.TH IP\-ROUTE 8 "13 Dec 2012" "iproute2" "Linux"

.SH "NAME"

ip-route \- routing table management

.SH "SYNOPSIS"

.sp

.ad l

.in +8

.ti -8

.B ip

.RI "[ " ip-OPTIONS " ]"

.B route

.RI " { " COMMAND " | "

.BR help " }"

.sp

.ti -8

.ti -8

.BR "ip route" " { "

.BR show " | " flush " } "

.I  SELECTOR

.ti -8

.BR "ip route save"

.I SELECTOR

.ti -8

.BR "ip route restore"

.ti -8

.B  ip route get

.I ROUTE_GET_FLAGS

.IR ADDRESS " [ "

.BI from " ADDRESS " iif " STRING"

.RB " ] [ " oif

.IR STRING " ] [ "

.B  mark

.IR MARK " ] [ "

.B  tos

.IR TOS " ] [ "

.B  vrf

.IR NAME " ] [ "

.B  ipproto

.IR PROTOCOL " ] [ "

.B  sport

.IR NUMBER " ] [ "

.B  dport

.IR NUMBER " ] "

.ti -8

.BR "ip route" " { " add " | " del " | " change " | " append " | "\

replace " } "

.I  ROUTE

.ti -8

.IR SELECTOR " := "

.RB "[ " root

.IR PREFIX " ] [ "

.B  match

.IR PREFIX " ] [ "

.B  exact

.IR PREFIX " ] [ "

.B  table

.IR TABLE_ID " ] [ "

.B  vrf

.IR NAME " ] [ "

.B  proto

.IR RTPROTO " ] [ "

.B  type

.IR TYPE " ] [ "

.B  scope

.IR SCOPE " ]"

.ti -8

.IR ROUTE " := " NODE_SPEC " [ " INFO_SPEC " ]"

.ti -8

.IR NODE_SPEC " := [ " TYPE " ] " PREFIX " ["

.B  tos

.IR TOS " ] [ "

.B  table

.IR TABLE_ID " ] [ "

.B  proto

.IR RTPROTO " ] [ "

.B  scope

.IR SCOPE " ] [ "

.B  metric

.IR METRIC " ] [ "

.B  ttl-propagate

.RB "{ " enabled " | " disabled " } ]"

.ti -8

.IR INFO_SPEC " := { " NH " | "

.B nhid

.IR ID " } " "OPTIONS FLAGS" " ["

.B  nexthop

.IR NH " ] ..."

.ti -8

.IR NH " := [ "

.B  encap

.IR ENCAP " ] [ "

.B  via

[

.IR FAMILY " ] " ADDRESS " ] [ "

.B  dev

.IR STRING " ] [ "

.B  weight

.IR NUMBER " ] " NHFLAGS

.ti -8

.IR FAMILY " := [ "

.BR inet " | " inet6 " | " mpls " | " bridge " | " link " ]"

.ti -8

.IR OPTIONS " := " FLAGS " [ "

.B  mtu

.IR NUMBER " ] [ "

.B  advmss

.IR NUMBER " ] [ "

.B  as

[

.B to

]

.IR ADDRESS " ]"

.B  rtt

.IR TIME " ] [ "

.B  rttvar

.IR TIME " ] [ "

.B  reordering

.IR NUMBER " ] [ "

.B  window

.IR NUMBER " ] [ "

.B  cwnd

.IR NUMBER " ] [ "

.B  ssthresh

.IR NUMBER " ] [ "

.B  realms

.IR REALM " ] [ "

.B  rto_min

.IR TIME " ] [ "

.B  initcwnd

.IR NUMBER " ] [ "

.B  initrwnd

.IR NUMBER " ] [ "

.B  features

.IR FEATURES " ] [ "

.B  quickack

.IR BOOL " ] [ "

.B  congctl

.IR NAME " ] [ "

.B  pref

.IR PREF " ] [ "

.B  expires

.IR TIME " ] ["

.B  fastopen_no_cookie

.IR BOOL " ]"

.ti -8

.IR TYPE " := [ "

.BR unicast " | " local " | " broadcast " | " multicast " | "\

throw " | " unreachable " | " prohibit " | " blackhole " | " nat " ]"

.ti -8

.IR TABLE_ID " := [ "

