Link Aggregation Configuration

[MARTIN HUERTER]

I have two pairs of VSS catalyst 6500 switches and in between them I would like to place a pair of Source Fire FirePOWER appliances. The appliances look like layer 2 switches and can be configured for link aggregation, but wanted to get verification they would work properly as depicted in the diagram below. As you can see, interface Port-channel 9 between the Catalyst 6500 switches is a routed link and is currently configured this way on the VSS pairs.

[Madhukrishnan Gopinathan Nair]

I think it will not work as currently lacp is running between 2 devices (both are logically one and have one lacp id). When you introduce another layer 2 device and bundle it up, each switch sees neighbor as 2 devices...and 2 links will not join the same bundle on each 6500.

Thanks,

Madhu

[MARTIN HUERTER]

Madhu,

Thank you for your response. I have two diagrams, one is "Option A" and the other is "Option B". Which one of these two should I configure my LAG interfaces? I am guessing Option A will work?

Thanks,

Martin

[Madhukrishnan Gopinathan Nair]

Hello Martin,

I took a look at both. I can't spot a difference apart from Port-channel numbering being used, but configuration and funcationality its the same.  Thought option A seems clearer to understand.

I think it should work, I hope you are planning to create 2 port-channels group in each Layer 2 (one upwards to VSS and one downwards to VSS).

However if you are making it on production devices, please plan a sufficient Maintenance window time inorder to carry this out. Consider incase of issues you need to back out also. 

Hope this helps and please rate all useful posts..

Thanks,

Madhu

[Madhukrishnan Gopinathan Nair]

One more thing i am thinking it may not give you an intended result. Looking at your current topology, you have a port-channel having 4 links between 2 switches.

When you introduce this layer devices, one of the path may get blocked by STP. As we 2 redundant L2 path between 2 VSS switches. Did you get my point? 

Thanks,

Madhu

[MARTIN HUERTER]

Madhu,

Thanks for your response. Could I use either ECMP or ECLB to solve the STP problem between the appliances and the VSS pairs?

Thanks,

Martin

[Madhukrishnan Gopinathan Nair]

Hello Martin,

Can you explain ECMP or ECLB in this context? How you are going/planning to do that?

Thanks,
Madhu

[MARTIN HUERTER]

Madhu,

The LAG links between the VSS pairs will be running as layer 3 links on top of OSPF.  See attached diagram called appliance4.jpg.

Thanks,

Martin