Sess1bc Networking Review

8/8/2019 Sess1bc Networking Review

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Session 1b: Introductory

TCP/IP Networking(An Example)

1

Objective

This lecture illustrates the interactions of the protocols of the TCP/IPprotocol suite with the help of an example.

The example intents to motivate the study of the TCP/IP protocols.


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Review: TCP/IP Based Networks

Internet is based on TCP/IP

TCP/IP is a suite of protocols

IP is Internet protocol at the network layer level

TCP is connection-oriented transport protocol

and ensures end-to-end connection

UDP is connectionless transport protocol andprovides datagram service

E-mail, WWW, FTP, Telnet: TCP/IP

Network mgmt. (SNMP): UDP/IP ICMP: part of TCP/IP suite


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TCP/IP Based Networks (cont.)

(Protocols used in Network Management)

SNMP(v1, v2, v3)

Simple Network Management Protocol ICMP

Internet Control Message Protocol

Ping , traceroute (or tracert)

ARP/RARP Address Resolution Protocol/ (Reverse ARP)

TCP Socket

Telnet/SSH

HTTP+XML


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TCP/IP Suite and OSI Reference Model

Application

Layer

ApplicationLayer

Presentation

LayerSessionLayer

TransportTransportLa er

The TCP/IP protocol stack does notdefine the lower layers of a completeprotocol stack

4

NetworkLayer

(Data) LinkLayer

PhysicalLayer

NetworkLayer

OSIReference

Model

(Data) LinkLayer

TCP/IP Suite


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Application protocol

IP is the highest layer protocol which is implemented at both

routers and hosts

5


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IP: The waist of the hourglass IP is the waist of the

hourglass of the Internet

protocol architecture

-

Applications

HTTP FTP SMTP

TCP UDP

6

Multiple lower-layer protocols

Only one protocol at the network

layer.

IP

Data link layerprotocols

Physical layerprotocols


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Client

ApplicationApplication

Message (Frame)

Data Communication Network

tat on

Mobile Client

Station

Station

Router

Mobile Client

Station

Access

Line

Trunk

Line

Switch

Switch

Switch

Trunk

Line

Outside

World


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Internet/internet

LAN

LAN

LAN

LAN

WAN

LAN

: router


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HTTP Request and HTTP response Web browser runs an HTTP client program

Web server runs an HTTP server program HTTP client sends an HTTP request to HTTP server

HTTP server responds with HTTP response

9

HTTP client

Argon

HTTP server

Neon

HTTP request

HTTP response


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A simple TCP/IP Example A user on host argon.tcpip-lab.edu (Argon) makes a web

access to URL

http://Neon. tcpip-lab.edu/index.html.

- -

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What actually happens in the network?

. .

("Argon")

. .

("Neon")

Web request

Web page

Web client Web server


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HTTP Request

GET /example.html HTTP/1.1

Accept: image/gif, */*

Accept-Language: en-us

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Accept-Encoding: gzip, deflateUser-Agent: Mozilla/4.0

Host: 192.168.123.144

Connection: Keep-Alive


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HTTP ResponseHTTP/1.1 200 OK

Date: Sat, 25 May 2002 21:10:32 GMT

Server: Apache/1.3.19 (Unix)

Last-Modified: Sat, 25 May 2002 20:51:33 GMT

ETag: "56497-51-3ceff955"

Accept-Ranges: bytes

Content-Length: 81

Keep-Alive: timeout=15, max=100

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Connection: Keep-Alive

Content-Type: text/html

Internet Lab

Click here for theInternet Lab webpage.

Q: How does the HTTP request get from Argon to Neon?


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From HTTP to TCP To send request, HTTP client program establishes an TCP

connection to the HTTP server Neon.

The HTTP server at Neon has a TCP server running

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HTTP client

TCP client

Argon

HTTP server

TCP server

Neon

HTTP request / HTTP response

TCP connection


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Resolving hostnames and port

numbers Since TCP does not work with hostnames and also would not

know how to find the HTTP server program at Neon, two

things must happen:

-

14

. . .

into a 32-bit IP address.

2. The HTTP server at Neon must be identified by a

16-bit port number.


