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IP(8)                                Linux                               IP(8)

       ip - show / manipulate routing, devices, policy routing and tunnels

       ip [ OPTIONS ] OBJECT { COMMAND | help }

       OBJECT := { link | addr | route | rule | neigh | tunnel | maddr |
               mroute | monitor }

       OPTIONS := { -V[ersion] | -s[tatistics] | -r[esolve] | -f[amily] { inet
               | inet6 | ipx | dnet | link } | -o[neline] }

       ip link set DEVICE { up | down | arp { on | off } |
               promisc { on | off } |
               allmulti { on | off } |
               dynamic { on | off } |
               multicast { on | off } |
               txqueuelen PACKETS |
               name NEWNAME |
               address LLADDR | broadcast LLADDR |
               mtu MTU }

       ip link show [ DEVICE ]

       ip addr { add | del } IFADDR dev STRING

       ip addr { show | flush } [ dev STRING ] [ scope SCOPE-ID ] [ to PREFIX
               ] [ FLAG-LIST ] [ label PATTERN ]

       IFADDR := PREFIX | ADDR peer PREFIX [ broadcast ADDR ] [ anycast ADDR ]
               [ label STRING ] [ scope SCOPE-ID ]

       SCOPE-ID := [ host | link | global | NUMBER ]


       FLAG := [ permanent | dynamic | secondary | primary | tentative | dep-
               recated ]

       ip route { list | flush } SELECTOR

       ip route get ADDRESS [ from ADDRESS iif STRING  ] [ oif STRING ] [ tos
               TOS ]

       ip route { add | del | change | append | replace | monitor } 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 ADDRESS ] [ dev STRING ] [ weight NUMBER ] NHFLAGS

       OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ rtt NUMBER ] [
               rttvar NUMBER ] [ window NUMBER ] [ cwnd NUMBER ] [ ssthresh
               REALM ] [ realms REALM ]

       TYPE := [ unicast | local | broadcast | multicast | throw | unreachable
               | prohibit | blackhole | nat ]

       TABLE_ID := [ local| main | default | all | NUMBER ]

       SCOPE := [ host | link | global | NUMBER ]

       FLAGS := [ equalize ]

       NHFLAGS := [ onlink | pervasive ]

       RTPROTO := [ kernel | boot | static | NUMBER ]

       ip rule  [ list | add | del ] SELECTOR ACTION

       SELECTOR := [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK ]
               [ dev STRING ] [ pref NUMBER ]

       ACTION := [ table TABLE_ID ] [ nat ADDRESS ] [ prohibit | reject |
               unreachable ] [ realms [SRCREALM/]DSTREALM ]

       TABLE_ID := [ local | main | default | NUMBER ]

       ip neigh { add | del | change | replace } { ADDR [ lladdr LLADDR ] [
               nud { permanent | noarp | stale | reachable } ] | proxy ADDR }
               [ dev DEV ]

       ip neigh { show | flush } [ to PREFIX ] [ dev DEV ] [ nud STATE ]

       ip tunnel { add | change | del | show } [ NAME ]
               [ mode { ipip | gre | sit } ]
               [ remote ADDR ] [ local ADDR ]
               [ [i|o]seq ] [ [i|o]key KEY ] [ [i|o]csum ] ]
               [ ttl TTL ] [ tos TOS ] [ [no]pmtudisc ]
               [ dev PHYS_DEV ]

       ADDR := { IP_ADDRESS | any }

       TOS := { NUMBER | inherit }

       TTL := { 1..255 | inherit }

       KEY := { DOTTED_QUAD | NUMBER }

       ip maddr [ add | del ] MULTIADDR dev STRING

       ip maddr show [ dev STRING ]

       ip mroute show [ PREFIX ] [ from PREFIX ] [ iif DEVICE ]

       ip monitor [ all | LISTofOBJECTS ]

       -V, -Version
              print the version of the ip utility and exit.

       -s, -stats, -statistics
              output more information.  If the option appears twice  or  more,
              the amount of information increases.  As a rule, the information
              is statistics or some time values.

