A Question On Networking (CentOS 6)

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Hi AllThis is NOT specifically related to CentOS per se.  I have 2 servers that are on two networks.  I did NOT set this up.  The NIC went bad and it has been replaced.  I knew enough to update the HW address in the ifcfg-* files.  The network service restarts successfully without errors.  However I cannot connect via ping or SSH with the pt2pt network setup on 192.168.x.*.  When I use our internal network ip addresses it is fine. I am not sure how to troubleshoot this separate connection.   What can I provide here that will allow someone to help?  Thanks in advance.  I tried searching a bit but didn’t find anything of use so far. KM

4 thoughts on - A Question On Networking (CentOS 6)

  • That’s not much to go on. The output of “ip addr show” and “ip route show” might help you figure out what’s going on. Do your interfaces have the expected names? Do they have the expected IP addresses?

    One thing that might be problematic is that there are multiple systems that attempt to maintain consistent interface names. If your interface names are not what you expect, you might need to look at
    /etc/udev/rules.d/70-persistent-net.rules where there may be additional rules mapping specific MAC addresses to an interface name.

  • I will get back to the mailing list.   But to answer your questions, yes the IP addresses and interface names are as expected (as before) with the new MAC/HW addresses.  I have someone else looking into it because when we plugged in the cable the light on the card did not light up.   when we connect the pair server to another separate server it did.  That’s not much to go on.  The output of “ip addr show” and “ip route show” might help you figure out what’s going on.  Do your interfaces have the expected names?  Do they have the expected IP addresses?

    One thing that might be problematic is that there are multiple systems that attempt to maintain consistent interface names.  If your interface names are not what you expect, you might need to look at
    /etc/udev/rules.d/70-persistent-net.rules where there may be additional rules mapping specific MAC addresses to an interface name.

  • Like I said, wishful thinking. The light is still out, so it could be the HW. I ran those commands (ip addr show, ip route show) on the 2 servers.  The output is identical except for the IP addresses and the MAC addresses, except on the server with the new card, it is missing the following IPV6 info for the interface name p2p1 which is the interface in question. inet6 fe80::6a05:caff:fe06:9122/64 scope link
           valid_lft forever preferred_lft forever

    Somehow I doubt we are using IPV6 but does it need to be there for some reason?  …. and if so , what do I do about it. I apologize if these questions make no sense.  Other than the original setup, and sometimes editing the ifcfg files I usually don’t have to do much else to get my network connections going. KM

    From: KM
    To: CentOS mailing list
    Sent: Monday, February 13, 2017 12:49 PM
    Subject: Re: [CentOS] A question on networking (CentOS 6)

    I will get back to the mailing list.   But to answer your questions, yes the IP addresses and interface names are as expected (as before) with the new MAC/HW addresses.  I have someone else looking into it because when we plugged in the cable the light on the card did not light up.   when we connect the pair server to another separate server it did.  That’s not much to go on.  The output of “ip addr show” and “ip route show” might help you figure out what’s going on.  Do your interfaces have the expected names?  Do they have the expected IP addresses?

    One thing that might be problematic is that there are multiple systems that attempt to maintain consistent interface names.  If your interface names are not what you expect, you might need to look at
    /etc/udev/rules.d/70-persistent-net.rules where there may be additional rules mapping specific MAC addresses to an interface name.

  • seems to be a driver issue or something, according to some co-workers.  Thanks for the help, but I guess I need to upgrade the OS or use another card. ThxKM

    From: KM
    To: KM
    ; CentOS mailing list
    Sent: Monday, February 13, 2017 1:31 PM
    Subject: Re: [CentOS] A question on networking (CentOS 6)

    Like I said, wishful thinking. The light is still out, so it could be the HW. I ran those commands (ip addr show, ip route show) on the 2 servers.  The output is identical except for the IP addresses and the MAC addresses, except on the server with the new card, it is missing the following IPV6 info for the interface name p2p1 which is the interface in question. inet6 fe80::6a05:caff:fe06:9122/64 scope link
           valid_lft forever preferred_lft forever

    Somehow I doubt we are using IPV6 but does it need to be there for some reason?  …. and if so , what do I do about it. I apologize if these questions make no sense.  Other than the original setup, and sometimes editing the ifcfg files I usually don’t have to do much else to get my network connections going. KM

    From: KM
    To: CentOS mailing list
    Sent: Monday, February 13, 2017 12:49 PM
    Subject: Re: [CentOS] A question on networking (CentOS 6)

    I will get back to the mailing list.   But to answer your questions, yes the IP addresses and interface names are as expected (as before) with the new MAC/HW addresses.  I have someone else looking into it because when we plugged in the cable the light on the card did not light up.   when we connect the pair server to another separate server it did.  That’s not much to go on.  The output of “ip addr show” and “ip route show” might help you figure out what’s going on.  Do your interfaces have the expected names?  Do they have the expected IP addresses?

    One thing that might be problematic is that there are multiple systems that attempt to maintain consistent interface names.  If your interface names are not what you expect, you might need to look at
    /etc/udev/rules.d/70-persistent-net.rules where there may be additional rules mapping specific MAC addresses to an interface name.

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