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New Member

Etherchannel mode

Hi Experts,

What are the difrerence in different Ether-Channel Type

For Eg:- ON , Auto Desirable , LACP, PagP

Asking this b'coz we have a setup lets say End "A" & End "B" .

End A having Cisco Switch & End B is non cisco .... recently we created Etherchannel between these two ends with "Auto Desirable" Mode , suddenly End B went unreachable. After changing STP mode from mst to Pvst all remote end devices came reachable and working fine now.

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Accepted Solutions

Re: Etherchannel mode

Hi there,

LACP is a standards based protocol for forming etherchannels whereas PAgP is a Cisco proprietary protocol. The two protocols use different commands when configured:

LACP uses the "Active" and "Passive" keywords to designate whether to dynamically attempt to form an etherchannel (Active) or listen for LACP messages (Passive)

PAgP uses the "Auto" and "desirable" keywords for the same function.

It sounds like that by configuring "desirable" on the Cisco end of your link, you will prevent the non-cisco device from forming an etherchannel as it will not support the PAgP protocol.

I would recommend using the LACP protocol (Channel group x Active/Passive) or simply hard-coding each end of the etherchannel with the "on" command.

Is there currently any etherchannel between the devices, or has STP simply blocked one of the links causing the network to function again? It may be that by disabling the MST config and simply enabling PVST you have made the topology work, but not necessarily in the most efficient way.

There is some more info on PAgP and LACP in the following Cisco document:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml#ioscat4k

Hope this helps,

Jonathan

5 REPLIES

Re: Etherchannel mode

Hi there,

LACP is a standards based protocol for forming etherchannels whereas PAgP is a Cisco proprietary protocol. The two protocols use different commands when configured:

LACP uses the "Active" and "Passive" keywords to designate whether to dynamically attempt to form an etherchannel (Active) or listen for LACP messages (Passive)

PAgP uses the "Auto" and "desirable" keywords for the same function.

It sounds like that by configuring "desirable" on the Cisco end of your link, you will prevent the non-cisco device from forming an etherchannel as it will not support the PAgP protocol.

I would recommend using the LACP protocol (Channel group x Active/Passive) or simply hard-coding each end of the etherchannel with the "on" command.

Is there currently any etherchannel between the devices, or has STP simply blocked one of the links causing the network to function again? It may be that by disabling the MST config and simply enabling PVST you have made the topology work, but not necessarily in the most efficient way.

There is some more info on PAgP and LACP in the following Cisco document:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml#ioscat4k

Hope this helps,

Jonathan

New Member

Re: Etherchannel mode

Txns Jonathan for wspecific reply.

But here what you meant by "Hard Coding Each end of etherchannel"

"I would recommend using the LACP protocol (Channel group x Active/Passive) or simply hard-coding each end of the etherchannel with the "on" command."

Re: Etherchannel mode

Hi ,

With mode on , no negotiation will take place.

As far as i know , Cisco recomends : Pagp , both ends configured as "desirable"

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a00800949c2.shtml#pagptoconfig

Dan

Re: Etherchannel mode

Hi there,

With regards to "Hard Coding" I meant what Dan has said - you don't use either LACP or PAgP to negotiate the etherchannel, you simply force the port to join the bundle.

Personally, I am a fan of this, for not other reason than me wanting the etherchannel on, so why leave it to a protocol to negotiate? I am not sure what benefits using a dynamic protocol give you, but if anyone can fill me in that would be great.

If you are using a non-cisco device at the other end, you will either need to use LACP or hard code to On as the PAgP protocol is Cisco proprietary.

Many thanks

Jonathan

Re: Etherchannel mode

Hi Jonathan,

if the equipemts are direcly connected its ok to use no negotiation , because if there is a phisical problem everything will be ok, BUT:

if you have a transparent equipement ( for example a IPS/IDS ) between the 2 switches that are doing port bundling and you have a phisical problem on one link (between the switch and the transparent equipment) you will have for sure issues, like packet loss , because one of the switches will not detect the phisical problem of the other one and will use the link to forward traffic.


===  -------------link 1 ------- ===== --------------------link1 --------------- ===

SW1                                          IDS                                                           SW2

===---------------link 2 --------=====---------------------link2---------------- ===

Dan

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