The Cisco multicast Rendezvous Point (RP) router must be configured to filter Protocol Independent Multicast (PIM) Register messages received from the Designated Router (DR) for any undesirable multicast groups and sources.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-216811	SRG-NET-000019-RTR-000013	CISC-RT-000830	SV-216811r531087_rule	2024-08-22	3

Description
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.

ℹ️ Check
Verify that the RP router is configured to filter PIM register messages. 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. ipv4 access-list PIM_REGISTER_FILTER 10 deny ipv4 any 239.5.0.0 0.0.255.255 20 permit ipv4 host 10.1.2.6 any 30 permit ipv4 host 10.1.2.7 any 40 deny ipv4 any any … … … router pim address-family ipv4 rp-address 2.2.2.2 accept-register PIM_REGISTER_FILTER If the RP router peering with PIM-SM routers is not configured with a policy to block registration messages for any undesirable multicast groups and sources, this is a finding.

ℹ️ Check

Verify that the RP router is configured to filter PIM register messages. 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. ipv4 access-list PIM_REGISTER_FILTER 10 deny ipv4 any 239.5.0.0 0.0.255.255 20 permit ipv4 host 10.1.2.6 any 30 permit ipv4 host 10.1.2.7 any 40 deny ipv4 any any … … … router pim address-family ipv4 rp-address 2.2.2.2 accept-register PIM_REGISTER_FILTER If the RP router peering with PIM-SM routers is not configured with a policy to block registration messages for any undesirable multicast groups and sources, this is a finding.

✔️ Fix
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. RP/0/0/CPU0:R2(config)#ipv4 access-list PIM_REGISTER_FILTER RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any 239.5.0.0 0.0.255.255 RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.6 any RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.7 any RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any any RP/0/0/CPU0:R2(config-ipv4-acl)#exit RP/0/0/CPU0:R2(config)#router pim RP/0/0/CPU0:R2(config-pim)#address-family ipv4 RP/0/0/CPU0:R2(config-pim-default-ipv4)#accept-register PIM_REGISTER_FILTER RP/0/0/CPU0:R2(config-pim-default-ipv4)#end

✔️ Fix

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. RP/0/0/CPU0:R2(config)#ipv4 access-list PIM_REGISTER_FILTER RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any 239.5.0.0 0.0.255.255 RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.6 any RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.7 any RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any any RP/0/0/CPU0:R2(config-ipv4-acl)#exit RP/0/0/CPU0:R2(config)#router pim RP/0/0/CPU0:R2(config-pim)#address-family ipv4 RP/0/0/CPU0:R2(config-pim-default-ipv4)#accept-register PIM_REGISTER_FILTER RP/0/0/CPU0:R2(config-pim-default-ipv4)#end