Step 4 (Optional) Define an access list to define which Class D addresses
(multicast addresses) are allowed to traverse the Security Appliance.
Then, use the igmp access-group command to apply the access list to a
specific interface.
Assume that you want to allow protected hosts to join the multicast group 224.0.1.100 from
a multicast router that is located outside the protected network. To accomplish this, you
would use the following commands:
pix515a(config)# access-list 120 permit udp any host 224.0.1.100
pix515a(config)# multicast interface outside
pix515a(config-multicast)# igmp access-group 120
pix515a(config-multicast)# exit
pix515a(config)# multicast interface inside
pix515a(config-multicast)# igmp forward interface outside
pix515a(config-multicast)# exit