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.
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3 Answers
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.
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5one correction (but not sure if your one will also work. for the second command:
ip route add default dev eth4 table <name>(tabledirective should go at the end I think, just like in the first command... alsodefaultcan be replaced by a subnet, just like in your example)– AlexJan 12, 2012 at 2:23 -
I had to issue these commands in reverse order: 1st
sudo ip route add default via <router-addr> dev <device-name> table <table-id>, 2ndsudo ip rule add from <source-addr>/<mask> lookup <table-id>. I think the 1st one creates the table and the 2nd adds a line to it, so the reverse order shouldn't work.– kolAug 11, 2022 at 9:38
http://wiki.wlug.org.nz/SourceBasedRouting
This site has a nice example of source based routing.
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2Please quote the essential parts of the answer from the reference link(s), as the answer can become invalid if the linked page(s) change.– DavidPostill ♦Nov 1, 2020 at 8:23
Another great description how it works:
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