pagp and lacp

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Jun 7th, 2008
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i want to know the following :

1) what does " number of aggregator" mean in the command" show etherchannel summary " ?

2)what is the purpose of pAgp priority ?

3) sw1 is connected to sw 2 by f0/1,f0/2

and sw2 is connected to sw 1 by f0/1, f0/2

If f0/1 on sw1 and sw2 use PagP and f0/2 on both switches use Lacp,

Will they ( fo/1,f0/2)be able to form etherchannel ?

thanks alot !

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riftjameel Sun, 06/08/2008 - 09:22
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I believe the ports that are being bundled have to have the same settings for it to negotiate etherchannel

babatunde_sanda Thu, 06/12/2008 - 07:07
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I understand this two protocols do the same thing. But one is Cisco proprietary (PAGP) and the other is industry standard (LACP). For it to work the above senarior isn't ideal after all isn't it supposed to optimize connection. So you need at least two ports in the same group. What I mean by this is assumming I want to use the above ports and I have a cisco switch I will not hardcode the port with the "channel-protocol" command. I will just say something like "channel-group 1 on" (forgive me I forgot the actual syntax but a question mark will help after the "channel-group" command to complete the syntax. The 1 represents the group number the interface belongs. So at the end if both port where a 100mbps once you configure the two as etherchannels, you should have 200mbps.

This can be done for both a L2 or L3 switch the only difference is L3 can be assigned an IP address. Also if you hardcode this ports already with either PAGP or LACP, I think you will only have options such as desirable and auto but you can verify this with the question mark where you are stuck

Hope this helps


sarahr202 Sat, 11/22/2008 - 08:03
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thanks for your reply! I performed the above idea in lab enviroment, The result was ether channel did not perform.

I configured the pagp for both ports ,once the etherchannel is formed, i changed the protocol on one port to lacp, the result was ether channel broke down.

glen.grant Sat, 11/22/2008 - 08:08
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PAGP and LACP are 2 different channel protocols. PAGP is cisco proprietary while LACP is the IEEE standard . If using pagp each side must either be desirable or desirable and the other side as auto . With LACP one side has to be ACTIVE and the other side can be active or passive to form the channel. You can run both forms of etherchannel on the same switch just not in the same channel group.


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