ip-route

routing table management

SYNOPSIS

-8 ip [ip-OPTIONS] route {COMMAND| help}

-8
-8 ip route{ show|flush} SELECTOR
-8 iproutesave SELECTOR
-8 iprouterestore
-8 ip route get ROUTE_GET_FLAGS ADDRESS[ fromADDRESSiifSTRING ] [oif STRING] [ mark MARK] [ tos TOS] [ vrf NAME] [ ipproto PROTOCOL] [ sport NUMBER] [ dport NUMBER]
-8 ip route{add|del|change|append| replace " } " ROUTE
-8 SELECTOR:= [root PREFIX] [ match PREFIX] [ exact PREFIX] [ table TABLE_ID] [ vrf NAME] [ proto RTPROTO] [ type TYPE] [ scope SCOPE]
-8 ROUTE:=NODE_SPEC[INFO_SPEC]
-8 NODE_SPEC:= [TYPE]PREFIX[ tos TOS] [ table TABLE_ID] [ proto RTPROTO] [ scope SCOPE] [ metric METRIC] [ ttl-propagate {enabled|disabled} ]
-8 INFO_SPEC:=NH OPTIONS FLAGS[ nexthop NH] ...
-8 NH:= [ encap ENCAP] [ via [ FAMILY]ADDRESS] [ dev STRING] [ weight NUMBER]NHFLAGS
-8 FAMILY:= [ inet|inet6|mpls|bridge|link]
-8 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]
-8 TYPE:= [ unicast|local|broadcast|multicast| throw " | " unreachable " | " prohibit " | " blackhole " | " nat " ]"
-8 TABLE_ID:= [ local|main|default|all| NUMBER]
-8 SCOPE:= [ host|link|global| NUMBER]
-8 NHFLAGS:= [ onlink|pervasive]
-8 RTPROTO:= [ kernel|boot|static| NUMBER]
-8 FEATURES:= [ ecn| ]
-8 PREF:= [ low|medium|high]
-8 ENCAP:= [ ENCAP_MPLS|ENCAP_IP|ENCAP_BPF| ENCAP_SEG6|ENCAP_SEG6LOCAL]
-8 ENCAP_MPLS:= mpls[ LABEL] [ ttl TTL]
-8 ENCAP_IP:= ip id TUNNEL_ID dst REMOTE_IP[ tos TOS] [ ttl TTL]
-8 ENCAP_BPF:= bpf[ in PROG] [ out PROG] [ xmit PROG] [ headroom SIZE]
-8 ENCAP_SEG6:= seg6 mode[ encap|inline|l2encap] segs SEGMENTS[ hmac KEYID]
-8 ENCAP_SEG6LOCAL:= seg6local action SEG6_ACTION[ SEG6_ACTION_PARAM]
-8 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

toTYPE 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.

tosTOS

dsfieldTOS 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.

metricNUMBER

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

tableTABLEID 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,broadcastandnat routes, which are put into the local table by default.

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

devNAME 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.

srcADDRESS the source address to prefer when sending to the destinations covered by the route prefix.

realmREALMID the realm to which this route is assigned. REALMID may be a number or a string from the file /etc/iproute2/rt_realms.

mtuMTU

mtu lockMTU 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.

windowNUMBER 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.

rttTIME 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.

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

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

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

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

initcwndNUMBER(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.

initrwndNUMBER(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.

featuresFEATURES(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.

quickackBOOL(Linux 3.11+ only) Enable or disable quick ack for connections to this destination.

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

congctlNAME(Linux 3.20+ only)

congctl lockNAME(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.

advmssNUMBER(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.)

reorderingNUMBER(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.

nexthopNEXTHOP 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.

devNAME - is the output device.

weightNUMBER - 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.

scopeSCOPE_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 unicastandbroadcast routes and scope hostforlocal routes.

protocolRTPROTO 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.

prefPREF 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

encapENCAPTYPE 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[ 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 ( Linux4.14+ 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).

expiresTIME(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,preferenceandtable) 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.

toSELECTOR(default) only select routes from the given range of destinations. SELECTOR consists of an optional modifier (root,matchorexact) and a prefix. rootPREFIX selects routes with prefixes not shorter than PREFIX. F.e. root0/0 selects the entire routing table. matchPREFIX selects routes with prefixes not longer than PREFIX. F.e. match10.0/16 selects 10.0/16, 10/8and0/0, but it does not select 10.1/16and10.0.0/24. And exactPREFIX (or just PREFIX) selects routes with this exact prefix. If neither of these options are present, ip assumes root0/0 i.e. it lists the entire table.

tosTOS

dsfieldTOS only select routes with the given TOS.

tableTABLEID 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.

vrfNAME 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.

fromSELECTOR 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.

protocolRTPROTO only list routes of this protocol.

scopeSCOPE_VAL only list routes with this scope.

typeTYPE only list routes of this type.

devNAME only list routes going via this device.

via[ FAMILY ] PREFIX only list routes going via the nexthop routers selected by PREFIX.

srcPREFIX only list routes with preferred source addresses selected by PREFIX.

realmREALMID

realmsFROMREALM/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

toADDRESS(default) the destination address.

fromADDRESS the source address.

tosTOS

dsfieldTOS the Type Of Service.

iifNAME the device from which this packet is expected to arrive.

oifNAME force the output device on which this packet will be routed.

markMARK the firewall mark (fwmark)

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

ipprotoPROTOCOL ip protocol as seen by the route lookup

sportNUMBER source port as seen by the route lookup

dportNUMBER destination port as seen by the route lookup

connected if no source address (optionfrom) 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 iprouteshow 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.

AUTHOR

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