[CentOS] Bonding modes

Thu Jan 14 16:50:35 UTC 2010
Dirk H. Schulz <dirk.schulz at kinzesberg.de>

> Thanks for you input. 802.3ad seems better but I am not in a position 
> to terminate both links in the same switch or same stack.
Some switches support LACP across several devices - for example the 
cisco 3750 with extended image can "glue" several switches together to 
one virtual switch and thus provide LACP support over several devices.

Of course there is a good deal of money involved.

By the way, using other modes over multiple switches involves using ISLs 
(inter switch links, that means direct connections between switches)*. 
If you use that you have to make sure algorithms that take time for 
recalculation (like spanning tree) do not interfere at the moment of a 
link failure because then your cluster communication maybe runs into a 
timeout also.


* the reason is that you have to handle the following case:
server a bonds to switch 1 and switch 2 with link 1a and 2a
server b bonds to switch 1 and switch 2 with link 1b and 2b
Now link 1a failes. And before you fix that, link 2b fails as well. Now 
you are glad to have an ISL. :-)