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Cross Stack EtherChannel - between 2 stacks - is it possible?

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May 9th, 2014
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Below is my intent, but I read somewhere that, "The port channel cannot span chassis which means that in order for that EtherChannel to work, they need to be going to the same location and you are not able to split up the EtherChannel".


Is this possible?

Correct Answer by Bilal Nawaz about 3 years 3 months ago

Yes I have done it, with 3750, 3750X, 3650 and 3850. It is entirely possible. The posts were just trying to help you understand the technology, just logically its entirely possible if we understand what stacking is, I think that was Leo's point and also mine.

Also I think the quote could be misleading, "it is true" depending on what they mean there.

 

What I think it might mean, is if we actually break it down...

 "The port channel cannot span chassis which means that in order for that EtherChannel to work, they need to be going to the same location and you are not able to split up the EtherChannel".

The port-channel cannot span two separate chassis

I.e. From a Switch-Stack, to switch A and switch B

In order for the etherchannel to work, they need to be going to the same location, i.e. Switch A and Switch B must be logically one switch (which is the same location)

I.e. From Switch-StackA to Switch-Stack B

Correct Answer by Leo Laohoo about 3 years 3 months ago

You are correct and the statement is also correct.   Que?  

 

The statement is taking from an old, old, old manuscript.  You can't do an etherchannel to two (or more) physical switch.  Back then, there was no such concept as a "logical" switch.  Enter stacking technology.  You stack your switch to form a single "logical" entity that the software can see as a single psuedo-physical unit.  

 

Therefore, the answer is YES.  You can enable etherchannel to multiple switches in a single-stack because when stacked, these switches form a single logical switch.

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Correct Answer
Leo Laohoo Fri, 05/09/2014 - 17:28
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You are correct and the statement is also correct.   Que?  

 

The statement is taking from an old, old, old manuscript.  You can't do an etherchannel to two (or more) physical switch.  Back then, there was no such concept as a "logical" switch.  Enter stacking technology.  You stack your switch to form a single "logical" entity that the software can see as a single psuedo-physical unit.  

 

Therefore, the answer is YES.  You can enable etherchannel to multiple switches in a single-stack because when stacked, these switches form a single logical switch.

Bilal Nawaz Sun, 05/11/2014 - 09:02
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    Questions Answered, June 2015

Agreed, When it comes to switch-stacks, they are logically a single switch which is the key point i guess. You can have etherchannels that go from switch stack A to switch stack B, not necessarily having to plug in directly adjacent ports.

Just like your diagram is like = you could also have x

Logically it will also be one singular etherchannel/port-channel interface from the switch stacks point of view.

JAMES WAGNER Fri, 02/20/2015 - 07:43
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I just wanted to follow this up by saying I did get this to work.

Thanks for the input.

Joseph W. Doherty Fri, 02/20/2015 - 09:06
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Always nice to read a follow-up comment; thank you.

BTW, Etherchannel cannot (I believe) span a chassis, but when you stack or use VSS, you've created a single logical chassis.  Most (all?) current Cisco stacks require close physical proximity.  VSS units, however, can be far apart.  (NB: BTW, some other vendor stacking supports units far apart too.)

Correct Answer
Bilal Nawaz Wed, 05/14/2014 - 11:11
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Yes I have done it, with 3750, 3750X, 3650 and 3850. It is entirely possible. The posts were just trying to help you understand the technology, just logically its entirely possible if we understand what stacking is, I think that was Leo's point and also mine.

Also I think the quote could be misleading, "it is true" depending on what they mean there.

 

What I think it might mean, is if we actually break it down...

 "The port channel cannot span chassis which means that in order for that EtherChannel to work, they need to be going to the same location and you are not able to split up the EtherChannel".

The port-channel cannot span two separate chassis

I.e. From a Switch-Stack, to switch A and switch B

In order for the etherchannel to work, they need to be going to the same location, i.e. Switch A and Switch B must be logically one switch (which is the same location)

I.e. From Switch-StackA to Switch-Stack B

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