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ROUTE(8)                       Linux System Administrator's Manual                       ROUTE(8)

NAME
       route - show / manipulate the IP routing table

SYNOPSIS
       route [-CFvnNee] [-A family |-4|-6]

       route  [-v]  [-A  family |-4|-6] add [-net|-host] target [netmask Nm] [gw Gw] [metric N] [mss
              M] [window W] [irtt I] [reject] [mod] [dyn] [reinstate] [[dev] If]

       route  [-v] [-A family |-4|-6] del [-net|-host] target [gw Gw] [netmask Nm] [metric M] [[dev]
              If]

       route  [-V] [--version] [-h] [--help]

DESCRIPTION
       Route manipulates the kernel's IP routing tables.  Its primary use is to set up static routes
       to specific hosts or networks via an interface after it has been configured with  the  ifcon-
       fig(8) program.

       When  the  add or del options are used, route modifies the routing tables.  Without these op-
       tions, route displays the current contents of the routing tables.

OPTIONS
       -A family
              use the specified address family (eg `inet'). Use route --help for a  full  list.  You
              can use -6 as an alias for --inet6 and -4 as an alias for -A inet

       -F     operate  on the kernel's FIB (Forwarding Information Base) routing table.  This is the
              default.

       -C     operate on the kernel's routing cache.

       -v     select verbose operation.

       -n     show numerical addresses instead of trying to determine symbolic host names.  This  is
              useful if you are trying to determine why the route to your nameserver has vanished.

       -e     use netstat(8)-format for displaying the routing table.  -ee will generate a very long
              line with all parameters from the routing table.

       del    delete a route.

       add    add a new route.

       target the destination network or host. You can provide an addresses or symbolic  network  or
              host name. Optionally you can use /prefixlen notation instead of using the netmask op-
              tion.

       -net   the target is a network.

       -host  the target is a host.

       netmask NM
              when adding a network route, the netmask to be used.

       gw GW  route packets via a gateway.
              NOTE: The specified gateway must be reachable first. This usually means that you  have
              to  set up a static route to the gateway beforehand. If you specify the address of one
              of your local interfaces, it will be used to decide about the interface to  which  the
              packets should be routed to. This is a BSDism compatibility hack.

       metric M
              set  the metric field in the routing table (used by routing daemons) to M. If this op-
              tion is not specified the metric for inet6 (IPv6) address family defaults to '1',  for
              inet  (IPv4) it defaults to '0'. You should always specify an explicit metric value to
              not rely on those defaults - they also differ from iproute2.

       mss M  sets MTU (Maximum Transmission Unit) of the route to M bytes.  Note that  the  current
              implementation  of the route command does not allow the option to set the Maximum Seg-
              ment Size (MSS).

       window W
              set the TCP window size for connections over this route to W bytes. This is  typically
              only used on AX.25 networks and with drivers unable to handle back to back frames.

       irtt I set  the  initial round trip time (irtt) for TCP connections over this route to I mil-
              liseconds (1-12000). This is typically only used on AX.25 networks. If omitted the RFC
              1122 default of 300ms is used.

       reject install  a blocking route, which will force a route lookup to fail.  This is for exam-
              ple used to mask out networks before using the default route. This is  NOT  for  fire-
              walling.

       mod, dyn, reinstate
              install  a dynamic or modified route. These flags are for diagnostic purposes, and are
              generally only set by routing daemons.

       dev If force the route to be associated with the specified device, as the kernel will  other-
              wise  try  to determine the device on its own (by checking already existing routes and
              device specifications, and where the route is added to). In most normal  networks  you
              won't need this.

              If dev If is the last option on the command line, the word dev may be omitted, as it's
              the default. Otherwise the order of  the  route  modifiers  (metric  netmask  gw  dev)
              doesn't matter.

