[139395] in North American Network Operators' Group
Re: LAGing backbone links
daemon@ATHENA.MIT.EDU (Daniel Roesen)
Wed Apr 6 18:18:02 2011
Date: Thu, 7 Apr 2011 00:17:01 +0200
From: Daniel Roesen <dr@cluenet.de>
To: nanog@nanog.org
Mail-Followup-To: nanog@nanog.org
In-Reply-To: <4D9B6817.6060708@foobar.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Tue, Apr 05, 2011 at 08:05:59PM +0100, Nick Hilliard wrote:
> Some older equipment will unequally prefer certain links over others,
> depending on the number of members in the LAG. I.e. a 2-member LAG might
> load balance equally under ideal conditions, but a 3-member LAG might
> naturally load balance 2:2:1.
Even newer gear does that. TurboIron 24X for example. Some Force10
switch model(s) as well, no clue how old though.
LAGs have one big advantage over ECMP: with gear implementing
"minimum-links" feature, you can make sure your LAG bandwidth doesn't
fall below a certain capacity before being removed from IGP topology
so you can make sure redundant (full!) capacity elsewhere can automatically
kick in.
With ECMP traffic engineering and capacity/redundancy planning
becomes... "interesting". Aside of all the operational problems
regarding troubleshooting (traceroutes/mtr do love such ECMP hells) and
operational consequences of having a lot of adjacencies and links.
For all those reasons, I usually prefer LAGs (with LACP) above ECMP, even
when that means "more bugs" (vendors tend to not properly test all their
features on LAGs too).
Best regards,
Daniel
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