ROUTE(8) Linux System Administrator's Manual ROUTE(8)
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 N] [[dev] If]
route [-V] [--version] [-h] [--help]
NOTE
This program is obsolete. For replacement check ip route.
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 dis‐
plays 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 IP addresses in dotted decimal or host/network names.
-net the target is a network.
-host the target is a host.
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 deter‐
mine 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
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
ip(8)
HISTORY
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