       -f, -family
              followed by protocol family  identifier:  inet,  inet6  or  link
              ,enforce  the  protocol  family  to  use.   If the option is not
              present, the protocol family is guessed  from  other  arguments.
              If the rest of the command line does not give enough information
              to guess the family, ip falls back to the default  one,  usually
              inet  or  any.  link is a special family identifier meaning that
              no networking protocol is involved.

       -4     shortcut for -family inet.

       -6     shortcut for -family inet6.

       -0     shortcut for -family link.

       -o, -oneline
              output each record on a single line, replacing line  feeds  with
              the  '\'  character.  This  is convenient when you want to count
              records with wc(1)
               or to grep(1) the output.

       -r, -resolve
              use the system's name resolver to print  DNS  names  instead  of
              host addresses.

       link   - network device.

              - protocol (IP or IPv6) address on a device.

              - ARP or NDISC cache entry.

       route  - routing table entry.

       rule   - rule in routing policy database.

              - multicast address.

       mroute - multicast routing cache entry.

       tunnel - tunnel over IP.

       The  names  of  all objects may be written in full or abbreviated form,
       f.e.  address is abbreviated as addr or just a.

       Specifies the action to perform on the object.   The  set  of  possible
       actions  depends on the object type.  As a rule, it is possible to add,
       delete and show (or list ) objects, but some objects do not  allow  all
       of these operations or have some additional commands.  The help command
       is available for all objects.  It prints out a list of  available  com-
       mands and argument syntax conventions.

       If no command is given, some default command is assumed.  Usually it is
       list or, if the objects of this class cannot be listed, help.

ip link - network device configuration
       link is a network device and the  corresponding  commands  display  and
       change the state of devices.

   ip link set - change device attributes
       dev NAME (default)
              NAME specifies network device to operate on.

       up and down
              change the state of the device to UP or DOWN.

       arp on or arp off
              change the NOARP flag on the device.

       multicast on or multicast off
              change the MULTICAST flag on the device.

       dynamic on or dynamic off
              change the DYNAMIC flag on the device.

       name NAME
              change  the  name  of  the device.  This operation is not recom-
              mended if the device is running or has  some  addresses  already

       txqueuelen NUMBER

       txqlen NUMBER
              change the transmit queue length of the device.

       mtu NUMBER
              change the MTU of the device.

       address LLADDRESS
              change the station address of the interface.

       broadcast LLADDRESS

       brd LLADDRESS

       peer LLADDRESS
              change the link layer broadcast address or the peer address when
              the interface is POINTOPOINT.

       Warning: If multiple parameter changes are requested, ip aborts immedi-
       ately after any of the changes have failed.  This is the only case when
       ip can move the system to an unpredictable state.  The solution  is  to
       avoid changing several parameters with one ip link set call.

   ip link show - display device attributes
       dev NAME (default)
              NAME  specifies the network device to show.  If this argument is
              omitted all devices are listed.

       up     only display running interfaces.

ip address - protocol address management.
       The address is a protocol (IP or IPv6) address attached  to  a  network
       device.   Each  device must have at least one address to use the corre-
       sponding protocol.  It is possible to have several different  addresses
       attached to one device.  These addresses are not discriminated, so that
       the term alias is not quite appropriate for them and we do not  use  it
       in this document.

       The  ip  addr command displays addresses and their properties, adds new
       addresses and deletes old ones.

   ip address add - add new protocol address.
       dev NAME
              the name of the device to add the address to.

       local ADDRESS (default)
              the address of the interface. The format of the address  depends
              on  the  protocol.  It is a dotted quad for IP and a sequence of
              hexadecimal halfwords separated by colons for IPv6.  The ADDRESS
              may  be  followed  by a slash and a decimal number which encodes
              the network prefix length.

       peer ADDRESS
              the address of the remote endpoint for  pointopoint  interfaces.
              Again, the ADDRESS may be followed by a slash and a decimal num-
              ber, encoding the network prefix length.  If a peer  address  is
              specified,  the  local address cannot have a prefix length.  The
              network prefix is associated with the peer rather than with  the
              local address.

       broadcast ADDRESS
              the broadcast address on the interface.

