Cisco IOS XR Router RTR STIG

Cisco IOS XR Router RTR Security Technical Implementation Guide

The Cisco IOS XR Router RTR Security Technical Implementation Guide (V3 R3) has 96 STIG checks. New to STIG checklists? Read What is a STIG checklist?, CKL vs CKLB, and STIG vs SCAP benchmark.

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Severity

Version

V3 · R3

CurrentPublished Wed Oct 01 2025 What changed in V3R3

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.

Cisco IOS XR Router RTR Security Technical Implementation Guide

Assessment Title

Rule Text

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.

Description

Discussion Text

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.

New to STIG checklists? Read What is a STIG checklist? and CKL vs CKLB.

Objective

V-216810

Rule

SV-216810r856449_rule

Severity

low

Rule Version

CISC-RT-000820

Documentable

false

IA Controls

NIST SP 800-53

Rev 5

Assessment Procedure

Check Text

The Cisco router does not have a mechanism to limit the multicast forwarding cache. However, the risk associated with this requirement can be fully mitigated by configuring the router to:

1. Filter PIM register messages.
2. Rate limiting the number of PIM register messages.
3. Accept MSDP packets only from known MSDP peers.

Step 1: Verify that the RP router is configured to filter PIM register messages 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.

ipv4 access-list PIM_REGISTER_FILTER
10 deny ipv4 any 239.5.0.0 0.0.255.255
20 permit ipv4 host 10.1.2.6 any
30 permit ipv4 host 10.1.2.7 any
40 deny ipv4 any any
…
…
…
router pim
address-family ipv4
rp-address 2.2.2.2
accept-register PIM_REGISTER_FILTER

Step 2: Verify that the router is configured to rate limiting the number of PIM register messages as shown in the example below.

router pim
address-family ipv4
allow-rp group-list FILTER_PIM_JOINS
rp-address 10.2.2.2
accept-register PIM_REGISTER_FILTER
maximum register-states 250

Note: The maximum register-states command is used to set an upper limit for PIM register states. When the limit is reached, PIM discontinues route creation from PIM register messages. If not configured, the default is 2000 which would be an overage for a small to average size multicast deployment.

Step 3: Review the router configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers as shown in the example below.

Step 3a: Determine which interfaces would be peering MSDP with an external router by the configured peer addresses as shown in the example below.

router msdp
peer x.14.2.1
remote-as nn
!
peer x.15.3.5
remote-as nn
!
!

Step 3b: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example.

interface GigabitEthernet0/0/0/1
ipv4 address x.14.2.2 255.255.255.252
ipv4 access-group EXTERNAL_ACL_INBOUND ingress

Step 3c: Verify that the ACL restricts MSDP peering to only known sources.

ipv4 access-list EXTERNAL_ACL_INBOUND
10 permit tcp host x.1.28.2 host x.1.28.8 eq 639
20 deny tcp any host x.1.28.8 eq 639 log
30 permit tcp host x.1.28.2 host x.1.28.8 eq bgp
40 permit tcp host x.1.28.2 eq bgp host x.1.28.8
50 permit pim host x.1.28.2 host x.1.28.8
60 permit tcp any any established
…
…
…
140 deny ipv4 any any log

Note: MSDP connections is via TCP port 639

If the RP router is not configured to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers, this is a finding.

Implementation Procedure

Fix Text

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

STIG check 67 of 96 in the Cisco IOS XR Router RTR STIG checklist

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