CISC-RT-000820 - The Cisco multicast Rendezvous Point (RP) router must be configured to limit the multicast forwarding cache so that its resources are not saturated by managing an overwhelming number of Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP) source-active entries.

Information

MSDP peering between networks enables sharing of multicast source information. Enclaves with an existing multicast topology using PIM-SM can configure their RP routers to peer with MSDP routers. As a first step of defense against a denial of service (DoS) attack, all RP routers must limit the multicast forwarding cache to ensure that router resources are not saturated managing an overwhelming number of PIM and MSDP source-active entries.

Solution

The risk associated with this requirement can be fully mitigated by configuring the router to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers.

Step 1: Configure the router to filter PIM register messages received from a multicast DR for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources 10.1.2.6 and 10.1.2.7.

R2(config)#ip access-list extended PIM_REGISTER_FILTER
R2(config-ext-nacl)#deny ip any 239.5.0.0 0.0.255.255
R2(config-ext-nacl)#permit ip host 10.1.2.6 any
R2(config-ext-nacl)#permit ip host 10.1.2.7 any
R2(config-ext-nacl)#deny ip any any
R2(config-ext-nacl)#exit
R2(config)#ip pim accept-register list PIM_REGISTER_FILTER
R2(config)#end

Step 2: Configure the RP to rate limit the number of multicast register messages.

R2(config)#ip pim register-rate-limit nn

Step 3: Configure the receive path or interface ACLs to only accept MSDP packets from known MSDP peers.

R8(config)#ip access-list extended EXTERNAL_ACL_INBOUND
R8(config-ext-nacl)#permit tcp any any established
R8(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq 639
R8(config-ext-nacl)#deny tcp any host x.1.28.8 eq 639
R8(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq bgp
R8(config-ext-nacl)#permit tcp host x.1.28.2 eq bgp host x.1.28.8
R8(config-ext-nacl)#permit pim host x.1.28.2 host x.1.28.8
...
...
...
R8(config-ext-nacl)#deny ip any any

Item Details

Audit Name: DISA STIG Cisco IOS XE Router RTR v3r1

Category: SYSTEM AND COMMUNICATIONS PROTECTION

Plugin: Cisco

Control ID: e43e4fbbf378a0675e6c0f0db4aa3f0196990fa7a9f7d98e6f875d5dea188670

Detections

Analytics

Information

Solution

See Also

Item Details