              It is possible to use the special symbols '+' and '-' instead of
              the broadcast address.  In this case, the broadcast  address  is
              derived by setting/resetting the host bits of the interface pre-

       label NAME
              Each address may be tagged with a label  string.   In  order  to
              preserve  compatibility  with Linux-2.0 net aliases, this string
              must coincide with the name of the device or  must  be  prefixed
              with the device name followed by colon.

       scope SCOPE_VALUE
              the  scope  of the area where this address is valid.  The avail-
              able scopes are listed in file /etc/iproute2/rt_scopes.   Prede-
              fined scope values are:

                      global - the address is globally valid.

                      site - (IPv6 only) the address is site local, i.e. it is
                      valid inside this site.

                      link - the address is link local, i.e. it is valid  only
                      on this device.

                      host - the address is valid only inside this host.

   ip address delete - delete protocol address
       Arguments: coincide with the arguments of ip addr add.  The device name
       is a required argument.  The rest are optional.  If  no  arguments  are
       given, the first address is deleted.

   ip address show - look at protocol addresses
       dev NAME (default)
              name of device.

       scope SCOPE_VAL
              only list addresses with this scope.

       to PREFIX
              only list addresses matching this prefix.

       label PATTERN
              only  list  addresses with labels matching the PATTERN.  PATTERN
              is a usual shell style pattern.

       dynamic and permanent
              (IPv6 only) only  list  addresses  installed  due  to  stateless
              address  configuration  or  only  list  permanent  (not dynamic)

              (IPv6 only) only list addresses which  did  not  pass  duplicate
              address detection.

              (IPv6 only) only list deprecated addresses.

       primary and secondary
              only list primary (or secondary) addresses.

   ip address flush - flush protocol addresses
       This command flushes the protocol addresses selected by some criteria.

       This command has the same arguments as show.  The difference is that it
       does not run when no arguments are given.

       Warning: This command (and other flush  commands  described  below)  is
       pretty  dangerous.   If you make a mistake, it will not forgive it, but
       will cruelly purge all the addresses.

       With the -statistics option, the command becomes verbose. It prints out
       the  number of deleted addresses and the number of rounds made to flush
       the address list.  If this option is given twice, ip  addr  flush  also
       dumps all the deleted addresses in the format described in the previous

ip neighbour - neighbour/arp tables management.
       neighbour objects establish bindings  between  protocol  addresses  and
       link  layer  addresses  for  hosts  sharing  the  same link.  Neighbour
       entries are organized into tables. The IPv4 neighbour table is known by
       another name - the ARP table.

       The corresponding commands display neighbour bindings and their proper-
       ties, add new neighbour entries and delete old ones.

   ip neighbour add - add a new neighbour entry
   ip neighbour change - change an existing entry
   ip neighbour replace - add a new entry or change an existing one
       These commands create new neighbour records or update existing ones.

       to ADDRESS (default)
              the protocol address of the neighbour. It is either an  IPv4  or
              IPv6 address.

       dev NAME
              the interface to which this neighbour is attached.

       lladdr LLADDRESS
              the  link layer address of the neighbour.  LLADDRESS can also be

       nud NUD_STATE
              the state of the neighbour entry.  nud is  an  abbreviation  for
              'Neigh  bour  Unreachability Detection'.  The state can take one
              of the following values:

                      permanent - the neighbour entry is valid forever and can
                      be only be removed administratively.

                      noarp  -  the  neighbour  entry is valid. No attempts to
                      validate this entry will be made but it can  be  removed
                      when its lifetime expires.

                      reachable  -  the  neighbour  entry  is  valid until the
                      reachability timeout expires.

                      stale - the neighbour entry  is  valid  but  suspicious.
                      This  option  to  ip neigh does not change the neighbour
                      state if it was valid and the address is not changed  by
                      this command.

   ip neighbour delete - delete a neighbour entry
       This command invalidates a neighbour entry.

       The arguments are the same as with ip neigh add, except that lladdr and
       nud are ignored.

