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Internet Traffic Monitoring and Analysis:Wireshark Tutorial

OutlineWhat is Wireshark?

Capturing Packets

Analyzing Packets

Filtering Packets

Saving and Manipulating Packets

Packet Statistics

Colorizing Specific Packets

References

What is Wireshark?The De-Facto Network Protocol Analyzer

◦ Open-Source (GNU Public License)

◦ Multi-platform (Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and others)

◦ Easily extensible

◦ Large development group

Previously Named “Ethereal”

What is Wireshark?Features

◦ Deep inspection of thousands of protocols

◦ Live capture and offline analysis

◦ Standard three-pane packet browser

◦ Captured network data can be browsed via a GUI, or via the TTY-mode TShark utility

◦ The most powerful display filters in the industry

◦ Rich VoIP analysis

◦ Live data can be read from Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others

◦ Coloring rules can be applied to the packet list for quick, intuitive analysis

◦ Output can be exported to XML, PostScript®, CSV, or plain text

What is Wireshark?What we can:

◦ Capture network traffic

◦ Decode packet protocols using dissectors

◦ Define filters – capture and display

◦ Watch smart statistics

◦ Analyze problems

◦ Interactively browse that traffic

Some examples people use Wireshark for: ◦ Network administrators: troubleshoot network problems

◦ Network security engineers: examine security problems

◦ Developers: debug protocol implementations

◦ People: learn network protocol internals

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Tools Overview

Tcpdump◦ Unix-based command-line tool used to intercept packets

◦ Including filtering to just the packets of interest

◦ Reads “live traffic” from interface specified using -i option …◦ … or from a previously recorded trace file specified using -r option

◦ You create these when capturing live traffic using -w option

Tshark◦ Tcpdump-like capture program that comes w/ Wireshark◦ Very similar behavior & flags to tcpdump

Wireshark◦ GUI for displaying tcpdump/tshark packet traces

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Tcpdump example

01:46:28.808262 IP danjo.CS.Berkeley.EDU.ssh > adsl-69-228-230-7.dsl.pltn13.pacbell.net.2481: . 2513546054:2513547434(1380) ack 1268355216 win 12816

01:46:28.808271 IP danjo.CS.Berkeley.EDU.ssh > adsl-69-228-230-7.dsl.pltn13.pacbell.net.2481: P 1380:2128(748) ack 1 win 12816

01:46:28.808276 IP danjo.CS.Berkeley.EDU.ssh > adsl-69-228-230-7.dsl.pltn13.pacbell.net.2481: . 2128:3508(1380) ack 1 win 12816

01:46:28.890021 IP adsl-69-228-230-7.dsl.pltn13.pacbell.net.2481 > danjo.CS.Berkeley.EDU.ssh: P 1:49(48) ack 1380 win 16560

• Ran tcpdump on a Unix machine

• First few lines of the output:

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01:46:28.808262 IP danjo.CS.Berkeley.EDU.ssh >

adsl-69-228-230-7.dsl.pltn13.pacbell.net.2481: . 2513546054:2513547434(1380) ack 1268355216 win 12816

Timestamp This is an IP packetSource host nameSource port number (22)

Destination host name Destination port number

TCP specific information

• Different output formats for different packet types

What does a line convey?

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Similar Output from Tshark1190003744.940437 61.184.241.230 -> 128.32.48.169 SSH Encrypted request packet len=48

1190003744.940916 128.32.48.169 -> 61.184.241.230 SSH Encrypted response packet len=48

1190003744.955764 61.184.241.230 -> 128.32.48.169 TCP 6943 > ssh [ACK] Seq=48 Ack=48 Win=65514 Len=0 TSV=445871583 TSER=632535493

1190003745.035678 61.184.241.230 -> 128.32.48.169 SSH Encrypted request packet len=48

1190003745.036004 128.32.48.169 -> 61.184.241.230 SSH Encrypted response packet len=48

1190003745.050970 61.184.241.230 -> 128.32.48.169 TCP 6943 > ssh [ACK] Seq=96 Ack=96 Win=65514 Len=0 TSV=445871583 TSER=632535502

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Demo 1 – Basic RunSyntax:

tcpdump [options] [filter expression]

Unfortunately, Eustis machine does not allow normal users to run tcpdump

I will demonstrate it on my group’s Unix machine: acnserver.fils.edu◦ $ sudo tcpdump –i eth0

◦ On your own Unix machine, you can run it using “sudo” or directly run “tcpdump”

Observe the output

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FiltersWe are often not interested in all packets flowing through the network

Use filters to capture only packets of interest to us

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Demo 21. Capture only udp packets

• tcpdump “udp”

2. Capture only tcp packets• tcpdump “tcp”

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Demo 2 (contd.)

