ip-route(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLES | SEE ALSO | AUTHOR | COLOPHON

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

NAME         top

       ip-route - routing table management

SYNOPSIS         top

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

       ip route { show | flush } SELECTOR

       ip route save SELECTOR

       ip route restore

       ip route get ROUTE_GET_FLAGS ADDRESS [ from ADDRESS iif STRING  ] [
               oif STRING ] [ mark MARK ] [ tos TOS ] [ vrf NAME ] [ ipproto
               PROTOCOL ] [ sport NUMBER ] [ dport NUMBER ]

       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 ] [ ttl-propagate {
               enabled | disabled } ]

       INFO_SPEC := { NH | nhid ID } OPTIONS FLAGS [ nexthop NH ] ...

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

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

       OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS
               ] rtt TIME ] [ rttvar TIME ] [ reordering NUMBER ] [ window
               NUMBER ] [ cwnd NUMBER ] [ ssthresh NUMBER ] [ realms REALM ]
               [ rto_min TIME ] [ initcwnd NUMBER ] [ initrwnd NUMBER ] [
               features FEATURES ] [ quickack BOOL ] [ congctl NAME ] [ pref
               PREF ] [ expires TIME ] [ fastopen_no_cookie 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 ]

       FEATURES := [ ecn | ]

       PREF := [ low | medium | high ]

       ENCAP := [ ENCAP_MPLS | ENCAP_IP | ENCAP_BPF | ENCAP_SEG6 |
               ENCAP_SEG6LOCAL ]

       ENCAP_MPLS := mpls [ LABEL ] [ ttl TTL ]

       ENCAP_IP := ip id TUNNEL_ID dst REMOTE_IP [ src SRC ] [ tos TOS ] [
               ttl TTL ]

       ENCAP_BPF := bpf [ in PROG ] [ out PROG ] [ xmit PROG ] [ headroom
               SIZE ]

       ENCAP_SEG6 := seg6 mode [ encap | inline | l2encap ] segs SEGMENTS [
               hmac KEYID ]

       ENCAP_SEG6LOCAL := seg6local action SEG6_ACTION [ SEG6_ACTION_PARAM ]

       ROUTE_GET_FLAGS :=  [ fibmatch  ]

DESCRIPTION         top

       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 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
               error.

               local - the destinations are assigned to this host. The
               packets 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
               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 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 2^32-1 or by name from
       the file /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 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.

              tos TOS

              dsfield TOS
                     the Type Of Service (TOS) key. This key has no
                     associated 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 number or an identifier from /rt_dsfield.

              metric NUMBER

              preference NUMBER
                     the preference value of the route.  NUMBER is an
                     arbitrary 32bit number, where routes with lower values
                     are preferred.

              table TABLEID
                     the table to add this route to.  TABLEID may be a
                     number or a string from the file /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.

              vrf NAME
                     the vrf name to add this route to. Implicitly means the
                     table associated with the VRF.

              dev NAME
                     the output device name.

              via [ FAMILY ] ADDRESS
                     the address of the nexthop router, in the address
                     family FAMILY.  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 /rt_realms.

              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 discovery 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 maximal 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 milliseconds.

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

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

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

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

              initcwnd NUMBER (Linux 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 (Linux 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 (Linux3.18+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 (Linux 3.11+ only)
                     Enable or disable quick ack for connections to this
                     destination.

              fastopen_no_cookie BOOL (Linux 4.15+ only)
                     Enable TCP Fastopen without a cookie for connections to
                     this destination.

              congctl NAME (Linux 3.20+ only)

              congctl lock NAME (Linux 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 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 (Linux 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 (Linux 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 [ FAMILY ] 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.

                     The internal buffer used in iproute2 limits the maximum
                     number of nexthops that may be specified in one go. If
                     only ADDRESS is given, the current buffer size allows
                     for 144 IPv6 nexthops and 253 IPv4 ones. For IPv4, this
                     effectively limits the number of nexthops possible per
                     route. With IPv6, further nexthops may be appended to
                     the same route via ip route append command.

              scope SCOPE_VAL
                     the scope of the destinations covered by the route
                     prefix.  SCOPE_VAL may be a number or a string from the
                     file /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 /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.
                             Routing 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 interface prefix.

              pref PREF
                     the IPv6 route preference.  PREF is a string specifying
                     the route preference as defined in RFC4191 for Router
                     Discovery messages. Namely:

                             low - the route has a lowest priority

                             medium - the route has a default priority

                             high - the route has a highest priority

              nhid ID
                     use nexthop object with given id as nexthop
                     specification.

              encap ENCAPTYPE ENCAPHDR
                     attach tunnel encapsulation attributes to this route.

