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Introduction:

I am configuring a server to have two ethernet ports (one as primary, the other is redundant) connected to two different switches. In the switches, I enabled the sticky MAC address and configured the two ports on the server as Net Switch Team and fixed a MAC address for the team.

the issue:

when doing the failover test, I unplugged the primary and the redundant link was up (as expected) but when I unplug the redundant before restoring the primary then restoring both links the server will not be able to ping the switch unless I turn off the Sticky MAC address off in the switches.

Note:

I am thinking maybe because the Ethernet Adapter Card has both ports in it and if I applied the same thing on two different ports in two different Ethernet adapter cards it will work fine. Is that true? and if yes why?

Thanks in advanced, Best regards.

2 Answers 2

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Sticky MAC doesn't work because you're programming the network to have that MAC in a specific place (port). A MAC can only be in one place in the network. If that port is physically up, that's always where the traffic will go. When a MAC is pinned to two places -- on different switches, traffic on each of those switches will always flow to the local port, because that's how you've programmed it: Sticky MAC permanently populates the CAM table. A third switch will see that MAC bouncing from switch to switch depending on where it sees traffic. [In Cisco terms a "MAC FLAP"] With a MAC pinned to more than one place, you're relying on the redundant port(s) to be physically down, so the MAC is removed from the CAM table; when they aren't traffic doesn't go where it must.

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It isn't entirely clear how the host fails over but the basic approach for active/passive is don't configure anything on the switch.

Instead, the host just needs to transmit a single frame with the redundant MAC address as source (physical or virtual), so the switch moves that MAC to the currently active port on failover or recovery. Making a MAC sticky on a certain port may prevent that mechanism from working, depending on the overall configuration.

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  • Could you please explain why making a MAC sticky on a certain port will prevent this mechanism?
    – Mhd Ghd
    Dec 4, 2022 at 8:35
  • also, I have enabled port teaming and fixed a MAC address for both ports so they have the same MAC address.
    – Mhd Ghd
    Dec 4, 2022 at 9:45
  • Please add the full, sanitized switch config to your question using the {} preformat option. What is it that you are trying to achieve with stickiness?
    – Zac67
    Dec 4, 2022 at 10:09
  • In fact I don't need to have the sticky feature on, but I want to understand why when I enable the port teaming in (SEL-3390E4 network adapter -both ports in the same network adapter-) and I start testing the failover I am unable to ping the switch even if I restored both links
    – Mhd Ghd
    Dec 4, 2022 at 13:43
  • I'm afraid, host configurations and issues are explicitly off topic here, see the help center - especially when we have no details on how the 'port teaming' really works (there are several ways to do it).
    – Zac67
    Dec 4, 2022 at 15:12

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