[c-nsp] 3750 etherchannel only using 1 port

[Fred Reimer]

I'm not sure what you meant by the term "purely statistical" when referring
to EtherChannel load balancing, but I think it may give a false impression.
If you meant that the results of the load balancing would be "by chance" and
statistically average out over time then that's incorrect.  EtherChannel
load balancing is very deterministic.  You can tell exactly what port will
be selected based on the load-balancing protocol and the number of ports.
There's even a SP command to tell you what would be selected on the 6500
platform (test etherchannel load-balance interface pox ip y.y.y.y z.z.z.z in
a remote login switch session).

If you have a relatively low number of very high throughput streams you can
use the actual protocols to map out what ports would be selected, and choose
the appropriate protocol for your specific needs.

Fred Reimer, CISSP, CCNP, CQS-VPN, CQS-ISS
Senior Network Engineer
Coleman Technologies, Inc.
954-298-1697


> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Andre Beck
> Sent: Wednesday, May 07, 2008 7:05 AM
> To: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] 3750 etherchannel only using 1 port
> 
> 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 <-
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