ip-route


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 ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS

       OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ rtt TIME ] [ rttvar
               TIME ] [ reordering NUMBER ] [ window NUMBER ] [ cwnd NUMBER ]
               [ ssthresh REALM ] [ realms REALM ] [ rto_min TIME ] [ initcwnd
               NUMBER ] [ initrwnd NUMBER ] [ quickack BOOL ]

       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 ]



DESCRIPTION
       ip route is used to manipulate entries in the kernel routing tables.

       Route types:

               unicast - the route entry describes real paths to the destina-
               tions covered by the route prefix.

               prohibited is generated.  The local senders get an EACCES
               error.


               local - the destinations are assigned to this host.  The pack-
               ets 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 ENETUN-
               REACH 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 forward-
               ing.  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.
                     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 fol-
                     lowed 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 associ-
                     ated 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 num-
                     ber or an identifier from /etc/iproute2/rt_dsfield.


              metric NUMBER

              preference NUMBER
                     the preference value of the route.  NUMBER is an arbi-
                     trary 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 ADDRESS
                     the address of the nexthop router.  Actually, the sense
                     of this field depends on the route type.  For normal uni-
                     cast 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 destina-
                     tions covered by the route prefix.


                     used, no path MTU discovery will be tried, all packets
                     will be sent without the DF bit in IPv4 case or frag-
                     mented to MTU for IPv6.


              window NUMBER
                     the maximal window for TCP to advertise to these destina-
                     tions, 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 suf-
                     fix is specified the units are raw values passed directly
                     to the routing code to maintain compatibility with previ-
                     ous 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 commu-
                     nicating 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 mul-
                     tiplied by the MSS (``Maximal Segment Size'') for same
                     connection. The default is zero, meaning to use the val-
                     ues 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.
                     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 argu-
                     ment lists:

                             via 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 pre-
                     fix.  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.

                     The rest of the values are not reserved and the adminis-
                     trator 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.


       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.

                     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 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 argu-
              ments 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.

                     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 infor-
              mation exactly as it was at the time of the save, so any trans-
              lation 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.



AUTHOR
       Original Manpage by Michail Litvak <mci@owl.openwall.com>



iproute2                          13 Dec 2012                      IP-ROUTE(8)
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