Etherchannel vs Spanning-tree

[Manoj Wadhwa]

Dear Team,

Have a clarification regarding a LAN design. I have Cisco 3750 in stack configuration acting as core switch. The access layer switches are 2960X in stack mode. I plan to have link level redundancy as well with the ports from each of the 2960X switches connected to each of the 3750 switch respectively.

Further, I plan to have port aggregation using etherchannel configured, so that in effect I can have a uplink bandwidth of 2 Gb. Can a similar setup be done with spanning tree as well. If yes, how can it be implemented. Do share any design document using spanning tree if any.  What are the advantages of Etherchannel vs spanning-tree and which is the recommended practice. Your feedback will be highly appreciated.

[Jon Marshall]

It's not really etherchannel vs STP because STP still runs when you etherchannel.

With stacked switches etherchannel is the way to go because STP sees the etherchannel as a single logical link and you get even more redudancy because it is spread across multiple physical switches.

If, for example, you had non stacking switches such as 3560s connected via a L2 trunk then your access switch could still connect to both 3560s but they would have to be different etherchannels so on a per vlan basis one would be blocking because you have a L2 loop.

You can effectively set up per vlan load balancing by manually setting up STP root and HSRP active on the 3560s so one switch is root and HSRP active for the odd vlans and one for the even vlans but it is more configuration.

An alternative is, if each access switch has a unique client vlan that is not shared across switches you can have a L3 link between the 3560s and then both uplinks are forwarding.

But if you can use stacked switchces, 4500/6500 VSS or Nexus vPC which all support MEC (Multichassis Etherchannel) then that is the way to go.

Jon

[Joseph W. Doherty]

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Posting

As Jon says, Etherchannel, vs. STP redundancy, is the "way to go".

Another big advantage of Etherchannel, much faster failover/recovery than STP (faster than L3 too and doesn't burn p2p addressing or add to the L3 topology maintenance).