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-221137	CISC-RT-000840	SV-221137r622190_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 NX-OS Switch RTR Security Technical Implementation Guide	2021-03-29

Details

Check Text ( C-22852r409900_chk )

Verify that the RP switch 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. route-map PIM_JOIN_FILTER deny 10 match ip multicast group 239.0.0.0/8 route-map PIM_JOIN_FILTER permit 20 match ip multicast group 224.0.0.0/4 … … … interface Ethernet2/1 no switchport ip address 10.1.12.1/24 ip pim sparse-mode ip pim jp-policy PIM_JOIN_FILTER in 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-22841r409901_fix)

Configure the RP to filter PIM join messages for any undesirable multicast groups as shown in the example below: Step 1: Configure a PIM Join filter as shown in the example below: SW1(config)# route-map PIM_JOIN_FILTER deny SW1(config-route-map)# match ip multicast group 239.8.0.0/8 SW1(config-route-map)# route-map PIM_JOIN_FILTER permit 20 SW1(config-route-map)# match ip multicast group 224.0.0.0/4 SW1(config-route-map)# exit Step 2: Apply the PIM Join filter to the appropriate interfaces. SW1(config)# int e2/1 SW1(config-if)# ip pim jp-policy PIM_JOIN_FILTER in SW1(config-if)# end