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Dual 2960G switches, duplicate MAC addresses.

I have two 2960G switches that are trunked and connected to dual Foundry load balancers to provide an HA configuration.

I want to connect my servers dual network cards to the two switches for redundancy. Mysql configuration would be a lot simpler if I could have a single IP address for these two network cards.

I've tried link aggregation using LACP (ethertrunk) but it wont work because the 2960 doesnt support "cross-switch ethertrunk". (It would work fine if both cards went to the same switch).

The only thing I have left, other than two ip's, is to do static link aggregation. In static mode, the server monitors the link state of the interface and bonds them without communication to the switch (LACP). However, in this configuration, both cards show up with the same MAC (one on each switch).

Few questions I have about this configuration:

- I have no idea how the switches will behave in this config. Will it route traffic properly?

- The mac address table will have the servers mac in both the port its plugged into and the trunk port. Will it send all traffic to both cards? What will the server do - throw one away?

- Any other ideas of how I can get just one IP without LACP?

- Anyone actually tried static link aggregation in a production HA environment?

Any help would be greatly appreciated as I need to get this online asap and the mysql configuration is a mess with dual ip's.


Foundry 4G x2, Cisco 2960G x2, Apple Xserve 10.6.1

Hall of Fame Super Silver

Re: Dual 2960G switches, duplicate MAC addresses.

Hello Jonathan,

if the two switches cannot be placed in a switch stack you have two options:

active/active teaming putting both NICs on a single switch

active/standby teaming putting a NIC on one switch and one NIC on the other one.

having two active NICs using the same source MAC address on the two switches would be seen a problem and would cause troubles with each switch updating the CAM table of the other one.

Hope to help