ROUTE(8)            Linux Programmer's Manual            ROUTE(8)

NAME
       route - show / manipulate the IP routing table

SYNOPSIS
       route [-CFvnee]

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

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

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.

OPTIONS
       -v     select verbose operation.

       -A family
              Use   the  specified  address  family  (eg  `inet',
              `inet6').

       -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.

       -net   the target is a network.

       -host  the target is a host.

       -F     displays  the  kernel FIB routing table. The layout
              can be changed with -e and -ee

       -C     displays the kernel's route cache.

       del    deletes a route.

       add    adds a route.

       target The destination network or host. You can provide IP
              addresses  in dotted decimal or host/network names.

       netmask Nm
              modifier specifies the netmask of the route  to  be
              added.

       gw Gw  Any  IP packets for the target network/host will be
              routed through the specified  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  com-
              patibility hack.

       metric M
              Set  the metric field in the routing table (used by
              routing daemons) to M.

       mss M  Set the TCP Maximum Segment Size (MSS) for  connec-
              tions  over this route to M bytes. This is normally
              used only for fine optimisation of routing  setups.
              The default is 536.

       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 con-
              nections   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. Both flags are
              generally only set by a  routing  daemon.  This  is
              only for diagnostic purpose.

       dev If Forces  the  route to be associated with the speci-
              fied 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
              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
              Adds  the  route  to  the  "ipx4" host via the SLIP
              interface (assuming that "ipx4" is the SLIP  host).

       route add -net 192.57.66.0 netmask 255.255.255.0 gw ipx4
              This command adds the net "192.57.66.x" to be gate-
              wayed through the former route to the  SLIP  inter-
              face.

       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 cor-
              rect normal configuration line with a  multicasting
              kernel.

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

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 are
              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 rederict)
              !  (reject route)

       Metric The  'distance'  to  the target (usually counted in
              hops). It is not used by recent kernels, but may be
              needed by routing daemons.

       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  segement 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 (possible 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)

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.Blun-
       dell@pobox.com>.

net-tools                 8 August 1997                         1