During the migration process to a fabric, we may encounter scenarios in which we receive traffic from a DHCP relay outside our fabric. This article discusses one such scenario and its solution.

• External DHCP relays for remote sites or PODs coexisting with internal DHCP relays within the fabric 
• L2 handoff as a method of interconnection between the fabric and remote services

After reviewing the fabric, it was found that the VLAN used by the hosts for DHCP was extended to remote hosts via a Layer 2 handoff.

Clients → SRX Cluster → leaf→ spine → Firewall → DHCP Server

DHCP functioned correctly locally for the fabric, which rules out server reachability issues as well as local DHCP relay configuration issues.

DHCP did not work for the remote relay received via the L2 handoff. After reviewing the traffic, it was found that the IRB used as a P2P connection to the L2 handoff was configured within the fabric’s internal DHCP relay group, causing it to drop packets previously marked with option 82