Protocol rules identify which protocols may be utilized for communication, between the internal network and external public domain or Internet. Protocol rules are processed at the application level of the OSI model.
Protocol rule functionality.
B) The table above describes what protocols protocol rules can be applied to when installed in its respective mode. (This information is according to Microsoft but I have noticed very little differences when testing the all IP in cache mode scenario)
The steps below are used when creating a protocol definition.
When an ISA client requests a web resource using a specific protocol, ISA Server first checks the protocol rules. If one of the protocol rules specifically denies the use of the protocol, then request is denied.
Summary: Protocol rules are one of the key components of the ISA Access policy, and protocol rules function together with site and content rules to give clients using ISA access to the internet. Protocol rules determine what protocols can be used by the ISA clients to access the internet. This can be a powerful tool when used correctly as you can allow and deny access to particular protocols that best suits your organizations needs. I have outlined protocol rules in this tutorial, and this information should give you a better understanding of what protocol rules are and what they can do.