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.
use the specified address family (eg `inet'; use `route --help' for a full list).
operate on the kernel's FIB (Forwarding Information Base) routing table. This is the default.
operate on the kernel's routing cache.
select verbose operation.
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.
use netstat(8)-format for displaying the routing table. -ee will generate a very long line with all parameters from the routing table.
delete a route.
add a new route.
the destination network or host. You can provide IP addresses in dotted decimal or host/network names.
the target is a network.
the target is a host.
when adding a network route, the netmask to be used.
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.
set the metric field in the routing table (used by routing daemons) to 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)
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.
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.
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.
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.
route add -net 127.0.0.0
adds the normal loopback entry, using netmask 255.0.0.0 (class A net, determined from the destination address) and associated with the ifconfig__(8)?).
route add -net 126.96.36.199 netmask 255.255.255.0 dev eth0
adds a route to the network 192.56.76.x via
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
route add ipx4 sl0
Adds the route to the
route add -net 188.8.131.52 netmask 255.255.255.0 gw ipx4
This command adds the net
route add -net 184.108.40.206 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
route add -net 10.0.0.0 netmask 255.0.0.0 reject
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; '255.255.255.255' for a host destination and '0.0.0.0' for the default route.
The 'distance' to the target (usually counted in hops). It is not used by recent kernels, but may be needed by routing daemons.
Number of references to this route. (Not used in the Linux kernel.)
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).
Interface to which packets for this route will be sent.
Default maximum segement size for TCP connections over this route.
Default window size for TCP connections over this route.
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 cached route (e.g. lo).
Arp (cached only)