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 /usr/share/iproute2/rt_dsfield or /etc/iproute2/rt_dsfield (has precedence if exists).

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 /usr/share/iproute2/rt_tables or /etc/iproute2/rt_tables (has precedence if exists). 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 /usr/share/iproute2/rt_realms or /etc/iproute2/rt_realms (has precedence if exists).

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 /usr/share/iproute2/rt_scopes or /etc/iproute2/rt_scopes (has precedence if exists). 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 /usr/share/iproute2/rt_protos or /etc/iproute2/rt_protos (has precedence if exists). 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

xfrm - encapsulation type XFRM

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 encap.red - Encapsulate packet in an outer IPv6 header with SRH applying the reduced segment list. When there is only one segment and the HMAC is not present, the SRH is omitted.

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

mode l2encap.red - Encapsulate ingress L2 frame within an outer IPv6 header and SRH applying the reduced segment list. When there is only one segment and the HMAC is not present, the SRH is omitted.

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 [ flavors FLAVORS ] - Regular SRv6 processing as intermediate segment endpoint. This action only accepts packets with a non-zero Segments Left value. Other matching packets are dropped. The presence of flavors can change the regular processing of an End behavior according to the user-provided Flavor operations and information carried in the packet. See Flavors parameters section.

End.X nh6 NEXTHOP [ flavors FLAVORS ] - 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. The presence of flavors can change the regular processing of an End.X behavior according to the user-provided Flavor operations and information carried in the packet. See Flavors parameters section.

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 /usr/share/iproute2/rt_tables or /etc/iproute2/rt_tables (has precedence if exists). 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 /usr/share/iproute2/rt_tables or /etc/iproute2/rt_tables (has precedence if exists). 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 /usr/share/iproute2/rt_tables or /etc/iproute2/rt_tables (has precedence if exists). 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).

Flavors parameters

The flavors represent additional operations that can modify or extend a subset of the existing behaviors.

flavors OPERATION[,OPERATION] [ATTRIBUTES]

OPERATION := { psp | usp | usd | next-csid }

ATTRIBUTES := { KEY VALUE } [ ATTRIBUTES ]

KEY := { lblen | nflen }

psp - The Penultimate Segment Pop (PSP) copies the last SID from the SID List (carried by the outermost SRH) into the IPv6 Destination Address (DA) and removes (i.e. pops) the SRH from the IPv6 header. The PSP operation takes place only at a penultimate SR Segment Endpoint node (e.g., the Segment Left must be one) and does not happen at non-penultimate endpoint nodes. This flavor is currently only supported by End behavior.

usp - Ultimate Segment Pop of the SRH (not yet supported in kernel)

usd - Ultimate Segment Decapsulation (not yet supported in kernel)

next-csid - The NEXT-C-SID mechanism offers the possibility of encoding several SRv6 segments within a single 128 bit SID address. The NEXT-C-SID flavor can be configured to support user-provided Locator-Block and Locator-Node Function lengths. If Locator-Block and/or Locator-Node Function lengths are not provided by the user during configuration of an SRv6 End behavior instance with NEXT-C-SID flavor, the default value is 32-bit for Locator-Block and 16-bit for Locator-Node Function.

lblen VALUE - defines the Locator-Block length for NEXT-C-SID flavor. The Locator-Block length must be greater than 0 and evenly divisible by 8. This attribute can be used only with NEXT-C-SID flavor.

nflen VALUE - defines the Locator-Node Function length for NEXT-C-SID flavors. The Locator-Node Function length must be greater than 0 and evenly divisible by 8. This attribute can be used only with NEXT-C-SID flavor.

ioam6
freq K/N - Inject IOAM in K packets every N packets (default is 1/1).

mode inline - Directly insert IOAM after IPv6 header (default mode).

mode encap - Encapsulate packet in an outer IPv6 header with IOAM.

mode auto - Automatically use inline mode for local packets and encap mode for in-transit packets.

tundst ADDRESS - IPv6 address of the tunnel destination (outer header), not used with inline mode.

type IOAM6_TRACE_TYPE - List of IOAM data required in the trace, represented by a bitfield (24 bits).

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

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

xfrm
if_id IF_ID [ link_dev LINK_DEV ]

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 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.

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.

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 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 behaves like ip route show except that the output is raw data suitable for passing to ip route restore.

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.

Show all route entries in the kernel.

Adds a default route (for all addresses) via the local gateway 192.168.1.1 that can be reached on device eth0.

Adds an ipv4 route with mpls encapsulation attributes attached to it.

Adds an IPv6 route with SRv6 encapsulation and two segments attached.

Adds an IPv6 route with SRv6 decapsulation and forward with lookup in VRF table.

Adds an IPv6 route with SRv6 End behavior with psp flavor enabled.

Adds an IPv6 route with SRv6 End behavior with next-csid flavor enabled.

Adds an IPv6 route with SRv6 End behavior with next-csid flavor enabled and user-provided Locator-Block and Locator-Node Function lengths.

Adds an IPv6 route with an IOAM Pre-allocated Trace encapsulation (ip6ip6) 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 (will be injected in 2 packets every 5 packets).

Adds an ipv4 route using nexthop object with id 10.