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The Cisco Multicast Source Discovery Protocol (MSDP) router must be configured to only accept MSDP packets from known MSDP peers.


Overview

Finding ID Version Rule ID IA Controls Severity
V-216818 CISC-RT-000900 SV-216818r531087_rule Medium
Description
MSDP peering with customer network routers presents additional risks to the DISN Core, whether from a rogue or misconfigured MSDP-enabled router. To guard against an attack from malicious MSDP traffic, the receive path or interface filter for all MSDP-enabled RP routers must be configured to only accept MSDP packets from known MSDP peers.
STIG Date
Cisco IOS XR Router RTR Security Technical Implementation Guide 2020-09-23

Details

Check Text ( C-18050r288828_chk )
Review the router configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers.

Step 1: 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 2: 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 3: 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 router is not configured to only accept MSDP packets from known MSDP peers, this is a finding.
Fix Text (F-18048r288829_fix)
Configure the interface ACLs to only accept 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