The Juniper EX switch must be configured to enable IP Source Guard on all user-facing or untrusted access VLANs with active access interfaces.

IP Source Guard provides source IP address filtering on an untrusted layer 2 interface to prevent a malicious host from impersonating a legitimate host by assuming the legitimate host's IP address. The feature uses dynamic DHCP snooping and static IP source binding to match IP addresses to hosts on untrusted layer 2 access interfaces. Initially, all IP traffic on the protected access interface is blocked except for DHCP packets. After a client receives an IP address from the DHCP server, or after static IP source binding is configured by the administrator, all traffic with that IP source address is permitted from that client. Traffic from other hosts is denied. This filtering limits a host's ability to attack the network by claiming a neighbor host's IP address.