Which protocol does DHCP use at the Transport layer?

Dynamic Host Configuration Protocol (DHCP) operates over the User Datagram Protocol (UDP) at the Transport layer. This is significant because UDP is a connectionless protocol that allows DHCP to send messages without establishing a formal connection, which is suitable for the dynamic nature of IP address allocation.

DHCP clients typically send their requests to a broadcast address using UDP, allowing them to reach all potential DHCP servers on the local network segment. The servers respond also using UDP, which facilitates the quick exchange of messages necessary for IP address assignment. This efficiency is crucial in environments where devices frequently join or leave the network.

Using TCP, which is a connection-oriented protocol, would introduce additional overhead due to the need for establishing a connection before data transmission, which is not ideal for the quick operation required for DHCP. Furthermore, since ARP operates at the Link layer to resolve IP addresses to MAC addresses, it does not serve as a fitting transport protocol in the context of DHCP.

Therefore, UDP is the correct and efficient protocol choice for DHCP's operations at the Transport layer.