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-96669	CISC-RT-000920	SV-105807r1_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.

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 Router RTR Security Technical Implementation Guide	2020-06-30

Details

Check Text ( C-95505r1_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. ip msdp peer x.1.28.2 remote-as 2 ip msdp sa-filter in x.1.28.2 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. ip access-list extended INBOUND_MSDP_SA_FILTER deny ip any host 224.0.1.3 deny ip any host 224.0.1.24 deny ip any host 224.0.1.22 deny ip any host 224.0.1.2 deny ip any host 224.0.1.35 deny ip any host 224.0.1.60 deny ip any host 224.0.1.39 deny ip any host 224.0.1.40 deny ip any 232.0.0.0 0.255.255.255 deny ip any 239.0.0.0 0.255.255.255 deny ip 10.0.0.0 0.255.255.255 any deny ip 127.0.0.0 0.255.255.255 any deny ip 172.16.0.0 0.15.255.255 any deny ip 192.168.0.0 0.0.255.255 any permit ip any any If the router is not configured with an import policy to filter undesirable SA multicast advertisements, this is a finding.

Check Text ( C-95505r1_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.

ip msdp peer x.1.28.2 remote-as 2
ip msdp sa-filter in x.1.28.2 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.

ip access-list extended INBOUND_MSDP_SA_FILTER
deny ip any host 224.0.1.3
deny ip any host 224.0.1.24
deny ip any host 224.0.1.22
deny ip any host 224.0.1.2
deny ip any host 224.0.1.35
deny ip any host 224.0.1.60
deny ip any host 224.0.1.39
deny ip any host 224.0.1.40
deny ip any 232.0.0.0 0.255.255.255
deny ip any 239.0.0.0 0.255.255.255
deny ip 10.0.0.0 0.255.255.255 any
deny ip 127.0.0.0 0.255.255.255 any
deny ip 172.16.0.0 0.15.255.255 any
deny ip 192.168.0.0 0.0.255.255 any
permit ip 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-102343r1_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. R8(config)#ip access-list extended INBOUND_MSDP_SA_FILTER R8(config-ext-nacl)#deny ip any host 224.0.1.3 ! Rwhod R8(config-ext-nacl)#deny ip any host 224.0.1.24 ! Microsoft-ds R8(config-ext-nacl)#deny ip any host 224.0.1.22 ! SVRLOC R8(config-ext-nacl)#deny ip any host 224.0.1.2 ! SGI-Dogfight R8(config-ext-nacl)#deny ip any host 224.0.1.35 ! SVRLOC-DA R8(config-ext-nacl)#deny ip any host 224.0.1.60 ! hp-device-disc R8(config-ext-nacl)#deny ip any host 224.0.1.39 ! Auto-RP R8(config-ext-nacl)#deny ip any host 224.0.1.40 ! Auto-RP R8(config-ext-nacl)#deny ip any 232.0.0.0 0.255.255.255 ! SSM range R8(config-ext-nacl)#deny ip any 239.0.0.0 0.255.255.255 ! Admin scoped range R8(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any ! RFC 1918 address range R8(config-ext-nacl)#deny ip 127.0.0.0 0.255.255.255 any ! RFC 1918 address range R8(config-ext-nacl)#deny ip 172.16.0.0 0.15.255.255 any ! RFC 1918 address range R8(config-ext-nacl)#deny ip 192.168.0.0 0.0.255.255 any ! RFC 1918 address range R8(config-ext-nacl)#permit ip any any R8(config-ext-nacl)#exit R8(config)#ip msdp sa-filter in x.1.28.2 list INBOUND_MSDP_SA_FILTER

Fix Text (F-102343r1_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.

R8(config)#ip access-list extended INBOUND_MSDP_SA_FILTER
R8(config-ext-nacl)#deny ip any host 224.0.1.3 ! Rwhod
R8(config-ext-nacl)#deny ip any host 224.0.1.24 ! Microsoft-ds
R8(config-ext-nacl)#deny ip any host 224.0.1.22 ! SVRLOC
R8(config-ext-nacl)#deny ip any host 224.0.1.2 ! SGI-Dogfight
R8(config-ext-nacl)#deny ip any host 224.0.1.35 ! SVRLOC-DA
R8(config-ext-nacl)#deny ip any host 224.0.1.60 ! hp-device-disc
R8(config-ext-nacl)#deny ip any host 224.0.1.39 ! Auto-RP
R8(config-ext-nacl)#deny ip any host 224.0.1.40 ! Auto-RP
R8(config-ext-nacl)#deny ip any 232.0.0.0 0.255.255.255 ! SSM range
R8(config-ext-nacl)#deny ip any 239.0.0.0 0.255.255.255 ! Admin scoped range
R8(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any ! RFC 1918 address range
R8(config-ext-nacl)#deny ip 127.0.0.0 0.255.255.255 any ! RFC 1918 address range
R8(config-ext-nacl)#deny ip 172.16.0.0 0.15.255.255 any ! RFC 1918 address range
R8(config-ext-nacl)#deny ip 192.168.0.0 0.0.255.255 any ! RFC 1918 address range
R8(config-ext-nacl)#permit ip any any
R8(config-ext-nacl)#exit
R8(config)#ip msdp sa-filter in x.1.28.2 list INBOUND_MSDP_SA_FILTER