route

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 ifconfig(8) program.

       When the add or del options are used, route modifies  the  routing  ta-
       bles.   Without  these  options, 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)  rout-
              ing 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 option.

       -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 usu-
              ally means that you have to set up a static route to the gateway
              beforehand.  If you specify the address of one of your local in-
              terfaces, 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  dae-
              mons) to M. If this option is not specified the metric for inet6
              (IPv6) address family defaults to '1', for inet  (IPv4)  it  de-
              faults  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 Segment 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 milliseconds (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 example used to mask out networks before us-
              ing the default route. This is NOT for firewalling.

       mod, dyn, reinstate
              install a dynamic or modified route. These flags are  for  diag-
              nostic 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 otherwise 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 as-
              sociated with the "lo" device (assuming this device  was  previ-
              ously 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 omitted here.

       route del default
              deletes the current default route, which is labeled "default" or
              0.0.0.0 in the destination 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  using  this  route  will  be  gatewayed
              through  the  address  of a node named "mango". The device 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 configuration 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  ker-
              nel.)

       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 protocol parameters without waiting on  (pos-
              sibly 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 interface 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@uwalt.nl.mugnet.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  Ecken-
       fels.

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

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