CEF load sharing performance

[richard.jeanmaire]

hello,

i am using curently CEF "per destination load sharing" between 2 wan link, and facing problems of dysymetrical usage of the 2 links.

I plan to use CEF "per packet load sharing" and would like to know the impact of this algorythme on the whole performance of the routeur.

Are the performances the same, or is there a difference of 10 , 20 , 30 ... percents ?

thank

[pkhatri]

Richard,

There is an inherent problem with using per-packet load balancing - there is a likelihood of packet re-ordering which would cause you far greater problems than using per-destination load-sharing.

Why is this asymmetric behaviour causing issues for you ?

Paresh

[richard.jeanmaire]

Hello Paresh

100 % of the the first link bandwidth is used, but only 20 % of the second one.

The reason is that there is only a few boxes on the lan, and only one do ftp transfert. So the transfert is limited to the bandwidth of a link. Due to the low number of boxes, i can't have a fair load balancing.

As i can't use MLPPP to aggregate the two links (my CPE router is connected to two different PE), i have to use CEF per packet load balancing.

I am aware of the drawback of a such method: some traffics like VOIP don't support re-ordered packets.

Assume i have only TCP traffic like FTP.

Richard

[pkhatri]

Richard,

What you have run into is the inherent problem with using load-sharing over multiple links - you only get performance approaching reasonable load-sharing when you have a large number of flows. I'm afraid that is something you have to live with if you can't do MLPPP.

Seeing that you are using a TCP-based application, I would strongly advise against using per-packet load balancing. The re-ordering risks of that would result in much worse performance, in my opinion. Give it a shot if you really want to but I think you'll run into problems.

As I said, I believe it's something you'll just have to live with.

Hope that helps - pls do remember to rate posts that help.

Paresh

[Richard Burts]

In this situation where the number of destinations is small and especially where a single station is generating a large amount of traffic because of FTP I believe that Policy Based Routing might be helpful. It would be possible to configure the routing such that one link was preferred over the other, so most traffic would use that link. Then configure PBR so that the FTP uses the other link. This will give better utilization of both links and will allow either link to carry all the traffic if either of the links suffers a failure.

I agree with what Paresh has said about the impact of out of order packets when per packet load share is configured. The increase in traffic on the links due to TCP retransmission may offset the benefits of more equal link utilization.

HTH

Rick

[richard.jeanmaire]

Thanx

Richard