       Warning: Attempts to delete or manually change a noarp entry created by
       the  kernel  may  result in unpredictable behaviour.  Particularly, the
       kernel may try to resolve this address even on a NOARP interface or  if
       the address is multicast or broadcast.

   ip neighbour show - list neighbour entries
       This commands displays neighbour tables.

       to ADDRESS (default)
              the prefix selecting the neighbours to list.

       dev NAME
              only list the neighbours attached to this device.

       unused only list neighbours which are not currently in use.

       nud NUD_STATE
              only list neighbour entries in this state.  NUD_STATE takes val-
              ues listed below or  the  special  value  all  which  means  all
              states.   This  option may occur more than once.  If this option
              is absent, ip lists all entries except for none and noarp.

   ip neighbour flush - flush neighbour entries
       This command flushes neighbour tables, selecting entries  to  flush  by
       some criteria.

       This  command has the same arguments as show.  The differences are that
       it does not run when no arguments  are  given,  and  that  the  default
       neighbour states to be flushed do not include permanent and noarp.

       With  the  -statistics  option, the command becomes verbose.  It prints
       out the number of deleted neighbours and the number of rounds  made  to
       flush  the  neighbour  table.   If  the option is given twice, ip neigh
       flush also dumps all the deleted neighbours.

ip route - routing table management
       Manipulate route entries in the kernel routing tables keep  information
       about paths to other networked nodes.

       Route types:

               unicast  - the route entry describes real paths to the destina-
               tions 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

               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.

               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 255 or by name from the
       file /etc/iproute2/rt_tables main table (ID 254) and  the  kernel  only
       uses this table when calculating routes.

       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

       metric NUMBER

       preference NUMBER
              the preference value of the route.  NUMBER is an arbitrary 32bit

       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 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 dis-
              covery 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 NUMBER
              the initial RTT ('Round Trip Time') estimate.

       rttvar NUMBER (2.3.15+ only)
              the initial RTT variance estimate.

       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.

       advmss NUMBER (2.3.15+ only)
              the MSS ('Maximal Segment Size') to advertise to these  destina-
              tions  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

       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 ADDRESS - is the nexthop router.

                      dev NAME - is the output device.

                      weight NUMBER - is a weight for this element of a multi-
                      path 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  redi-

                      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  proto-

              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.

              allow packet by packet randomization on multipath routes.  With-
              out this modifier, the route will be frozen to one selected nex-
              thop,  so  that load splitting will only occur on per-flow base.
              equalize only works if the kernel is patched.

   ip route delete - delete route
       ip route del has the same arguments as ip route add, but  their  seman-
       tics 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.  SELEC-
              TOR 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 PRE-
              FIX.  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 tablemain.  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.


       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 PREFIX
              only list routes going via the nexthop routers selected by  PRE-

       src PREFIX
              only  list  routes  with  preferred source addresses selected by

       realm REALMID

              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  subsec-

   ip route get - get a single route
       this  command  gets a single route to a destination and prints its con-
       tents 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

       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 rule - routing policy database management
       Rules  in the routing policy database control the route selection algo-

       Classic routing algorithms used in the Internet make routing  decisions
       based  only  on  the destination address of packets (and in theory, but
       not in practice, on the TOS field).

       In some circumstances we want to route  packets  differently  depending
       not  only  on  destination  addresses, but also on other packet fields:
       source address, IP protocol, transport protocol ports  or  even  packet
       payload.  This task is called 'policy routing'.

       To  solve  this task, the conventional destination based routing table,
       ordered according to the longest match rule, is replaced with a  'rout-
       ing  policy database' (or RPDB), which selects routes by executing some
       set of rules.

       Each policy routing rule consists of a selector and  an  action  predi-
       cate.   The  RPDB  is  scanned in the order of increasing priority. The
       selector of each  rule  is  applied  to  {source  address,  destination
       address,  incoming interface, tos, fwmark} and, if the selector matches
       the packet, the action is performed.  The action predicate  may  return
       with  success.   In  this  case, it will either give a route or failure
       indication and the RPDB lookup is terminated. Otherwise, the RPDB  pro-
       gram continues on the next rule.

