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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
              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
              occurred. 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

       route add -net 127.0.0.0 netmask 255.0.0.0 dev lo
              adds the normal loopback entry, using netmask 255.0.0.0  and  associated  with  the
              "lo"   device   (assuming   this  device  was  previously  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 local network 192.56.76.x via "eth0".  The word  "dev"  can  be
              omitted here.

       route del default
              deletes  the  current  default  route, which is labeled "default" or 0.0.0.0 in the
              destination field of the current routing table.

       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 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 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 segment 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>  and  Bernd  Eckenfels
       <net-tools@lina.inka.de>.