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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-101851	CISC-RT-000930	SV-110955r1_rule		Low

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.

STIG	Date
Cisco IOS-XE Switch RTR Security Technical Implementation Guide	2020-05-20

Details

Check Text ( C-100739r1_chk )
Review the switch 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: ip msdp peer 10.1.28.8 remote-as 8 ip msdp sa-filter out 10.1.28.8 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. ip access-list extended OUTBOUND_MSDP_SA_FILTER deny ip 10.0.0.0 0.255.255.255 any permit ip any any If the switch is not configured with an export policy to filter local source-active multicast advertisements, this is a finding.

Check Text ( C-100739r1_chk )

Review the switch 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:

ip msdp peer 10.1.28.8 remote-as 8
ip msdp sa-filter out 10.1.28.8 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.

ip access-list extended OUTBOUND_MSDP_SA_FILTER
deny ip 10.0.0.0 0.255.255.255 any
permit ip any any

If the switch is not configured with an export policy to filter local source-active multicast advertisements, this is a finding.

Fix Text (F-107857r1_fix)
Configure the switch with an export policy avoid global visibility of local multicast (S, G) states. The example below will prevent exporting multicast active sources belonging to the private network. SW1(config)#ip access-list extended OUTBOUND_MSDP_SA_FILTER SW1(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any SW1(config-ext-nacl)#permit ip any any SW1(config-ext-nacl)#exit SW1(config)#ip msdp sa-filter in x.1.28.2 list OUTBOUND_MSDP_SA_FILTER

Fix Text (F-107857r1_fix)

Configure the switch with an export policy avoid global visibility of local multicast (S, G) states. The example below will prevent exporting multicast active sources belonging to the private network.

SW1(config)#ip access-list extended OUTBOUND_MSDP_SA_FILTER
SW1(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any
SW1(config-ext-nacl)#permit ip any any
SW1(config-ext-nacl)#exit
SW1(config)#ip msdp sa-filter in x.1.28.2 list OUTBOUND_MSDP_SA_FILTER