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CISC-RT-000820 - The Cisco multicast Rendezvous Point (RP) router must be configured to filter Protocol Independent Multicast (PIM) Join messages received from the Designated Router (DR) for any undesirable multicast groups - 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.

RP/0/0/CPU0:R2(config)#ipv4 access-list PIM_REGISTER_FILTER
RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any 239.5.0.0 0.0.255.255
RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.6 any
RP/0/0/CPU0:R2(config-ipv4-acl)#permit ipv4 host 10.1.2.7 any
RP/0/0/CPU0:R2(config-ipv4-acl)#deny ipv4 any any
RP/0/0/CPU0:R2(config-ipv4-acl)#exit
RP/0/0/CPU0:R2(config)#router pim
RP/0/0/CPU0:R2(config-pim)#address-family ipv4
RP/0/0/CPU0:R2(config-pim-default-ipv4)#accept-register PIM_REGISTER_FILTER
RP/0/0/CPU0:R2(config-pim-default-ipv4)#end

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

RP/0/0/CPU0:R2(config)#router pim
RP/0/0/CPU0:R2(config-pim)#address-family ipv4
RP/0/0/CPU0:R2(config-pim-default-ipv4)#maximum register-states 250
RP/0/0/CPU0:R2(config-pim-default-ipv4)#end

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

RP/0/0/CPU0:R2(config)#ipv4 access-list EXTERNAL_ACL_INBOUND
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp host x.1.28.2 host x.1.28.8 eq 639
RP/0/0/CPU0:R2(config-ipv4-acl)#deny tcp any host x.1.28.8 eq 639 log
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp host x.1.28.2 host x.1.28.8 eq bgp
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp host x.1.28.2 eq bgp host x.1.28.8
RP/0/0/CPU0:R2(config-ipv4-acl)#permit pim host x.1.28.2 host x.1.28.8
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any any established
...
...
...
RP/0/0/CPU0:R2(config-ipv4-acl)#deny ip any any log

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS-XR_Router_Y24M07_STIG.zip

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-5, CAT|III, CCI|CCI-002385, Rule-ID|SV-216810r856449_rule, STIG-ID|CISC-RT-000820, STIG-Legacy|SV-105965, STIG-Legacy|V-96827, Vuln-ID|V-216810

Plugin: Cisco

Control ID: 546b42667e17e4dd4a6f479f2ef483b04865db64cdfe538832d7b30fb4398d8f