1. Capture only UDP packets with destination port 53 (DNS requests)• tcpdump “udp dst port 53”

2. Capture only UDP packets with source port 53 (DNS replies)• tcpdump “udp src port 53”

3. Capture only UDP packets with source or destination port 53 (DNS requests and replies)

• tcpdump “udp port 53”

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Demo 2 (contd.)1. Capture only packets destined to quasar.cs.berkeley.edu

• tcpdump “dst host quasar.cs.berkeley.edu”

2. Capture both DNS packets and TCP packets to/from quasar.cs.berkeley.edu

• tcpdump “(tcp and host quasar.cs.berkeley.edu) or udp port 53”

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How to write filtersRefer the tcpdump/tshark man page

Many example webpages on the Internet

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Running tcpdump

Requires superuser/administrator privileges on Unix◦ http://www.tcpdump.org/

◦ You can do it on your own Unix machine

◦ You can install a Linux OS in Vmware on your machine

Tcpdump for Windows◦ WinDump: http://www.winpcap.org/windump/

◦ Free software

So What is WireShark?

Packet sniffer/protocol analyzer

Open Source Network Tool

Latest version of the ethereal tool

Wireshark Interface

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Wireshark Interface

Interfaces

Packet

List

Packet

Details

Packet

Bytes

Status Bar

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Capturing Packets (1/3)

Capture Options

Capture Filter

Capturing Packets (2/3)

Buffer size – in order not

to fill your laptop disk

Capture all packets on the

network

Capture filter

Capture in

multiple files

When to

automatically

stop the

capture

Display

options

Name

resolution

options

Capturing Packets (3/3)

Example (W-LAN):

Received Signal Strength

Indication (RSSI) and Link

speed (BW)

Capture Filter exampleshost 10.1.11.24

host 192.168.0.1 and host 10.1.11.1

tcp port http

ip

not broadcast not multicast

ether host 00:04:13:00:09:a3

Capture Buffer Usage

Capture Interfaces

Interface Details: Characteristics

Interface Details: Statistics

Interface Details: 802.3 (Ethernet)

Display Filters (Post-Filters)Display filters (also called post-filters) only filter the view of what you are seeing. All packets in the capture still exist in the trace

Display filters use their own format and are much more powerful then capture filters

Display Filter

Display Filter Examplesip.src==10.1.11.00/24

ip.addr==192.168.1.10 && ip.addr==192.168.1.20

tcp.port==80 || tcp.port==3389

!(ip.addr==192.168.1.10 && ip.addr==192.168.1.20)

(ip.addr==192.168.1.10 && ip.addr==192.168.1.20) && (tcp.port==445 || tcp.port==139)

(ip.addr==192.168.1.10 && ip.addr==192.168.1.20) && (udp.port==67 || udp.port==68)

tcp.dstport == 80

Display Filter

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Display FilterString1, String2 (Optional settings):

◦ Sub protocol categories inside the protocol.

◦ Look for a protocol and then click on the "+" character.

◦ Example:

◦ tcp.srcport == 80

◦ tcp.flags == 2◦ SYN packet

◦ Tcp.flags.syn==1

◦ tcp.flags == 18◦ SYN/ACK

◦ Note of TCP Flag field:

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Display Filter Expressions

snmp || dns || icmp◦ Display the SNMP or DNS or ICMP traffics.

tcp.port == 25◦ Display packets with TCP source or destination

port 25.

tcp.flags◦ Display packets having a TCP flags

tcp.flags.syn == 0x02◦ Display packets with a TCP SYN flag.

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If the filter syntax is correct, it will be highlighted in green, otherwise if there is a syntax mistake it will be highlighted in red.

Correct syntax

Wrong syntax

Save Filtered Packets After Using Display Filter

We can also save all filtered packets in text file for further analysis

Operation:

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FileExport packet dissections as “plain text” file

1). In “packet range” option, select “Displayed”

2). In choose “summary line” or “detail”

Analyzing Packets (1/9)❖ Ethernet Frame Example

Analyzing Packets (2/9)

IP Packet Example

Analyzing Packets (3/9)

TCP Packet Example

Analyzing Packets (4/9)

TCP 3-way Handshake

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Connection-Oriented

Before any data transfer, TCP establishes a connection:

◦ One TCP entity is waiting for a connection (“server”)

◦ The other TCP entity (“client”) contacts the server

The actual procedure for setting up connections is more complex.

