LTM query

A pool using Priority Groups should do the job, like Surgeon said.

1. Enable Priority Groups in the pool by setting the Priority Group Activation to be Less than 1 Available Member(s).
2. Under the Pool Member for group A, set the Priorty Group to be 20
3. Under the Pool Member for group B, set the Priorty Group to be 10

Example of what your pool should look like:

pool my_pool { 
lb_mode fastest 
min active members 1
member ServerA:82801 priority 20
member ServerB:82801 priority 20
member ServerA:83801 priority 10
member ServerB:83801 priority 10
}

Now if both pool members ServerA and ServerB on port 82301 as disabled or the monitors fail, all traffic will be load balanced to ServerA and ServerB on port 83801.