Re: [LARTC] bandwidth aggregation between 2 hosts in the same subnet

From: Grant Taylor <gtaylor@riverviewtech.net>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] bandwidth aggregation between 2 hosts in the same subnet
Date: Mon, 30 Jul 2007 21:19:12 +0000	[thread overview]
Message-ID: <46AE55D0.3050005@riverviewtech.net> (raw)
In-Reply-To: <20070730141010.GA27667@p15145560.pureserver.info>

On 07/30/07 15:12, Ralf Gross wrote:
> I've tried bonding before. But this didn't work either because the 
> cisco switch decides on a src/dst mac/ip hash which port of the port 
> channel will be used. But in my case the hash is always the same 
> because between host A and host B. Thus always the same interface was 
> used.

Dough!  So the switch is failing you.

> But not between host A and host B. I've gone through this a while 
> ago, everyone told me than that I've to solve the problem on L3 ;)

*SIGH*

> I think it's not possible with the Cisco switches we use here to 
> increase the bandwidth between 2 hosts on L2.

It sounds like a "per packet" or "per flow" decision that is defaulting 
to "per flow" for deciding which port on an EtherChannel to use.

I'm not that much of a Cisco person so I can't say for sure, but I'd 
think there would be a setting that could be changed in the switch that 
would alter this so that you could get an aggregate bandwidth increase.

Doing a quick Google search 
(http://www.google.com/search?hl=en&q=Cisco+CEF&btnG=Google+Search) 
reminded me that we had to turn on Cisco Express Forwarding (a.k.a. CEF) 
and set the CEF to be "per packet" rather than "per flow".  You might 
want to do some research on your switches to see if they support CEF or 
not.  If your switches do support it you may want to talk to your switch 
support staff (if it is not your self) to see if they would consider 
setting such up.

I am presently using CEF between a 3640 and an upstream 7204-ubr to load 
balance ethernet connections (bridged to SDSL) and am getting an 
aggregate bandwidth increase in "per packet" fashion.  So, this will 
work between routers and I believe switches that support it.

Good luck.  Let me know if there is any thing else that I can do to help.

Grant. . . .
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