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
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 ] -
Operation to perform on matching packets.
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.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).
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 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.
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
to ADDRESS (default)
the destination address.
from ADDRESS
the source address.
tos TOS
dsfield TOS
the Type Of Service.
iif NAME
the device from which this packet is expected to
arrive.
oif NAME
force the output device on which this packet will
be routed.
mark MARK
the firewall mark (fwmark)
vrf NAME
force the vrf device on which this packet will be
routed.
ipproto PROTOCOL
ip protocol as seen by the route lookup
sport NUMBER
source port as seen by the route lookup
dport NUMBER
destination port as seen by the route lookup
connected
if no source address (option from) was given,
relookup the route with the source set to the
preferred address received from the first lookup.
If policy routing is used, it may be a different
route.
Note that this operation is not equivalent to ip route
show. show shows existing routes. get resolves them and
creates new clones if necessary. Essentially, get is
equivalent to sending a packet along this path. If the
iif argument is not given, the kernel creates a route to
output packets towards the requested destination. This is
equivalent to pinging the destination with a subsequent ip
route ls cache, however, no packets are actually sent.
With the iif argument, the kernel pretends that a packet
arrived from this interface and searches for a path to
forward the packet.
ip route save
save routing table information to stdout
This command behaves like ip route show except that the
output is raw data suitable for passing to ip route
restore.
ip route restore
restore routing table information from stdin
This command expects to read a data stream as returned
from ip route save. It will attempt to restore the
routing table information exactly as it was at the time of
the save, so any translation of information in the stream
(such as device indexes) must be done first. Any existing
routes are left unchanged. Any routes specified in the
data stream that already exist in the table will be
ignored.
