Analyzing Network Traffic with Wireshark
When to Use
- Investigating suspected network intrusions by examining packet-level evidence of command-and-control traffic, data exfiltration, or lateral movement
- Diagnosing network performance issues such as retransmissions, fragmentation, or DNS resolution failures
- Analyzing malware communication patterns by capturing traffic from sandboxed or isolated hosts
- Validating firewall and IDS rules by confirming what traffic is actually traversing network segments
- Extracting files, credentials, or indicators of compromise from captured network sessions
Do not use to capture traffic on networks without authorization, to intercept private communications without legal authority, or as a substitute for full-featured SIEM platforms in production monitoring.
Prerequisites
- Wireshark 4.0+ and tshark command-line utility installed
- Root/sudo privileges or membership in the
wiresharkgroup for live packet capture - Network interface access (physical NIC, span port, or network tap) to the monitored segment
- Sufficient disk space for packet capture files (estimate 1 GB per minute on busy gigabit links)
- Familiarity with TCP/IP protocols, HTTP, DNS, TLS, and SMB at the packet level
Workflow
Step 1: Configure Capture Environment
Set up the capture interface and filters to target relevant traffic:
bash# List available interfaces tshark -D # Start capture on eth0 with a capture filter to limit scope tshark -i eth0 -f "host 10.10.5.23 and (port 80 or port 443 or port 445)" -w /tmp/capture.pcapng # Capture with ring buffer to manage disk usage (10 files, 100MB each) tshark -i eth0 -b filesize:102400 -b files:10 -w /tmp/rolling_capture.pcapng # Capture on multiple interfaces simultaneously tshark -i eth0 -i eth1 -w /tmp/multi_interface.pcapng
For Wireshark GUI, set capture filter in the Capture Options dialog before starting.
Step 2: Apply Display Filters for Targeted Analysis
bash# Filter HTTP traffic containing suspicious user agents tshark -r capture.pcapng -Y "http.user_agent contains \"curl\" or http.user_agent contains \"Wget\"" # Find DNS queries to suspicious TLDs tshark -r capture.pcapng -Y "dns.qry.name contains \".xyz\" or dns.qry.name contains \".top\" or dns.qry.name contains \".tk\"" # Identify TCP retransmissions indicating network issues tshark -r capture.pcapng -Y "tcp.analysis.retransmission" # Filter SMB traffic for lateral movement detection tshark -r capture.pcapng -Y "smb2.cmd == 5 or smb2.cmd == 3" -T fields -e ip.src -e ip.dst -e smb2.filename # Find cleartext credential transmission tshark -r capture.pcapng -Y "ftp.request.command == \"PASS\" or http.authbasic" # Detect beaconing patterns (regular interval connections) tshark -r capture.pcapng -Y "ip.dst == 203.0.113.50" -T fields -e frame.time_relative -e ip.src -e tcp.dstport
Step 3: Protocol-Specific Deep Analysis
bash# Follow a TCP stream to reconstruct a conversation tshark -r capture.pcapng -q -z follow,tcp,ascii,0 # Analyze HTTP request/response pairs tshark -r capture.pcapng -Y "http" -T fields -e frame.time -e ip.src -e ip.dst -e http.request.method -e http.request.uri -e http.response.code # Extract DNS query/response statistics tshark -r capture.pcapng -q -z dns,tree # Analyze TLS handshakes for weak cipher suites tshark -r capture.pcapng -Y "tls.handshake.type == 2" -T fields -e ip.src -e ip.dst -e tls.handshake.ciphersuite # SMB file access enumeration tshark -r capture.pcapng -Y "smb2" -T fields -e frame.time -e ip.src -e ip.dst -e smb2.filename -e smb2.cmd
Step 4: Extract Artifacts and IOCs
bash# Export HTTP objects (files transferred over HTTP) tshark -r capture.pcapng --export-objects http,/tmp/http_objects/ # Export SMB objects (files transferred over SMB) tshark -r capture.pcapng --export-objects smb,/tmp/smb_objects/ # Extract all unique destination IPs for threat intelligence lookup tshark -r capture.pcapng -T fields -e ip.dst | sort -u > unique_dest_ips.txt # Extract SSL/TLS certificate information tshark -r capture.pcapng -Y "tls.handshake.type == 11" -T fields -e x509sat.uTF8String -e x509ce.dNSName # Extract all URLs accessed tshark -r capture.pcapng -Y "http.request" -T fields -e http.host -e http.request.uri | sort -u > urls.txt # Hash extracted files for IOC matching find /tmp/http_objects/ -type f -exec sha256sum {} \; > extracted_file_hashes.txt
Step 5: Statistical Analysis and Anomaly Detection
bash# Protocol hierarchy statistics tshark -r capture.pcapng -q -z io,phs # Conversation statistics sorted by bytes tshark -r capture.pcapng -q -z conv,tcp -z conv,udp # Identify top talkers tshark -r capture.pcapng -q -z endpoints,ip # IO graph data (packets per second) tshark -r capture.pcapng -q -z io,stat,1,"COUNT(frame) frame" # Detect port scanning patterns tshark -r capture.pcapng -Y "tcp.flags.syn == 1 and tcp.flags.ack == 0" -T fields -e ip.src -e tcp.dstport | sort | uniq -c | sort -rn | head -20
