LACP or not? channel-group 1 mode passive/active or on

[gael.clavadetscher]

Hello,

What is the advantage of enabling LACP or not?

Our backbone is 6 3750 stacked together.

The Access switch are 3750 alone.

Each access switch have 2 giga interfaces to the backbone, this configured with etherchannel.

We got the advices

1. To configure the access switch connected to the backbone with 1000BaseSX with no LACP ->

channel-group 1 mode on

and

2. To configure the one conneted to the backbone with 1000BaseLX with LACP ->

channel-group 1 mode passive/active

Is that true? if yes why?

Many thanks for your help.

Cheers Gael

[Craig Balfour]

Cisco said it best at http://www.cisco.com/en/US/tech/tk389/tk213/tk833/tsd_technology_support_sub-protocol_home.html:

"Link Aggregation Control Protocol (LACP) is part of an IEEE specification (802.3ad) that allows you to bundle several physical ports together to form a single logical channel. LACP allows a switch to negotiate an automatic bundle by sending LACP packets to the peer. It performs a similar function as Port Aggregation Protocol (PAgP) with Cisco EtherChannel."

LACP is usually used where you need to channel the equipment of multiple vendors together. We for example use it to create a 4 Gig channel between a Nortel 8610 and a Cisco 3750.

In a purely Cisco environment there is no benefit to using LACP - you should probably use etherchannel with PAgP.

[gael.clavadetscher]

Hi and thanks for your advices,

According to

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00806cb982.shtml

It said that we can't use PAgP in the case of a Cross-stack (which is what I have).

So it is better, in the case of 1000BaseLX, and why to have a:

Configure Cross-Stack EtherChannel Without PAgP or LACP

-> channel-group 1 mode on

or

Configure Cross-Stack EtherChannel with LACP

-> channel-group 1 mode active/passive

Thanks for your help

Gael

[glen.grant]

Cross stack would give you redundancy if one switch dies you dont lose everything .

[gael.clavadetscher]

Hi,

Thanks for your reply,

But my question is what is better when using only cisco, when having 1000BaseLx,

LACP or nothing->

Better

channel-group 1 mode passive/active

or

channel-group 1 mode on

Thanks

Cheers.

Gael

[jimmcgrady]

Did you ever get an answer?  Seems a simple enough question - which is best? mode active or mode on?

[Giuseppe Larosa]

Hello Jim,

LACP mode active is to be preferred as it allows to exchange LACP control frames on each member link and allows to prevent some issues that can arise from errors in cabling

mode on makes the member links to bundle unconditionally: an error in cabling involving three switches can lead to a bridging loop that can block the whole network ( real world experience ))

I recommend LACP for this reason.

Hope to help

Giuseppe

[Jewgeni Uschegow]

Hello!

If you want use LACP then mode active/passive.