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Preventing duplicate MAC-Addresses in the CAM tables

We have a svr with 1 NIC running TCP/IP configured in 1 VLAN, & a 2nd NIC running IPX in another VLAN. Both NIC's connect to ports on the same access switch (6509 with CATOS).

Problem= svr team have bridged the NIC's. This results in duplicate MAC Addresses in the CAM tables on Access & Distribution switches.

Question: Is there any way to stop the duplicates in the CAM tables?

I have considered extended ACL's but still need traffic to flow across the VLAN interfaces. I cannot filter MAC-Addresses from the CAM table because this would involve an entry for every duplicate. Finally I have looked at Bridge groups but do not understand them fully.


Re: Preventing duplicate MAC-Addresses in the CAM tables

I think you mean the switch is complaining about the same mac-address being learned on two different ports due to the loop created by bridging the server nics, duplicate macs is not possible, you can have the same mac address in the cam table but they would belong in different vlans, totally normal. The loop created by bridging the NICs maybe a PortFast BPDU Guard might work if the NIC bridged is transparently switching everything from one NIC to the other including BPDU's. If the port with BPDU guard rx'd a BPDU it will errdisble that port. Other than that, it will take network policy to let users know it's a no-no.

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New Member

Re: Preventing duplicate MAC-Addresses in the CAM tables

Did your server team set up a virtual MAC for the 2 NICs? In that case, they should set it up that one NIC comes up only when the other goes down.

If both NIC needs to be up at the same time, use their native MAC address instead of the virtual MAC. That would give each NIC its own IP address and each MAC would have a one-to-one match in CAM table even if 2 NICs are bridging.

Let me know if that works out.


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