Each connection is full duplex

CLIENT SERVER

waiting for

connection

request

Request a connection

Accept a connection

Disconnect

Data Transer

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Reliable

Byte stream is broken up into chunks which are called seg-

ments

Receiver sends acknowledgements (ACKs) for segments

TCP maintains a timer. If an ACK is not received in time,

the segment is retransmitted

Detecting errors:

TCP has checksums for header and data. Segments with invalid checksums are discarded

Each byte that is transmitted has a sequence number

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Byte Stream Service To the lower layers, TCP handles data in blocks, the segments.

To the higher layers TCP handles data as a sequence of bytes and does not identify boundaries between bytes

So: Higher layers do not know about the beginning and end of segments !

TCP

Application

1. write 100 bytes

2. write 20 bytes

queue of

bytes to be

transmitted TCP

queue of

bytes that

have been

received

Application

1. read 40 bytes

2. read 40 bytes

3. read 40 bytes

Segments

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TCP Format

IP header TCP header TCP data

Sequence number (32 bits)

DATA

20 bytes 20 bytes

0 15 16 31

Source Port Number Destination Port Number

Acknowledgement number (32 bits)

window sizeheader

length0 Flags

Options (if any)

TCP checksum urgent pointer

20

byte

s

TCP segments have a 20 byte header with >= 0 bytes of data.

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TCP header fieldsPort Number:

◦ A port number identifies the endpoint of a connection.

◦ A pair <IP address, port number> identifies one endpoint of a connection.

◦ Two pairs <client IP address, server port number>

and <server IP address, server port number> identify a TCP connection.

TCP

IP

Applications

23 10480Ports:

TCP

IP

Applications

7 1680 Ports:

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TCP header fieldsSequence Number (SeqNo):

◦ Sequence number is 32 bits long.

◦ So the range of SeqNo is 0 <= SeqNo <= 232 -1 4.3 Gbyte

◦ Each sequence number identifies a byte in the byte stream

◦ Initial Sequence Number (ISN) of a connection is set during connection establishment

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TCP header fieldsAcknowledgement Number (AckNo):

◦ Acknowledgements are piggybacked, I.ea segment from A -> B can contain an acknowledgement for a data sent in the B -> A direction

◦ A hosts uses the AckNo field to send acknowledgements. (If a host sends an AckNo in a segment it sets the “ACK flag”)

◦ The AckNo contains the next SeqNo that a hosts wants to receiveExample: The acknowledgement for a segment with

sequence numbers 0-1500 is AckNo=1501

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TCP header fieldsAcknowledge Number (cont’d)

◦ TCP uses the sliding window flow protocol (see CS 457) to regulate the flow of traffic from sender to receiver

◦ TCP uses the following variation of sliding window:◦ no NACKs (Negative ACKnowledgement)

◦ only cumulative ACKs

Example:Assume: Sender sends two segments with “1..1500” and “1501..3000”, but

receiver only gets the second segment.

In this case, the receiver cannot acknowledge the second packet. It can only send AckNo=1

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TCP header fieldsHeader Length ( 4bits):

◦ Length of header in 32-bit words

◦ Note that TCP header has variable length (with minimum 20 bytes)

Analyzing Packets (5/9)Flow Graph

◦ Giving us a graphical flow, for better understanding of what we see

Analyzing Packets (6/9)

Flow Graph

Analyzing Packets (7/9)

Filtering Specific TCP Stream

Analyzing Packets (8/9)Filtering Specific TCP Stream

Analyzing Packets (9/9)

RTP Stream Analysis

Stable stream BW

Filtering Packets (1/4)Applying Filter when Capturing Packets

Capture Interfaces Options:

Filtering Packets (2/4)

❖ Applying Filter when Analyzing Packets

Filtering Packets (3/4)

Examples:◦ Capture only traffic to or from IP address 172.18.5.4

◦ host 172.18.5.4

◦ Capture traffic to or from a range of IP addresses◦ net 192.168.0.0/24

◦ net 192.168.0.0 mask 255.255.255.0

◦ Capture traffic from a range of IP addresses◦ src net 192.168.0.0/24

◦ src net 192.168.0.0 mask 255.255.255.0

◦ Capture traffic to a range of IP addresses◦ dst net 192.168.0.0/24

◦ dst net 192.168.0.0 mask 255.255.255.0

◦ Capture only DNS (port 53) traffic◦ port 53

◦ Capture non-HTTP and non-SMTP traffic on your server◦ host www.example.com and not (port 80 or port 25)

◦ host www.example.com and not port 80 and not port 25

Filtering Packets (4/4)

Examples:◦ Capture except all ARP and DNS traffic

◦ port not 53 and not arp

◦ Capture traffic within a range of ports ◦ (tcp[2:2] > 1500 and tcp[2:2] < 1550) or (tcp[4:2] > 1500 and tcp[4:2] < 1550)

