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Protocol layers and Wireshark Rahul Hiran TDTS11:Computer Networks and Internet Protocols

Textbook: “Computer Networking: A Top Down Approach”, by Jim Kurose and Keith Ross. Note: The slides are adapted and modified based on slides from the book’s companion Web site, as well as modified slides by Niklas Carlsson 1

What will I talk about? • Short description from lecture 1 about computer networks • Internet protocol stack • How to see what different stack layer does • Using network analysis tool called wireshark

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What’s the Internet: Slide from lecture 1 PC

 millions of connected

computing devices: hosts = end systems  running network apps

server wireless laptop cellular handheld 

 fiber, copper, radio, satellite

access points wired links



router

communication links

Mobile network Global ISP

Home network Regional ISP

Institutional network

routers: forward packets (chunks of data)

3 1-3 Introduction

What’s a protocol? (slide from lecture 1) human protocols:  “what’s the time?”  “I have a question”  introductions

… specific msgs sent … specific actions taken when msgs received, or other events

network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

4 1-4 Introduction

More about protocols • There are many protocols that are involved in working of computer network • There is a internet protocol stack. A protocol normally belongs to one of the layers in the stack. • Let us look at the airline functionality

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Layering of airline functionality ticket (purchase)

ticket (complain)

ticket

baggage (check)

baggage (claim

baggage

gates (load)

gates (unload)

gate

runway (takeoff)

runway (land)

takeoff/landing

airplane routing

airplane routing

airplane routing departure airport

airplane routing

airplane routing

intermediate air-traffic control centers

arrival airport

Layers: each layer implements a service

– via its own internal-layer actions – relying on services provided by layer below 6 Introduction 1-6

Internet protocol stack 

application: supporting network applications  FTP, SMTP, HTTP



transport: process-process data transfer  TCP, UDP



network: routing of datagrams from source to destination  IP, routing protocols



link: data transfer between neighboring network elements

application transport network link physical

 Ethernet, 802.111 (WiFi), PPP 

physical: bits “on the wire” 7 Introduction 1-7

Encapsulation

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wireshark • How can we analyze the network data? • Using tools such as wireshark • Wireshark: a network packet analyzer. A network packet analyzer will try to capture network packets and tries to display that packet data as detailed as possible. • Let us start wireshark….!

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Start screen of wireshark

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Make your own capture or open existing trace files

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Graphical User Interface

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Reduce clutter • Disable the checksum error messages from Views->Coloring rules…menu item • Enter data in the filter to show only http packets • Let us look at the example

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After unnecessary data is removed

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Let us look at the application level data

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Internet protocol stack 

application: supporting network applications  FTP, SMTP, HTTP



transport: process-process data transfer  TCP, UDP  TCP is responsible for the establishment of a TCP connection, the sequencing and acknowledgment of packets sent, and the recovery of packets lost during transmission



network: routing of datagrams from source to destination  IP, routing protocols



link: data transfer between neighboring network elements

application transport network Link physical

 Ethernet, 802.111 (WiFi), PPP 

physical: bits “on the wire”

16 Introduction 1-16

Encapsulation

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TCP header

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TCP header data in our packet

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How to look at time/sequence plot • • • •

Select tcp-ethereal-trace-1 Filter by entering tcp Select TCP segment Go to statistics-> TCP streamgraph -> Timesequence graph (stevens)

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Internet protocol stack 

application: supporting network applications  FTP, SMTP, HTTP



transport: process-process data transfer  TCP, UDP



network: routing of datagrams from source to destination  IP, routing protocols  The Internet layer is responsible for addressing, packaging, and routing functions.



link: data transfer between neighboring network elements

application transport network Link physical

 Ethernet, 802.111 (WiFi), PPP 

physical: bits “on the wire”

21 Introduction 1-21

Encapsulation

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Internet layer • Let us first open ip-ethereal-trace-1 • And look at the first ICMP message • We also look at the IP protocol header format

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IP header

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IP header in collected traces

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Internet protocol stack 

application: supporting network applications  FTP, SMTP, HTTP



transport: process-process data transfer  TCP, UDP



network: routing of datagrams from source to destination  IP, routing protocols.



link: data transfer between neighboring network elements

application transport network Link physical

 Ethernet, 802.111 (WiFi), PPP 

physical: bits “on the wire” 26 Introduction 1-26

What’s the Internet: Slide from lecture 1 • Network layers job is end-toend movement of data from source to destination • Link layers job is node-tonode movement of networklayer datagrams over a single link in the path • Ethernet is quite popular protocol • Let us look at the header

Mobile network Global ISP

Home network Regional ISP

Institutional network

27 1-27 Introduction

Ethernet header and trailer

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Conclusion 

application: supporting network applications  FTP, SMTP, HTTP



transport: process-process data transfer  TCP, UDP



network: routing of datagrams from source to destination  IP, routing protocols



link: data transfer between neighboring network elements

application transport network link physical

 Ethernet, 802.111 (WiFi), PPP 

physical: bits “on the wire” 29 Introduction 1-29

Conclusion

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Questions…?

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www.liu.se

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