bionic (8) route.8.gz

Provided by: net-tools_1.60+git20161116.90da8a0-1ubuntu1_amd64 bug

NAME

       route - show / manipulate the IP routing table

SYNOPSIS

       route [-CFvnNee] [-A family |-4|-6]

       route  [-v] [-A family |-4|-6] 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 |-4|-6] del [-net|-host] target [gw Gw] [netmask Nm] [metric M] [[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. You can use -6  as
              an alias for --inet6 and -4 as an alias for -A inet

       -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 an addresses or symbolic network or host name.
              Optionally you can use /prefixlen notation instead of using the netmask option.

       -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. If this option is not
              specified the metric for inet6 (IPv6) address family defaults to '1', for inet (IPv4) it  defaults
              to  '0'.  You  should always specify an explicit metric value to not rely on those defaults - they
              also differ from iproute2.

       mss M  sets  MTU  (Maximum  Transmission  Unit)  of  the  route  to  M  bytes.   Note  that  the  current
              implementation  of  the  route  command  does not allow the option to set the Maximum Segment Size
              (MSS).

       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 metric 1024 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 metric 1024 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 del -net 192.56.76.0 netmask 255.255.255.0
              deletes the route. Since the Linux routing kernel  uses  classless  addressing,  you  pretty  much
              always have to specify the netmask that is same as as seen in 'route -n' listing.

       route add default gw mango
              adds a default route (which will be used if no other route matches).  All packets using this route
              will be gatewayed through the address of a node named "mango". The device which will  actually  be
              used  for  that  route depends on how we can reach "mango" - "mango" must be on directly reachable
              route.

       route add mango sl0
              Adds the route to the host named "mango" via the SLIP interface (assuming that "mango" is the SLIP
              host).

       route add -net 192.57.66.0 netmask 255.255.255.0 gw mango
              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 metric 1024 reject
              This installs a rejecting route for the private network "10.x.x.x."

       route -6 add 2001:0002::/48 metric 1 dev eth0
              This adds a IPv6 route with the specified metric to be directly reachable via eth0.

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).

       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), ip(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>.