Re: PAgP Learn Method and Port-channel Loadbalancing

In my opinion (I could be wrong) pagp learn-method is setting the
source-address learning of incoming packets received from an ether-channel,
now as far as LB in ether-channels is concerned, it is done for the outgoing
packets not incoming.

On Tue, Nov 10, 2009 at 4:00 PM, Miroslav Kosut <miroslav.kosut_at_me.com>wrote:

> Assume the following scenario:
>
> Two switches (SW1 and SW2), interconnected via 4-membered L2 etherchannels
> (on both ends, using fa0/1 - 4).
>
> SW1 fa0/1 <------------> SW2 fa0/1
> SW1 fa0/2 <------------> SW2 fa0/2
> SW1 fa0/3 <------------> SW2 fa0/3
> SW1 fa0/4 <------------> SW2 fa0/4
>
> Each physical interface on SW1 is configured with the command:
>
> *pagp learn-method physical-port*
>
> Then, some frame with src mac address DE:AD:DE:AD:DE:AD :-) is received on
> the SW1 etherchannel, on the fa0/2 physically. We are using physical-port
> learning so the mac address entry looks like this:
>
> *DE:AD:DE:AD:DE:AD fa0/2 (if I was using "aggregate-port" learning
> method, I would see here, let's say Po1)*
>
> If SW1 receives the frame with a destination mac address of
> DE:AD:DE:AD:DE:AD, will it load-balance using a hash? It is already learned
> on the physical interface so I don't see any reason of wasting a time with
> loadbalancing.
>
> If my question is completely wrong, let me know.
>
> Regards,
> Miroslav
>
> On Nov 10, 2009, at 9:39 PM, Rick Mur wrote:
>
> The loadsharing on portchannels works with so-called hashes. In your case
> for each destination MAC address that is seen outgoing on the port-channel
a
> hash is generated and divided over 1 of the links (buckets). So after a
> while all the possible variations are divided and are 'shared' on the
links.
> But keep in mind that this is fixed, traffic to the same destination MAC
> address is using only 1 of the links.
>
> Therefore it's highly recommended to use layer 3 and if possible layer 4
> information to get the best balancing over the links in the channel.
>
>
> --
> Regards,
>
> Rick Mur
> CCIE2 #21946 (R&S / Service Provider)
> Sr. Support Engineer  IPexpert, Inc.
> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>
> On 10 nov 2009, at 21:09, Miroslav Kosut wrote:
>
> Dear group,
>
>
> a quick question to confirm my understanding. Suppose I configure the
> following on the same etherchannel:
>
>
> 1. PAgP learning method to be a "physical-port learning"
>
> 2. Port-channel loadbalancing to be based on a "destination mac address"
>
>
> Then, am I right when I am saying that load-balancing method is ignored
> when a destination mac address is already learned (on a physical-port) ?
>
>
> My understanding:
>
> Since the mac is already learned on a physical-port, there is no need to
> calculate the outgoing member interface (load-balancing).
>
> Of course, if the mac address hasn't been learned, frames would be
> unicast-flooded. Then, load balancing IS performed and the outgoing
> interface is chosen.
>
>
> Regards,
>
> Miroslav Kosut
>
>
>
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Received on Tue Nov 10 2009 - 16:19:56 ART