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Network traffic with 2 NICs

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  • Network traffic with 2 NICs

    Hello,
    how network traffic will flow in the scenario below:

    HP DL380 G7 4 NICs on board.

    The server acts as Application server. Initially, one NIC with static address was connected. Then 2 NIC (DHCP) was connected. No HP Teaming.

    Thanks,
    Michael.
    "When you hit a wrong note it's the next note that makes it good or bad". Miles Davis

  • #2
    Re: Network traffic with 2 NICs

    Have you configured static routes?

    Does this machine now have multiple Default Gateways? Every NIC that has a default gateway adds a 0.0.0.0 route (default route) to the routing table. The route most likely to be used is the default gateway for the primary NIC that is bound to TCP/IP, but this is not always the case. If the TCP session on the active default gateway times out, TCP can switch to the next default gateway. This can present a problem depending on your network configuration. (MS)

    /Rems

    This posting is provided "AS IS" with no warranties, and confers no rights.

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    • #3
      Re: Network traffic with 2 NICs

      Both NICs have one Default Gateway.
      Thanks for explaining time out point.
      Let me ask different way...
      Does addition of a second NIC (DHCP) address provides any advantage, or no impact, or just is not good (or recommended) or what are the benefit of having it.

      The server will serve couple of vLans.
      "When you hit a wrong note it's the next note that makes it good or bad". Miles Davis

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      • #4
        Re: Network traffic with 2 NICs

        If both NICs are in the same subnet then you should use NIC teaming Or, if you like to set up multiple ip address on the machine from the same range, add them manually as additional addresses to one network adapter. You can enter additional default gateways as necessary. The gateway listed at the top of the Gateways list box is always used first. Additional gateways are used only when a gateway is unavailable.

        Configure TCP/IP to use DHCP and a Static IP Address at the Same Time

        What I have heard is that it is not recommend having both nics in the same subnet.

        /Rems
        Last edited by Rems; 4th November 2011, 19:37.

        This posting is provided "AS IS" with no warranties, and confers no rights.

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        • #5
          Re: Network traffic with 2 NICs

          Both nics in the same subnet without teaming is never a good idea.
          Sessions can go wrong when data flows through the first nic and the system answers with the second nic. Also there is no guarantee that the system uses a "preferred gateway". Although it depends a bit on the costs set for the gateway.

          However multiple gateways is never recommended. Always use static routes when using multiple nics. A gateway is used as the last resort to forward the packet. Basically quite simple, if every route calculation fails then send it to the gateway.

          I'm sorry Rems, but this time I've to disagree with you.
          Marcel
          Technical Consultant
          Netherlands
          http://www.phetios.com
          http://blog.nessus.nl

          MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
          "No matter how secure, there is always the human factor."

          "Enjoy life today, tomorrow may never come."
          "If you're going through hell, keep going. ~Winston Churchill"

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          • #6
            Re: Network traffic with 2 NICs

            +1

            Originally posted by Dumber View Post
            I'm sorry Rems, but this time I've to disagree with you.
            To be clear I did not encourage to use multiple gateways. I would never recommend it. In fact in my first reply I wrote "This can present a problem depending on your network configuration".



            /Rems
            Last edited by Rems; 5th November 2011, 20:59.

            This posting is provided "AS IS" with no warranties, and confers no rights.

            __________________

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            • #7
              Re: Network traffic with 2 NICs

              Well, instead of it can present a problem, it will present a problem

              But I basically responded on this;
              You can enter additional default gateways as necessary. The gateway listed at the top of the Gateways list box is always used first.
              Although technically it might be possible in Windows there is no guarantee unless the cost changes.
              I believe Windows doesn't adjust the costs, and even if it did, then the next gateway should be a real gateway.
              Marcel
              Technical Consultant
              Netherlands
              http://www.phetios.com
              http://blog.nessus.nl

              MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
              "No matter how secure, there is always the human factor."

              "Enjoy life today, tomorrow may never come."
              "If you're going through hell, keep going. ~Winston Churchill"

              Comment


              • #8
                Re: Network traffic with 2 NICs

                thank you guys.
                From your friendly "battle" and other sources I made a simple conclusion (hope you'll agree with me).
                Since there is no performance issue on the server I will just pull out DHCP NIC cable.
                One NIC is enough. Don't want to mess up with a teaming on this machine.
                I have 4 NICs on this server and NIC failure nowdays is a very rare event.
                "When you hit a wrong note it's the next note that makes it good or bad". Miles Davis

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                • #9
                  Re: Network traffic with 2 NICs

                  ick...
                  I just tried doing this and ran into problems.

                  added second NIC (or rather plugged a cable into the second NIC) to a second switch, removed an IP address from the first NIC (there were three) and used it for the second.
                  (using the same gateway)
                  Hey - Fail over and extra speed right?
                  obviosly not:
                  couldn't ping the second NIC using that address. gave up and put it back the way it was. (actualy figured this out two days later when there were strange network problems - people not getting mapped drives, other odd network related things, guess I got distracted and didn't test it properly at the time, duh) (edit: on closer inspection I found I'd used a crossover cable. which could be why it wasn't working at all)

                  I now understand that what I was trying to do was 'not a good idea'
                  but:
                  why did it fail compleatly?
                  What's 'teaming'?

                  it seams my understanding of this stuff is a little wanting... anyone got a link to explain why what I was trying to do was bad?
                  Last edited by se5a; 8th December 2011, 00:14.

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