ether-channel load balance

[Roel Reyes]

Hi, 

Is there any documents that states methods of load balancing works or not depending on type of operation? 

like src-ip will not work on L2 etherchannel since it will be based on frames not packets or l3 addresses? 

Thanks,

[balaji.bandi]

here is the good reference document for various models :

https://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html

[Roel Reyes]

Yes,

But still they do not mention properly that using layer 3 load balancing like src ip or dst ip will not work on layer 2 etherchannel,

[Giuseppe Larosa]

Hello Roel,

Layer2 etherchannels are not limited to load balancing methods at OSI Layer2.

For IPv4 traffic they can use methods like source IP and destination IP addresses.

The method uses an EXOR of last significant three bits of both source and destination addresses.

To see load balancing happening a variety of IP flows are needed.

For non IP traffic they will use L2 only methods.

What switch model are you using and what IOS version is running on it?

Hope to help

Giuseppe

[Roel Reyes]

I'm using old cisco 2960, im just confused, what happen if i tried to use SRC ip or DST ip as method of load balancing on L2 etherchannel? ofcourse it will not work and no load balancing will happen right?

[Giuseppe Larosa]

Hello Roel,

in the case of old Cisco 2950 switches load balancing is not supported at all, they are just able to use the second link if the first link fails.

I had this issue and I have found this limitation.

IF you have a cisco 2950 switch the support is limited.

Hope to help

Giuseppe

[balaji.bandi · Accepted solution]

just confused here, if i understand correctly  you have CISCO 2960 ( since @Giuseppe Larosa  confused with 2950 i guess)

here is 2960 Loadbalance mechanism mentioned in the document ?

port-channel load-balance { dst-ip | dst-mac | src-dst-ip | src-dst-mac | src-ip | src-mac }

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_55_se/configuration/guide/scg_2960/swethchl.html#78975

[Giuseppe Larosa]

Hello Balaji,

yes I thought the original poster has a C2950.

Best Regards

Giuseppe

[Joseph W. Doherty]

"ofcourse it will not work and no load balancing will happen right?"

No, it can work assuming the frames on the link are contain IP packets. I.e. it doesn't matter the link is L2, it matters what kind of traffic is crossing the link. BTW, generally the "best" choice with your 2960 would be to use src-dst-ip, but the real best choice would depend on the nature of your traffic. In some situations like traffic between a pair of hosts, src-dst-ip with port numbers is needed, but that's only available on higher end switches, like the Catalyst 6K series.

[Roel Reyes]

Hi,


“No, it can work assuming the frames on the link are contain IP packets.”

Yes frames do contain ip packets, but how do the switch read the ip packets? As far as i know, switch or the l2 operation will only read L2 data’s like physical or mac addresses not the L3 or logical addresses. Kindly enlighten me.

Thank you,

[Joseph W. Doherty · Accepted solution]

A "pure" L2 switch cannot read more than the frame information but enhanced/smart/plus/etc. "L2 switches" often can examine and/or use L3 information. A 2960 falls into the latter, which is why there are load-balancing options using IP.

[Roel Reyes]

Oh so, cisco will not include those load balancing method if the switch does not support that? I’m right?

[Joseph W. Doherty]

Correct (unless it's a bug).