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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221058	CISC-RT-000840	SV-221058r622190_rule		Low

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 join messages are only accepted for authorized multicast groups.

STIG	Date
Cisco IOS-XE Switch RTR Security Technical Implementation Guide	2022-09-13

Details

Check Text ( C-22773r408968_chk )

Verify that the RP is configured to filter PIM join messages for any undesirable multicast groups. In the example below, groups from 239.8.0.0/16 are not allowed. ip pim rp-address 10.2.2.2 ip pim accept-rp 10.2.2.2 FILTER_PIM_JOINS … … … ip access-list standard FILTER_PIM_JOINS deny 239.8.0.0 0.0.255.255 permit any ! If the RP is not configured to filter join messages received from the DR for any undesirable multicast groups, this is a finding.

Fix Text (F-22762r408969_fix)
Configure the RP to filter PIM join messages for any undesirable multicast groups as shown in the example below: SW2(config)#ip access-list standard PIM_JOIN_FILTER SW2(config-std-nacl)#deny 239.8.0.0 0.0.255.255 SW2(config-std-nacl)#permit any SW2(config-std-nacl)#exit SW2(config)#ip pim accept-rp 10.2.2.2 PIM_JOIN_FILTER SW2(config)#end