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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-217042	JUNI-RT-000370	SV-217042r639663_rule		Medium

Description
When Proxy ARP is enabled on a 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 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
Juniper Router RTR Security Technical Implementation Guide	2021-02-11

Details

Check Text ( C-18271r296994_chk )
Review the router configuration to determine if IP Proxy ARP is disabled on all external interfaces. interfaces { description "NIPRNet"; ge-0/0/0 { unit 0 { proxy-arp restricted; family inet { If IP Proxy ARP is enabled on any external interface, this is a finding.

Fix Text (F-18269r296995_fix)
This requirement is not applicable for the DoDIN Backbone. Disable Proxy ARP on all external interfaces as shown in the example below. [edit interfaces em0 unit 0] delete proxy-arp restricted