← Back to Cisco NX OS Switch RTR Security Technical Implementation Guide

V-221137

CAT III (Low)

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.

Rule ID

SV-221137r1137932_rule

STIG

Cisco NX OS Switch RTR Security Technical Implementation Guide

Version

V3R4

CCIs

CCI-001414

Discussion

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.

Check Content

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

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