Wireshark Lab: Getting Started v8.0 COMPUTER NETWORKING 2005-2020.J.F Kurose and K.W.Ross,All Rights Reserved One's understandi etwork protocols y“seeing protocols in actio messages exchanged vith pro d by"playngntities,delving down into the d the etween two prot 50 protocol operation,and causing protocols to per form certain actions and then observing these actions and their consequences.This can be done in simulated scenari os or in a 'real"network environment such as the Internet.In the Wireshark labs you'll be doing in this course,you'll be running various network applications in different scenarios using your own computer.You'll observe the network protocols in your computer"in action, interacting and exchanging messages with protocol entities executing elsewhere in the Internet.Thus,you and your computer will be an integral part of these"live"labs. You'll observe,and you'll learn,by doing. In this first Wireshark lab.you'll get acquainted with Wireshark,and make some simple packet captures and observations. The basic tool for observing the messages exchanged between executing protocol entities called a packet sniffer.As the ame ggests,a packet sniff es ("sniffs") eived fro it will also nd/or e ntents oft col fields s in the itself is pas ive.It observes messages being sent ons nd protocols running on y our co s pa et iffer.Instead,a packet sni receives a copy of packets that are sent/received from/by application and protocols executing on your machine. Figure 1 shows the structure of a packet sniffer.At the right of Figure I are the protocols (in this case,Internet protocols)and applications(such as a web browser or email client) that normally run on your computer.The packet sniffer,shown within the dashed rectangle in Figure 1 is an addition to the usual software in your computer,and consists of two parts.The packet capture library receives a copy of every link-layer frame tha is sent from or received by your computer over a given interface(link layer,such as
Wireshark Lab: Getting Started v8.0 Supplement to Computer Networking: A Top-Down Approach, 8th ed., J.F. Kurose and K.W. Ross “Tell me and I forget. Show me and I remember. Involve me and I understand.” Chinese proverb © 2005-2020, J.F Kurose and K.W. Ross, All Rights Reserved One’s understanding of network protocols can often be greatly deepened by “seeing protocols in action” and by “playing around with protocols” – observing the sequence of messages exchanged between two protocol entities, delving down into the details of protocol operation, and causing protocols to perform certain actions and then observing these actions and their consequences. This can be done in simulated scenarios or in a “real” network environment such as the Internet. In the Wireshark labs you’ll be doing in this course, you’ll be running various network applications in different scenarios using your own computer. You’ll observe the network protocols in your computer “in action,” interacting and exchanging messages with protocol entities executing elsewhere in the Internet. Thus, you and your computer will be an integral part of these “live” labs. You’ll observe, and you’ll learn, by doing. In this first Wireshark lab, you’ll get acquainted with Wireshark, and make some simple packet captures and observations. The basic tool for observing the messages exchanged between executing protocol entities is called a packet sniffer. As the name suggests, a packet sniffer captures (“sniffs”) messages being sent/received from/by your computer; it will also typically store and/or display the contents of the various protocol fields in these captured messages. A packet sniffer itself is passive. It observes messages being sent and received by applications and protocols running on your computer, but never sends packets itself. Similarly, received packets are never explicitly addressed to the packet sniffer. Instead, a packet sniffer receives a copy of packets that are sent/received from/by application and protocols executing on your machine. Figure 1 shows the structure of a packet sniffer. At the right of Figure 1 are the protocols (in this case, Internet protocols) and applications (such as a web browser or email client) that normally run on your computer. The packet sniffer, shown within the dashed rectangle in Figure 1 is an addition to the usual software in your computer, and consists of two parts. The packet capture library receives a copy of every link-layer frame that is sent from or received by your computer over a given interface (link layer, such as
