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4 Comments

  1. http://www.bing.com/search?q=route+explain+linux

    When you say “googling has paid off”.

    I prefer Bing, you should try it.

  2. What about a slightly different situation? I have a 2 NIC system, but only one gatway. I want to firewall traffic per NIC by interace. For example, say eth0 has an ip of 192.168.1.2, and eth1 has an ip of 192.168.1.3. If traffic in-bound comes over .2, I want it to only go out .2. if traffic goes into .3, I only want it to go out .3. I am trying to completely isolate traffic per interface. I think a variant of what you showed above would allow for this? But I am not a routing guru, so I am not sure I understand everything completely. A classic example would be DNS or HTTP based traffic, I want isolate DNS/HTTP on .2 interface, so the .3 interface is not impacted. And I want the .3 interface to handle all NFS traffic, so the .2 interface is not impacted. I have DNS, HTTP, and NFS setup correctly, but I still save all traffic following the default out-bound route of course. Any suggestions?

    • Hi Schorsci,

      Please keep future comments on the relevant blog post page (https://kindlund.wordpress.com/2007/11/19/configuring-multiple-default-routes-in-linux/).

      To answer your question, let’s assume:
      eth0 – 192.168.1.2 netmask 255.255.255.0
      eth0′s gateway is: 192.168.1.1

      eth1 – 192.168.1.3 netmask 255.255.255.0
      eth1′s gateway is: 192.168.1.1

      Here are the corresponding commands:

      printf “1\tuplink0\n” >> /etc/iproute2/rt_tables
      printf “2\tuplink1\n” >> /etc/iproute2/rt_tables

      ip route add 192.168.1.0/24 dev eth0 src 192.168.1.2 table uplink0
      ip route add default via 192.168.1.1 dev eth0 table uplink0
      ip rule add from 192.168.1.2/32 table uplink0
      ip rule add to 192.168.1.2/32 table uplink0

      ip route add 192.168.1.0/24 dev eth1 src 192.168.1.3 table uplink1
      ip route add default via 192.168.1.1 dev eth1 table uplink1
      ip rule add from 192.168.1.3/32 table uplink1
      ip rule add to 192.168.1.3/32 table uplink1

      ip route flush

  3. Thanks, great assistance, appreciated… sorry for the mislocated post. Side note, Fedora 15 does not seem to support the flush option, but otherwise no issues.


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