ip-route (8) - Linux Manuals
ip-route: routing table management
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 ]
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_IOAM6 ]
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 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 /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
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
/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 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
/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 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
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 implemented: 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 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.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 either 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 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 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 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 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 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).
ioam6 IOAM6_TRACE_TYPE - List of IOAM data required in the trace, represented 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-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 del
has the same arguments as
ip route add,
but their semantics are a bit different.
- 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.
-
the command displays the contents of the routing tables or the route(s)
selected by some criteria.
- 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.
-
this command flushes routes selected by some criteria.
- ip route get
-
get a single route
-
this command gets a single route to a destination and prints its
contents exactly as the kernel sees 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.
-
this command gets a single route to a destination and prints its
contents exactly as the kernel sees it.
- 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.
AUTHOR
Original Manpage by Michail Litvak <mci [at] owl.openwall.com>