EXAMPLES
       route add -net 127.0.0.0 netmask 255.0.0.0 metric 1024 dev lo
              adds  the  normal loopback entry, using netmask 255.0.0.0 and associated with the "lo"
              device (assuming this device was previously set up correctly with ifconfig(8)).

       route add -net 192.56.76.0 netmask 255.255.255.0 metric 1024 dev eth0
              adds a route to the local network 192.56.76.x via "eth0".  The word "dev" can be omit-
              ted here.

       route del default
              deletes the current default route, which is labeled "default" or 0.0.0.0 in the desti-
              nation field of the current routing table.

       route del -net 192.56.76.0 netmask 255.255.255.0
              deletes the route. Since the Linux  routing  kernel  uses  classless  addressing,  you
              pretty  much  always have to specify the netmask that is same as as seen in 'route -n'
              listing.

       route add default gw mango
              adds a default route (which will be used if no other route matches).  All packets  us-
              ing  this route will be gatewayed through the address of a node named "mango". The de-
              vice which will actually be used for that route depends on how we can reach "mango"  -
              "mango" must be on directly reachable route.

       route add mango sl0
              Adds the route to the host named "mango" via the SLIP interface (assuming that "mango"
              is the SLIP host).

       route add -net 192.57.66.0 netmask 255.255.255.0 gw mango
              This command adds the net "192.57.66.x" to be gatewayed through the  former  route  to
              the SLIP interface.

       route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0
              This  is  an  obscure one documented so people know how to do it. This sets all of the
              class D (multicast) IP routes to go via "eth0". This is the correct normal  configura-
              tion line with a multicasting kernel.

       route add -net 10.0.0.0 netmask 255.0.0.0 metric 1024 reject
              This installs a rejecting route for the private network "10.x.x.x."

       route -6 add 2001:0002::/48 metric 1 dev eth0
              This adds a IPv6 route with the specified metric to be directly reachable via eth0.

OUTPUT
       The output of the kernel routing table is organized in the following columns

       Destination
              The destination network or destination host.

       Gateway
              The gateway address or '*' if none set.

       Genmask
              The  netmask  for  the  destination  net; '255.255.255.255' for a host destination and
              '0.0.0.0' for the default route.

       Flags  Possible flags include
              U (route is up)
              H (target is a host)
              G (use gateway)
              R (reinstate route for dynamic routing)
              D (dynamically installed by daemon or redirect)
              M (modified from routing daemon or redirect)
              A (installed by addrconf)
              C (cache entry)
              !  (reject route)

       Metric The 'distance' to the target (usually counted in hops).

       Ref    Number of references to this route. (Not used in the Linux kernel.)

       Use    Count of lookups for the route.  Depending on the use of -F and -C this will be either
              route cache misses (-F) or hits (-C).

       Iface  Interface to which packets for this route will be sent.

       MSS    Default maximum segment size for TCP connections over this route.

       Window Default window size for TCP connections over this route.

       irtt   Initial RTT (Round Trip Time). The kernel uses this to guess about the best TCP proto-
              col parameters without waiting on (possibly slow) answers.

       HH (cached only)
              The number of ARP entries and cached routes that refer to the  hardware  header  cache
              for  the cached route. This will be -1 if a hardware address is not needed for the in-
              terface of the cached route (e.g. lo).

       Arp (cached only)
              Whether or not the hardware address for the cached route is up to date.

FILES
       /proc/net/ipv6_route
       /proc/net/route
       /proc/net/rt_cache

SEE ALSO
       ifconfig(8), netstat(8), arp(8), rarp(8), ip(8)

HISTORY
       Route for Linux was originally written by Fred N.  van  Kempen,  <waltje AT uwalt.org>
       and  then modified by Johannes Stille and Linus Torvalds for pl15. Alan Cox added the mss and
       window options for Linux 1.1.22. irtt support and merged with netstat from Bernd Eckenfels.

AUTHOR
       Currently maintained by Phil Blundell <Philip.Blundell AT pobox.com> and Bernd  Eckenfels  <net-
       tools AT lina.de>.

net-tools                                   2014-02-17                                   ROUTE(8)