Ethernet or WiFi).Recall from the discussion from section 1.5 in the text(Figure 1.24) that messages exchanged by higher layer protocols such as HTTP,FTP,TCP,UDP, DNS,or IP all are eventually encapsulated in link-layer frames that are transmitted over physical media such as an Ethernet cable or an 802.11 WiFi radio.Capturing all link- layer frames thus gives you all messages sent/received across the monitored link from/by all protocols and applications executing in your computer. acket sniffer Figure 1:packet sniffer structure The second component of a packet sniffer is the packet analyzer which displays the contents of all fields within a protocol message.In order to do so,the packet analyzer must"understand"the stru cture of all me ro into sted in ed by protocols.For splaying o the a s fields in ed by the 1 The he f of Ethe and so 6,+ them rstands h e IP datagram it can ext ct the TCP egment e IP dat agran Pinally,it und s the TCP segment structure e,so it an exu act the HTTP mes ned in the TCP HTTP prote example,knows "POST,"or "HEAD,"as shown in Figure 2.8 in the text. We will be using the Wireshark packet sniffer [http://www.wireshark.org/]for these labs. allowing us to display the contents of messages being sent/received from/by protocols at different levels of the protocol stack.(Technically speaking,Wireshark is a packet analyzer that uses a packet capture library in your computer.Also,technically speaking Wireshark captures link-layer frames as shown in Figure 1,but uses the generic term "packet"to refer to link-layer frames,network-layer datagrams,transport-layer segments. and application-layer messages.so we'll use the less-precise "packet"term here to go along with Wireshark conve tion)wireshark is a free network protocol analyzer that runs on Windo ws.Mac.and Linux/Unix co oputers it's an ideal packet analyzer for our labs- it is stabl has that includes guide (http pport ww wire org/docs/wsug html c edl),man pages Fec m020. er Networks,A Top-down
Ethernet or WiFi). Recall from the discussion from section 1.5 in the text (Figure 1.241 ) that messages exchanged by higher layer protocols such as HTTP, FTP, TCP, UDP, DNS, or IP all are eventually encapsulated in link-layer frames that are transmitted over physical media such as an Ethernet cable or an 802.11 WiFi radio. Capturing all linklayer frames thus gives you all messages sent/received across the monitored link from/by all protocols and applications executing in your computer. Figure 1: packet sniffer structure The second component of a packet sniffer is the packet analyzer, which displays the contents of all fields within a protocol message. In order to do so, the packet analyzer must “understand” the structure of all messages exchanged by protocols. For example, suppose we are interested in displaying the various fields in messages exchanged by the HTTP protocol in Figure 1. The packet analyzer understands the format of Ethernet frames, and so can identify the IP datagram within an Ethernet frame. It also understands the IP datagram format, so that it can extract the TCP segment within the IP datagram. Finally, it understands the TCP segment structure, so it can extract the HTTP message contained in the TCP segment. Finally, it understands the HTTP protocol and so, for example, knows that the first bytes of an HTTP message will contain the string “GET,” “POST,” or “HEAD,” as shown in Figure 2.8 in the text. We will be using the Wireshark packet sniffer [http://www.wireshark.org/] for these labs, allowing us to display the contents of messages being sent/received from/by protocols at different levels of the protocol stack. (Technically speaking, Wireshark is a packet analyzer that uses a packet capture library in your computer. Also, technically speaking, Wireshark captures link-layer frames as shown in Figure 1, but uses the generic term “packet” to refer to link-layer frames, network-layer datagrams, transport-layer segments, and application-layer messages, so we’ll use the less-precise “packet” term here to go along with Wireshark convention). Wireshark is a free network protocol analyzer that runs on Windows, Mac, and Linux/Unix computers. It’s an ideal packet analyzer for our labs – it is stable, has a large user base and well-documented support that includes a userguide (http://www.wireshark.org/docs/wsug_html_chunked/), man pages 1 References to figures and sections are for the 8th edition of our text, Computer Networks, A Top-down Approach, 8th ed., J.F. Kurose and K.W. Ross, Addison-Wesley/Pearson, 2020
