DHCP and transport layer choice: At the Transport layer, which protocol does DHCP rely on for message delivery between clients and servers/relays?

Introduction / Context:
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and other configuration parameters to clients. Because clients may not yet have an IP or full stack ready, the underlying transport must be simple, connectionless, and broadcast-friendly on local segments.

Given Data / Assumptions:

• DHCP must work before an address is assigned.
• The protocol should tolerate broadcast and relay via DHCP helpers.
• We are identifying the Transport layer protocol only.

Concept / Approach:

DHCP uses UDP: clients send from port 68 to server port 67, initially via broadcast (0.0.0.0 to 255.255.255.255) or via a relay agent (DHCP helper) that forwards the request as unicast to the server. TCP would require a prior connection, which is not possible without established addressing. ARP is a link-layer resolution protocol and IP is the network layer, not transport.

Step-by-Step Solution:

Verification / Alternative check:

Packet captures show BOOTP/DHCP over UDP with the specified ports; RFCs for DHCP/BOOTP affirm UDP usage.

Why Other Options Are Wrong:

TCP requires a handshake and is not used by DHCP.

ARP is not a Transport protocol.

“IP” is a layer below transport and does not fulfill the transport role.

Common Pitfalls:

Blocking broadcast UDP 67/68 at access layers; misconfiguring DHCP relay on routers, causing clients to time out.

Final Answer:

UDP