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V-216656

CAT II (Medium)

The Cisco router must be configured to have Internet Control Message Protocol (ICMP) mask reply messages disabled on all external interfaces.

Rule ID

SV-216656r855817_rule

STIG

Cisco IOS XE Router RTR Security Technical Implementation Guide

Version

V3R5

CCIs

CCI-002385

Discussion

The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Mask Reply ICMP messages are commonly used by attackers for network mapping and diagnosis.

Check Content

Review the router configuration and verify that ip mask-reply command is not enabled on any external interfaces as shown in the example below: 

interface GigabitEthernet0/1
 ip address x.x.x.x 255.255.255.0
 ip mask-reply

If the ip mask-reply command is configured on any external interface, this is a finding.

Fix Text

Disable ip mask-reply on all external interfaces as shown below:

R4(config)#int g0/1
R4(config-if)#no ip mask-reply