when to use layer 3 etherchannel

kaustubhchavan · ‎01-13-2009

when to use layer 3 etherchannel ?

please briefly explain

Marwan ALshawi · ‎01-13-2009

brifelly ether channel is a method of bundelling or grouping more than one link together to get more bandwith

etherchannel can be used AS L2 which forward traffic as access link or as trunk

and can be configured as L3

in this case the link will have single IP to for all group

for example if u have three links group as one L3 etherchannel they will have single IP

and this way u can use it in you routed network as single interface

it is based on ur topology

maybe u used as uplink to a router

may be u use it as inter switch links between tow core or destribution layer switches

hope this helps

rohitrattan · ‎01-13-2009

Hello Dear,

You should use a Layer 2 etherchannel if your Switching Topology is Layer 2 i.e. you rely on Spanning Tree Protocol to manage the redundancy etc. If in case you are running any routing Protocol in you LAN and essentially your LAN topology is L3 you can go ahead and configure a layer 3 etherchannel.

Theres one major difference between L2 and L3 etherchannel which dictates the traffic flow and thats Load Sharing/Balancing across the individual links.

A L2 ether channel can load balance using Source Mac, Destination MAC or a combination of both only whereas a L3 etherchannel can Load balance using Source IP, Destination IP, or a combination of both and on Cat 4500/6500 a Layer3 Etherchannel can Loadbalance using Source Port, Destination port or a combination of both.

So i hope you can decide which one to use but be consistent with your LAN topology (L2 or L3)

Regards

Rohit

gagamboy15 · ‎01-13-2009

Hello guys,

Can you please explaing the difference using a command? It seems I am a little bit confused in theory. Thanks in advance.

Cheers!

Jon Marshall · ‎01-13-2009

Irvine

Have a look at this link which shows how to configure L2 and L3 etherchannels on the 3560, principle is the same for all switches -

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/configuration/guide/swethchl.html#wp1275918

If it helps just think of etherchannel as a bundle of links and there is one logical interface (the port channel) that represents the physical links.

With L2 etherchannel each individual link is a L2 link ie. it is either an access port in one vlan or it is a trunk port.

With L3 etherchannel each individual link is a L3 link ie. it is a routed link. You assign the IP address to the logical interface.

Jon