iproute is used to manipulate entries in the kernel routing tables.
Routetypes: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 hostunreachable 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
communicationadministrativelyprohibited 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 netunreachable 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 - notimplemented 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.
Routetables: 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 /usr/share/iproute2/rt_tables or /etc/iproute2/rt_tables (has precedence
if exists). 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 policyrouting is used.
ip route add
add new route
ip route change
change route
ip route replace
change or add new one
toTYPEPREFIX(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 PREFIXdefault - which is equivalent to IP 0/0
or to IPv6 ::/0.
tosTOSdsfieldTOS
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).
metricNUMBERpreferenceNUMBER
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
/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.
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
/usr/share/iproute2/rt_realms or /etc/iproute2/rt_realms (has precedence if exists).
mtuMTUmtulockMTU
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(Linux2.3.15+only)
the initial RTT variance estimate. Values are specified as with rtt above.
rto_minTIME(Linux2.6.23+only)
the minimum TCP Retransmission TimeOut to use when communicating with this destination.
Values are specified as with rtt above.
ssthreshNUMBER(Linux2.3.15+only)
an estimate for the initial slow start threshold.
cwndNUMBER(Linux2.3.15+only)
the clamp for congestion window. It is ignored if the lock flag is not used.
initcwndNUMBER(Linux2.5.70+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(Linux2.6.33+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(Linux3.11+only)
Enable or disable quick ack for connections to this destination.
fastopen_no_cookieBOOL(Linux4.15+only)
Enable TCP Fastopen without a cookie for connections to this destination.
congctlNAME(Linux3.20+only)congctllockNAME(Linux3.20+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(Linux2.3.15+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(Linux2.3.15+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 iprouteappend command.
scopeSCOPE_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.
protocolRTPROTO
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, ipassumesprotocolboot (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
nhidID
use nexthop object with given id as nexthop specification.
encapENCAPTYPEENCAPHDR
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.mplsMPLSLABEL - mpls label stack with labels separated by /ttlTTL - TTL to use for MPLS header or 0 to inherit from IP header
ipidTUNNEL_ID - Tunnel ID (for example VNI in VXLAN tunnel)
dstREMOTE_IP - Outer header destination IP address (IPv4 or IPv6)
srcSRC - Outer header source IP address (IPv4 or IPv6)
tosTOS - Outer header TOS
ttlTTL - Outer header TTL
key - Outer header flags with key in GRE tunnel
csum - Outer header flags with csum in GRE tunnel
seq - Outer header flags with seq in GRE tunnel
GENEVE_OPTS - Specified in the form CLASS:TYPE:DATA, where CLASS is represented
as a 16bit hexadecimal value, TYPE as an 8bit hexadecimal value and DATA as a
variable length hexadecimal value. Additionally multiple options may be listed
using a comma delimiter.
VXLAN_OPTS - Specified in the form GBP, as a 32bit number. Multiple options is
not supported.
ERSPAN_OPTS - Specified in the form VERSION:INDEX:DIR:HWID, where VERSION is
represented as a 8bit number, INDEX as an 32bit number, DIR and HWID as a 8bit
number. Multiple options is not supported. Note INDEX is used when VERSION is 1,
and DIR and HWID are used when VERSION is 2.
bpfinPROG - BPF program to execute for incoming packets
outPROG - BPF program to execute for outgoing packets
xmitPROG - BPF program to execute for transmitted packets
headroomSIZE - Size of header BPF program will attach (xmit)
seg6modeinline - Directly insert Segment Routing Header after IPv6 header
modeencap - Encapsulate packet in an outer IPv6 header with SRH
modeencap.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.
model2encap - Encapsulate ingress L2 frame within an outer IPv6 header and SRH
model2encap.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).
seg6localSEG6_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 (Linux4.14+only).
End [ flavorsFLAVORS ] - 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 Flavorsparameters
section.
End.Xnh6NEXTHOP [ flavorsFLAVORS ] - 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 Flavorsparameters
section.
End.DX6nh6NEXTHOP - 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.DT4vrftableTABLEID - 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.DT46vrftableTABLEID - 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.B6srhsegsSEGMENTS [ hmacKEYID ] - 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.EncapssrhsegsSEGMENTS [ hmacKEYID ] - 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).
Flavorsparameters
The flavors represent additional operations that can modify or extend a subset
of the existing behaviors.
flavorsOPERATION[,OPERATION] [ATTRIBUTES]
OPERATION := { psp | usp | usd | next-csid }
ATTRIBUTES := { KEYVALUE } [ 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.
lblenVALUE - 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.
nflenVALUE - 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.
ioam6freqK/N - Inject IOAM in K packets every N packets (default is 1/1).
modeinline - Directly insert IOAM after IPv6 header (default mode).
modeencap - Encapsulate packet in an outer IPv6 header with IOAM.
modeauto - Automatically use inline mode for local packets and encap mode for
in-transit packets.
tunsrcADDRESS - IPv6 address of the tunnel source (outer header), not used
with inline mode. It is optional: if not provided, the tunnel source address
is chosen automatically.
tundstADDRESS - IPv6 address of the tunnel destination (outer header), not
used with inline mode.
typeIOAM6_TRACE_TYPE - List of IOAM data required in the trace, represented by
a bitfield (24 bits).
nsIOAM6_NAMESPACE - Numerical value to represent an IOAM namespace. See ip-ioam(8).
sizeIOAM6_TRACE_SIZE - Size, in octets, of the pre-allocated trace data block.
xfrmif_idIF_ID[link_devLINK_DEV ]
expiresTIME(Linux4.4+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
iproutedel has the same arguments as iprouteadd, 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, iproutedel 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, match or exact) 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,
10/8 and 0/0, but it does not select 10.1/16 and 10.0.0/24. 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.
tosTOSdsfieldTOS
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
clonedcached 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 tablecache.
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.
realmREALMIDrealmsFROMREALM/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 iprouteshow, 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, iprouteflush 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.
tosTOSdsfieldTOS
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 (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.
flowlabelFLOWLABEL
ipv6 flow label as seen by the route lookup
Note that this operation is not equivalent to iprouteshow. 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 iproutelscache, 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
iprouterestore.
ip route restore
restore routing table information from stdin
This command expects to read a data stream as returned from iproutesave. 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.
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