       Semantically,  natural  action  is to select the nexthop and the output

       At startup time the kernel configures the default  RPDB  consisting  of
       three rules:

       1.     Priority:  0,  Selector:  match anything, Action: lookup routing
              table local (ID 255).  The local table is a special routing  ta-
              ble containing high priority control routes for local and broad-
              cast addresses.

              Rule 0 is special. It cannot be deleted or overridden.

       2.     Priority: 32766, Selector: match anything, Action: lookup  rout-
              ing  table  main (ID 254).  The main table is the normal routing
              table containing all non-policy routes. This rule may be deleted
              and/or overridden with other ones by the administrator.

       3.     Priority:  32767, Selector: match anything, Action: lookup rout-
              ing table default (ID 253).  The default table is empty.  It  is
              reserved  for  some post-processing if no previous default rules
              selected the packet.  This rule may also be deleted.

       Each RPDB entry has  additional  attributes.   F.e.  each  rule  has  a
       pointer  to  some  routing  table.   NAT and masquerading rules have an
       attribute to select new IP address  to  translate/masquerade.   Besides
       that,  rules  have  some optional attributes, which routes have, namely
       realms.  These values do not override those contained  in  the  routing
       tables.  They are only used if the route did not select any attributes.

       The RPDB may contain rules of the following types:

               unicast  - the rule prescribes to return the route found in the
               routing table referenced by the rule.

               blackhole - the rule prescribes to silently drop the packet.

               unreachable - the rule prescribes to  generate  a  'Network  is
               unreachable' error.

               prohibit  -  the  rule prescribes to generate 'Communication is
               administratively prohibited' error.

               nat - the rule prescribes to translate the  source  address  of
               the IP packet into some other value.

   ip rule add - insert a new rule
   ip rule delete - delete a rule
       type TYPE (default)
              the type of this rule.  The list of valid types was given in the
              previous subsection.

       from PREFIX
              select the source prefix to match.

       to PREFIX
              select the destination prefix to match.

       iif NAME
              select the incoming device to match.  If the interface is  loop-
              back,  the rule only matches packets originating from this host.
              This means that you may create separate routing tables for  for-
              warded and local packets and, hence, completely segregate them.

       tos TOS

       dsfield TOS
              select the TOS value to match.

       fwmark MARK
              select the fwmark value to match.

       priority PREFERENCE
              the  priority of this rule.  Each rule should have an explicitly
              set unique priority value.

       table TABLEID
              the routing table identifier to  lookup  if  the  rule  selector

       realms FROM/TO
              Realms  to  select  if  the  rule  matched and the routing table
              lookup succeeded.  Realm TO is only used if the  route  did  not
              select any realm.

       nat ADDRESS
              The  base  of  the  IP  address  block  to translate (for source
              addresses).  The ADDRESS may be either the start of the block of
              NAT  addresses  (selected by NAT routes) or a local host address
              (or even zero).  In the last case the router does not  translate
              the packets, but masquerades them to this address.

              Warning:  Changes  to  the  RPDB made with these commands do not
              become active immediately.  It is assumed that  after  a  script
              finishes  a  batch of updates, it flushes the routing cache with
              ip route flush cache.

   ip rule show - list rules
       This command has no arguments.

ip maddress - multicast addresses management
       maddress objects are multicast addresses.

   ip maddress show - list multicast addresses
       dev NAME (default)
              the device name.

   ip maddress add - add a multicast address
   ip maddress delete - delete a multicast address
       these commands attach/detach a static link layer multicast  address  to
       listen  on  the interface.  Note that it is impossible to join protocol
       multicast groups statically.  This  command  only  manages  link  layer

       address LLADDRESS (default)
              the link layer multicast address.

       dev NAME
              the device to join/leave this multicast address.

ip mroute - multicast routing cache management
       mroute  objects  are  multicast routing cache entries created by a user
       level mrouting daemon (f.e.  pimd or mrouted ).

