Cisco – How to forward a TCP/UDP broadcast to another VLAN on a Cisco switch

UDP packets don't establish a connection, they're literally fire and forget! A simple permit udp host XX.xx.xx.xx host xx.xx.xx.xx eq xx should be all that's required.

The router's DHCP relay agent will receive the broadcast DHCP request from the client, put its own IP address into the GIADDR field of the DHCP packet (identifying itself as the relay agent forwarding the DHCP request) and send a unicast IP packet out whatever interface is "closest" to the destination DHCP server. This unicast IP packet will be encapsulated in an Ethernet frame (if that interface is an Ethernet interface) with a source MAC address of the router (or, in the case of an HSRP pair, the virtual MAC address of the HSRP address). The client MAC address (stored in the CHADDR field of the DHCP request) will be unchanged by the DHCP relay agent on the router. (The DHCP Relaying portion of the Wikipedia article on DHCP might be helpful to you to get a deeper understanding.)

If there are "hops" between the DHCP server and the router relating the DHCP request for the client then the source MAC address on the relayed DHCP request packet will end up being the interface of the last-hop router between the DHCP server and the relaying-router.

I'd start sniffing traffic closest to the provisioning system looking for DHCP packets and whittling things down from there. I'd also make sure that I can get other types of traffic (like, say, PING) from the relaying router to the DHCP server.