.BR local "| " main " | " default " | " all " |"

.IR NUMBER " ]"

.ti -8

.IR SCOPE " := [ "

.BR host " | " link " | " global " |"

.IR NUMBER " ]"

.ti -8

.IR NHFLAGS " := [ "

.BR onlink " | " pervasive " ]"

.ti -8

.IR RTPROTO " := [ "

.BR kernel " | " boot " | " static " |"

.IR NUMBER " ]"

.ti -8

.IR FEATURES " := [ "

.BR ecn " | ]"

.ti -8

.IR PREF " := [ "

.BR low " | " medium " | " high " ]"

.ti -8

.IR ENCAP " := [ "

.IR ENCAP_MPLS " | " ENCAP_IP " | " ENCAP_BPF " | "

.IR ENCAP_SEG6 " | " ENCAP_SEG6LOCAL " ] "

.ti -8

.IR ENCAP_MPLS " := "

.BR mpls " [ "

.IR LABEL " ] ["

.B  ttl

.IR TTL " ]"

.ti -8

.IR ENCAP_IP " := "

.B ip

.B id

.IR TUNNEL_ID

.B  dst

.IR REMOTE_IP " [ "

.B src

.IR SRC " ] ["

.B tos

.IR TOS " ] ["

.B  ttl

.IR TTL " ]"

.ti -8

.IR ENCAP_BPF " := "

.BR bpf " [ "

.B in

.IR PROG " ] ["

.B out

.IR PROG " ] ["

.B xmit

.IR PROG " ] ["

.B headroom

.IR SIZE " ]"

.ti -8

.IR ENCAP_SEG6 " := "

.B seg6

.BR mode " [ "

.BR encap " | " inline " | " l2encap " ] "

.B segs

.IR SEGMENTS " [ "

.B hmac

.IR KEYID " ]"

.ti -8

.IR ENCAP_SEG6LOCAL " := "

.B seg6local

.BR action

.IR SEG6_ACTION " [ "

.IR SEG6_ACTION_PARAM " ] "

.ti -8

.IR ROUTE_GET_FLAGS " := "

.BR " [ "

.BR fibmatch

.BR " ] "

.SH DESCRIPTION

.B ip route

is used to manipulate entries in the kernel routing tables.

.sp

.B Route types:

.in +8

.B unicast

- the route entry describes real paths to the destinations covered

by the route prefix.

.sp

.B unreachable

- these destinations are unreachable. Packets are discarded and the

ICMP message

.I host unreachable

is generated.

The local senders get an

.I EHOSTUNREACH

error.

.sp

.B blackhole

- these destinations are unreachable. Packets are discarded silently.

The local senders get an

.I EINVAL

error.

.sp

.B prohibit

- these destinations are unreachable. Packets are discarded and the

ICMP message

.I communication administratively prohibited

is generated. The local senders get an

.I EACCES

error.

.sp

.B local

- the destinations are assigned to this host. The packets are looped

back and delivered locally.

.sp

.B broadcast

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

link broadcasts.

.sp

.B 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

.I net unreachable

is generated. The local senders get an

.I ENETUNREACH

error.

.sp

.B 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

.BR "via" .

.B Warning:

Route NAT is no longer supported in Linux 2.6.

.sp

.B anycast

.RI "- " "not implemented"

the destinations are

.I anycast

addresses assigned to this host. They are mainly equivalent

to

.B local

with one difference: such addresses are invalid when used

as the source address of any packet.

.sp

.B multicast

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

normal routing tables.

.in -8

.P

.B 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

.B @SYSCONFDIR@/rt_tables

By default all normal routes are inserted into the

.B 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.

.sp

Actually, one other table always exists, which is invisible but

even more important. It is the

.B 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

.I policy routing

is used.

.TP

ip route add

add new route

.TP

ip route change

change route

.TP

ip route replace

change or add new one

.RS

.TP

.BI to " TYPE PREFIX " (default)

the destination prefix of the route. If

.I TYPE

is omitted,

.B ip

assumes type

.BR "unicast" .

Other values of

.I TYPE

are listed above.

