STP

[rorysjavarro]

sss

[Jon Marshall]

You are referring to etherchannel. Etherchannel allows you to connect mutliple physical ports (usually up to 8) and treat them as one logical link. So lets say you have sw1 and sw2. On sw1 you can allocate 3 100Mbps to be in an etherchannel and you do the same on sw2. You then conect the 2 switches using the 3 links and configure those physical links to be part of an etherchannel ie. a logical link.

The switches now see one link between them which is a 300Mbps link. Note that the ports don't have to be 100Mbps, they can be 1Gbps or 10Gbps but within an etherchannel they must be all the same speed.

As for STP, this doesn't disable STP. If the links were treated as separate links then as you rightly say 2 would be blocked. But STP treats an etherchannel as one link so all 3 physical links can be forwarding and none of them will be blocked. But STP still runs on the etherchannel.

Jon

[Giuseppe Larosa]

Hello Rory,

your colleague is probably referrring to etherchannel bundling:  a bundle can be built of 3 or more links and STP treats it as a single link.

There is no need to disable STP on the two switches, as STP can deal with bundles, and to be honest I strongly recommend to avoid to disable STP in this scenario or others.

if they have disabled STP they did an unsafe move

for etherchannels see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_52_se/configuration/guide/swethchl.html

if you connect 3 cables between two switches and you disable STP you just get a bridging loop.

if you configure etherchannel and you have STP disabled you can survive, but the network is exposed to possible loops

the safer choice is to use etherchannels without disabling STP.

Hope to help

Giuseppe