IP Proxy ARP must be disabled on all external interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-3082	NET0780	SV-3082r2_rule	ECSC-1	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. You should always disable proxy ARP 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. You should always disable proxy ARP on router interfaces that do not require it, unless the router is being used as a LAN bridge.

STIG	Date
Perimeter Router Security Technical Implementation Guide Cisco	2015-04-06

Details

Check Text ( C-3576r2_chk )
Review the device configuration to determine if IP Proxy ARP is disabled on all external interfaces. If IP Proxy ARP is enabled on external interfaces, this is a finding.

Fix Text (F-3107r2_fix)
Disable IP Proxy ARP on all external interfaces.