ROUTE(8) Linux System Administrator’s Manual ROUTE(8)
NAME top
route – show / manipulate the IP routing table
SYNOPSIS top
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 top
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 top
-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 top
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 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 top
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 top
/proc/net/ipv6_route
/proc/net/route
/proc/net/rt_cache
SEE ALSO top
ifconfig(8), netstat(8), arp(8), rarp(8), ip(8)
HISTORY top
Route for Linux was originally written by Fred N. van Kempen,
<[email protected]> 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 top
Currently maintained by Phil Blundell <[email protected]> and
Bernd Eckenfels <[email protected]>.
COLOPHON top
This page is part of the net-tools (networking utilities) project.
Information about the project can be found at
⟨http://net-tools.sourceforge.net/⟩. If you have a bug report for
this manual page, see ⟨http://net-tools.sourceforge.net/⟩. This page
was obtained from the project’s upstream Git repository
(git://git.code.sf.net/p/net-tools/code) on 2014-12-30. If you dis‐
cover any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to [email protected]
net-tools 2014-02-17 ROUTE(8)