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 only multicast groups that have been approved by the organization.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-96835	CISC-RT-000860	SV-105973r1_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 IOS XR Router RTR Security Technical Implementation Guide	2020-06-30

Details

Check Text ( C-95671r1_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. router igmp interface GigabitEthernet0/0/1/0 access-group IGMP_JOIN_FILTER ! interface GigabitEthernet0/0/1/1 access-group IGMP_JOIN_FILTER ! Step 2: Verify that the ACL denies unauthorized groups or permits only authorized groups. The example below denies all groups from 239.8.0.0/16 range. ipv4 access-list IGMP_JOIN_FILTER 10 deny ipv4 239.8.0.0 0.0.255.255 any 20 permit ipv4 any any ! 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 router. If the DR is not filtering IGMP or MLD Membership Report messages, this is a finding.

Check Text ( C-95671r1_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.

router igmp
interface GigabitEthernet0/0/1/0
access-group IGMP_JOIN_FILTER
!
interface GigabitEthernet0/0/1/1
access-group IGMP_JOIN_FILTER
!

Step 2: Verify that the ACL denies unauthorized groups or permits only authorized groups. The example below denies all groups from 239.8.0.0/16 range.

ipv4 access-list IGMP_JOIN_FILTER
10 deny ipv4 239.8.0.0 0.0.255.255 any
20 permit ipv4 any any
!

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 router.

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

Fix Text (F-102515r1_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 ACL to filter IGMP Membership Report messages as shown in the example. RP/0/0/CPU0:R5(config)#ipv4 access-list IGMP_JOIN_FILTER RP/0/0/CPU0:R5(config-ipv4-acl)#deny 239.8.0.0 0.0.255.255 RP/0/0/CPU0:R5(config-ipv4-acl)#exit Step 2: Apply the filter to all host facing interfaces. RP/0/0/CPU0:R5(config)#router igmp RP/0/0/CPU0:R5(config-igmp)#interface g0/0/1/0 RP/0/0/CPU0:R5(config-igmp-default-if)#access-group IGMP_JOIN_FILTER RP/0/0/CPU0:R5(config-igmp-default-if)#exit RP/0/0/CPU0:R5(config-igmp)#interface g0/0/1/1 RP/0/0/CPU0:R5(config-igmp-default-if)#end

Fix Text (F-102515r1_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 ACL to filter IGMP Membership Report messages as shown in the example.

RP/0/0/CPU0:R5(config)#ipv4 access-list IGMP_JOIN_FILTER
RP/0/0/CPU0:R5(config-ipv4-acl)#deny 239.8.0.0 0.0.255.255
RP/0/0/CPU0:R5(config-ipv4-acl)#exit

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

RP/0/0/CPU0:R5(config)#router igmp
RP/0/0/CPU0:R5(config-igmp)#interface g0/0/1/0
RP/0/0/CPU0:R5(config-igmp-default-if)#access-group IGMP_JOIN_FILTER
RP/0/0/CPU0:R5(config-igmp-default-if)#exit
RP/0/0/CPU0:R5(config-igmp)#interface g0/0/1/1
RP/0/0/CPU0:R5(config-igmp-default-if)#end