Etherchannel Between Four 3560 Switches and a 2960S Switch

[bobv62683]

Hi,

Ok, so I have more of a will this work question. We have four 3560 switches, which I understand are not stackable, but they are clustered. We also have a 2960S switch. What we'd like to do is take two ports from each 3560 and connect them to ports on the 2960S in an etherchannel.

Basically, the 2960S switch is connected via an Etherchannel that combines two 10GB ports connected to a server Chassis that has two VM blades and two SAN blades. The idea is to get the pipe wide as possible between the 8 port Etherchannel setup and the 20GB etherchannel.

So here's the two scenarios we'd like to get working if it's possible.

1. A single Etherchannel that combines all 8 ports (two from each 3560) into one 800Mb Etherchannel (I'm thinking that this will not work because the switches are not stackable)

or

2. Four seperate 200Mb Etherchannels that on the 3560 switches that can all be configured from one place.

Any help would be greatly appreciated. I guess any input on what would be the best configuration for this that maybe I haven't thought of would also be useful.

Thanks for your time!

[krahmani323 · Accepted solution]

Hi Bob !

Please find some informations/ideas about your questions :

• As you may doubt, it is not possible to set up a « Cross –Cluster » Etherchannel (ie port-channel members configured through differents switches belonging to the same cluster). Clustering being a way to centralize the managment of a group of switches, but cannot support such a feature.
• Unlike clusters, it is possible to run cross-stack Etherchannels through different stacked switches (Cat3750 – Cat2960-S) => Thanks to Flexstack of 2960S / Stackwise(+) for 3750...
• This kind of feature (distributing an Etherchannel through 2 « independant control-plane » devices is possible on very high end platforms => Nexus 5000/7000 (VpC) – and also on Cisco7600 with the recent feature mlacp (multi-chassis lacp), but not on such access switch.

So as you stated, scenario 1 could not work and you should move to scenario 2. As per your indications I understand that you have some Gig utilization limitation so you will use 100M interfaces for the Etherchannels.

• Be  careful of the traffic flow to expect before (20G vs 200M)… ! I think that you have already considered this fact and the potential actions to take…
• Distribute the Etherchannel links between the 2906-S units (The port-channel interface from the 2960S stack should be distributed through each unit towards one 3560).

Also pay attention about the following configuration guidelines (some of them are described below ) http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_53_se/configuration/guide/swethchl.html#wp1275881

. Do not try to configure more than 6 EtherChannels on the switch stack.

. For cross-stack EtherChannel configurations, ensure that all ports targeted for the EtherChannel are either configured for LACP or are manually configured to be in the channel group using the channel-group channel-group-number mode on interface configuration command. The PAgP protocol is not supported on cross- stack EtherChannels.

(In the case lacp mode active between 2960S stack and 3560s would be recommended).

• The Etherchannel default load-balancing is based on source-MAC address of the incoming packet. Based on the traffic pattern and interfaces utilization, you could optimize it with the command port-channel load-balance {dst-ip | dst-mac | src-dst-ip | src-dst-mac | src-ip |src-mac}

Other sources of information regarding 2960-S =>

Cisco Catalyst 2960-S FlexStack: Description, Usage, and Best Practices (Recommended Deployment Strategies for Building FlexStack)

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/white_paper_c11-578928.html

Catalyst 2960-S and 2960 performance and scalability information – Table 4

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/product_data_sheet0900aecd80322c0c.html

Hope that helps.

Kind regards.

Karim

[bobv62683]

Hi Karim,

Thank you so much for your very extensive response. Very helpful and answered my question. Kudos to you!