(http://www.wireshark org/docs/man-pages/),and a detailed FAQ (http://www.wireshark.org/faq.html),rich functionality that includes the capability to analyze hundreds of protocols,and a well-designed user interface.It operates in computers using Ethernet,serial (PPP),802.11(WiFi)wireless LANs,and many other link-layer technologies. Getting Wireshark In order to run Wireshark,you'll need to have access to a computer that supports both Wireshark and the libpcap or WinPCap packet capture library.The libpcap software will be installed for you,if it is not installed within your operating system,when you install Wireshark.See http://www.wireshark.org/download html for a list of supported operating systems and download sites. Download and install the Wireshark software: .Go to http://www wireshark org/download html and download and install the Wireshark bin The Wire ha ing tidbits of information particularly if you have trouble installing or running Wireshark Running Wireshark When you run the Wireshark program.you get a t looks something like the Ow. 01 ve an tantup screens o don't panic if yours d k exactly lik creen b The documentation states"As Wireshark runs on many different platf ms with many different window managers,different styles applied and there are different versions of the underlying GUI toolkit used,your screen might look different from the provided screenshots.But as there are no real differences in functionality these screenshots should still be well understandable."Well said
(http://www.wireshark.org/docs/man-pages/), and a detailed FAQ (http://www.wireshark.org/faq.html), rich functionality that includes the capability to analyze hundreds of protocols, and a well-designed user interface. It operates in computers using Ethernet, serial (PPP), 802.11 (WiFi) wireless LANs, and many other link-layer technologies. Getting Wireshark In order to run Wireshark, you’ll need to have access to a computer that supports both Wireshark and the libpcap or WinPCap packet capture library. The libpcap software will be installed for you, if it is not installed within your operating system, when you install Wireshark. See http://www.wireshark.org/download.html for a list of supported operating systems and download sites. Download and install the Wireshark software: • Go to http://www.wireshark.org/download.html and download and install the Wireshark binary for your computer. The Wireshark FAQ has a number of helpful hints and interesting tidbits of information, particularly if you have trouble installing or running Wireshark. Running Wireshark When you run the Wireshark program, you’ll get a startup screen that looks something like the screen below. Different versions of Wireshark will have different startup screens – so don’t panic if yours doesn’t look exactly like the screen below! The Wireshark documentation states “As Wireshark runs on many different platforms with many different window managers, different styles applied and there are different versions of the underlying GUI toolkit used, your screen might look different from the provided screenshots. But as there are no real differences in functionality these screenshots should still be well understandable.” Well said
Figure 2:Initial Wireshark Screen There's not much that's very interesting on this screen.But note that under the Capture section,there is a list of so-called interfaces.The Mac computer we're taking these screenshots from has just one interface-"Wi-Fi en0."(shaded in blue in Figure 2)which is the interface for Wi-Fi access.All packets to/from this computer will pass through the Wi-Fi interfac so it's he on this s interfac where we 111 ts On a Mac.double click r compute e the nt e packe ge thr Interne tconnectivity,e.g mostly likely a WiFior Ethern interface,an that interface) Let's take Wireshark out for a spin!If you lick on one of these interfaces to start packet capture(iefor Wireshark to begin captu ring all packets being sent to/from tha interface),a screen like the one below will be displayed,showing information about the packets being captured.Once you start packet capture,you can stop it by using the Capture pull down menu and selecting Stop (or by clicking on the red square button next to the Wireshark fin in Figure 2).2 look at r's(Jim's)compute 0 haron one packet traces that were captured h vere collected by wireshark tunning on one of the or's (lim's)com while the steps indicated above.Once you have downloaded the trace.you can load it into Wireshark and view the trace using the File pull down menu,choosing Open,and then selecting the wireshark-intro-trace trace file.The resulting display should look similar to Figures 3 and 5. (The Wireshark use interface displays just a bit differently on different operating systems,and in different versions of Wireshark)
