Switch behaviour with configured static mac addresses

[shanemoss]

I have a situation where I need to configure three switches with static mac addresses for servers using microsoft network load balancing between two servers using a multicast mac address.  Lets say for example the servers are attached to ports fa0/48 on switches A and B.  These switches are linked together via their gi0/1 interfaces, they are also uplinked to a third switch C via their gi0/2 interfaces.

I have static mac address entries on the ports on switch C connected to A and B and everything is working fine.  However this is not ideal as any traffic to the servers is forwarded out all ports on switches A & B.  I want to configure static entries on the ports on A & B that the servers are attached to and on the ports that connect A & B together for redundancy purposes.  My question is, if I do this what will happen to frames received on for example gi0/1 on switch A - it will be forwarded out the port to the server as required but will it also send it back out the port it was learned on, in which case frames will be bounced back and forward between A & B? Is there another way to do this?

I hope this rather convoluted question makes sense!

Thanks in advance.

[Yogesh Ramdoss]

Shane,

  |
  |
  |
(g0/1)
SW_A(fa0/47)----------(fa0/47)SW_B
(f0/48)                     (f0/48)
  |                           |
  |                           |
Srv_A                       Srv_B

I assumed SW_A and SW_B has static CAM enties (for mcast mac-addr) mapped to Fas0/47 and Fas0/48.

When SW_A receives a frame on g0/1, it sends the drame to 0/47 as well as 0/48. Sw_B sends the frame received on 0/47 to 0/48 only.

Switches do not send the frame out on an interface it received that frame.

So, there should not be any flooding condition or layer2 loop.

Catalyst Switches for Microsoft Network Load Balancing Configuration Example

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml

Hope this clarifies.

- Yogesh

[shanemoss]

Thanks for your response Yogesh,

I wasn't sure with a static mac address entry in the CAM table if it would override the normal operation of the switch by forwarding frames out an interface it was received on but you have clarified the situation.

Thanks again,

Shane.