There are two main servers that we're using for PRPNet now:
Each one with several ports. It's best to choose a back-up port from each server. That way if a physical server goes down, your cores can continue to work on the other server. Below are examples of back-up ports with short WU's:
They are not commented and have 0 share. Work will only be retrieved if all other active ports are down.
NOTE: Although PPSElow and PPSElow2 settings ask for 5 WU's, since they have 0 share, they will only ask for 1 WU. This intended effect is to get the host back to it's original ports as soon as possible.
[EDIT] In the rare event that both physical servers are down, the SR5 sister project is available at a third physical location:
You could set this up as back-up as well.