route(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | OUTPUT | FILES | SEE ALSO | HISTORY | AUTHOR | COLOPHON

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

NAME         top

       route - show / manipulate the IP routing table

SYNOPSIS         top

       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         top

       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         top

       -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         top

       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 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         top

       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         top

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

SEE ALSO         top

       ethers(5), arp(8), rarp(8), route(8), ifconfig(8), netstat(8)

HISTORY         top

       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         top

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

COLOPHON         top

       This page is part of the net-tools (networking utilities)
       project.  Information about the project can be found at 
       ⟨http://net-tools.sourceforge.net/⟩.  If you have a bug report for
       this manual page, see ⟨http://net-tools.sourceforge.net/⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨git://git.code.sf.net/p/net-tools/code⟩ on 2021-06-20.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-04-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

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

Pages that refer to this page: networks(5)proc(5)arp(8)ifconfig(8)netstat(8)rarp(8)route(8)