The Cisco Multicast Source Discovery Protocol (MSDP) router must be configured to filter source-active multicast advertisements to external MSDP peers to avoid global visibility of local-only multicast sources and groups.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-216821	SRG-NET-000018-RTR-000008	CISC-RT-000930	SV-216821r531087_rule	2024-08-22	3

Description
To avoid global visibility of local information, there are a number of source-group (S, G) states in a PIM-SM domain that must not be leaked to another domain, such as multicast sources with private address, administratively scoped multicast addresses, and the auto-RP groups (224.0.1.39 and 224.0.1.40). Allowing a multicast distribution tree, local to the core, to extend beyond its boundary could enable local multicast traffic to leak into other autonomous systems and customer networks.

Description

To avoid global visibility of local information, there are a number of source-group (S, G) states in a PIM-SM domain that must not be leaked to another domain, such as multicast sources with private address, administratively scoped multicast addresses, and the auto-RP groups (224.0.1.39 and 224.0.1.40). Allowing a multicast distribution tree, local to the core, to extend beyond its boundary could enable local multicast traffic to leak into other autonomous systems and customer networks.

ℹ️ Check
Review the router configuration to determine if there is export policy to block local source-active multicast advertisements. Step 1: Verify that an outbound source-active filter is bound to each MSDP peer as shown in the example below. router msdp sa-filter in list INBOUND_MSDP_SA_FILTER sa-filter out list OUTBOUND_MSDP_SA_FILTER Step 2: Review the access lists referenced by the source-active filters and verify that MSDP source-active messages being sent to MSDP peers do not leak advertisements that are local. ipv4 access-list OUTBOUND_MSDP_SA_FILTER 10 deny ipv4 10.0.0.0 0.255.255.255 any 20 permit ipv4 any any If the router is not configured with an export policy to filter local source-active multicast advertisements, this is a finding.

ℹ️ Check

Review the router configuration to determine if there is export policy to block local source-active multicast advertisements. Step 1: Verify that an outbound source-active filter is bound to each MSDP peer as shown in the example below. router msdp sa-filter in list INBOUND_MSDP_SA_FILTER sa-filter out list OUTBOUND_MSDP_SA_FILTER Step 2: Review the access lists referenced by the source-active filters and verify that MSDP source-active messages being sent to MSDP peers do not leak advertisements that are local. ipv4 access-list OUTBOUND_MSDP_SA_FILTER 10 deny ipv4 10.0.0.0 0.255.255.255 any 20 permit ipv4 any any If the router is not configured with an export policy to filter local source-active multicast advertisements, this is a finding.

✔️ Fix
Configure the router with an export policy to avoid global visibility of local multicast (S, G) states. The example below will prevent exporting multicast active sources belonging to the private network. RP/0/0/CPU0:R2(config)#ipv4 access-list OUTBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 10.0.0.0 0.255.255.255 any RP/0/0/CPU0:R2(config-ipv4-acl)#permit ip any any RP/0/0/CPU0:R2(config-ipv4-acl)#exit RP/0/0/CPU0:R2(config)#router msdp RP/0/0/CPU0:R2(config-msdp)#sa-filter out list OUTBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-msdp)#end

✔️ Fix

Configure the router with an export policy to avoid global visibility of local multicast (S, G) states. The example below will prevent exporting multicast active sources belonging to the private network. RP/0/0/CPU0:R2(config)#ipv4 access-list OUTBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 10.0.0.0 0.255.255.255 any RP/0/0/CPU0:R2(config-ipv4-acl)#permit ip any any RP/0/0/CPU0:R2(config-ipv4-acl)#exit RP/0/0/CPU0:R2(config)#router msdp RP/0/0/CPU0:R2(config-msdp)#sa-filter out list OUTBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-msdp)#end