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


Overview

Finding ID Version Rule ID IA Controls Severity
V-221057 CISC-RT-000830 SV-221057r622190_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 register messages are accepted only for authorized multicast groups and sources.
STIG Date
Cisco IOS-XE Switch RTR Security Technical Implementation Guide 2021-03-26

Details

Check Text ( C-22772r408965_chk )
Verify that the RP 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 x.1.2.6 and x.1.2.7.

ip pim rp-address 10.1.12.3
ip pim accept-register list PIM_REGISTER_FILTER



ip access-list extended PIM_REGISTER_FILTER
deny ip any 239.5.0.0 0.0.255.255
permit ip host x.1.2.6 any
permit ip host x.1.2.7 any
deny ip any any

If the RP switch peering with PIM-SM switches is not configured with a policy to block registration messages for any undesirable multicast groups and sources, this is a finding.
Fix Text (F-22761r408966_fix)
Configure the switch 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 x.1.2.6 and x.1.2.7.

SW2(config)#ip access-list extended PIM_REGISTER_FILTER
SW2(config-ext-nacl)#deny ip any 239.5.0.0 0.0.255.255
SW2(config-ext-nacl)#permit ip host x.1.2.6 any
SW2(config-ext-nacl)#permit ip host x.1.2.7 any
SW2(config-ext-nacl)#deny ip any any
SW2(config-ext-nacl)#exit
SW2(config)#ip pim accept-register list PIM_REGISTER_FILTER
SW2(config)#end