The perimeter router must be configured to have Proxy ARP disabled on all external interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-78251	SRG-NET-000364-RTR-000112	SV-92957r1_rule		Medium

Description
When Proxy ARP is enabled on a Cisco router, it allows that router to extend the network (at Layer 2) across multiple interfaces (LAN segments). Because proxy ARP allows hosts from different LAN segments to look like they are on the same segment, proxy ARP is only safe when used between trusted LAN segments. Attackers can leverage the trusting nature of proxy ARP by spoofing a trusted host and then intercepting packets. Proxy ARP should always be disabled on router interfaces that do not require it, unless the router is being used as a LAN bridge.

Description

When Proxy ARP is enabled on a Cisco router, it allows that router to extend the network (at Layer 2) across multiple interfaces (LAN segments). Because proxy ARP allows hosts from different LAN segments to look like they are on the same segment, proxy ARP is only safe when used between trusted LAN segments. Attackers can leverage the trusting nature of proxy ARP by spoofing a trusted host and then intercepting packets. Proxy ARP should always be disabled on router interfaces that do not require it, unless the router is being used as a LAN bridge.

STIG	Date
Router Security Requirements Guide	2020-06-30

Details

Check Text ( C-77807r1_chk )
This requirement is not applicable for the DoDIN Backbone. Review the router configuration to determine if IP Proxy ARP is disabled on all external interfaces. If IP Proxy ARP is enabled on any external interface, this is a finding.

Fix Text (F-84979r1_fix)
This requirement is not applicable for the DoDIN Backbone. Disable IP Proxy ARP on all external interfaces.