.I PREFIX

is an IP or IPv6 address optionally followed by a slash and the

prefix length. If the length of the prefix is missing,

.B ip

assumes a full-length host route. There is also a special

.I PREFIX

.B default

- which is equivalent to IP

.B 0/0

or to IPv6

.BR "::/0" .

.TP

.BI tos " TOS"

.TP

.BI 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.

.I TOS

is either an 8 bit hexadecimal number or an identifier

from

.BR "@SYSCONFDIR@/rt_dsfield" .

.TP

.BI metric " NUMBER"

.TP

.BI preference " NUMBER"

the preference value of the route.

.I NUMBER

is an arbitrary 32bit number, where routes with lower values are preferred.

.TP

.BI table " TABLEID"

the table to add this route to.

.I TABLEID

may be a number or a string from the file

.BR "@SYSCONFDIR@/rt_tables" .

If this parameter is omitted,

.B ip

assumes the

.B main

table, with the exception of

.BR local ", " broadcast " and " nat

routes, which are put into the

.B local

table by default.

.TP

.BI vrf " NAME"

the vrf name to add this route to. Implicitly means the table

associated with the VRF.

.TP

.BI dev " NAME"

the output device name.

.TP

.BI 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

.B 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.

.TP

.BI src " ADDRESS"

the source address to prefer when sending to the destinations

covered by the route prefix.

.TP

.BI realm " REALMID"

the realm to which this route is assigned.

.I REALMID

may be a number or a string from the file

.BR "@SYSCONFDIR@/rt_realms" .

.TP

.BI mtu " MTU"

.TP

.BI "mtu lock" " MTU"

the MTU along the path to the destination. If the modifier

.B lock

is not used, the MTU may be updated by the kernel due to

Path MTU Discovery. If the modifier

.B 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.

.TP

.BI 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.

.TP

.BI 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.

.TP

.BI rttvar " TIME " "(Linux 2.3.15+ only)"

the initial RTT variance estimate. Values are specified as with

.BI rtt

above.

.TP

.BI 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

.BI rtt

above.

.TP

.BI ssthresh " NUMBER " "(Linux 2.3.15+ only)"

an estimate for the initial slow start threshold.

.TP

.BI cwnd " NUMBER " "(Linux 2.3.15+ only)"

the clamp for congestion window. It is ignored if the

.B lock

flag is not used.

.TP

.BI 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.

.TP

.BI 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.

.TP

.BI features " FEATURES " (Linux 3.18+ only)

Enable or disable per-route features. Only available feature at this

time is

.B 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

.B net.ipv4.tcp_ecn

sysctl is set to 0.

.TP

.BI quickack " BOOL " "(Linux 3.11+ only)"

Enable or disable quick ack for connections to this destination.

.TP

.BI fastopen_no_cookie " BOOL " "(Linux 4.15+ only)"

Enable TCP Fastopen without a cookie for connections to this destination.

.TP

.BI congctl " NAME " "(Linux 3.20+ only)"

.TP

.BI "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

.B lock

is not used, an application may nevertheless overwrite the suggested congestion

control algorithm for that destination. If the modifier

.B 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.

.TP

.BI 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.)

.TP

.BI 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

.B sysctl

variable

.BR "net/ipv4/tcp_reordering" .

.TP

.BI nexthop " NEXTHOP"

the nexthop of a multipath route.

.I NEXTHOP

is a complex value with its own syntax similar to the top level

argument lists:

.in +8

.BI via " [ FAMILY ] ADDRESS"

- is the nexthop router.

.sp

.BI dev " NAME"

- is the output device.

.sp

.BI weight " NUMBER"

- is a weight for this element of a multipath

route reflecting its relative bandwidth or quality.

.in -8

The internal buffer used in iproute2 limits the maximum number of nexthops that

may be specified in one go. If only

.I 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

.B "ip route append"

command.

.TP

.BI scope " SCOPE_VAL"

the scope of the destinations covered by the route prefix.

.I SCOPE_VAL

may be a number or a string from the file

.BR "@SYSCONFDIR@/rt_scopes" .

If this parameter is omitted,

.B ip

assumes scope

.B global

for all gatewayed

.B unicast

routes, scope

.B link

for direct

.BR unicast " and " broadcast

routes and scope

.BR host " for " local

routes.

.TP

.BI protocol " RTPROTO"

the routing protocol identifier of this route.

