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RedHat 9 (Linux i386) - man page for route (redhat section 8)

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) 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 van-
	      ished.

       -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 before-
	      hand. 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  typi-
	      cally  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 oth-
	      erwise 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 net-
	      works 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 actu-
	      ally 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 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 configu-
	      ration 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 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 (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 Eckenfels.

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

net-tools				  2 January 2000				 ROUTE(8)


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