Last weekend we did OS Upgrade on SG 15600 Cluster ( Active/Standby setup ) from R77.30 to R80.20 and after the upgrade dhcp relay stopped working , offer packets were being dropped with error ( offer fw_postvm_chain_handler Reason: 'dhcp_request_code' drop ) . Drops were not seen on CLM Logs , but were seen via Zdebug commandmon cli.
we were using legacy dhcp services ( bootp, dhcp-rep-localmodule etc) and manual NAT rules as per SK98839. The MDS is on R80.10.
After we replaced all the legacy services with New dhcp services (dhcp-request, dhcp-reply ) dhcp relay started working.
As per SK98839 legacy services are still supported so I would like to know the reason why it stopped working as OS was upgraded on the gateways to R80.20.