The Cisco multicast Rendezvous Point (RP) must be configured to rate limit the number of Protocol Independent Multicast (PIM) Register messages.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216813	CISC-RT-000850	SV-216813r856450_rule		Medium

Description
When a new source starts transmitting in a PIM Sparse Mode network, the Designated Router (DR) will encapsulate the multicast packets into register messages and forward them to the RP using unicast. This process can be taxing on the CPU for both the DR and the RP if the source is running at a high data rate and there are many new sources starting at the same time. This scenario can potentially occur immediately after a network failover. The rate limit for the number of register messages should be set to a relatively low value based on the known number of multicast sources within the multicast domain.

Description

When a new source starts transmitting in a PIM Sparse Mode network, the Designated Router (DR) will encapsulate the multicast packets into register messages and forward them to the RP using unicast. This process can be taxing on the CPU for both the DR and the RP if the source is running at a high data rate and there are many new sources starting at the same time. This scenario can potentially occur immediately after a network failover. The rate limit for the number of register messages should be set to a relatively low value based on the known number of multicast sources within the multicast domain.

STIG	Date
Cisco IOS XR Router RTR Security Technical Implementation Guide	2024-06-06

Details

Check Text ( C-18045r288813_chk )
Review the configuration of the RP to verify that it is limiting the number of PIM register states as shown in the example. router pim address-family ipv4 allow-rp group-list FILTER_PIM_JOINS rp-address 10.2.2.2 accept-register PIM_REGISTER_FILTER maximum register-states 250 Note: The maximum register-states command is used to set an upper limit for PIM register states. When the limit is reached, PIM discontinues route creation from PIM register messages. If not configured, the default is 2000 which would be an overage for a small to average size multicast deployment. If the RP is not limiting PIM register states, this is a finding.

Check Text ( C-18045r288813_chk )

Review the configuration of the RP to verify that it is limiting the number of PIM register states as shown in the example.

router pim
address-family ipv4
allow-rp group-list FILTER_PIM_JOINS
rp-address 10.2.2.2
accept-register PIM_REGISTER_FILTER
maximum register-states 250

Note: The maximum register-states command is used to set an upper limit for PIM register states. When the limit is reached, PIM discontinues route creation from PIM register messages. If not configured, the default is 2000 which would be an overage for a small to average size multicast deployment.

If the RP is not limiting PIM register states, this is a finding.

Fix Text (F-18043r288814_fix)
Configure the RP to rate limit the number of multicast register states. 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)#maximum register-states 250 RP/0/0/CPU0:R2(config-pim-default-ipv4)#end