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

From Juniper Router RTR Security Technical Implementation Guide

Associated with: CCI-002403

JUNI-RT-000370_rule The Juniper perimeter router must be configured to have Proxy ARP disabled on all external interfaces.

Vulnerability discussion

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.

Check content

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

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

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