[c-nsp] 3750 etherchannel only using 1 port

Andre Beck cisco-nsp at ibh.net
Wed May 7 07:05:21 EDT 2008


Hi Paul,

On Tue, May 06, 2008 at 12:40:25PM -0400, Paul wrote:
> C3750 Software (C3750-ADVIPSERVICESK9-M), Version 12.2(44)SE1, RELEASE 
> SOFTWARE (fc1)
> 
> Running two etherchannels with two gig ports not cross stack.  Here's an 
> example of one of them.
> What's happening is that only one port is being used for outgoing 
> traffic, no matter what I set the port-channel load-balance to.     Is 
> etherchannel broken in 12.2.44SE1? This is a new setup.

I'm running 12.2(44)SE1 on a bunch of 3560E chassis which are similar
enough to the 3750E, but maybe not the 3750. They're running multiple
port-channels that look quite similar to yours (LACP) and I see egress
traffic on both group members.
 
> Ports in the Port-channel:
> 
> Index   Load   Port     EC state        No of bits
> ------+------+------+------------------+-----------
>   0     00     Gi1/0/1  Active             0
>   0     00     Gi1/0/2  Active             0

Looks the same here, but doesn't seem to indicate a problem.

Of course you will see a certain flow always taking just one member
egress path, any load balancing is purely statistical. I was running
the default (source MAC only) load balancing method. Thanks you triggered
me to revise this, which was forgotten after the replacements. I've
changed it to src-dst-ip. I'm just not sure if that will really make
a difference on an L2 port-channel or if that incarnation will always
take the "Non-IP" branch. Using just Source MAC (or even Src XOR Dst MAC)
is often bad when routers are talking to each other, as most traffic is
going from/to a single MAC, so having this work even on L2 port-channels
would be a win. I'll see whether my Torrus graphs show significantly
better distribution after the change. But it still might be due to just
the

 Non-IP: Source XOR Destination MAC address

balancing still better than the default.

HTH,
Andre.
-- 
   Real men don't make backups of their mail. They just send it out
    on the Internet and let the secret services do the hard work.

-> Andre Beck    +++ ABP-RIPE +++      IBH IT-Service GmbH, Dresden <-


More information about the cisco-nsp mailing list