◦ tcp portrange 1501-1549

◦ Capture only Ethernet type EAPOL◦ ether proto 0x888e

◦ Capture only IP traffic(the shortest filter, but sometimes very useful to get rid of lower layer protocols like ARP and STP)

◦ ip

◦ Capture only unicast traffic(useful to get rid of noise on the network if you only want to see traffic to and from your machine, not, for example, broadcast and multicast announcements)

◦ not broadcast and not multicast

Protocol Hierarchy

Protocol Hierarchy

Follow TCP Stream

Follow TCP Streamred - stuff you sent blue - stuff you get

Filter out/in Single TCP StreamWhen click “filter out this TCP stream” in previous page’s box, new filter string will contain like:

◦ http and !(tcp.stream eq 5)

So, if you use “tcp.stream eq 5” as filter string, you keep this HTTP session

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Saving and Manipulating Packets (1/3)

Save only displayed packets

Saving and Manipulating Packets (2/3)

Export to CSV file

Saving and Manipulating Packets (3/3)

Exported CSV File

Packet Statistics (1/8)

Protocol Hierarchy

Packet Statistics (2/8)Conversation◦ Traffic between two specific endpoints

With some manipulation

Packet Statistics (3/8)

I/O Graph

Packet Statistics (4/8)Configurable Options

◦ I/O Graphs ◦ Graph 1-5: enable the specific graph 1-5 (graph 1 by default)

◦ Filter: a display filter for this graph (only the packets that pass this filter will be taken into account for this graph)

◦ Style: the style of the graph (Line/Impulse/FBar/Dot)

◦ X Axis ◦ Tick interval: an interval in x direction lasts

(10/1 minutes or 10/1/0.1/0.01/0.001 seconds)

◦ Pixels per tick: use 10/5/2/1 pixels per tick interval

◦ View as time of day: option to view x direction labels as time of day instead of seconds or minutes since beginning of capture

◦ Y Axis◦ Unit: the unit for the y direction

(Packets/Tick, Bytes/Tick, Bits/Tick, Advanced...)

◦ Scale: the scale for the y unit (Logarithmic,Auto,10,20,50,100,200,...)

Packet Statistics (5/8)

TCP Stream Graph

Packet Statistics (6/8)

Round-Trip Time Graph

RTT Vs. Sequence numbers gives us the time that take

to Ack every packet.

In case of variations, it can cause DUPACKs and even

Retransmissions

Usually will happen on communications lines:

Over the Internet

Over cellular networks

Packet Statistics (7/8)Time / Sequence Graph

Seq No [B]

Time [Sec]

Time / Sequence representes how sequence numbers

advances with time

In a good connection (like in the example), the line will

be linear

The angle of the line indicates the speed of the

connection. In this example – fast connection

Packet Statistics (8/8)Time / Sequence GraphSeq No [B]

Time [Sec]

In this case, we see a non-

contiguous graph

Can be due to:

Severe packet loss

Server response (processing)

time

Colorizing Specific Packets (1/4)

Packet Colorization◦ Colorize packets according to a filter

◦ Allow to emphasize the packets interested in

◦ A lot of Coloring Rule examples at the Wireshark Wiki Coloring Rules page at http://wiki.wireshark.org/ColoringRules

We want to watch a specific protocol through out the capture file

Colorizing Specific Packets (2/4)

Colorizing Specific Packets (3/4)

Colorizing Specific Packets (4/4)

TLS Connection Establishment

Basic usage of Grep

Command-line text-search program in Linux

Some useful usage:◦ Grep ‘word’ filename # find lines with ‘word’◦ Grep –v ‘word’ filename # find lines without ‘word’◦ Grep ‘^word’ filename # find lines beginning with ‘word’◦ Grep ‘word’ filename > file2 # output lines with ‘word’ to file2◦ ls -l | grep rwxrwxrwx # list files that have ‘rwxrwxrwx’ feature◦ grep '^[0-4]‘ filename # find lines beginning with any of the numbers from 0-4◦ Grep –c ‘word’ filename # find lines with ‘word’ and print out the number of these

lines◦ Grep –i ‘word’ filename # find lines with ‘word’ regardless of case

Many tutorials on grep online◦ http://www.cyberciti.biz/faq/howto-use-grep-command-in-linux-unix/◦ http://www.thegeekstuff.com/2009/03/15-practical-unix-grep-command-examples/

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ReferencesWireshark Website

◦ http://www.wireshark.org

Wireshark Documentation◦ http://www.wireshark.org/docs/

Wireshark Wiki◦ http://wiki.wireshark.org

Network analysis Using Wireshark Cookbook◦ http://www.amazon.com/Network-Analysis-Using-Wireshark-

Cookbook/dp/1849517649

Q&A