In IPv4 networks, which UDP port numbers are reserved for the DHCP client and DHCP server?

Introduction / Context:
Dynamic Host Configuration Protocol (DHCP) is widely used in IP networks to automatically assign IP addresses and other parameters to hosts. For Cisco and general networking exams, you must know the well-known port numbers associated with DHCP and whether the protocol uses UDP or TCP.

Given Data / Assumptions:

• The question asks specifically about port numbers used by DHCP.
• We are in an IPv4 context, using the standard DHCP protocol defined over UDP.
• We want to identify which ports are reserved for the server and the client.

Concept / Approach:
DHCP uses UDP, not TCP, because DHCP messages are small, connectionless, and must work even before a host has a full IP configuration. By convention, the DHCP server listens on UDP port 67 and the DHCP client listens on UDP port 68. During discovery and offer, a client often uses a source port of 68 and a destination port of 67, and servers respond from port 67 back to port 68.

Step-by-Step Solution:
Step 1: Recall that DHCP is an extension of BOOTP and operates over UDP, not over TCP.Step 2: The server side of DHCP services must use a well-known port so that clients know where to send requests; this is UDP port 67.Step 3: The client uses UDP port 68 so that its DHCP process can receive replies from the server.Step 4: When a client sends a DHCPDISCOVER broadcast, it typically uses source port 68 and destination port 67.Step 5: The server replies with DHCPOFFER and other messages, using source port 67 and destination port 68, preserving the same mapping.

Verification / Alternative check:
On a router or firewall that can display session tables or packet captures, you can observe DHCP traffic. You will see UDP packets with source and destination ports 67 and 68, confirming the reserved ports for client and server roles.

Why Other Options Are Wrong:
Option B is wrong because the client does not use a random high port; it specifically uses UDP port 68.Option C incorrectly states that DHCP uses UDP port 69, which is reserved for TFTP, not for DHCP.Option D is incorrect because DHCP does not use TCP; reliable delivery is not guaranteed by the transport layer but is handled by retransmission logic in the DHCP protocol.

Common Pitfalls:
A common exam mistake is to confuse DHCP ports with other well-known ports such as TFTP (69) or to think that DHCP relies on TCP because it is an important control protocol. Memorizing that DHCP uses UDP 67 and 68 is an easy way to avoid this confusion.

Final Answer:
The correct statement is that UDP port 67 for the DHCP server and UDP port 68 for the DHCP client are reserved for DHCP.