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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-101833 CISC-RT-000840 SV-110937r1_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 2020-05-20

Details

Check Text ( C-100721r1_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-107517r1_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