How to route only specific subnet (source ip) to a particular interface?

Question

How to route only specific subnet (source ip) to a particular interface?
OS: Linux

I know I can do easily by destination IP by using something like

route add 1.2.3.4/24 dev eth4

but I do not see how can route based on source IP.

Solution 1

You need to use policy based routing. Something kind of like

ip rule add from <source>/<mask> table <name>
ip route add 1.2.3.4/24 via <router> dev eth4 table <name>

<name> is either table name specified in /etc/iproute2/rt_tables or you can use numeric id ...

This pretty much says, that all traffic from 1.2.3.4/24 will be routed using routing table <name>. IIRC it doesen't use the default table after going through this, so if you need other routes (ie. default gateway), you need to add them to the table as well.

Solution 2

http://wiki.wlug.org.nz/SourceBasedRouting

This site has a nice example of source based routing.

Comments

[Alex]

one correction (but not sure if your one will also work. for the second command: ip route add default dev eth4 table <name> (table directive should go at the end I think, just like in the first command... also default can be replaced by a subnet, just like in your example)

[DavidPostill]

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