PCAP Analysis and Packet Editing: The Complete Wireshark PCAP Guide for Network Engineers
Complete PCAP analysis guide covering TCP diagnostics, HTTP troubleshooting, TLS handshake analysis, network protocol debugging, PCAP editing and repair. Every network problem mapped to a diagnostic page.
This is the hub page for PCAP-based network diagnostics. Whether you're debugging TCP retransmissions, TLS handshake failures, HTTP errors, or editing packet captures, this guide maps every scenario to the right diagnostic approach.
TCP diagnostics
TCP problems make up the majority of PCAP analysis work. These pages cover every common TCP failure mode.
Connection and handshake
TCP SYN retransmission: no SYN-ACK — SYN packets retransmitted with no response. Firewall, server down, or network path broken.
TCP close_wait and fin_wait analysis — Connection termination problems. Why CLOSE_WAIT accumulates and how to diagnose.
TCP keepalive debugging — Idle connection timeouts, firewall state table expiry, and keepalive configuration.
Congestion and loss
TCP SACK and DSACK in Wireshark — Selective acknowledgments, sack_perm option, packet loss recovery, reordering.
TCP ECN: CE, ECE, CWR flags — Explicit congestion notification without packet loss. Middlebox compatibility issues.
Packet loss and retransmission analysis — Identifying loss patterns: random, burst, tail-drop.
TCP zero window analysis — Receiver window exhaustion. Application not reading fast enough.
Performance
TCP Nagle and delayed ACK — Small packet latency, interactive application slowdown.
TCP MSS clamping and VPN MTU — VPN MTU issues, MSS negotiation, fragmentation.
HTTP slow request and TTFB analysis — Time to first byte problems, server-side delays.
HTTP and application layer
- HTTP 502/504 gateway timeout — Proxy and gateway errors. Backend unreachable or timing out.
TLS and security
- SNI vs ALPN: TLS handshake analysis — TLS ClientHello extensions, HTTP/2 negotiation, protocol fallback.
Network layer
ARP duplicate IP address conflict — IP conflicts, gratuitous ARP, duplicate address detection.
Asymmetric routing: one-sided PCAP — When you only see half the traffic. Diagnosing routing asymmetry from a single capture point.
IPv6 DAD and neighbor solicitation — IPv6 duplicate address detection and neighbor discovery.
VLAN tag missing 802.1Q — VLAN tagging problems, trunk port configuration.
PCAP editing and repair
Repair corrupt PCAP files — Fix checksums, adjust timestamps, recover partial captures.
Anonymize PCAP sensitive data — Strip IP addresses and sensitive payload data before sharing.
Tool comparison
- PCAP Surgery vs Wireshark/editcap/TraceWrangler — When to use a visual PCAP editor vs command-line tools.
Getting started
- PCAP Surgery overview — What PCAP Surgery does and doesn't do.
- Capture scope — Supported PCAP and PCAPNG formats.
- License — Community vs Professional edition.