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New Member

PAgP

Does the PAgP protocol sends out the BPDU's every 30 sec's ? If yes, what are they meant to?

And as per my understanding PAgP has 3 modes:1. Auto 2.Desirable 3.On

Auto makes a port to listen for PAgP messages.

Desirable generate PAgP messages, by default the interface configured like this will not be part of any channel.

On generates PAgP messages, the interface is part of a channel. But when i configure any interface to be a part of PAgP protocol and try to configure the mode as ON. I'm getting "Command Rejected" error. Can someone please help me out of this?

--------

Switch(config-if-range)#channel-protocol pagp
Switch(config-if-range)#channel-group 1 mode on
Command rejected (the interface Fa0/1 is ): is already part of a channel with a different type of protocol enabled   //Here is configured pagp, right?
Command rejected (the interface Fa0/2 is ): is already part of a channel with a different type of protocol enabled
Switch(config-if-range)#

-------

Thanks in advance.

Regards,
Chandu       

Regards, Chandu
2 ACCEPTED SOLUTIONS

Accepted Solutions
Purple

Re: PAgP

You ar specifing pagp as the protocol so your only interface options are either desirable or auto . One end "must" be desirable to run pagp.

   Mode "on" forces the channel on using no aggregation protocol.

Re: PAgP

Mode

Description

active

Places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending LACP packets.

auto

Places an interface into a passive negotiating state, in which the interface responds to PAgP packets it receives but does not start PAgP packet negotiation. This setting minimizes the transmission of PAgP packets.

desirable

Places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending PAgP packets.

on

Forces the interface into an EtherChannel without PAgP or LACP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.

passive

Places an interface into a passive negotiating state, in which the interface responds to LACP packets that it receives, but does not start LACP packet negotiation. This setting minimizes the transmission of LACP packets.

Channel-group mode on does not use PAgP. PAgP and LACP are negotiation protocols. On just forces it to be one etherchannel. Therefore, there is no negotiation traffic between ports with this mode. This is my understanding from Cisco's documentation anyway.

hth

Please rate useful posts & remember to mark any solved questions as answered. Thank you.
12 REPLIES
VIP Super Bronze

PAgP

Can you post

sh run int fa0/1 and fa0/2

also

sh run int po1

What type of switch are you using and what IOS?

Purple

Re: PAgP

You ar specifing pagp as the protocol so your only interface options are either desirable or auto . One end "must" be desirable to run pagp.

   Mode "on" forces the channel on using no aggregation protocol.

Re: PAgP

Mode

Description

active

Places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending LACP packets.

auto

Places an interface into a passive negotiating state, in which the interface responds to PAgP packets it receives but does not start PAgP packet negotiation. This setting minimizes the transmission of PAgP packets.

desirable

Places an interface into an active negotiating state, in which the interface starts negotiations with other interfaces by sending PAgP packets.

on

Forces the interface into an EtherChannel without PAgP or LACP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.

passive

Places an interface into a passive negotiating state, in which the interface responds to LACP packets that it receives, but does not start LACP packet negotiation. This setting minimizes the transmission of LACP packets.

Channel-group mode on does not use PAgP. PAgP and LACP are negotiation protocols. On just forces it to be one etherchannel. Therefore, there is no negotiation traffic between ports with this mode. This is my understanding from Cisco's documentation anyway.

hth

Please rate useful posts & remember to mark any solved questions as answered. Thank you.
New Member

PAgP

Thanks for the help. But my first question didn't got clarified.

----------

Does the PAgP/LACP protocol sends out the BPDU's every 30 sec's ? If yes, what are they meant to?

----------

Regards,
Chandu

Regards, Chandu

PAgP

No they do not send BPDU's. The switches do that in STP process.
PAgP and LACP are there to negotiate the port-channel/etherchannel between devices (switches/servers/routers).

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

Please rate useful posts & remember to mark any solved questions as answered. Thank you.
Purple

PAgP

  BPDU's are part of the spanning tree process and have nothing to do with etherchannel negotiation protocols.

New Member

PAgP

Sure i'll rate the posts & mark this as answered. But i left with one more thing on this.

Does anyone have the Wireshark capture of the PAgP and LACP frames ? If yes, please post.

Thanks again in advance.

Regards,
Chandu

Regards, Chandu

Re: PAgP

Chandu,

I've attached some captures from both protocols, but I'm not sure whether this will be helpful for your preparations.

Both protocols allow Etherchannels (aggregated physical links, which then appear as one [virtual] link) to negotiate and control link-operation.

The on-mode, in contrast, doesn't use such a negotiation-protocol.

You can find a lot of documents here: Technology Support | LAN Switching | Etherchannel

I always encourage people to dig into the protocol details, but learning all the details of link aggregation operations will certainly be a huge task.

HTH

Rolf

New Member

PAgP

Rolf- Thanks a lot.

Regards,
Chandu

Regards, Chandu
Silver

Re: PAgP

Hi Chandra,

BPDU are related to Spanning Tree. BPDU or Bridge Protocol Data Unit, are of two types... Configuration BPDU and TCN BPDU which are sent at the time of spanning tree convergence and afterwards every 2 seconds.

There is no relation between BPDU and etherchannel.

PAGP and LACP are negotiation protocols and negotiation packets are sent across the link.

Attached are LACP and PAGP sample captures.

Thanks

Ankur

"Please rate the post if found useful"

Re: PAgP

Ankur,

Chandu,

There is no relation between BPDU and etherchannel.

well, an interesting fact might be that also from the spanning-tree protocol's perspective an EtherChannel is just a single link, like is is for any type of traffic. BPDUs are send across one of the member-ports and the EC ports will result in one of the normal STP port states. In other words:The (physical) member-ports are excluded from STP-operation when they are bundled in an EC. This is one of the reasons why the on-mode is not recommended.

Without EC, the redundant ports would have to result in blocking state at some place in order to cut the loop.

HTH

Rolf

New Member

PAgP

Thanks each and everyone for helping me in this and thanks for tha attachemnets Rolf & Ankur.

Regards,
Chandu

Regards, Chandu
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