Etherchannel vs 2 separate links

Unanswered Question
Mar 8th, 2009

What is the better configuration (please provide pros and cons) ?

- to use 2 separate links between 2 switches

- or to use 1 etherchannel with those 2 links

I have this problem too.
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Richard Burts Sun, 03/08/2009 - 15:45

Petru

If you can help us understand your criteria then we can help you choose the best configuration. Is "best" the most simple configuration? If so then 2 separate links is more simple than Etherchannel and would be best.

Is to achieve redundancy the "best"? Both choices achieve redundancy but do so in different ways. The 2 separate links will use spanning tree so that a loop does not form. The spanning tree will put 1 link into blocking state to prevent a loop. So the result is that 1 link at a time can carry traffic and if that active link fails then the Spanning Tree must converge before the second link becomes active. An advantage of Etherchannel is that Spanning Tree sees the single Etherchannel and not the 2 individual links. So both links are actively carrying traffic with Etherchannel. And if there is a failure of one of the active links there is no need to wait for Spanning Tree to converge.

So most people would probably choose Etherchannel as best.

HTH

Rick

Giuseppe Larosa Sun, 03/08/2009 - 15:48

Hello Petru,

if the two parallel links are between two switches I would use an etherchannel:

for STP the bundle is a single logical link and both links are used (each side uses them according to its own algorythm(s))

if the question involves a router and a switch I would prefer two distinct links with IRB on the router.

Actually, I've seen some problems of bundles on routers.

This is my opinion and I saw others using etherchannels on routers.

Between two routers I would always use parallel indipendent links taking advantage of IP load balancing.

Hope to help

Giuseppe

Jon Marshall Sun, 03/08/2009 - 16:15

Petru

Etherchannel places a number of restrictions on the ports that are part of the bundle ie. they must be same speed/duplex, same range of allowed vlans etc.

In a standard L2 setup between 2 switches i would generally go with etherchannel if redundancy is your objective. As others have said big pro of etherchannel is

1) increased throughput

2) STP sees etherchannel as only one link

For L3 between 2 switches - L3 etherchannel.

For L3 between switch and router - 2 equal cost paths is often easiest.

Jon

hobbe Tue, 03/10/2009 - 06:12

as a general rule I like the etherchannel setup best. I use it to make redundant links between 3750 stacks.

but here comes a curveball noone have touched in this thread before.

However since you can do load balancing on the links, there should be a word of warning.

be aware that in the event of a link faliure in the etherchannel there might be a problem with overwhelming the remaining links.

so monitor the link activities and make shure that a link going down does not bring the whole switch system down.

good luck

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