Etherchannel Question

[gdrandles]

I have read different articles concerning combining trunk ports on a Cisco switch.  I have five 3750X switches stacked together and currently have just the top and bottom switch 1GB Fiber ports trunked together connecting to the core.  This creates a redundant 2GB uplink port.  Bandwidth to the core is steadily increasing so I wanted to go ahead and add some additional trunk ports on the stack to the etherchannel (i.e. 2GB to 5GB).  Will I really get 5GB if I combine five 1GB trunk ports in a single etherchannel?  If there is no advantage of combining the maximum number of ports together then I would have to upgrade the PID to 10GB ports.

Thanks

[Leo Laohoo]

Will I really get 5GB if I combine five 1GB trunk ports in a single etherchannel?

Yes and no.  Data traffic won't be "dividided" to the 5 links.  Instead traffic is sent to ports that are not used.  For example, you have TEN data queued up.  First five goes to links 1 to 5, obviously.  But let's say that data 1 and data 5 are large files.  So data 6 goes "who is ready to take me across" and link 2 probably raises a flag and says, I'm free and so on.

If there is no advantage of combining the maximum number of ports together then I would have to upgrade the PID to 10GB ports.

IF you have the funds, you can't go wrong with two (at least) 10Gb links in an etherchannel.  If you have financial constraints, I'd consider etherchannel the 1Gb until you have enough data to go get a number of 10Gb modules.

[cashqoo · Accepted solution]

if my memory serves me correct,

>>  Will I really get 5GB if I  combine five 1GB trunk ports in a single etherchannel?

yes, you will get the a bundled link of up to 5gb

however, the load will not be evenly shared between the links. load balancing is determined by an algorithm using the source and destination address (mac and ip) as inputs. if you have the same source sending data to the same destination, it will always use the same link/interface.

etherchannel seems to support up to 8 active links. so using 1000baseX (1GB fiber links), it can gives you up to 8gbps.

more information on load balancing:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_55_se/configuration/guide/swethchl.html#wp1275731