10

I have several gateways and would like to route some traffic out of different gateways based on its destination. I'm guessing I'd need to use a combination of iproute2 and iptables rules, but am not sure where to start.
Can someone provide an example?

Improve this question

3 Answers 3

Reset to default
10

You can probably do what you want with ip route:

ip route add 8.8.8.8 via 10.0.0.1 dev enp3s8
ip route add 10.0.0.0/24 dev eth0

The first ip route add shows a single IP address, sent out a given ethernet interface (ep3s8) to the next hop router, 10.0.0.1

The second route is for a whole network, 10.x.y.z, sent out a given ethernet card, eth0. That's the "local network", which doesn't have a next hop router, it's all on the same logical wire.

You want to read man ip-route before doing anything, though. Also, be prepared to have to reboot, and do not do this remotely. You can very easily create incorrect routes that terminate your remote access. I am the voice of experience in this last recommendation.

Improve this answer
2
  • 1
    Note that you can also specify gateways for entire blocks, ``ip route add 10.1.0.0/16 via 192.168.0.1`
    – jthill
    Nov 17, 2013 at 16:22
  • Thanks for your answer, that will help point me in the right direction. I'll give this a try and let you know.
    – Walter
    Nov 21, 2013 at 1:46
6

What you are asking about is policy-based routing or source-based routing. There is an excellent introduction by David Schwartz on this very same site.

I would like to point out that there is also a neat little program, which can be found here, that allows you to bind specific applications to a given interface. This is of course easy with apps like openssh which have options to bind to the desired listening address. But this library allows you to bind even applications without such options (like Firefox) to a given IP address.

In this way, you can choose whether you wish to provide separate routing tables for all applications, or override those same specifications on a per-application basis.

Improve this answer
2
  • You don't need policy routing if you want to route by destination.
    – Diego Woitasen
    Nov 18, 2013 at 12:02
  • Hi, that is also a good point, hmm, that will allow greater flexibility which is probably more advanced than I want to be at this point. Definitely something to learn though.
    – Walter
    Nov 21, 2013 at 1:47
4

A good place to read about source base routing is Linux Advanced Routing & Traffic Control.
You can also read manuals from the command line:

man ip rule
man ip route

Note: on some systems, you may need to do man ip-rule and man ip-route.  Or you can read them online: rule and  route.  Warning: the online versions might not be identical to the versions on your system.

In general, you should add a rule.  I specified an interface in my example (eth1).  This is optional and can be omitted.

# ip rule add dev eth1 to 170.10.0.10 table 2 priority 20000

Breakdown:

  • dev eth1   – device that will be used to send packets
  • to 170.10.0.10 – the destination
  • table 2    – table where you should add your routes
  • priority 20000 – priority of rule

You can see your rule by running this command:

# ip ru sh
0:     from all lookup local
20000: from all to 170.10.0.10 iif eth1 lookup 2
32766: from all lookup main
32767: from all lookup default

Next, you should add routes, specifying the table in which they will be added.  In this case it would be table 2.

# ip route add table 2 via 170.10.0.1 default

In order to see your routes, you should run:

# ip route show ta 2
Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .