Diagnosing a DNS Resolution Failure with tcpdump

"In cybersecurity, the ability to quickly diagnose and resolve network issues is crucial. I recently tackled a project that put this skill to the test: analyzing a DNS resolution failure that prevented users from accessing a website.

The problem? Users were hitting a "destination port unreachable" error. My role involved diving into the network traffic using tcpdump to pinpoint the root cause. The analysis revealed that the DNS server wasn't responding to UDP queries on port 53, the standard port for DNS. This meant the server wasn't providing the necessary IP address to connect to the website.

This type of issue can have significant consequences, disrupting business operations and impacting user experience. More importantly, it can sometimes indicate malicious activity. Being able to efficiently diagnose and resolve these network issues is a critical skill for any cybersecurity professional.

By analyzing the ICMP error messages, I was able to trace the issue and provide a clear explanation of the problem. This project honed my skills in network protocol analysis, incident reporting, and troubleshooting – skills that are essential for any cybersecurity professional. #cybersecurity #networksecurity #dns #icmp #tcpdump #troubleshooting #incidentresponse"

 

 

 Analyze network layer communication

 

Project Overview (Concise):

This activity involves analyzing DNS and ICMP network traffic data from a protocol analyzer to identify the network protocol used in a cybersecurity incident. You'll learn to recognize potentially malicious traffic by examining IP datagram information, which helps cybersecurity analysts assess network security risks.

"In this project, we will analyze DNS and ICMP traffic – specifically, ICMP messages, which can report errors related to DNS – to understand potential malicious activity or network problems that may be affecting DNS functionality."

 

Scenario

Users report being unable to access www.yummyrecipesforme.com, receiving a "destination port unreachable" error. A cybersecurity analyst investigates using tcpdump. The issue is traced to a failure in DNS resolution: while the browser attempts a UDP-based DNS query on port 53, the DNS server responds with ICMP "udp port 53 unreachable" errors.

 

 

 

The tcpdump log shows a failed DNS lookup for www.yummyrecipesforme.com. The initial UDP request from the user's computer to the DNS server (203.0.113.2) is met with an ICMP "udp port 53 unreachable" error. Timestamps in the log indicate the time of the incident. The source and destination IPs are provided for both the UDP request and the ICMP response. The UDP request includes a query identification number (35084) and a DNS "A?" flag. The ICMP error message confirms that the DNS server did not respond on port 53, the standard DNS port. This indicates the DNS server was not listening or responding on port 53. The error repeats in subsequent ICMP packets. This analysis aims to identify the affected network protocol and service (DNS) to inform a follow-up report. Security engineers are addressing the issue.

"As I understand it, our computer sends a DNS request to the DNS server on destination port 53, using a random source port and the UDP protocol. The DNS server at port 53 doesn't respond, and this lack of response triggers an ICMP "unreachable" message. ICMP, the Internet Control Message Protocol, is used to report network communication errors, including errors related to DNS communication."

 

Cybersecurity Incident Report: Network Layer Communication Issue

Part 1: Summary of the Problem

The network protocol analyzer (tcpdump) logs indicate a failure in DNS resolution for the website www.yummyrecipesforme.com. Specifically, the logs show that the DNS server is not responding to UDP queries on port 53. The client's initial UDP request to the DNS server to resolve the domain name is met with an ICMP "udp port 53 unreachable" error. This prevents the client from obtaining the website's IP address, which is necessary for accessing the site.

Part 2: Analysis of the Data and Cause of the Incident

The incident was reported when users were unable to access www.yummyrecipesforme.com, encountering a "destination port unreachable" error. Initial troubleshooting by the cybersecurity analyst involved replicating the error and using tcpdump to capture network traffic.

The tcpdump analysis revealed that when the analyst's browser attempted to load the webpage, it sent a DNS query to the DNS server using the UDP protocol. The query was sent to the standard DNS port, 53. However, the DNS server responded with an ICMP error message, "udp port 53 unreachable." This ICMP message indicates that the DNS server was not listening or not responding to requests on port 53.

The current status of the issue is that the website remains inaccessible due to the DNS resolution failure. The investigation has confirmed that the problem lies with the DNS server's inability to process DNS queries on port 53.

Next steps in troubleshooting and resolving this issue include:

·       Verifying the status and configuration of the DNS server.

·       Checking the network connectivity between the client's network and the DNS server.

·       Investigating potential causes of the DNS server's failure to respond on port 53, such as:

·       A misconfiguration of the DNS server.

·       A network outage affecting the DNS server.

·       A potential denial-of-service (DoS) attack targeting the DNS server on port 53.

The suspected root cause of the problem is a DNS server malfunction or unavailability, preventing it from responding to DNS queries.

#cybersecurity #networksecurity #dns #icmp #tcpdump #troubleshooting #incidentresponse #networkanalysis #cybersecurityanalyst