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The Cisco multicast edge router must be configured to establish boundaries for administratively scoped multicast traffic.


Overview

Finding ID Version Rule ID IA Controls Severity
V-96825 CISC-RT-000810 SV-105963r1_rule Low
Description
If multicast traffic is forwarded beyond the intended boundary, it is possible that it can be intercepted by unauthorized or unintended personnel. Administrative scoped multicast addresses are locally assigned and are to be used exclusively by the enterprise network or enclave. Administrative scoped multicast traffic must not cross the enclave perimeter in either direction. Restricting multicast traffic makes it more difficult for a malicious user to access sensitive traffic. Admin-Local scope is encouraged for any multicast traffic within a network intended for network management, as well as for control plane traffic that must reach beyond link-local destinations.
STIG Date
Cisco IOS XR Router RTR Security Technical Implementation Guide 2019-07-24

Details

Check Text ( C-95661r1_chk )
Review the router configuration and verify that admin-scope multicast traffic is blocked at the external edge as shown in the example below.

ipv4 access-list MULTICAST_SCOPE
10 deny ipv4 239.0.0.0 0.255.255.255 any
20 permit ipv4 any any




multicast-routing
address-family ipv4
interface GigabitEthernet0/0/0/1
enable
boundary MULTICAST_SCOPE
!
interface GigabitEthernet0/0/0/2
enable
!
!
!

If the router is not configured to establish boundaries for administratively scoped multicast traffic, this is a finding.
Fix Text (F-102505r1_fix)
Step 1: Configure the ACL to deny packets with multicast administratively scoped destination addresses as shown in the example below.

RP/0/0/CPU0:R2(config)#Ipv4 access-list MULTICAST_SCOPE
RP/0/0/CPU0:R2(config-ipv4-acl)#deny 239.0.0.0 0.255.255.255
RP/0/0/CPU0:R2(config-ipv4-acl)#permit any

Step 2: Apply the multicast boundary at the appropriate interfaces as shown in the example below.

RP/0/0/CPU0:R2(config)#multicast-routing
RP/0/0/CPU0:R2(config-mcast)#address-family ipv4
RP/0/0/CPU0:R2(config-mcast-default-ipv4)#int g0/0/0/1
RP/0/0/CPU0:R2(config-mcast-default-ipv4-if)#boundary MULTICAST_SCOPE
RP/0/0/CPU0:R2(config-mcast-default-ipv4-if)#end