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 -- CLUE-RIPE -- Jabber: dr@cluenet.de -- dr@IRCnet -- PGP: 0xA85C8AA0