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Translating a hostname into an IP

address The translation of the hostname neon.tcpip-lab.edu into an IP

address is done via a database lookup

HTTP client DNS Server

neon.tcpip-lab.edu

128.143.71.21

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The distributed database used is called the Domain NameSystem (DNS)

All machines on the Internet have an IP address:argon.tcpip-lab.edu 128.143.137.144neon.tcpip-lab.edu 128.143.71.21

argon.tcpip-lab.edu 128.143.136.15


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Finding the port number Note: Most services on the Internet are reachable via well-

known ports. E.g. All HTTP servers on the Internet can be

reached at port number 80. So: Argon simply knows the port number of the HTTP

server at a remote machine.

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On most Unix systems, the well-known ports are listed in afile with name /etc/services. The well-known port numbersof some of the most popular services are:

ftp 21 finger 79

telnet 23 http 80smtp 25 nntp 119


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Requesting a TCP Connection The HTTP client at argon.tcpip-lab.edu requests the TCP client to establish

a connection to port 80 of the machine with address 128.141.71.21

argon.tcpip-lab.edu

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c ent

TCP client

Establish a TCP connectionto port 80 of 128.143.71.21


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Invoking the IP Protocol The TCP client atArgon sends a

request to establish a connection

to port 80 at Neon

TCP client

argon.tcpip-lab.edu

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module to send an IP datagramto 128.143.71.21

(The data portion of the IP datagram contains

the request to open a connection)

IP

128.143.71.21


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Sending the IP datagram to an IP

router Argon (128.143.137.144) can deliver the IP datagram directly to

Neon (128.143.71.21), only if it is on the same local network

(subnet)

ButArgon and Neon are not on the same local network

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(Q: How doesArgon know this?)

So,Argon sends the IP datagram to its default gateway

The default gateway is an IP router The default gateway forArgon is Router137.tcpip-lab.edu

(128.143.137.1).


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The route from Argon to Neonneon.tcpip-lab.edu

"Neon"

128.143.71.21

argon.tcpip-lab.edu

"Argon"128.143.137.144

router137.tcpip-lab.edu

"Router137"

128.143.137.1


"Router71"

128.143.71.1

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Note that the gateway has a different name for each of its interfaces.

Ethernet NetworkEthernet Network

Router


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Finding the MAC address of the gateway

To send an IP datagram to Router137,Argon puts the IP

datagram in an Ethernet frame, and transmits the frame.

However, Ethernet uses different addresses, so-called Media

Access Control (MAC) addresses (also called: physical

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Therefore,Argon must first translate the IP address

128.143.137.1 into a MAC address.

The translation of addressed is performed via the Address

Resolution Protocol (ARP)


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Address resolution with ARP

ARP message: What is the MAC

address of 128.143.137.1?

ARP message: IP address 128.143.137.1belongs to MAC address 00:e0:f9:23:a8:20

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argon.tcpip-lab.edu

128.143.137.144

00:a0:24:71:e4:44


128.143.137.1

00:e0:f9:23:a8:20


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Invoking the device driver The IP module at Argon, tells its Ethernet device driver to send

an Ethernet frame to address 00:e0:f9:23:a8:20

argon.tcpip-lab.edu

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IP module

Ethernet

Send an Ethernet frameto 00:e0:f9:23:a8:20


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Sending an Ethernet frame The Ethernet device driver ofArgon sends the Ethernet frame

to the Ethernet network interface card (NIC)

The NIC sends the frame onto the wire

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argon.tcpip-lab.edu128.143.137.144

00:a0:24:71:e4:44

IP Datagram for Neon

router137.tcpip-lab.edu128.143.137.1

00:e0:f9:23:a8:20


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Forwarding the IP datagram The IP router receives the Ethernet frame at interface 128.143.137.1,

recovers the IP datagram and determines that the IP datagram should

be forwarded to the interface with name 128.143.71.1 The IP router determines that it can deliver the IP datagram directly

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neon.tcpip-lab.edu"Neon"

128.143.71.21

argon.tcpip-lab.edu"Argon"

128.143.137.144


"Router137"

128.143.137.1


"Router71"

128.143.71.1

Ethernet NetworkEthernet Network

Router


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Another lookup of a MAC address The rouer needs to find the MAC address ofNeon.

