Application Delivery (ADX)

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Contributor
Posts: 24
Registered: ‎05-04-2009

How to influence the traffic distribution in a dual-WSM setup?

I do have a customer with a dual-WSM setup (two WSM6 blades in a ServerIron 450). They have added the second WSM6 a few weeks ago. The traffic distribution in between the 6 available BPs does not seem to be perfect. Some BPs do have a lot more work than others. Is there any way to change this? Any tricks?

Super Contributor
Posts: 316
Registered: ‎05-01-2009

Re: How to influence the traffic distribution in a dual-WSM setup?

The internal distribution to the BPs (processors doing the L4-7 processing) is based on IP addresses. I can think of two reasons for an uneven load distribution:

1. there are just a few IP addresses acting as clients which would result in a bad distribution

2. the distribution by default is not "perfect"

Looking at 1 there is not a lot you can do. The only option you have is to enable source port based BP distribution via "server jc-source-port-hash" - this is described in the documentation. Be careful with it because not all features are supported together with source port based BP distribution. Check the manual at:

http://www.foundrynet.com/services/documentation/SISLB/11000/slb.3.41.html#269970

Looking at 2 there is something else you can do. The ServerIron is using the last 4 bits of the source IP address for the BP selection by default. The distribution is of the traffic is like shown in the table "System with Dual Management Modules" under the link above.

18,75% of the traffic will hit the CPUs 1-4 and 12,5% of the traffic will hit the CPUs 5-6 talking about evenly distributed client IPs. The CPUs 5 and 6 do not get as much load as the CPUs 1-4 as you can see.

You can use the command "server jc-enhanced-hash" to tell the ServerIron to use 8 bits of the source IP. This would result in 256 possible values instead of 16. The distribution is therfore more granular and a lot better.

Keep in mind that a reboot is required after putting this into the configuration.

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