The Cisco Multicast Source Discovery Protocol (MSDP) router must be configured to filter received source-active multicast advertisements for any undesirable multicast groups and sources.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216820	CISC-RT-000920	SV-216820r531087_rule		Low

Description

The interoperability of BGP extensions for interdomain multicast routing and MSDP enables seamless connectivity of multicast domains between autonomous systems. MP-BGP advertises the unicast prefixes of the multicast sources used by Protocol Independent Multicast (PIM) routers to perform RPF checks and build multicast distribution trees. MSDP is a mechanism used to connect multiple PIM sparse-mode domains, allowing RPs from different domains to share information about active sources. When RPs in peering multicast domains hear about active sources, they can pass on that information to their local receivers, thereby allowing multicast data to be forwarded between the domains. Configuring an import policy to block multicast advertisements for reserved, Martian, single-source multicast, and any other undesirable multicast groups, as well as any source-group (S, G) states with Bogon source addresses, would assist in avoiding unwanted multicast traffic from traversing the core.

STIG	Date
Cisco IOS XR Router RTR Security Technical Implementation Guide	2020-09-23

Details

Check Text ( C-18052r288834_chk )

Review the router configuration to determine if there is import policy to block source-active multicast advertisements for any undesirable multicast groups, as well as any (S, G) states with undesirable source addresses. Step 1: Verify that an inbound source-active filter is bound to each MSDP peer. router msdp sa-filter in list INBOUND_MSDP_SA_FILTER Step 2: Review the access lists referenced by the source-active filter to verify that undesirable multicast groups, auto-RP, single source multicast (SSM) groups, and advertisements from undesirable sources are blocked. ipv4 access-list INBOUND_MSDP_SA_FILTER 10 deny ipv4 any host 224.0.1.3 20 deny ipv4 any host 224.0.1.24 30 deny ipv4 any host 224.0.1.22 40 deny ipv4 any host 224.0.1.2 50 deny ipv4 any host 224.0.1.35 60 deny ipv4 any host 224.0.1.60 70 deny ipv4 any host 224.0.1.39 80 deny ipv4 any host 224.0.1.40 90 deny ipv4 any 232.0.0.0 0.255.255.255 100 deny ipv4 any 239.0.0.0 0.255.255.255 110 deny ipv4 10.0.0.0 0.255.255.255 any 120 deny ipv4 127.0.0.0 0.255.255.255 any 130 deny ipv4 172.16.0.0 0.15.255.255 any 140 deny ipv4 192.168.0.0 0.0.255.255 any 150 permit ipv4 any any If the router is not configured with an import policy to filter undesirable SA multicast advertisements, this is a finding.

Fix Text (F-18050r288835_fix)

Configure the MSDP router to filter received source-active multicast advertisements for any undesirable multicast groups and sources as shown in the example below. RP/0/0/CPU0:R2(config)#ipv4 access-list INBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-ipv4-acl)#deny ip any host 224.0.1.3 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.24 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.22 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.2 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.35 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.60 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.39 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any host 224.0.1.40 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any 232.0.0.0 0.255.255.255 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any 239.0.0.0 0.255.255.255 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)#deny ipv4 127.0.0.0 0.255.255.255 any RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 172.16.0.0 0.15.255.255 any RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 192.168.0.0 0.0.255.255 any RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 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 in list INBOUND_MSDP_SA_FILTER RP/0/0/CPU0:R2(config-msdp)#end