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NAME    [Toc]    [Back]

       route - show / manipulate the IP routing table

SYNOPSIS    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       -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) 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 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  daemons)
 to M.

       mss M  set the TCP Maximum Segment Size (MSS) for connections over this
	      route to M bytes.  The default is the device MTU minus  headers,
	      or a lower MTU when path mtu discovery occured. This setting can
	      be used to force smaller TCP packets on the other end when  path
	      mtu  discovery  does  not work (usually because of misconfigured
	      firewalls that block ICMP Fragmentation Needed)

       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    [Toc]    [Back]

       route add -net
	      adds the normal loopback entry, using netmask (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 netmask 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 (assuming
 that "ipx4" is the SLIP host).

       route add -net netmask 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 netmask 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 netmask reject
	      This   installs  a  rejecting  route  for  the  private  network

OUTPUT    [Toc]    [Back]

       The output of the kernel routing table is organized  in	the  following

       Destination    [Toc]    [Back]
	      The destination network or destination host.

       Gateway    [Toc]    [Back]
	      The gateway address or '*' if none set.

       Genmask    [Toc]    [Back]
	      The  netmask  for  the  destination net; '' for a
	      host destination and '' 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 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

       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)    [Toc]    [Back]
	      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)    [Toc]    [Back]
	      Whether or not the hardware address for the cached route	is  up
	      to date.

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

       ifconfig(8), netstat(8), arp(8), rarp(8)

HISTORY    [Toc]    [Back]

       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    [Toc]    [Back]

       Currently maintained by Phil Blundell <Philip.Blundell@pobox.com>.

net-tools			2 January 2000			      ROUTE(8)
[ Back ]
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