Figure 2: Initial Wireshark Screen There’s not much that’s very interesting on this screen. But note that under the Capture section, there is a list of so-called interfaces. The Mac computer we’re taking these screenshots from has just one interface – “Wi-Fi en0,” (shaded in blue in Figure 2) which is the interface for Wi-Fi access. All packets to/from this computer will pass through the Wi-Fi interface, so it’s here where we’ll want to capture packets. On a Mac, double click on this interface (or on another computer locate the interface on startup page through which you are getting Internet connectivity, e.g., mostly likely a WiFi or Ethernet interface, and select that interface). Let’s take Wireshark out for a spin! If you click on one of these interfaces to start packet capture (i.e., for Wireshark to begin capturing all packets being sent to/from that interface), a screen like the one below will be displayed, showing information about the packets being captured. Once you start packet capture, you can stop it by using the Capture pull down menu and selecting Stop (or by clicking on the red square button next to the Wireshark fin in Figure 2). 2 2 If you are unable to run Wireshark, you can still look at packet traces that were captured on one of the author’s (Jim’s) computer. Download the zip file http://gaia.cs.umass.edu/wiresharklabs/wireshark-traces-8E.zip and extract the file wireshark-intro-trace. The traces in this zip file were collected by Wireshark running on one of the author’s (Jim’s) computers, while performing the steps indicated above. Once you have downloaded the trace, you can load it into Wireshark and view the trace using the File pull down menu, choosing Open, and then selecting the wireshark-intro-trace trace file. The resulting display should look similar to Figures 3 and 5. (The Wireshark user interface displays just a bit differently on different operating systems, and in different versions of Wireshark)
wireshark File Edit view Go Capture Analyze Statistics Telephony Wireless Tools Help display filter specification isting of captured packets Details of selected packe packet content(in hexadecimal and ASCIl) Figure 3:Wireshark window,during and after capture This looks more interesting!The Wireshark interface has five major components: The command menus are standard pulldown menus located at the top of the Wireshark window(and on a Mac at the top of the screen as well;the screenshot in Figure 3 is from a Mac).Of interest to us now are the File and Capture menus The File menu allows you to save captured packet data or open a file containing previously captured packet data and exit the Wireshark application.The Capture menu allows you to begin packet capture. The packet-listing window displays a one-line summary for each packet ed includi e pa ber (eder).the ti ed by wiresharl acket nu note that this is ny pro at which the pa ket's nd desti addr ap eod gcdacordfgl n on o cket listi ries packet.thas the sourimate in 0d e proto type s the highest-level rotocol ent r rec The packet-header details window provides details about the packet selected (highlighted)in the packet-listing window.(To select a packet in the packet listing window,place the cursor over the packet's one-line summary in the packet-listing window and click with the left mouse button.).These details include information about the Ethernet frame(assuming the packet was sent/received over an Ethernet interface)and IP datagram that contains this packet.The amount of Ethernet and IP-layer detail displayed can be expanded or
Figure 3: Wireshark window, during and after capture This looks more interesting! The Wireshark interface has five major components: • The command menus are standard pulldown menus located at the top of the Wireshark window (and on a Mac at the top of the screen as well; the screenshot in Figure 3 is from a Mac). Of interest to us now are the File and Capture menus. The File menu allows you to save captured packet data or open a file containing previously captured packet data and exit the Wireshark application. The Capture menu allows you to begin packet capture. • The packet-listing window displays a one-line summary for each packet captured, including the packet number (assigned by Wireshark; note that this is not a packet number contained in any protocol’s header), the time at which the packet was captured, the packet’s source and destination addresses, the protocol type, and protocol-specific information contained in the packet. The packet listing can be sorted according to any of these categories by clicking on a column name. The protocol type field lists the highest-level protocol that sent or received this packet, i.e., the protocol that is the source or ultimate sink for this packet. • The packet-header details window provides details about the packet selected (highlighted) in the packet-listing window. (To select a packet in the packetlisting window, place the cursor over the packet’s one-line summary in the packet-listing window and click with the left mouse button.). These details include information about the Ethernet frame (assuming the packet was sent/received over an Ethernet interface) and IP datagram that contains this packet. The amount of Ethernet and IP-layer detail displayed can be expanded or