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Etherchannel on Cisco switches

Posted on 2003-03-14
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Last Modified: 2008-01-09
can etherchannel span 2 boxes? Can you have port gig0/1 on switch A and port gig0/1 on switch B belong to etherchannel 1 if A and B are connected and terminate at C.
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Question by:lenyo
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by:pedrow
ID: 8140440
no.

i suppose you mean that C would be configured as a port channel? nope.

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by:lenyo
ID: 8141004
What is the reason why this can't be done. Where does the problem come in?
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by:pedrow
ID: 8141139
port channel is to create a logically larger pipe.

i.e. bind two 100mb or two gige ports between a pair of switches so that you can increase your throughput.

To have a port-channel configuration where there are two ports on switch c, but the it splits off into two single ports connecting to different switches makes no sense. Try it, the port channel won't come up. Spanning tree would probably kill it off if you can configure it at all.

Do you mean setting up trunks to pass all (or most) of your configured vlans?
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by:Don Johnston
ID: 8146304
FWIW, Nortel supports this "feature".

-don
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by:pedrow
ID: 8147609
hey donjohnston - i'm just confused as to how that would be different from having two trunks, one going from switch A->B and another from switch A->C. I just don't see where the gain is...

Frankly though, I've rarely come across situations where 100mb links come even close to saturation, let alone GigE.

However, GigE portchannels between cisco's do allow for a way to provide some redundancy, in that if one of the channels fails, the other one keeps working.

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by:Don Johnston
ID: 8147628
It's like Multi-chassis, Multi-link PPP. Obviously, B & C have to also be connected to each other for it to work. I've never done it myself. I just heard it's on the list of "neat stuff Nortel switches can do".

I've never been able to figure out an application for it myself.

As for 100mb links being saturated, imagine a switch to switch link with 40 users at 10mb on one switch trying to get across that link. You'd be looking at about 400mb of traffic trying to cross a 100mb link. Of course Gigabit Ehternet fixes that, but what if Gig wasn't an option?

-dj
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by:pedrow
ID: 8147650
thanks for the explanation :)

oh, i use etherchannel, both with gig and fastE links, but even the 40 users at 10mb almost *never* decide to transfer large files from the same source at the same time. Just for kicks, find the busiest box (mailserver, webserver, etc...) in your company, and from the Catalyst switch's enable, do a :
switch(enable)#sh top bytes 300

it will give you the top talkers over a 5 minute period. I'd be surprised if you see any port except perhaps the uplink port top 10% utilization of a 100mb port :)

at least that's been my findings....
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by:jgarr
ID: 8222593
Etherchannel has to exist on a single switch. It is logically a bundled link. For redundancy, be sure to use desirable on both sides of the channel. Setting either side to 'on' will force the channel to go errdisable if you lose one connection.

If you desire bandwidth, you should etherchannel.
 
If you desire redundancy, you can set links up between your IDF switch and two MDF switches with a link between the MDFs carrying the vlan (either an access link or a trunk to carry more than one IDF) Configure spanning tree with the root at an MDF switch.
Or build two etherchannels; one for each MDF link.





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by:lrmoore
ID: 8637236
lenyo,
No comment has been added lately (68 days), so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

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