Packet Capture Analysis - What You Really Need To Know

Identify whether a network issue warrants a packet capture by clarifying the problem and its possible root causes, then tailor capture settings, location, and filters to your hypothesis.

Balance capture buffer considerations across platforms, especially on embedded devices, with strategies like triggers, packet slice size, and multi-file outputs to ease loading and analysis.

Adjust slice size to control how much of each packet you capture, from headers to application data. Smaller slices save buffer space; larger slices reveal http and sql details.

Use the pre-capture filter to control traffic you capture and balance file size with data. Start narrow on specific hosts or web traffic; broaden later to avoid missing key data.

Capture network traffic relative to end points, using taps, span ports, or endpoint captures, and consider intermediate devices and multiple paths to set expectations and correctly interpret bandwidth and delay.

Understand the application's dependencies and the IP addresses, DNS addresses, and servers it talks to, then use pre/post capture filters for ports and protocols to analyze traffic and predict bottlenecks.

Apply the five why technique to multiple packet captures to uncover the true root cause, tracing delays from web servers to databases and beyond.

Think through the problem and perspective before you capture, then choose where to capture from, the filters, and appropriate slice sizes and buffers to maximize the benefit of packet captures.

Explore pre capture and post capture filters in Wireshark, build display filters to drill into packets by host, IP, and protocol, and save common filters for quick reuse.

Learn to find packets using the display filter and text string searches in a packet capture, including case-insensitive text matches, hex patterns, and keywords like installation.

Export specific packets from a packet capture to a separate file for targeted analysis, and export summary data to a spreadsheet to extend analysis with ICMP sequence checks.

Use the merge function to combine multiple packet capture files into a single, chronologically ordered capture. Synchronize time sources and merge requests with replies in Wireshark for analysis.

Explore how IO graphs in packet captures reveal throughput, delays, and bursts over time, using millisecond zooms, display filters, and time-of-day correlations to troubleshoot conversations.

Master pre- and post-capture filters, use display filter syntax to locate points of interest, export and merge data from multiple sources, and use io graphs to gauge traffic and delays.

Learn to use filters to locate delay points in packet captures, then remove them to reveal DNS lookups, backend queries to a sequel database, and authentication traffic around delay.

Analyze IO graphs in Wireshark to locate delay by zooming, spotting plateaus and valleys, and filtering data. Compare millisecond and second views to infer bandwidth limits and packet behavior.

Locate delay in a packet capture using Wireshark by applying display filters and frame time delta displayed, then refine with edit find and string searches in packet bytes.

Learn how TCP packet loss impacts network performance and how to detect it in Wireshark by inspecting sequence numbers, data lengths, and acknowledgments in the TCP handshake.

Analyze how TCP acknowledgement reflects received data, track sequence numbers, and trigger retransmission when gaps appear. Learn how selective acknowledgement and piggybacked acknowledgement boost efficiency and timing in data transfer.

Wireshark flags duplicate acks and retransmissions to identify packet loss, using the same acknowledgement number and zero-length packets. It distinguishes timeout-based retransmissions, fast retransmissions, and spurious retransmissions.

Explore how UDP's lack of sequence numbers and delivery guarantees hinders packet loss detection, and learn strategies using RTP sequence numbers, aligning captures from two endpoints, and recognizing protocol patterns.

Analyze RTP packet loss by using RTP sequence numbers to detect gaps, and export to a spreadsheet with a dedicated RTP sequence column to compute losses with a simple formula.

Explore how the encapsulating security payload (ESP) uses a sequence number in VPN traffic to indicate packet loss, and export packet summaries to a spreadsheet for analysis.

Identify false alarms in packet capture by recognizing duplicated packets and incomplete captures that inflate retransmission flags in Wireshark. Filter duplicates and export clean data to verify true loss.

Identify packet loss causes using ping and trace route to locate where loss occurs, then assess latency and queue behavior across hops to diagnose congestion or errors.

Use timescale to identify whether delays come from host, server, client, or network factors. Understand queues and partial packet loss limit delays, typically one to two seconds, from capture perspective.

Identify tcp ack versus response delay by linking a request to its response with a conversation filter and sequence numbers. Verify response matches the request to confirm host processing time.

Tcp zero window signals receiver buffer exhaustion and a stall in data flow. This lecture covers window size, window scale, and zero window probes that reveal and manage the halt.

Explain how zero TCP window halts data transfer when the receive window is small for a 500-byte packet. Emphasize verifying window scale from initial SYN to avoid misinterpretation in captures.

Explore how long tcp acks and retransmits reveal network loss or delay, and how capturing at endpoints helps identify whether loss occurs from a to b or b to a.

Assess whether delays are due to the application or the server by analyzing network patterns, such as quick tcp acks with delayed responses versus long ack-to-response gaps.

Correlate front end and back end traffic to identify server dependencies slowing client requests, use multi-interface captures, packet merge, and analyze delay by examining start and end of the gap.

Name lookups convert human-friendly names to numeric addresses via A and AAAA records, with DNS caching, primary or backup servers, and short name resolution used in enterprises.

Explore how DNS performance issues slow networks when primary servers fail or are slow, names have no match, or caching is absent, causing cascading delays.

DNS is the most popular name resolution protocol, but other protocols exist; learn to recognize them with quick checks and understand their basic workings without diving into depth.

Explore how active directory authenticates and authorizes users via domain controllers, Kerberos tickets, and LDAP queries, and how DNS and SSL patterns reveal delays.

Analyze how latency to a remote domain controller causes noticeable delays in Active Directory operations, including ticket caching, domain controller selection via DNS sites, and batch versus sequential queries.

Identify sql back end delays from slow queries, inefficient selects, and serial requests. Recognize sql traffic on ports like 1433 and 3306 and consider one big query strategy.

Identify dead host connections in packet captures by examining conversation statistics, filtering send packets, and spotting retransmissions when one direction shows zero packets and the other has traffic.

Apply the five y to dig into the root cause, analyze slow sequel server responses, Active Directory routing and packet loss, then capture data and tune with admins.

Explore how latency and bandwidth shape network throughput using a highway analogy, showing how window size and round-trip time constrain performance and TCP windowing.

Explore tcp windowing and how the advertised receive window limits outstanding data, from 64 kilobytes to window scaling. See how Wireshark scales windows and affects throughput.

Analyze application windowing by examining block sizes, parallel requests, and concurrent connections in SMB and other file protocols, and observe read patterns to diagnose throughput limits.

Identify normal versus interesting TPP reset packets, noting fin followed by reset after closure, and flag a TGP reset without a TCB fin as potential issues.

narrow down a TCB reset by checking if the port is listening, whether a firewall blocks traffic, or if an application crashes, using latency and context.

Recognize that host-based firewalls on servers or clients block inbound or outbound connections, potentially hiding packets from your capture. Check firewall logs and carefully modify rules.

Analyze encryption in packet captures and learn how SSL and IPsec encryption conceal application details, and how to use Wireshark to observe cipher suites, certificates, and handshake patterns.

Explore how proxies and WAN acceleration shape packet capture analysis in enterprise networks, revealing how transparent and explicit proxies, latency anomalies, and data optimization can distort troubleshooting.

Explore tcp offloading where the host offloads processing to the network interface card, causing false checksum warnings in wireshark and oversized packets. Disable checksum analysis to avoid false alarms.

This course ends with heartfelt thanks from the instructor, who encourages you to share feedback and questions to solidify what you learned and improve your packet capture analysis skills.