Ether channel question

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Feb 22nd, 2008
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Hi Friend

Currently i am reading Etherchannel topic, i have some doubts , can someone please clarify... thanks in advance.

1) What happend when any of the link down from bundel and then restore back ,should it take traffic automatecally ?

2) Do i need to put same vlan number on both side for proper operation on Etherchannel ?

3) As in LACp , you can configure standby bundle by using lower to higher priority , same thing is applicable to PAgP ?

4) As on LACP , who ever is lower priority will intiate channel bundel packet but in PAgP How it will happend ?

5) Can i create etherchannel on trunk link ?

6) when using PAgP desirable silent mode at both end , how channel will create ?

Give me good documents for better understanding...


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aijaz802 Fri, 02/22/2008 - 21:48
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Some points I can are for the experts...

1. yes, it takes care of the traffic when one of the links goes up/down state.

2. If its layer 2 ether channel (trunk) you can put vlan numbers in "switchport trunk allowed vlan x,y,z" w/o this line it will allow all vlans.

5. Yes, Layer 2 etherchannels i.e. trunks can be created... use the following steps..

int x/y


switchport trunk en dot1q/isl

switchport mode trunk

switchport trunk allowed vlan x,y,z

The following links might help u...

Pls. rate this post if its helpful..



Istvan_Rabai Fri, 02/22/2008 - 21:49
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Hi Vinod,

The answers are the following:

1. yes

2. yes

3. to configure standby links you need to configure them for priority values higher than the priority values of the active links. In PAgP this feature is not applicable as far as I know.

4. In PAgP you cannot influence the selection of a master.

5. yes, but the trunk configurations of all links must be the same: speed, duplex, native vlan, allowed vlans, trunking mode and encapsulation, spanning-tree settings.

6. In silent mode the channel will be set up even if the other side of the channel is "silent", i.e does not reply to the PAgp packets sent by one side.

In non-silent mode, the initiator of the PAgP packets expects that the other side be "non-silent", i.e will reply for the requests.

This feature is interesting, because it can be used to detect unidirectional link failures. If the other side does not reply in "non-silent" mode, this side will shut down the link and layer2 loops cannot form.

A good book on Etherchannel technology is :

CCNP BCMSN exam certification guide by Ciscopress.

You can also read this link:




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