Secure RPC communications across network segments whenever possible.
Create custom RPC protocol definitions to restrict RPC traffic to specific RPC UUID interfaces.
Use server publishing rules to protect servers and services from specific types of traffic, particularly RPC-based traffic.
Install and utilize Network Monitor on ISA server or on other systems to analyze traffic and create intelligent protocol filters with ISA.
Consider deploying multi-homed ISA servers to protect servers from client traffic by using server publishing rules and isolated server network VLANs.