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


Overview

Finding ID Version Rule ID IA Controls Severity
V-221064 CISC-RT-000900 SV-221064r856427_rule Medium
Description
MSDP peering with customer network switches presents additional risks to the DISN Core, whether from a rogue or misconfigured MSDP-enabled switch. To guard against an attack from malicious MSDP traffic, the receive path or interface filter for all MSDP-enabled RP switches must be configured to only accept MSDP packets from known MSDP peers.
STIG Date
Cisco IOS-XE Switch RTR Security Technical Implementation Guide 2022-09-13

Details

Check Text ( C-22779r408986_chk )
Review the switch configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers.

Step 1: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example below:

interface GigabitEthernet1/1
no switchport
ip address x.1.28.8 255.255.255.0
ip access-group EXTERNAL_ACL_INBOUND in
ip pim sparse-mode

Step 2: Verify that the ACL restricts MSDP peering to only known sources.

ip access-list extended EXTERNAL_ACL_INBOUND
permit tcp any any established
permit tcp host x.1.28.2 host x.1.28.8 eq 639
deny tcp any host x.1.28.8 eq 639 log
permit tcp host x.1.28.2 host 10.1.28.8 eq bgp
permit tcp host x.1.28.2 eq bgp host x.1.28.8
permit pim host x.1.28.2 host x.1.28.8



deny ip any any log

Note: MSDP connections is via TCP port 639.

If the switch is not configured to only accept MSDP packets from known MSDP peers, this is a finding.
Fix Text (F-22768r408987_fix)
Configure the receive path or interface ACLs to only accept MSDP packets from known MSDP peers.

SW1(config)#ip access-list extended EXTERNAL_ACL_INBOUND
SW1(config-ext-nacl)#permit tcp any any established
SW1(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq 639
SW1(config-ext-nacl)#deny tcp any host x1.28.8 eq 639
SW1(config-ext-nacl)#permit tcp host x.1.28.2 host x.1.28.8 eq bgp
SW1(config-ext-nacl)#permit tcp host x.1.28.2 eq bgp host x.1.28.8
SW1(config-ext-nacl)#permit pim host x.1.28.2 host x.1.28.8



SW1(config-ext-nacl)#deny ip any any