This document provides an overview of network traffic analysis. It discusses why traffic analysis is useful for gaining knowledge about a network, investigating issues, and network forensics. It also summarizes the basics of TCP/IP protocols, packet sniffing tools like Wireshark and Tcpdump, and how to analyze network traffic captures for troubleshooting and security purposes. Hands-on network forensics examples are provided to demonstrate these concepts.

1. Network Traffic Analysis
Presented By
Ahmed Elshaer
Security Operation Specialist

2. Agenda
● Why Traffic Analysis
● TCP/IP Review
● The Protocols
● Tcpdump/Tshark Basics
● Wireshark Foundation
● Hands-On Network Forensics

3. Why Traffic Analysis ?
● Gain special knowledge about the network.
● Investigate and troubleshoot abnormal behavior
– Abnormal packets.
– Network slow performance.
● Congestion.
● Retransmission.
– Unexpected traffic.
– Broken applications.
– Load balancer issues.

4. Why Traffic Analysis ?
● Network Forensics
– Collecting evidence.
– Incident Handling.
– Tracing attacks.
– Linking infected hosts.
– Determining patient zero.
● Stealing Sensitive information
● Pen-testing.
● Developing IPS/IDS signatures.

5. How Packet Sniffer Works
● Collection
– the packet sniffer collects raw binary data from the wire.
● Conversion
– the captured binary data is converted into a readable form
● Analysis
– the actual analysis of the captured and converted data.
– The packet sniffer verifies its protocol based on that
protocol’s specific features.

6. TCP/IP Overview: OSI Model

7. TCP/IP Overview: OSI Model

8. Network Traffic Analysis

9. Network Traffic Analysis
● Protocols
– Ethernet
– IP
– TCP/UDP
– DNS
– DHCP
– FTP
– Telnet
– HTTP

10. Ethernet Frame

11. IP Packet

12. TCP Packet

13. TCP session initiation/termination

14. TCP session initiation/termination

15. UDP

16. The Big Picture !!!

17. Network Traffic Analysis
● BPF Filters, what !!!
– Berkley Packet Filter
– A knowledge of BPF syntax is crucial as you dig
deeper into networks at the packet level.
– Allow you to specify exactly which packets you want to
capture.
– Get rid or Packets you don't want to capture
– BPF is how you talk to the Network Drivers :)

18. Network Traffic Analysis

19. Network Traffic Analysis
● Command Line Tools:
– TCPdump
– Tshark
– Dumpcap, why !!!
● Graphical Tools:
– Wireshark

20. Network Traffic Analysis
● TCPDUMP Basics (1)

21. Network Traffic Analysis
● TCPDUMP Basics (2)

22. Network Traffic Analysis
● TCPDUMP Basics (3)

23. Network Traffic Analysis
● TCPDUMP Examples (1):
– $sudo tcpdump -n -i eth0 -c 5
– $sudo tcpdump -n -i eth0 -c 10 -w test01.pcap
– $tcpdump -n -r test01.pcap
– $sudo tcpdump -n -i eth0 -c 10 - w icmp.pcap icmp
– $sudo tcpdump -n -i eth0 -s 0 port 53
– $sudo tcpdump -n -i eth0 -s 0 port 53 and tcp
– $sudo tcpdump -n -i eth0 -s 0 tcp port 53
– $sudo tcpdump -n -r icmp.pcap host 192.168.56.104

24. Network Traffic Analysis
●
TCPDUMP Examples (2):
– $sudo tcpdump -n -r icmp.pcap src host 10.10.5.10
– $sudo tcpdump -n -r icmp.pcap dst host 10.18.6.10
– $sudo tcpdump -n -r icmp.pcap net 10.10.56.0
– $sudo tcpdump -n -r icmp.pcap src net 10.10.56.0
– $sudo tcpdump -n -r icmp.pcap dst net 10.10.56.0
● Bash !!!
for file in ` find /pcaps/ -name '*.pcap' `; do
tcpdump -r $file 'port 21' -A|grep -iE 'USER|PASS'
; done

25. Network Traffic Analysis
● Tshark, Advanced analysis capabilities
● Tshark = tcpdump++
● Tshark Examples(1):
– To list the interfaces
● tshark -D
– To listen on interface
● tshark -i eth0
● tshark -i 1

26. Network Traffic Analysis
● Tshark Example (2):
● tshark -n -i wlan0 -p -a filesize:1000 -w 1MB.pcap
● tshark -n -i 7 -c 1000 -w test01.pcap -f 'tcp port 80'
● tshark -n -i 7 -f 'port 53'
● tshark -R "ip.addr == 192.168.56.101" -r test01.pcap
● tshark -R "not arp and not (udp.port == 53)" -r test.pcap
● tshark -Y "http contains user" -r httpcap.pcap -x
● tshark -T fields -e ip.src -e tcp.srcport -e ip.dst -e tcp.dstport
-E header=y -r test01.pcap

27. Network Traffic Analysis
● Dumpcap
– a network traffic dump tool
– It captures packet data from a live network and writes
the packets to a file.
– Why should I use it !!!

28. Network Traffic Analysis
● Wireshark Basic Operations
– Live Capture
– Open PCAP File
– Basic Filters
– Follow TCP Stream
– Time Stamps
– Expert Info
– Statistics

29. Network Traffic Analysis
● Wireshark Packet Inspection
– ARP
– IP
– TCP
– HTTP
– FTP
– DNS
– DHCP

30. Network Traffic Analysis
● Wireshark Advanced Tasks
– SSL Decryption
– Network Forensics and File Carving
● Extract Files from FTP
● Extract Files from HTTP

31. Network Traffic Analysis
CTF Time

32. References/more resources
● http://www.chrisbrenton.org/category/security/network/
● http://packetlife.net/library/cheat-sheets/
● Practical Packet Analysis - NoStarchPress
● http://packetlife.net/captures/
● http://wiki.wireshark.org/SampleCaptures
● http://www.netresec.com/?page=PcapFiles
● Network Analysis Sessions By Ahemd Adel