Information
Real-time multicast traffic can entail multiple large flows of data. An attacker can flood a network segment with multicast packets, over-using the available bandwidth and thereby creating a denial of service (DoS) condition. Hence, it is imperative that register messages are accepted only for authorized multicast groups and sources.
Solution
Configure the router to filter PIM register messages received from a multicast DR for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources 10.1.2.6 and 10.1.2.7.
R2(config)#ip access-list extended PIM_REGISTER_FILTER
R2(config-ext-nacl)#deny ip any 239.5.0.0 0.0.255.255
R2(config-ext-nacl)#permit ip host 10.1.2.6 any
R2(config-ext-nacl)#permit ip host 10.1.2.7 any
R2(config-ext-nacl)#deny ip any any
R2(config-ext-nacl)#exit
R2(config)#ip pim accept-register list PIM_REGISTER_FILTER
R2(config)#end