Mastering sngrep: A Comprehensive Guide for SIP Traffic Analysis

Introduction

sngrep is an invaluable tool for analyzing SIP (Session Initiation Protocol) traffic. This comprehensive guide will walk you through basic to advanced techniques, helping you harness the full power of sngrep for troubleshooting and analysis.

1. Basic Usage

Starting sngrep

To start sngrep and capture SIP traffic:

sngrep

This will capture traffic on the default interface.

Capturing on a Specific Interface

To capture on a specific network interface:

sngrep -d eth0

Replace eth0 with your desired interface name.

Reading from a PCAP File

To analyze a previously captured PCAP file:

sngrep -I capture.pcap

2. Filtering Options

Basic Filtering

Filter by IP address:

sngrep host 192.168.1.100

Filter by port:

sngrep port 5060

Advanced Filtering with Regular Expressions

Use the -f option for complex filters:

sngrep -f 'METHOD INVITE'
sngrep -f 'ip 192\.168\.1\.100'
sngrep -f 'METHOD INVITE && ip 192\.168\.1\.100'

Combining Multiple Filters

You can combine multiple filters:

sngrep host 192.168.1.100 and port 5060

3. Interface Navigation and Customization

F1: Help menu
q: Quit the current screen or sngrep
c: Clear the current session
C: Customize columns in the call list view
< and >: Adjust column widths
V: Toggle between different views
F: Switch between SIP message flow and RTP stream analysis
S: View detailed statistics for each RTP stream
W: Save the current session to a PCAP file

4. Advanced Call Flow Analysis

Displaying Only Matched Dialogs

sngrep -d eth0 -O

Saving Call Flow Diagrams

To save a call flow diagram as an image:

Select a call in the main interface
Press F2
Choose the image format (ASCII or SVG)

Analyzing RTP Streams

Select a call in the main interface
Press F
Use arrow keys to navigate between streams
Press S for detailed statistics

5. Packet Capture and Playback

Continuous Capture to File

To capture traffic continuously to a file:

sngrep -d eth0 -O capture.pcap

Reading Multiple PCAP Files

sngrep -I file1.pcap -I file2.pcap

Saving Current Session

Press W in the main interface to save the current session to a PCAP file.

6. Remote Monitoring

SSH Tunneling

To analyze traffic on a remote host:

ssh -C user@remote_host sngrep | sngrep -I -

Monitoring Multiple Interfaces

sngrep -d eth0 -d eth1

7. Scripting with sngrep

Extracting Specific SIP Headers

sngrep -I capture.pcap -O '%ua %to %from'

Counting Calls

sngrep -I capture.pcap -c | grep "INVITE" | wc -l

Generating Call Statistics

sngrep -I capture.pcap -s

8. Performance Tuning

Limiting Displayed Calls

sngrep -l 1000

This limits the display to 1000 calls.

Setting Maximum Memory Usage

sngrep -m 1024

This sets the maximum memory usage to 1024 MB.

9. Integration with Other Tools

Piping to awk for Custom Formatting

sngrep -I capture.pcap -O '%rs %rd' | awk '{print $2 " -> " $4}'

Using with tshark for Detailed Analysis

tshark -r capture.pcap -Y sip | sngrep -I -

Conclusion

This guide covers a wide range of sngrep functionalities, from basic usage to advanced techniques. By mastering these commands and options, you’ll be well-equipped to handle complex SIP traffic analysis scenarios. Remember to explore the built-in help (F1 key) for more details on each feature.