The Cisco multicast Designated switch (DR) must be configured to filter the Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Report messages to allow hosts to join only multicast groups that have been approved by the organization.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221138	CISC-RT-000860	SV-221138r622190_rule		Low

Description
Real-time multicast traffic can entail multiple large flows of data. Large unicast flows tend to be fairly isolated (i.e., someone doing a file download here or there), whereas multicast can have broader impact on bandwidth consumption, resulting in extreme network congestion. Hence, it is imperative that there is multicast admission control to restrict which multicast groups hosts are allowed to join via IGMP or MLD.

Description

Real-time multicast traffic can entail multiple large flows of data. Large unicast flows tend to be fairly isolated (i.e., someone doing a file download here or there), whereas multicast can have broader impact on bandwidth consumption, resulting in extreme network congestion. Hence, it is imperative that there is multicast admission control to restrict which multicast groups hosts are allowed to join via IGMP or MLD.

STIG	Date
Cisco NX-OS Switch RTR Security Technical Implementation Guide	2021-03-29

Details

Check Text ( C-22853r409903_chk )
Review the configuration of the DR to verify that it is filtering IGMP or MLD Membership Report messages, allowing hosts to join only those groups that have been approved. Step 1: Verify that all host facing interfaces are configured to filter IGMP Membership Report messages (IGMP joins) as shown in the example below: interface Ethernet2/4 no switchport ip address 10.2.22.3/24 ip pim sparse-mode ip igmp version 3 ip igmp report-policy ALLOWED_GROUPS Step 2: Verify that the report policy denies unauthorized groups or permits only authorized groups. route-map ALLOWED_GROUPS permit 10 match ip multicast group 233.1.1.0/24 route-map ALLOWED_GROUPS permit 20 match ip multicast group 233.1.1.0/32 route-map ALLOWED_GROUPS permit 30 match ip multicast group 233.1.1.1/32 route-map ALLOWED_GROUPS deny 40 match ip multicast group 224.0.0.0/4 Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. This requirement is not applicable to Any Source Multicast (ASM) since the filtering is being performed by the Rendezvous Point. If the DR is not filtering IGMP or MLD Membership Report messages, this is a finding.

Check Text ( C-22853r409903_chk )

Review the configuration of the DR to verify that it is filtering IGMP or MLD Membership Report messages, allowing hosts to join only those groups that have been approved.

Step 1: Verify that all host facing interfaces are configured to filter IGMP Membership Report messages (IGMP joins) as shown in the example below:

interface Ethernet2/4
no switchport
ip address 10.2.22.3/24 ip pim sparse-mode
ip igmp version 3
ip igmp report-policy ALLOWED_GROUPS

Step 2: Verify that the report policy denies unauthorized groups or permits only authorized groups.

route-map ALLOWED_GROUPS permit 10
match ip multicast group 233.1.1.0/24
route-map ALLOWED_GROUPS permit 20
match ip multicast group 233.1.1.0/32
route-map ALLOWED_GROUPS permit 30
match ip multicast group 233.1.1.1/32
route-map ALLOWED_GROUPS deny 40
match ip multicast group 224.0.0.0/4

Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. This requirement is not applicable to Any Source Multicast (ASM) since the filtering is being performed by the Rendezvous Point.

If the DR is not filtering IGMP or MLD Membership Report messages, this is a finding.

Fix Text (F-22842r409904_fix)
Configure the DR to filter the IGMP or MLD Membership Report messages to allow hosts to join only those multicast groups that have been approved. Step 1: Configure the report policy to filter IGMP Membership Report messages as shown in the example below: SW1(config)# route-map ALLOWED_GROUPS permit SW1(config-route-map)# match ip multicast group 233.1.1.0/24 SW1(config-route-map)# route-map ALLOWED_GROUPS permit 20 SW1(config-route-map)# match ip multicast group 233.1.1.0/32 SW1(config-route-map)# route-map ALLOWED_GROUPS permit 30 SW1(config-route-map)# match ip multicast group 233.1.1.1/32 SW1(config-route-map)# route-map ALLOWED_GROUPS deny 40 SW1(config-route-map)# match ip multicast group 224.0.0.0/4 SW1(config-route-map)# exit Step 2: Apply the report policy to all applicable interfaces. SW1(config)# int e2/4 SW1(config-if)# ip igmp report-policy ALLOWED_GROUPS SW1(config-if)# end

Fix Text (F-22842r409904_fix)

Configure the DR to filter the IGMP or MLD Membership Report messages to allow hosts to join only those multicast groups that have been approved.

Step 1: Configure the report policy to filter IGMP Membership Report messages as shown in the example below:

SW1(config)# route-map ALLOWED_GROUPS permit
SW1(config-route-map)# match ip multicast group 233.1.1.0/24
SW1(config-route-map)# route-map ALLOWED_GROUPS permit 20
SW1(config-route-map)# match ip multicast group 233.1.1.0/32
SW1(config-route-map)# route-map ALLOWED_GROUPS permit 30
SW1(config-route-map)# match ip multicast group 233.1.1.1/32
SW1(config-route-map)# route-map ALLOWED_GROUPS deny 40
SW1(config-route-map)# match ip multicast group 224.0.0.0/4
SW1(config-route-map)# exit

Step 2: Apply the report policy to all applicable interfaces.

SW1(config)# int e2/4
SW1(config-if)# ip igmp report-policy ALLOWED_GROUPS
SW1(config-if)# end