LB::reselect vlan rateclass virtual - what can these be used for?

There are three options on LB::reselect where I can't track down additional information on how they should be used..

 

For LB::reselect virtual i found a couple discussions which all seemed to point to NOT using this but just use the virtual command. Rateclass seems to be related to the client side connection.. but perhaps it can be used to define something on the server side (all servers in a certain subnet, for example), but I don't see how a rate class can be applied to a node or pool member. Same question about VLAN on a LB::reselect. What is it's purpose and use!?

 

Manuals come up blank. DevCentral provides the syntax but no use cases or detail on what it is for.

 

I'm looking at a pool where there are members in two different subnets (which happen to be at two separate data centers). If a failure occurs to a pesisted member I would like to reselect to another member in the same subnet. I was curious of rateclass (or VLAN) could help accomplish that.