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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216725	CISC-RT-000870	SV-216725r531086_rule		Medium

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 IOS XE Router RTR Security Technical Implementation Guide	2021-09-16

Details

Check Text ( C-17958r507591_chk )
Review the configuration of the DR to verify that it is filtering IGMP or MLD report messages, allowing hosts to only join multicast groups from sources 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 GigabitEthernet0/0 ip address 10.3.3.3 255.255.255.0 ip pim sparse-mode ip igmp access-group IGMP_JOIN_FILTER ip igmp version 3 Step 2: Verify that the ACL denies unauthorized sources or allows only authorized sources. The example below denies all groups from 232.8.0.0/16 range and permits sources only from the x.0.0.0/8 network. ip access-list extended IGMP_JOIN_FILTER deny ip any 232.8.0.0 0.0.255.255 permit ip x.0.0.0 0.255.255.255 any deny ip any any Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. If the DR is not filtering IGMP or MLD report messages, this is a finding.

Check Text ( C-17958r507591_chk )

Review the configuration of the DR to verify that it is filtering IGMP or MLD report messages, allowing hosts to only join multicast groups from sources 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 GigabitEthernet0/0
ip address 10.3.3.3 255.255.255.0
ip pim sparse-mode
ip igmp access-group IGMP_JOIN_FILTER
ip igmp version 3

Step 2: Verify that the ACL denies unauthorized sources or allows only authorized sources. The example below denies all groups from 232.8.0.0/16 range and permits sources only from the x.0.0.0/8 network.

ip access-list extended IGMP_JOIN_FILTER
deny ip any 232.8.0.0 0.0.255.255
permit ip x.0.0.0 0.255.255.255 any
deny ip any any

Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation.

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

Fix Text (F-17956r507592_fix)
Configure the DR to filter the IGMP and MLD report messages to allow hosts to join only those multicast groups from sources that have been approved as shown in the example. R3(config)#ip access-list extended IGMP_JOIN_FILTER R3(config-ext-nacl)#deny ip any 232.8.0.0 0.0.255.255 R3(config-ext-nacl)#permit ip x.0.0.0 0.255.255.255 any R3(config-ext-nacl)#deny ip any any R3(config-ext-nacl)#exit Step 2: Apply the filter to all host facing interfaces. R3(config)#int g0/0 R3(config-if)#ip igmp access-group IGMP_JOIN_FILTER

Fix Text (F-17956r507592_fix)

Configure the DR to filter the IGMP and MLD report messages to allow hosts to join only those multicast groups from sources that have been approved as shown in the example.

R3(config)#ip access-list extended IGMP_JOIN_FILTER
R3(config-ext-nacl)#deny ip any 232.8.0.0 0.0.255.255
R3(config-ext-nacl)#permit ip x.0.0.0 0.255.255.255 any
R3(config-ext-nacl)#deny ip any any
R3(config-ext-nacl)#exit

Step 2: Apply the filter to all host facing interfaces.

R3(config)#int g0/0
R3(config-if)#ip igmp access-group IGMP_JOIN_FILTER