Provided by: iproute2_4.3.0-1ubuntu3.16.04.5_amd64 bug


       ip-route - routing table management


       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 ]


       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 ]


       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

               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

               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

       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

              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

                             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

              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

                             all - list all of the tables.

                             cache - dump the routing cache.


              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.

                     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

       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.


       ip ro
           Show all route entries in the kernel.

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




       Original Manpage by Michail Litvak <>