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Question

Difficulty: MediumUtilizing Hardware Testers and Packet Analyzers

A network administrator is using a packet analyzer to troubleshoot an issue where client hosts on a remote subnet cannot obtain IP addresses automatically. The administrator suspects that DHCP relay messages are not reaching the centralized DHCP server. To verify if relayed bootstrap requests are arriving at the server's network interface card, which protocol and port criteria should the administrator filter for in the packet analyzer capture?

  1. UDP port 67Answer
  2. B
    TCP port 67
  3. C
    UDP port 68
  4. D
    IP Protocol 47

Answer

UDP port 67 is the correct filter criteria for inspecting incoming DHCP request and relay packets on the server interface.
DHCP uses UDP as its transport layer protocol. Centralized DHCP servers and relay agents send and receive requests on UDP port 67. To analyze incoming relay packets arriving at the server, filtering for UDP port 67 isolates the relevant BOOTREQUEST traffic.

Step-by-Step Solution

1
Identify the protocol transport model used by DHCP services
DHCP operates over User Datagram Protocol (UDP) for unacknowledged, low-latency transmission.
DHCP clients do not establish a TCP connection prior to obtaining an IP configuration.
2
Determine the specific port used by the server side of the DHCP communication
The server listens on destination UDP port 67 for incoming client requests and relay agent boot messages.
Port 67 receives requests (DHCPDISCOVER, DHCPREQUEST) and relayed BOOTREQUEST packets, while port 68 receives client responses (DHCPOFFER, DHCPACK).
3
Formulate the packet analyzer display filter
Filtering traffic for UDP destination port 67 isolates incoming DHCP relay traffic reaching the server.
This allows the technician to confirm whether the remote router successfully forwards relay packets to the server interface.

Key Concept

DHCP Protocol Operation and Packet Capture Filtering
Estimated Time:1m 30s
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Topics

Utilizing Hardware Testers and Packet Analyzers

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