Using an iRule to specify multiple allowed ports for a virtual server

Good point. "Gateway" is a bit ambiguous :). Typical next hops would be firewall appliances or IP routers. If it's routers, it allows static next hop redundancy but with health detection. So consider if you have two routers and you want to round-robin traffic between then. You could create a wildcard VS with two pool members; namely, the two router next hop addresses. Naturally, you would also apply a health monitor, so if a router goes down, the LTM would stop forwarding traffic. This can be done with OSPF equal cost, for example, but that is substantially more complex to setup and manage.

Alternatively, with the firewall case, the next hop is a firewall. Since BIG-IP sends all traffic in a flow to the same selected destination, this works well for even firewall clusters. Again, a health monitor would ensure LTM would stop forwarding traffic to a firewall that becomes unavailable.