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  1. #1

    Dual NICs dual networks problem

    I have a group of machines I am trying to set up with dual NICs, one on our public network and one on a private (172.16.1.*) network. For some reason when both NICs are active, any "search" for a destination always seems to originate from the NIC on the private network (just a hub connected to the NIC on my private network) instead of using the public network NIC, thus I am unable to see anyone in the world. However when I deactivate the 172.16.1.* NIC and restart network services, I can see the rest of the world again. Another oddity, is that for some reason, I can "see" up to our local DNS when I have both NICs active in a machine, but not beyond. TtBoMK, no firewalls or anything goofy like that going on (or at least settings for both NICs would be the same). All machines have a e100 NIC talking to the world on eth0 and a e1000 NIC on the private network at eth1.
    My goal is to have a group of machines that can communicate with the rest of the world and have dedicated e1000 private NICs where they can only talk amongst themselves. All machines are running CentOS 4.4 and are Dell PowerEdge 4400 or 2500's. I have a group of four machines, all of which are identically configured WRT OS/installed RPMs, disk space, memory, NICs, and all other major systems. The switch connecting the private network is a 3C16479 and has been independently tested and shown no problems

  2. #2

    Re: Dual NICs dual networks problem

    some questions to clarify your situation:

    1. what do you mean when you say: "..any "search" for a destination.." ? Are you
    referring to a DNS lookup?
    2. what do you actually do [which cmds] when you say: "..when I deactivate
    the 172.16.1.* NIC and restart network services..".. because if you use
    "ifconfig ethX down", then the default gateway route will be cleared, and you
    must remember to re-establish it after you "up" your NIC or you will never
    reach the Internet..

    It might help us understand your setup if you can run the following commands on both the "router" box and one of the private network client boxes and post those results back here:
    a. /sbin/ifconfig
    b. netstat -rn
    c. cat /etc/resolv.conf


  3. #3
    Yes any "search" refers to looking to DNS for an resolution (destination).
    When I deactivate, I remove the profile for the 172.16.1.* card completely and then restart, by doing /sbin/service network restart
    I'll try to get access to the router as network operations needs to grant that and I'll do a followup. Hope this will provide some insight. Thanks for the assist!


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