Super-Networking Blog

Sometimes it is quite hard to find info on the Cisco CSM Load balancer module so as I find info I try to post here for others.

Latest thing I was looking into was persistent rebalance. I new it was a good thing and it is enable by default but I am not a default kind of guy so I try to looking to setting to see what they are for and it the default is right in all situations. It the case of persistent rebalance I believe that it is. Normally what I had seen on this is just persistent rebalance allows for support of HTTP 1.1 persistence. My question was do you need this persistence if the content you are serving is just static content like pictures. The answer is yes and below is the reason why.

The CSM allows HTTP connections to be switched based on a URL, cookies, or other fields contained in the HTTP header. Persistent connection support in the CSM allows for each successive HTTP request in a persistent connection to be switched independently. As a new HTTP request arrives, it may be switched to the same server as the prior request, it may be switched to a different server, or it may be reset to the client preventing that request from being completed.

As of software release 2.1(1), the CSM supports HTTP 1.1 persistence. This feature allows browsers to send multiple HTTP requests on a single persistent connection. After a persistent connection is established, the server keeps the connection open for a configurable interval, anticipating that it may receive more requests from the same client. Persistent connections eliminate the overhead involved in establishing a new TCP connection for each request.

HTTP 1.1 persistence is enabled by default on all virtual servers configured with Layer 7 policies. To disable persistent connections, enter the no persistent rebalance command. To enable persistent connection, enter the persistent rebalance command.

So basically you are saving on TCP connection overhead by having this in place, always good to know exactly what the setting does not just that it is a default setting.