                     ENCAPTYPE is a string specifying the supported
                     encapsulation type. Namely:

                             mpls - encapsulation type MPLS

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

                             bpf - Execution of BPF program

                             seg6 - encapsulation type IPv6 Segment Routing

                             seg6local - local SRv6 segment processing

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

                             mpls
                               MPLSLABEL - mpls label stack with labels
                               separated by /

                               ttl TTL - TTL to use for MPLS header or 0 to
                               inherit from IP header

                             ip
                               id TUNNEL_ID dst REMOTE_IP [ src SRC ] [ tos
                               TOS ] [ ttl TTL ] [ key ] [ csum ] [ seq ]

                             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
                               transmitted packets

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

                             seg6
                               mode inline - Directly insert Segment Routing
                               Header after IPv6 header

                               mode encap - Encapsulate packet in an outer
                               IPv6 header with SRH

                               mode l2encap - Encapsulate ingress L2 frame
                               within an outer IPv6 header and SRH

                               SEGMENTS - List of comma-separated IPv6
                               addresses

                               KEYID - Numerical value in decimal
                               representation. See ip-sr(8).

                             seg6local
                               SEG6_ACTION [ SEG6_ACTION_PARAM ] - Operation
                               to perform on matching packets.  The
                               following actions are currently supported
                               (Linux 4.14+ only).

                                 End - Regular SRv6 processing as
                                 intermediate segment endpoint.  This action
                                 only accepts packets with a non-zero
                                 Segments Left value. Other matching packets
                                 are dropped.

                                 End.X nh6 NEXTHOP - Regular SRv6 processing
                                 as intermediate segment endpoint.
                                 Additionally, forward processed packets to
                                 given next-hop.  This action only accepts
                                 packets with a non-zero Segments Left
                                 value. Other matching packets are dropped.

                                 End.DX6 nh6 NEXTHOP - Decapsulate inner
                                 IPv6 packet and forward it to the specified
                                 next-hop. If the argument is set to ::,
                                 then the next-hop is selected according to
                                 the local selection rules. This action only
                                 accepts packets with either a zero Segments
                                 Left value or no SRH at all, and an inner
                                 IPv6 packet. Other matching packets are
                                 dropped.

                                 End.B6 srh segs SEGMENTS [ hmac KEYID ] -
                                 Insert the specified SRH immediately after
                                 the IPv6 header, update the DA with the
                                 first segment of the newly inserted SRH,
                                 then forward the resulting packet. The
                                 original SRH is not modified. This action
                                 only accepts packets with a non-zero
                                 Segments Left value. Other matching packets
                                 are dropped.

                                 End.B6.Encaps srh segs SEGMENTS [ hmac
                                 KEYID ] - Regular SRv6 processing as
                                 intermediate segment endpoint.
                                 Additionally, encapsulate the matching
                                 packet within an outer IPv6 header followed
                                 by the specified SRH. The destination
                                 address of the outer IPv6 header is set to
                                 the first segment of the new SRH. The
                                 source address is set as described in
                                 ip-sr(8).

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

              ttl-propagate { enabled | disabled }
                     Control whether TTL should be propagated from any encap
                     into the un-encapsulated packet, overriding any global
                     configuration. Only supported for MPLS 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
                     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
                     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 [ 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
              arguments 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.

              fibmatch
                     Return full fib lookup matched route. Default is to
                     return the resolved dst entry

              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.

              mark MARK
                     the firewall mark (fwmark)

              vrf NAME
                     force the vrf device on which this packet will be
                     routed.

              ipproto PROTOCOL
                     ip protocol as seen by the route lookup

              sport NUMBER
                     source port as seen by the route lookup

              dport NUMBER
                     destination port as seen by the route lookup

              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
              information exactly as it was at the time of the save, so any
              translation 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         top

       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         top

       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.

       ip route add 10.1.1.0/30 encap mpls 200/300 via 10.1.1.1 dev eth0
           Adds an ipv4 route with mpls encapsulation attributes attached to
           it.

       ip -6 route add 2001:db8:1::/64 encap seg6 mode encap segs
       2001:db8:42::1,2001:db8:ffff::2 dev eth0
           Adds an IPv6 route with SRv6 encapsulation and two segments
           attached.

       ip route add 10.1.1.0/30 nhid 10
           Adds an ipv4 route using nexthop object with id 10.

SEE ALSO         top

       ip(8)

AUTHOR         top

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

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-06-24.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

iproute2                         13 Dec 2012                     IP-ROUTE(8)

Pages that refer to this page: ip(8)ip-sr(8)ip-vrf(8)tc-route(8)wg(8)wg-quick(8)