Again, ARP is invoked, to translate the IP address ofNeon

(128.143.71.21) into the MAC address of neon

(00:20:af:03:98:28).

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address of 128.143.71.21?

ARP message: IP address 128.143.71.21belongs to MAC address 00:20:af:03:98:28

neon.tcpip-lab.edu

128.143.71.21

00:20:af:03:98:28


128.143.71.1


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Invoking the device driver at the router

The IP protocol at Router71, tells its Ethernet device driver

to send an Ethernet frame to address 00:20:af:03:98:28


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mo u e

Ethernet

Send a frame to00:20:af:03:98:28


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Sending another Ethernet frame The Ethernet device driver ofRouter71 sends the Ethernet

frame to the Ethernet NIC, which transmits the frame onto

the wire.

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IP Datagram for Neon

neon.tcpip-lab.edu

128.143.71.21

00:20:af:03:98:28


128.143.71.1


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Data has arrived at Neon Neon receives the Ethernet frame

The payload of the Ethernet frame is an IP

datagram which is passed to the IP protocol.

The payload of the IP datagram is a TCPNeon.cerf.edu

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Note: Since the TCP segment is a connection request (SYN),

the TCP protocol does not pass data to the HTTP program

for this packet. Instead, the TCP protocol at neon will

respond with a SYN segment toArgon.

TCP server

IP module

Ethernet


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Wrapping-up the example So far, Neon has only obtained a single packet

Much more work is required to establish an actual TCP

connection and the transfer of the HTTP Request

The exam le was sim lified in several wa s:

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No transmission errorsThe routebetweenArgon and Neon is short(only one IP router)

Argon knew how to contact the DNS server (without

routing or address resolution) .


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How many packets were really sent?

tcpdump: listening on fxp0

16:54:51.340712 128.143.137.144.1555 > 128.143.137.11.53: 1+ A? neon.cs. (25)

16:54:51.341749 128.143.137.11.53 > 128.143.137.144.1555: 1 NXDomain* 0/1/0 (98) (DF)

16:54:51.342539 128.143.137.144.1556 > 128.143.137.11.53: 2+ (41)

16:54:51.343436 128.143.137.11.53 > 128.143.137.144.1556: 2 NXDomain* 0/1/0 (109) (DF)

16:54:51.344147 128.143.137.144.1557 > 128.143.137.11.53: 3+ (38)

16:54:51.345220 128.143.137.11.53 > 128.143.137.144.1557: 3* 1/1/2 (122) (DF)

16:54:51.350996 arp who-has 128.143.137.1 tell 128.143.137.144

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16:54:51.351614 arp reply 128.143.137.1 is-at 0:e0:f9:23:a8:20

16:54:51.351712 128.143.137.144.1558 > 128.143.71.21.21: S 607568:607568(0) win 8192

(DF)

16:54:51.352895 128.143.71.21.80 > 128.143.137.144.1558: S 3964010655:3964010655(0)

ack 607569 win 17520 (DF)

16:54:51.353007 128.143.137.144.1558 > 128.143.71.21.80: . ack 1 win 8760 (DF)

16:54:51.365603 128.143.71.21.80 > 128.143.137.144.1558: P 1:60(59)

ack 1 win 17520 (DF) [tos 0x10]

16:54:51.507399 128.143.137.144.1558 > 128.143.71.21.80: . ack 60 win 8701 (DF)


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Session 1c: Review of Important

Networking Concepts

32

Objective (Introductory material).

This module uses the example from the previous module

to review important networking concepts: protocolarchitecture, protocol layers, encapsulation, demultiplexing,

network abstractions.


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Networking Concepts Protocol Architecture

Protocol Layers

33

Encapsulation

Network Abstractions


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Sending a packet from Argon to Neon

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Sending a packet from Argon to NeonDNS: The IP address of

neon.tcpip-lab.edu is

128.143.71.21

ARP: What is the MACaddress of 128.143.137.1?

DNS: What is the IP address

of neon.tcpip-lab.edu?ARP: The MAC address of

128.143.137.1 is 00:e0:f9:23:a8:20

128.143.71.21 is not on my local network.

