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

NAME
ip-route - routing table management

SYNOPSIS
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 ]

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_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 ] [ count ]

ENCAP_IOAM6 := ioam6 trace prealloc type IOAM6_TRACE_TYPE ns IOAM6_NAMESPACE size
IOAM6_TRACE_SIZE

ROUTE_GET_FLAGS := [ fibmatch ]

DESCRIPTION
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 in‐
valid 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 /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 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 uni‐‐
cast. 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 pre‐
fix 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
/etc/iproute2/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 /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.

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 /etc/iproute2/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 compati‐
bility 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 des‐
tination. 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 con‐
trol algorithm for that destination. If the modifier lock is used, then an ap‐
plication is not allowed to overwrite the specified congestion control algo‐
rithm for that destination, thus it will be enforced/guaranteed to use the pro‐
posed algorithm.

advmss NUMBER (Linux 2.3.15+ only)
the MSS ('Maximal Segment Size') to advertise to these destinations when estab‐
lishing TCP connections. If it is not given, Linux uses a default value calcu‐
lated 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 syn‐
tax 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 re‐
flecting 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 lim‐
its 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 /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 autoconfigura‐
tion.

boot - the route was installed during the bootup sequence. If a rout‐
ing daemon starts, it will purge all of them.

static - the route was installed by the administrator to override dy‐
namic routing. Routing daemon will respect them and, probably, even ad‐
vertise 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

ioam6 - encapsulation type IPv6 IOAM

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 ] [ count ] - Operation to perform on
matching packets. The optional count attribute is used to collect
statistics on the processing of actions. Three counters are imple‐
mented: 1) packets correctly processed; 2) bytes correctly processed;
3) packets that cause a processing error (i.e., missing SID List,
wrong SID List, etc). To retrieve the counters related to an action
use the -s flag in the show command. The following actions are cur‐
rently 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.DT6 { table | vrftable } TABLEID - Decapsulate the inner IPv6
packet and forward it according to the specified lookup table.
TABLEID is either a number or a string from the file
/etc/iproute2/rt_tables. If vrftable is used, the argument must be
a VRF device associated with the table id. Moreover, the VRF table
associated with the table id must be configured with the VRF strict
mode turned on (net.vrf.strict_mode=1). 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.DT4 vrftable TABLEID - Decapsulate the inner IPv4 packet and
forward it according to the specified lookup table. TABLEID is ei‐
ther a number or a string from the file /etc/iproute2/rt_tables.
The argument must be a VRF device associated with the table id.
Moreover, the VRF table associated with the table id must be con‐
figured with the VRF strict mode turned on (net.vrf.strict_mode=1).
This action only accepts packets with either a zero Segments Left
value or no SRH at all, and an inner IPv4 packet. Other matching
packets are dropped.

End.DT46 vrftable TABLEID - Decapsulate the inner IPv4 or IPv6
packet and forward it according to the specified lookup table.
TABLEID is either a number or a string from the file
/etc/iproute2/rt_tables. The argument must be a VRF device associ‐
ated with the table id. Moreover, the VRF table associated with
the table id must be configured with the VRF strict mode turned on
(net.vrf.strict_mode=1). This action only accepts packets with ei‐
ther a zero Segments Left value or no SRH at all, and an inner IPv4
or 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 pro‐
cessing as intermediate segment endpoint. Additionally, encapsu‐
late 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).

ioam6
IOAM6_TRACE_TYPE - List of IOAM data required in the trace, repre‐
sented by a bitfield (24 bits).

IOAM6_NAMESPACE - Numerical value to represent an IOAM namespace.
See ip-ioam(8).

IOAM6_TRACE_SIZE - Size, in octets, of the pre-allocated trace data
block.

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-encapsu‐
lated 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 at‐
tributes 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 en‐
tire 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 se‐
lect 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 equiva‐
lent 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 ac‐
tion: 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 de‐
scribed 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 en‐
try

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
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.

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 -6 route add 2001:db8:1::/64 encap seg6local action End.DT46 vrftable 100 dev vrf100
Adds an IPv6 route with SRv6 decapsulation and forward with lookup in VRF table.

ip -6 route add 2001:db8:1::/64 encap ioam6 trace prealloc type 0x800000 ns 1 size 12 dev
eth0
Adds an IPv6 route with an IOAM Pre-allocated Trace encapsulation that only includes the
hop limit and the node id, configured for the IOAM namespace 1 and a pre-allocated data
block of 12 octets.

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