8 comments on “Policy routing on Linux

  1. Hi

    I have 2 adsl broadband connections. Its like 5 pcs, connected to a switch and 2 routers connected to the same switch.

    Both routers are connected to their own respective ISPs.

    Is it possible to use both the internet connections from the pcs ? Like if one broadband is slow use the other one.

    The pcs are running ubuntu.

    • You can use this routing to accomplish this, but using one machine as a router where each ADSL router is connected to one Ethernet card, and this router you can connect to the switch (basically you will need 3 eth cards).
      Then all the other PCs can use that router as a gateway. For load balancing you will need to configure it a little bit more, I would use this configuration for servers that are accessed from two or more different links.
      I would suggest you to try some Linux router distributions (Zentyal, DD-WRT, Zeroshell etc.) and check if they already have load balancing feature, it will be much easier.

      • You mean I have to setup like this

        1 PC acts as router connected to both adsl routers.
        Other pcs use this PC as the router ?

        Is it not possible without using an additonal pc as a router ?

        • Yes. That is the right setup.

          Now that I think of it little bit, you could setup every machine with the policy routing for multiple gateways. If you have 5 PCs and there will be no more on the network than you can do the setup like this also. But I would suggest to do it otherwise.
          For example if you change something you will need to do it on every machine, instead in the above setup you have to do the configuration on one point only!

      • Yeah, I am fine with doing the settings on all machines.
        May be its a bunch of commands put together in a bash script.

        I dont have a spare pc to use an additional router.
        And all pcs have only 1 nic (eth0).

        So need to setup with these restrictions.
        Adsl routers are and

        Even a simple thing like this will do, if 1 gateway goes down or becomes very slow, switch to the other one.

        • I think it will work, but for better failover you will need some monitoring tool that will switch preferred gateway to the other one, so that you don`t have attempts to the one that is down.

  2. Sorry for late reply. I will have to try it, I don`t know the setup by heart. The tricky part is that this setup was meant for two Ethernet cards, not for one.

    First part of the config is meant for routing traffic on different Ethernet cards and the last line is defining multiple gateways. I would try something in this direction, for exmaple:

    ip route add default scope global nexthop via dev eth0 weight 1 nexthop via dev eth0 weight 1

    If this works, you can play with weight factor of the gateway to favor one of them.

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