ip-route(8)
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>
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