       Due to the limitations of the current interface to the multicast  rout-
       ing engine, it is impossible to change mroute objects administratively,
       so we may only display them.  This limitation will be  removed  in  the

   ip mroute show - list mroute cache entries
       to PREFIX (default)
              the  prefix  selecting  the  destination  multicast addresses to

       iif NAME
              the interface on which multicast packets are received.

       from PREFIX
              the prefix selecting the IP source addresses  of  the  multicast

ip tunnel - tunnel configuration
       tunnel  objects  are tunnels, encapsulating packets in IPv4 packets and
       then sending them over the IP infrastructure.

   ip tunnel add - add a new tunnel
   ip tunnel change - change an existing tunnel
   ip tunnel delete - destroy a tunnel
       name NAME (default)
              select the tunnel device name.

       mode MODE
              set the tunnel mode.  Three modes are currently available: ipip,
              sit and gre.

       remote ADDRESS
              set the remote endpoint of the tunnel.

       local ADDRESS
              set the fixed local address for tunneled packets.  It must be an
              address on another interface of this host.

       ttl N  set a fixed TTL N on tunneled packets.  N is  a  number  in  the
              range  1--255. 0 is a special value meaning that packets inherit
              the TTL value.  The default value is: inherit.

       tos T

       dsfield T
              set a fixed TOS T on tunneled packets.  The  default  value  is:

       dev NAME
              bind the tunnel to the device NAME so that tunneled packets will
              only be routed via this device and will not be able to escape to
              another device when the route to endpoint changes.

              disable  Path  MTU  Discovery  on this tunnel.  It is enabled by
              default.  Note that  a  fixed  ttl  is  incompatible  with  this
              option: tunnelling with a fixed ttl always makes pmtu discovery.

       key K

       ikey K

       okey K (  only  GRE  tunnels  ) use keyed GRE with key K. K is either a
              number or an IP address-like dotted  quad.   The  key  parameter
              sets  the  key  to  use  in  both directions.  The ikey and okey
              parameters set different keys for input and output.

       csum, icsum, ocsum
              ( only GRE tunnels )  generate/require  checksums  for  tunneled
              packets.  The ocsum flag calculates checksums for outgoing pack-
              ets.  The icsum flag requires that all input  packets  have  the
              correct  checksum.   The csum flag is equivalent to the combina-
              tion icsum ocsum.

       seq, iseq, oseq
              ( only GRE tunnels ) serialize packets.  The oseq  flag  enables
              sequencing of outgoing packets.  The iseq flag requires that all
              input packets are serialized.  The seq flag is equivalent to the
              combination iseq oseq.  It isn't work. Don't use it.

   ip tunnel show - list tunnels
       This command has no arguments.

ip monitor and rtmon - state monitoring
       The  ip  utility can monitor the state of devices, addresses and routes
       continuously.  This option has a slightly  different  format.   Namely,
       the  monitor  command  is  the  first  in the command line and then the
       object list follows:

       ip monitor [ all | LISTofOBJECTS ]

       OBJECT-LIST is the list of object types that we want  to  monitor.   It
       may  contain link, address and route.  If no file argument is given, ip
       opens RTNETLINK, listens on it and dumps state changes  in  the  format
       described in previous sections.

       If a file name is given, it does not listen on RTNETLINK, but opens the
       file containing RTNETLINK messages saved in  binary  format  and  dumps
       them.   Such  a  history  file can be generated with the rtmon utility.
       This utility has a command line syntax similar to ip monitor.  Ideally,
       rtmon  should be started before the first network configuration command
       is issued. F.e. if you insert:

               rtmon file /var/log/rtmon.log

       in a startup script, you will be able to view the full history later.

       Certainly, it is possible to start rtmon at any time.  It prepends  the
       history with the state snapshot dumped at the moment of starting.

       ip was written by Alexey N. Kuznetsov and added in Linux 2.2.

       IP Command reference ip-cref.ps
       IP tunnels ip-cref.ps

       Manpage maintained by Michail Litvak <mciATowl.com>

iproute2                        17 January 2002                          IP(8)