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The Juniper EX switch must be configured to enable Dynamic Address Resolution Protocol (ARP) Inspection (DAI) on all user VLANs.


Overview

Finding ID Version Rule ID IA Controls Severity
V-253961 JUEX-L2-000140 SV-253961r843916_rule Medium
Description
DAI intercepts Address Resolution Protocol (ARP) requests and verifies that each of these packets has a valid IP-to-MAC address binding before updating the local ARP cache and before forwarding the packet to the appropriate destination. Invalid ARP packets are dropped and logged. DAI determines the validity of an ARP packet based on valid IP-to-MAC address bindings stored in the DHCP snooping binding database. If the ARP packet is received on a trusted interface, the switch forwards the packet without any checks. On untrusted interfaces, the switch forwards the packet only if it is valid.
STIG Date
Juniper EX Series Switches Layer 2 Switch Security Technical Implementation Guide 2022-08-31

Details

Check Text ( C-57413r843914_chk )
Review the switch configuration to verify that Dynamic Address Resolution Protocol (ARP) Inspection (DAI) feature is enabled on all user VLANs. Configuring DAI automatically enables DHCP snooping.

Devices like printers, servers, and VoIP phones are under enterprise control and connected to controlled access interfaces (802.1x, Static MAC Bypass, or MAC RADIUS), making them trusted sources in non-user-facing VLANs.

Verify DAI on user-facing or untrusted VLANs.
[edit vlans]
{
vlan-id ;
forwarding-options {
dhcp-security {
arp-inspection;
}
}
}
Note: DAI depends upon DHCP snooping or static MAC address bindings.

If DAI is not enabled on all user VLANs, this is a finding.
Fix Text (F-57364r843915_fix)
Configure the switch to have Dynamic Address Resolution Protocol (ARP) Inspection (DAI) enabled on all user VLANs.

set vlans vlan-id
set vlans forwarding-options dhcp-security arp-inspection