ] [ dev STRING ] [
               weight NUMBER ] NHFLAGS

       FAMILY := [ inet | inet6 | ipx | dnet | mpls | bridge | link ]

       OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS ]
               rtt TIME ] [ rttvar TIME ] [ reordering NUMBER ] [ window NUM-
               BER ] [ cwnd NUMBER ] [ ssthresh REALM ] [ realms REALM ] [
               rto_min TIME ] [ initcwnd NUMBER ] [ initrwnd NUMBER ] [ fea-
               tures FEATURES ] [ quickack BOOL ] [ congctl NAME ] [ pref PREF
               ] [ 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 | ]

       PREF := [ low | medium | high ]

       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 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.

       routes for local and broadcast addresses. The kernel maintains this ta-
       ble 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 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.

                     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
                     /etc/iproute2/rt_realms.

              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
                     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.
                     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.

              features FEATURES (3.18+only)
                     Enable or disable per-route features. Only available fea-
                     ture 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 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
                             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
                             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
                             high - the route has a highest priority

              encap ENCAPTYPE ENCAPHDR
                     attach tunnel encapsulation attributes to this route.

                     ENCAPTYPE is a string specifying the supported encapsula-
                     tion type. Namely:

                             mpls - encapsulation type MPLS

                             ip - IP encapsulation (Geneve, GRE, VXLAN, ...)

                             bpf - Execution of BPF program

                     ENCAPHDR is a set of encapsulation attributes specific to
                     the ENCAPTYPE.

                             mpls
                               MPLSLABEL - mpls label stack with labels sepa-
                               rated by /

                             ip
                               id TUNNEL_ID dst REMOTE_IP [ tos TOS ] [ ttl
                               TTL ]

                             bpf
                               in PROG - BPF program to execute for incoming
                               packets

                               out PROG - BPF program to execute for outgoing
                               packets

                               xmit PROG - BPF program to execute for trans-
                               mitted packets

                               headroom SIZE - Size of header BPF program will
                               attach (xmit)

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

       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.

              vrf NAME
                     show the routes for the table associated with the vrf
                     name

              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

              dev NAME
                     only list routes going via this device.

              via [ FAMILY ] 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.

              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.


              vrf NAME
                     force the vrf 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
                     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.


NOTES

       Starting with Linux kernel version 3.6, there is no routing cache for
       IPv4 anymore. Hence ip route show cached will never print any entries
       on systems with this or newer kernel versions.


EXAMPLES

       ip ro
           Show all route entries in the kernel.



iproute2 13 Dec 2012 IP-ROUTE(8)



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