Therefore, I need to send the packet to mydefault gateway with address 128.143.137.1128.143.71.21 is on my local network.

Therefore, I can send the packet directly.

ARP: The MAC address of128.143.137.1 is 00:20:af:03:98:28

ARP: What is the MACaddress of 128.143.71.21?

35

frame

frame


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Communications Architecture

The complexity of the communication task is reducedby using

multiple protocol layers: Each protocol is implemented independently

36

Protocols are grouped in a hierarchy

A structured set of protocols is called a communications

architecture or protocol suite


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TCP/IP Protocol Suite

The TCP/IP protocol suite is

the protocol architecture of theInternet

Application

Transport

Operating system

User-level programs

37

e su e as our ayers:

Application, Transport, Network,and Data Link Layer

End systems (hosts)implement all four layers.

Gateways (Routers) only havethe bottom two layers.

Data Link

Data Link

Media AccessControl (MAC)

Sublayer inLocal AreaNetworks


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Functions of the Layers Data Link Layer:

Service: Reliable transfer offrames over a link

Media Access Control on a LAN Functions: Framing, media access control, error checking

Network Layer:

38

Functions: Routing, addressing Transport Layer:

Service: Delivery of data between hosts Functions: Connection establishment/termination, error

control, flow control Application Layer:

Service: Application specific (delivery of email, retrieval ofHTML documents, reliable transfer of file)

Functions: Application specific


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TCP/IP Suite and OSI Reference Model

ApplicationLayer

ApplicationLayer

Presentation

Layer

SessionLayer

TransportTransportLa er

The TCP/IP protocol stack does notdefine the lower layers of a completeprotocol stack

39

NetworkLayer

(Data) LinkLayer

Physical

Layer

NetworkLayer

OSIReference

Model

(Data) LinkLayer

TCP/IP Suite


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Assignment of Protocols to Layers

Routing Protocols

ApplicationLayer

Transport

LayerTCP UDP

SNMPFTP DNSHTTPping

applicationTelnet

40

Network

LayerPIM

OSPF

RIP

Data Link

Layer

IP

ARP Ethernet

NetworkInterface

ICMP

IGMP

DHCP


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Layered CommunicationsLayered CommunicationsLayered CommunicationsLayered Communications An entity of a particular layer can only communicate with:

1. a peer layer entity using a common protocol (Peer

Protocol)2. adjacent layers to provide services and to receive

services

41

N+1 LayerEntity

N+1 LayerEntity

N+1 Layer ProtocolN+1 Layer

N-1 LayerEntity

N-1 LayerEntity

N-1 Layer ProtocolN-1 Layer

N LayerEntity

N LayerEntity

N Layer ProtocolN Layer

layer N+1/Ninterface

layer N/N-1interface


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Service PrimitivesCommunication services are invoked via function calls. The functions

are called service primitives

N+1 LayerN+1 LayerN+1 LayerN+1 Layer

EntitEntitEntitEntit



N+1 Layer Peer ProtocolN+1 Layer Peer ProtocolN+1 Layer Peer ProtocolN+1 Layer Peer Protocol

42

N LayerN LayerN LayerN Layer

EntityEntityEntityEntity

N LayerN LayerN LayerN Layer

EntityEntityEntityEntity

RequestRequestRequestRequest

DeliveryDeliveryDeliveryDelivery

IndicateIndicateIndicateIndicate



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Service PrimitivesRecall: A layer N+1 entity sees the lower layers only as a service

provider





N+1 Layer Peer ProtocolN+1 Layer Peer ProtocolN+1 Layer Peer ProtocolN+1 Layer Peer Protocol

43

Service ProviderService ProviderService ProviderService Provider

RequestRequestRequestRequest


IndicateIndicateIndicateIndicate



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Service Access Points A service user accesses services of the service provider at

Service Access Points (SAPs)

A SAP has an address that uniquely identifies where the

service can be accessed

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Layer-NEntity

N Layer

Layer- N-1Entity

N-1Layer

layer N/N-1

service interface

Layer

N-1SAP


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Exchange of Data Assume a layer-N entity at A wants to send data to a layer-N

peer entity to B

The unit of data sent between peer entities is called a Protocol Data Unit(PDU)

