Provided by: iproute2_4.3.0-1ubuntu3.16.04.5_amd64 
NAME
ip-route - routing table management
SYNOPSIS
ip [ ip-OPTIONS ] route { COMMAND | help }
ip route { list | flush } SELECTOR
ip route save SELECTOR
ip route restore
ip route get ADDRESS [ from ADDRESS iif STRING ] [ oif STRING ] [ tos TOS ]
ip route { add | del | change | append | replace } ROUTE
SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table TABLE_ID ] [ 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 ]
INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ] ...
NH := [ via [ FAMILY ] ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS
FAMILY := [ inet | inet6 | ipx | dnet | mpls | bridge | link ]
OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS ] rtt TIME ] [ rttvar TIME ] [
reordering NUMBER ] [ window NUMBER ] [ cwnd NUMBER ] [ ssthresh REALM ] [ realms REALM ] [
rto_min TIME ] [ initcwnd NUMBER ] [ initrwnd NUMBER ] [ features FEATURES ] [ quickack BOOL ] [
congctl NAME ] pref PREF ]
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 ]
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 2^31 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.
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.
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 (2.3.15+ only)
the initial RTT variance estimate. Values are specified as with rtt above.
rto_min TIME (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 (2.3.15+ only)
an estimate for the initial slow start threshold.
cwnd NUMBER (2.3.15+ only)
the clamp for congestion window. It is ignored if the lock flag is not used.
initcwnd NUMBER (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 (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 (3.18+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 (3.11+ only)
Enable or disable quick ack for connections to this destination.
congctl NAME (3.20+ only)
congctl lock NAME (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 (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 (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.
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
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.
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.
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.
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.
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.
SEE ALSO
ip(8)
AUTHOR
Original Manpage by Michail Litvak <mci@owl.openwall.com>
iproute2 13 Dec 2012 IP-ROUTE(8)