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Hello, My company was running some DR tests with RH 4.x, 5.x and 6.x machines. What they were doing is configuring a new interface to allow remote access to the ...
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  1. #1
    Linux Guru Lazydog's Avatar
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    New interface and routing


    Hello,

    My company was running some DR tests with RH 4.x, 5.x and 6.x machines. What they were doing is configuring a new interface to allow remote access to the servers on a 192.168.x.x network. My manager tells me that when they did this none of the servers were accessible until they brought down the newly configured interfaces.

    It sounds like a routing issue to but I don't know as I was not present when they were working on these systems.

    I know that the last interface brought up during boot is the default gateway, what I am wondering is if configuring these extra interfaces and bringing them up would cause the routing table to be changed? The person who made the changes isn't present so I cannot ask him what all he checked during the issue so I do not know if they checked the routing tables when they see this issue.

    Thank you for your feed back.

    Regards
    Robert

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  2. #2
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    "I know that the last interface brought up during boot is the default gateway," I don't quite understand this.

    The "default gateway" is the box to which packets will be routed if their destination is not on a directly-connected interface.

    Is the configuration that you have three servers on 192.168.1.x, 2.x and 3.x and your new interfaces are configured for those networks or you have one interface on the client box but the servers are as above?

    What do you mean when you say that the interfaces were not accessible until they were brought down? If they are down, how can they be accessible?

  3. #3
    Linux Guru Lazydog's Avatar
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    For simplicity; Every box has 4 interfaces as follows

    eth0: DHCP PIX Boot
    eth1: Static Production
    eth2: Not used
    eth3: New interface configured for the 192.168.x.x network

    We are talking strictly local to the box. When eth3 was configured and activated eth1 stopped passing traffic and was not accessible from the network.
    Once eth3 was turned down eth1 started working. I am just looking for a reason why this happened and want to know if bringing up eth3 would have changed the default route.

    My thoughts are that whom ever configured erh3 didn't do it correctly and thus the default route changed or a second GW was added thus causing the issue they were seeing.

    Regards
    Robert

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    Are eth1 and e3th3 on the same network?

    What do you get when you issue the command "route"?

  5. #5
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    Sorry, posted a bit quick there!

    How are the two cards eth1 and eth3 configured? Usually, the DHCP one will supply the default route but not always.

  6. #6
    Linux Guru Lazydog's Avatar
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    The systems have since been taken down.

    System boots into PIX boot for RH install. After the install is finished the system is then booted and the production interface is configured and the DHCP interface is turned down. After this the service is restarted. Now we have eth0 (DHCP) downed and eth1 (Production=10.10.10.x) up. Next interface eth3 (remote 192.168.1.x) is configured and brought up manually.

    As I said I was not present when they had the issues so I do not know what the routing table looked like.

    Once eth3 is manually brought up routing stops working and only 192.168.1.x is accessible. I am thinking somehow the routing table is re-configured but I am not seeing how.

    Regards
    Robert

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  7. #7
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    Hmmm...

    If eth0 asks for the default route when it gets its address, then it is likely that it will be the gateway to it. Take it down and you have no gateway.

    After you have taken eth0 down and brought up eth1 and eth3, what do you get when you issue the command "route" (no quotes of course)?

    Can you ping to the 10.10.10. network? Since this is directly connected, routing as such shouldn't come into play. Can you do the same on the 192.168 interface?

  8. #8
    Linux Guru Lazydog's Avatar
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    This was for a DR test which has already ended. If it were still available I would have been able to figure out what happened. I am just looking for any feedback on what might have caused the default route to be changed. Everyone involved is telling me that did nothing but configure an ip address on eth3 and then manually bring it up. This caused traffic to stop to the production nic. After eth3 was turned down production side started working again.

    I am thinking that they didn't bring the interface up manually but instead used the service command to restart the netwok which would have caused eth3 to be the default route.

    Regards
    Robert

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    Yea. The only way you are going to get anywhere now is to set up a box in the same way and then try to replicate what they did.

    I wish I had a fiver for every time I was told "I didn't change anything" or "I changed that but it's not the problem".

    I suspect you are right. Just bringing the interface up would not change the default gateway, only to add a route via the new interface to the network that they configured the interface to be on.

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