.I RTPROTO

may be a number or a string from the file

.BR "@SYSCONFDIR@/rt_protos" .

If the routing protocol ID is not given,

.B ip assumes protocol

.B 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:

.in +8

.B redirect

- the route was installed due to an ICMP redirect.

.sp

.B kernel

- the route was installed by the kernel during autoconfiguration.

.sp

.B boot

- the route was installed during the bootup sequence.

If a routing daemon starts, it will purge all of them.

.sp

.B 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.

.sp

.B ra

- the route was installed by Router Discovery protocol.

.in -8

.sp

The rest of the values are not reserved and the administrator is free

to assign (or not to assign) protocol tags.

.TP

.B onlink

pretend that the nexthop is directly attached to this link,

even if it does not match any interface prefix.

.TP

.BI pref " PREF"

the IPv6 route preference.

.I PREF

is a string specifying the route preference as defined in RFC4191 for Router

Discovery messages. Namely:

.in +8

.B low

- the route has a lowest priority

.sp

.B medium

- the route has a default priority

.sp

.B high

- the route has a highest priority

.sp

.TP

.BI nhid " ID"

use nexthop object with given id as nexthop specification.

.sp

.TP

.BI encap " ENCAPTYPE ENCAPHDR"

attach tunnel encapsulation attributes to this route.

.sp

.I ENCAPTYPE

is a string specifying the supported encapsulation type. Namely:

.in +8

.BI mpls

- encapsulation type MPLS

.sp

.BI ip

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

.sp

.BI bpf

- Execution of BPF program

.sp

.BI seg6

- encapsulation type IPv6 Segment Routing

.sp

.BI seg6local

- local SRv6 segment processing

.in -8

.I ENCAPHDR

is a set of encapsulation attributes specific to the

.I ENCAPTYPE.

.in +8

.B mpls

.in +2

.I MPLSLABEL

- mpls label stack with labels separated by

.I "/"

.sp

.B ttl

.I TTL

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

.in -2

.sp

.B ip

.in +2

.B id

.I TUNNEL_ID

.B  dst

.IR REMOTE_IP " [ "

.B src

.IR SRC " ] ["

.B tos

.IR TOS " ] ["

.B  ttl

.IR TTL " ] [ "

.BR key " ] [ " csum " ] [ " seq " ] "

.in -2

.sp

.B bpf

.in +2

.B in

.I PROG

- BPF program to execute for incoming packets

.sp

.B out

.I PROG

- BPF program to execute for outgoing packets

.sp

.B xmit

.I PROG

- BPF program to execute for transmitted packets

.sp

.B headroom

.I SIZE

- Size of header BPF program will attach (xmit)

.in -2

.sp

.B seg6

.in +2

.B mode inline

- Directly insert Segment Routing Header after IPv6 header

.sp

.B mode encap

- Encapsulate packet in an outer IPv6 header with SRH

.sp

.B mode l2encap

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

.sp

.I SEGMENTS

- List of comma-separated IPv6 addresses

.sp

.I KEYID

- Numerical value in decimal representation. See \fBip-sr\fR(8).

.in -2

.sp

.B seg6local

.in +2

.IR SEG6_ACTION " [ "

.IR SEG6_ACTION_PARAM " ] "

- Operation to perform on matching packets.

The following actions are currently supported (\fBLinux 4.14+ only\fR).

.in +2

.B 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.

.B End.X nh6

.I 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.

.B End.DX6 nh6

.I 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.

.B End.B6 srh segs

.IR SEGMENTS " [ "

.B hmac

.IR 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.

.B End.B6.Encaps srh segs

.IR SEGMENTS " [ "

.B hmac

.IR 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 \fBip-sr\fR(8).

.in -4

.in -8

.TP

.BI expires " TIME " "(Linux 4.4+ only)"

the route will be deleted after the expires time.

.B Only

support IPv6 at present.

.TP

.BR 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.

.RE

.TP

ip route delete

delete route

.RS

.B ip route del

has the same arguments as

.BR "ip route add" ,

but their semantics are a bit different.

Key values

.RB "(" to ", " tos ", " preference " and " table ")"

select the route to delete. If optional attributes are present,

.B ip

verifies that they coincide with the attributes of the route to delete.

If no route with the given key and attributes was found,