route

NAME

       route - show / manipulate the IP routing table

SYNOPSIS

       route [ -vn ]

       route  [  -v  ] add [ -net | -host ] XXXX [gw GGGG]
              [metric MMMM]     [netmask NNNN] [mss NNNN] [window
              NNNN] [dev DDDD]

       route [ -v ] del XXXX

DESCRIPTION

       Route manipulates the kernel's IP routing table.  Its pri-
       mary  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.  This version of route is
       intended solely for use with kernel versions 0.99pl14n and
       newer kernels.

OPTIONS

       (none) prints out the kernel routing table, listing desti-
              nation address, gateway, netmask for  route  ("Gen-
              mask"),  flags  (U = Up, H = Host, G = Gateway, D =
              dynamic, M = Modified), Metric (currently not  sup-
              ported),  Ref, Use and Iface (i.e. which device the
              route maps to).

       -n     same as previous,  but  shows  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.

       -v     is a flag for verbose (not actually used).

       del XXXX
              deletes  the  route associated with the destination
              address XXXX.

       add [ -net | -host ] XXXX [gw GGGG] [metric MMMM] [netmask
              NNNN] [window WWWW] [dev DDDD]
              adds a route to the IP address XXXX. The route is a
              network  route  if (a) the -net modifier is used or
              (b) XXXX is found in /etc/networks by the getnetby-
              name()  library  function  and no -host modifier is
              used.

              The gw GGGG argument means that any IP packets sent
              to  this  address will be routed through the speci-
              fied 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.

              The  metric  MMMM  modifier  is not yet implemented
              (and with the -v option will actually print a warn-
              ing).

              The  netmask NNNN modifier specifies the netmask of
              the route to be added. This only makes sense for  a
              network  route,  and when the address XXXX actually
              makes sense with the specified netmask. If no  net-
              mask  is  given,  route  guesses it instead, so for
              most normal setups you won't need to specify a net-
              mask.

              The mss NNNN modifier specifies the TCP mss for the
              route to be added. This is normally used  only  for
              fine optimisation of routing setups.

              The  window  NNNN modifier specifies the TCP window
              for the route to be added. This is  typically  only
              used  on  AX.25 networks and with drivers unable to
              handle back to back frames.

              The dev DDDD modifier forces the route to be  asso-
              ciated  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 DDDD 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
              adds  the  normal  loopback  entry,  using  netmask
              255.0.0.0  (Class A net, determined from the desti-
              nation address) and associated with the  lo  device
              (assuming  this  device  was  prviously set up cor-
              rectly with ifconfig(8) ).

       route add -net 192.56.76.0 netmask 255.255.255.0 dev eth0
              adds a route to the network 192.56.76.x  via  eth0.
              The  Class  C netmask modifier is not really neces-
              sary here because 192.* is a Class  C  IP  address.
              The word dev can be omitted here.

       route add default gw mango-gw
              adds  a  default  route  (which  will be used if no
              other route matches).  All packets using this route
              will  be  gatewayed  through "mango-gw". The device
              which will actually be used for that route  depends
              on  how  we can reach "mango-gw" - the static route
              to "mango-gw" will have to be set up before.

       route add ipx4 sl0

       route add -net 192.57.66.0 netmask 255.255.255.0 gw ipx4
              This command sequence adds the route to the  "ipx4"
              host  via  the SLIP interface (assuming that "ipx4"
              is  the  SLIP  host),  and  then   adds   the   net
              192.57.66.0 to be gatewayed through that host.

       route add 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  (multi-
              cast) IP routes to go via eth0. This is the correct
              normal configuration line with a multicasting  ker-
              nel.

FILES

       /proc/net/route
       /etc/networks
       /etc/hosts

SEE ALSO

       ifconfig(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.

BUGS

       Alan needs to add the 'irtt' option for an  initial  round
       trip  time for slow (AX.25/NetROM) links. Unfortunately he
       has to get around to adding it to the kernel first.