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-221145	CISC-RT-000930	SV-221145r622190_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 NX-OS Switch RTR Security Technical Implementation Guide	2021-03-29

Details

Check Text ( C-22860r409924_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 x.1.28.2 connect-source Ethernet2/1 remote-as nn ip msdp sa-policy x.1.28.2 prefix-list OUTBOUND_MSDP_SA_FILTER out 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 prefix-list OUTBOUND_MSDP_SA_FILTER seq 10 deny 10.0.0.0/8 le 32 ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 20 permit 0.0.0.0/0 ge 8 If the switch is not configured with an export policy to filter local source-active multicast advertisements, this is a finding.

Check Text ( C-22860r409924_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 x.1.28.2 connect-source Ethernet2/1 remote-as nn
ip msdp sa-policy x.1.28.2 prefix-list OUTBOUND_MSDP_SA_FILTER out

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 prefix-list OUTBOUND_MSDP_SA_FILTER seq 10 deny 10.0.0.0/8 le 32
ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 20 permit 0.0.0.0/0 ge 8

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

Fix Text (F-22849r409925_fix)
Configure the switch 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. SW1(config)# ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 10 deny 10.0.0.0/8 le 32 SW1(config)# ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 20 permit 0.0.0.0/0 ge 8 SW1(config)# exit SW1(config)# ip msdp sa-policy x.1.28.2 prefix-list OUTBOUND_MSDP_SA_FILTER out SW1(config)# end

Fix Text (F-22849r409925_fix)

Configure the switch 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.

SW1(config)# ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 10 deny 10.0.0.0/8 le 32
SW1(config)# ip prefix-list OUTBOUND_MSDP_SA_FILTER seq 20 permit 0.0.0.0/0 ge 8
SW1(config)# exit
SW1(config)# ip msdp sa-policy x.1.28.2 prefix-list OUTBOUND_MSDP_SA_FILTER out
SW1(config)# end