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
       tables.  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)
              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 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
              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 option 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 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
              using the default route. This is NOT for firewalling.

       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 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
              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 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 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
              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 protocol 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 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
       Eckenfels.

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)