Etherchannel Load Balancing

Unanswered Question
Jun 15th, 2008


6500 has several options for etherchannelload balancing - MAC, IP adddress, port number and MPLS.

If an ethernet frame is received with type equal to MPLS and is to be switched over an etherchannel with load balancing set for IP address will it

a) look deeper in the frame for the IP address or

b) Use MAC load balancing or

c) Do something else.

Look forward to hearing from you.



I have this problem too.
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n.nandrekar Sun, 06/15/2008 - 20:21


If you check the default for loadbalancing for etherchannel on 6500, it is :

EtherChannel Load-Balancing Addresses Used Per-Protocol:

Non-IP: Source XOR Destination MAC address

IPv4: Source XOR Destination IP address

IPv6: Source XOR Destination IP address

MPLS: Label or IP

So, if mpls is enabled on the link, then the mpls packet will be loadbalanced using the MPLS rule(mpls label or IP).

The load balancing for MPLS packets over a port channel is similar to cef loadbalancing mpls over different ip paths. The hash is calculated based on the number of labels and the L3 protocol.

When the packet contains 3 or less number of labels, asic attempt to parse the underlying IP to obtain the IP addresses for the hash.

From the above link :

"Assume that you receive an MPLS packet, and that the packet can take multiple paths while leaving the

router. The router then looks for 0x4 under the bottom of the label stack. The first four bits in the IP

header indicate the version. 0x4 means that this is an IPv4 packet. If it is IP, then the router performs

load balancing based on the IP source and destination address (this is hardware-dependent).

Note If it is not IP, then the router performs load balancing depending on the bottommost label. For example,

in the case of AToM, the control word is different from 0x4 and the bottommost label is the VC label.

Remember that some platforms cannot go all the way down the label stack, so the bottommost label

might not be a VC label."

Hope this clears things.



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pbelletty Mon, 06/16/2008 - 00:33

Thanks Niranjan that is vey helpful.

Still a bit confused however - the document and text you refer to is primarily 'L3' routing and does not refer to L2 switching over an etherchannel. Any further thoughts?

Where did you find the information in respect of the first section of your reply about etherchannel load balancing - do you have the url.



n.nandrekar Mon, 06/16/2008 - 01:32


As far as I know, L2 or L3 etherchannel should cause no difference in the load balancing algo. The load balancing should depend only on the kind of traffic coming in. The ethertype in the frame should help in identifying the mpls traffic. So the loadbalancing should be according to what I explained even for L2 port-channel. I have the setup and will confirm that by tomorrow.

As to the exact info on the MPLS load balancing, I have it from an internal link / forum in cisco. I am not sure if I can share the doc with you. The info might be present in some external doc on cisco site but dont know now.



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pbelletty Mon, 06/16/2008 - 02:50

Thanks Niranjan greatly appreciated.

Look forward to see what you find tomorrow.




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