Questions about Etherchannel

[kevin ponzon]

Hi, i'm a beginner and i'm using Cisco Packet Tracer.

-I've this topology 

with STP and etherchannel activated.

I've configurated 3 channel groups with channel-protocol lacp :

-Fa 0/10-11 group 1 mode active ( switches in the north and south of topology)

-Fa 0/15-16 group 2 mode active ( switches in the north and east of topology)

-Fa 0/20-21 group 3 mode active ( switches in the east and south of topology)

I need to know what are the commands to see what are the links used in a etherchannel group  please ?

Can i try to force a channel group to use 2 links simultaneously ?

There's my pkt file if you need.

Thanks for your help ! 

[Jon Marshall]

"sh etherchannel summary" should show you the links in the etherchannel.

Not sure what you mean about using two links simultaneously. For any single flow only one of the links can be used but if there are multiple flows at the same time they can be spread across the physical links in the etherchannel.

How a flow is defined is dependant on what the switch supports. At its most basic it would be src and dst mac address but you can also have src and dst IPs and port numbers. The configuration guides for the switch model will give you the options.

Jon

[kevin ponzon]

Thanks for your help Jon,

indeed "sh etherchannel summary" has shown the links in the etherchannel and it's ok !

the command sh etherchannel load_balance shows me that etherchannel is organized with MAC source address !

I've also got etherchannel port-channel who shows me the status of ports and data (in bits) processed in the links but it's weird that all the links are active...

Because there's only one link used to process data in etherchannel and STP is also used so normally there's a part of these links who are passive no ?

Kevin

[Jon Marshall]

Kevin

I'm not sure where you have read only one of the links is used for data because that isn't true. Only one of the links is used for STP to send BPDUs and this may be where the confusion comes from.

But for data all links in an etherchannel are used subject to what I described in my previous post.

Jon

[kevin ponzon]

Thanks Jon , i've understand the situation.

For finish can you explain what's mean the column bits close to ports in " sh ethercahnnel

port-channnel"  please ?

[Jon Marshall · Accepted solution]

Can you post the output of the command you are asking about.

Jon

[kevin ponzon]

Sure it's in yellow

[Jon Marshall]

I suspect it is simply the number of bits of data on each physical link. I assume it is for both transmit and receive.

Jon

[Joseph W. Doherty]

To add to what Jon has already posted, Etherchannel is treated as one logical link for STP, so if STP blocks the Etherchannel port, all Etherchannel member ports will be blocked.

Etherchannel uses can different criteria (also platform dependent) for how it "hashes" traffic across the links.  If only src MAC was being used, flows with the same src MAC will use the same Etherchannel member link.  Flows with different src MACs may, or may not, use different member links.

A poor combination of the Etherchannel hashing algorithm will result in all or most traffic using just one member link.

Etherchannel doesn't react to member link usage, or split a flow across links.