Step 6: Generate Reports and Export Evidence
bash# Export filtered packets to a new PCAP for evidence preservation tshark -r capture.pcapng -Y "ip.addr == 10.10.5.23 and tcp.port == 4444" -w evidence_c2_traffic.pcapng # Generate packet summary in CSV format tshark -r capture.pcapng -T fields -E header=y -E separator=, -e frame.number -e frame.time -e ip.src -e ip.dst -e ip.proto -e tcp.srcport -e tcp.dstport -e frame.len > traffic_summary.csv # Create PDML (XML) output for programmatic analysis tshark -r capture.pcapng -T pdml > capture_analysis.xml # Calculate capture file hash for chain of custody sha256sum capture.pcapng > capture_hash.txt
Key Concepts
| Term | Definition |
|---|---|
| Capture Filter (BPF) | Berkeley Packet Filter syntax applied at capture time to limit which packets are recorded, reducing file size and improving performance |
| Display Filter | Wireshark-specific filter syntax applied to already-captured packets for focused analysis without altering the capture file |
| PCAPNG | Next-generation packet capture format supporting multiple interfaces, name resolution, annotations, and metadata in a single file |
| TCP Stream | Reassembled sequence of TCP segments representing a complete bidirectional conversation between two endpoints |
| Protocol Dissector | Wireshark module that decodes a specific protocol's fields and structure, enabling deep inspection of packet contents |
| IO Graph | Time-series visualization of packet or byte rates over the capture duration, useful for identifying traffic spikes or beaconing |
Tools & Systems
- Wireshark 4.0+: GUI-based packet analyzer with protocol dissectors for 3,000+ protocols, stream reassembly, and export capabilities
- tshark: Command-line version of Wireshark for headless capture, batch processing, and scripted analysis pipelines
- tcpdump: Lightweight packet capture tool for quick captures on remote systems without GUI dependencies
- mergecap: Wireshark utility for combining multiple capture files into a single PCAP for unified analysis
- editcap: Wireshark utility for splitting, filtering, and converting between capture file formats
Common Scenarios
Scenario: Investigating Suspected Data Exfiltration via DNS Tunneling
Context: The SOC team detected unusually high DNS query volumes from a workstation (10.10.3.45) to an external domain. The SIEM alert flagged DNS queries averaging 200 per minute compared to the baseline of 15. A packet capture was initiated from the network tap on the workstation's VLAN.
Approach:
- Capture traffic from the workstation's subnet using
tshark -i eth2 -f "host 10.10.3.45 and port 53" -w dns_exfil_investigation.pcapng - Analyze DNS query patterns:
tshark -r dns_exfil_investigation.pcapng -Y "dns.qry.name contains \"suspect-domain.xyz\"" -T fields -e frame.time -e dns.qry.name - Examine subdomain labels for encoded data (long base64-like subdomains indicate tunneling):
tshark -r dns_exfil_investigation.pcapng -Y "dns.qry.type == 16" -T fields -e dns.qry.name -e dns.txt - Calculate data volume by summing query name lengths to estimate exfiltration bandwidth
- Extract unique query names and decode base64 subdomains to recover exfiltrated content
- Export evidence packets to a separate PCAP and generate SHA-256 hash for chain of custody
Pitfalls:
- Capturing unfiltered traffic on a busy network and running out of disk space before collecting relevant data
- Using display filters instead of capture filters, resulting in massive files that are slow to process
- Overlooking encrypted DNS (DoH/DoT) traffic that bypasses traditional DNS capture on port 53
- Failing to establish packet capture hash and chain of custody documentation for forensic evidence
Output Format
## Traffic Analysis Report **Case ID**: IR-2024-0847 **Capture File**: dns_exfil_investigation.pcapng **SHA-256**: a3f2b8c1d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1 **Duration**: 2024-03-15 14:00:00 to 14:45:00 UTC **Source Interface**: eth2 (VLAN 30 span port) ### Findings **1. DNS Tunneling Confirmed** - Source: 10.10.3.45 - Destination DNS: 8.8.8.8 (forwarded to ns1.suspect-domain.xyz) - Query volume: 9,247 queries in 45 minutes (205/min vs 15/min baseline) - Average subdomain label length: 63 characters (base64-encoded data) - Estimated data exfiltrated: ~2.3 MB via TXT record responses **2. Indicators of Compromise** - Domain: suspect-domain.xyz (registered 3 days prior) - Nameserver: ns1.suspect-domain.xyz (203.0.113.50) - Query pattern: TXT record requests with base64-encoded subdomains - Response pattern: TXT records containing base64-encoded payloads
