Cirrocumulus
NimbostratusA persistence profile is attached to the virtual. With cookie insert, the cookie name is some value (by default something like BIGIP-poolname, though you can statically define it to something else).
The cookie value identifies the backend server and port. If a connection comes in with a cookie, the value is looked at, and assuming that server is available, it sends it to the pool member identified.
If there is no cookie presented, it just uses whatever LB mechanism is specified (like round robin).
Note, the cookie values are just encoded IP and Port of the backend server. It would be a good idea to add encryption, if your version of code supports that.