F5 BIG-IP LTM Load balancer Source Address Persistence

Source Address Persistence

Source Address Persistence, supports TCP and UDP protocols and direct client requests to the same server based solely on the clients IP address.

The default net mask is /32 on 255.255.255.255. with this mask set, BIG-IP creates a persistence second for each client that connects to the virtual server.

One limitation of source address persistence is that if a group of clients pass through a NAT device before they get to the BIG-IP, they may all have the same source address. Source address persistence will see them as the same client, and same them all to the same pool member. If this group of clients represents a significant percentage of the total number of clients for this virtual server, this can result in uneven distribution of clients across the pool.

In this animation the first client connection is load balanced and then the subsequent client request persist.

The net mask can be changed for source address persistence by the administrator. In this example, /24 or 255.255.255.0 is used. Any client that share the first three octets will match the same persistence record and there fore be sent to the same pool member. Using a net mask of /24 allows BIG-IP to maintain less persistence records and there for use less BIG-IP resources.

 

The first client from the 205.229.151.0 network will be load balanced and then persist. Any other client from the same network will also be sent to the same pool member.

However, the same limitation of source address persistence also applies if BIG-IP administrator decides to change the network. For example /24 network would not work well if all clients for a particular virtual server came from the internal network of 172.16.20.X or any class C network.

Configuring Source Address Persistence

General steps required to create a source address persistence profile.

1. Expand local traffic from the navigation panel and select Profiles. Select Persistence tab and then click the create button or select create from the flyout menu.
2. In the general properties section, type the name for the profile you are creating and then select Source Address affinity from the Type drop down menu.
3. In the Configuring section, you may want to select the custom check box and change the timeout from its default of 3 minutes. You may also want to change the mask from /32 to some thing appropriate for your client base and pool member count.

Customize the settings for your requirements and click finished.

Associating with virtual server

When creating a virtual server, a persistence profile is assigned in the Resources section of the new virtual server screen.

Assigning a persistence profile to an existing virtual server is accomplished from the resources tab.