ICMP unreachable notifications, mask replies, and redirects must be disabled on all external interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-3084	NET0800	SV-3084r2_rule	ECSC-1	Medium

Description
The Internet Control Message Protocol (ICMP) supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Three ICMP messages are commonly used by attackers for network mapping and diagnosis: Host unreachable, Redirect, and Mask Reply.

STIG	Date
Perimeter Router Security Technical Implementation Guide	2015-04-03

Details

Check Text ( C-3580r3_chk )
Review the device configuration to determine if controls have been defined to ensure the router does not send ICMP unreachables, redirects, and mask replies out to any external interfaces. If ICMP unreachables notifications, mask replies, and redirects are enabled on external interfaces, this is a finding.

Fix Text (F-3109r3_fix)
Disable ICMP unreachable notifications, mask replies, and redirects on all external interfaces.