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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 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).


       -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 IP addresses in
	      dotted decimal or host/network names.

       -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  dae-
	      mons) to M.

       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	 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
	      adds the normal loopback entry, using netmask 255.0.0.0 (class A
	      net,  determined	from  the  destination address) and associated
	      with the "lo" device (assuming this device was prviously set  up
	      correctly 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 necessary 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 (assum-
	      ing 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 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 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 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). It is
	      not used by recent kernels, but may be needed  by	 routing  dae-
	      mons.

       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	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
	      (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)


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>.



net-tools			2 January 2000			      ROUTE(8)
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