IP Multicast and Firewalls

Many organizations use a firewall computer that acts as a security gateway between the public Internet and their private, internal 'intranet'. In this document, we discuss the issues surrounding the traversal of IP multicast traffic across a firewall, and describe possible ways in which a firewall can implement and control this traversal. We also explain why some firewall mechanisms - such as SOCKS - that were designed specifically for unicast traffic, are less appropriate for multicast.