ROUTE linux command manual

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

       route - show / manipulate the IP routing table

       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]

       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.

       -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  sym-
              bolic 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  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 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 specifica-
              tions, 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.

       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

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

              The destination network or destination host.

              The gateway address or '*' if none set.

              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 dae-

       Ref    Number of references to this route. (Not used in the Linux ker-

       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 (pos-
              sibly 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.


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

       Route  for  Linux  was  originally  written  by  Fred  N.  van Kempen,
        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-

       Currently maintained by Phil Blundell .

net-tools                       2 January 2000                       ROUTE(8)