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) 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

       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.


       route add -net netmask dev lo
              adds the normal loopback entry, using netmask and associated with the "lo" device (assuming this device was previously
              set up correctly with ifconfig(8)).

       route add -net netmask 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 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 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 "10.x.x.x."


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

              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 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.




       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


       Currently maintained by Phil Blundell <> and Bernd Eckenfels <>.

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