http://www.cisco.com/en/US/products/sw/secursw/ps2120/products_configuration_guide_chapter09186a00800eb71e.html#wp1055792
"Enabling Stub Multicast Routing
This section describes how to implement the Stub Multicast Routing (SMR) feature, introduced with PIX Firewall version 6.2. It includes the following topics:
Overview
Allowing Hosts to Receive Multicast Transmissions
Forwarding Multicasts from a Transmission Source
Configuring IGMP Timers
Clearing IGMP Configuration
Viewing and Debugging SMR
For More Information about Multicast Routing "