For now, let us think of a PDU as a single packet

45

What actually happens: Layer N passes the PDU to one of As SAPs at layer N-1

The layer N-1 entity (at A) then constructs its own PDU which it sends to thelayer N-1 entity at B

Note: PDU at layer N-1 = Header + PDU at layer N

N Layer

Entity PDU(at layer N)N Layer

EntityAAAA BBBB


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Exchange of Data

Layer-NEntity

When passed to the SAP, the PDUis called a Service Data Unit(SDU)

- = - -

Layer-NEntity

AAAA BBBB

46

Layer- N-1Entity

SAPs

control

N PDUcontrolHeader

(of layer N-1)N PDU

PDU of Layer-N-1

Layer- N-1Entity


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Layers in the Example

47


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Layers in the ExampleSend HTTP Requestto neon

Establish a connection to 128.143.71.21 atport 80Open TCP connection to

128.143.71.21 port 80IP datagram is a TCP

48

Send a datagram (which contains a connection

request) to 128.143.71.21Send IP datagram to128.143.71.21

Send the datagram to 128.143.137.1

Send Ethernet frameto 00:e0:f9:23:a8:20

Send Ethernet frameto 00:20:af:03:98:28

Send IP data-gram to

128.143.71.21

Send the datagramto 128.143.7.21

Frame is an IPdatagram

Frame is an IPdatagram

segmen or por


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Layers and Services Service provided by TCP to HTTP:

reliable transmission of data over a logical connection

Service provided by IP to TCP:

unreliable transmission of IP datagrams across an IP network

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erv ce prov e y erne o :

transmission of a frame across an Ethernet segment

Other services: DNS: translation between domain names and IP addresses

ARP: Translation between IP addresses and MAC addresses


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Encapsulation and Demultiplexing


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in our Example Let us look in detail at the Ethernet framebetween

Argon and the Router, which contains the TCP

connection request to Neon.

This is the frame in hexadecimal notation.

51

00e0 f923 a820 00a0 2471 e444 0800

4500 002c 9d08 4000 8006 8bff 808f

8990 808f 4715 065b 0050 0009 465b

0000 0000 6002 2000 598e 0000 020405b4


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6 bytes

52

Application dataTCP HeaderIP HeaderEthernet Header Ethernet Trailer

Ethernet frame

est nat on a ress

source address

type CRC

4 bytes

Encapsulation and Demultiplexing:


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Ethernet Header

00:e0:f9:23:a8:20

6 bytes

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0:a0:24:71:e4:44

0x0800 CRC

4 bytes

Application dataTCP HeaderIP HeaderEthernet Header Ethernet Trailer

Ethernet frame



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IP Header (1/2)IP Header (1/2)IP Header (1/2)IP Header (1/2)

DS ECNversion

(4 bits)

header

length

Total Length (in bytes)

(16 bits)

Identification (16 bits)flags

(3 bits)Fragment Offset (13 bits)

TTL Time-to-Live(8 bits)

Protocol(8 bits)

Header Checksum (16 bits)

32 bits

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Application dataTCP HeaderEthernet Header Ethernet Trailer

Ethernet frame

IP Header

Source IP address (32 bits)

Destination IP address (32 bits)



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IP Header (2/2)IP Header (2/2)IP Header (2/2)IP Header (2/2)

0x0 0x00x4 0x5 4410

9d08 0102

00000000000002

12810

0x06 8bff

32 bits

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Application dataTCP HeaderEthernet Header Ethernet Trailer

Ethernet frame

IP Header

128.143.137.144

128.143.71.21



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p p g

TCP Header (1/2)TCP Header (1/2)TCP Header (1/2)TCP Header (1/2)

Sequence number (32 bits)

Source Port Number Destination Port Number

Acknowledgement number (32 bits)

32 bits

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window sizelength

0 Flags

TCP checksum urgent pointer

length Max. segment sizeoptiontype

Application dataEthernet Header Ethernet Trailer

Ethernet frame

IP Header TCP Header

Option:maximumsegment size



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p p g

TCP Header (2/2)

60783510

162710

8010

010

32 bits

57

819210

610

0000002 0000102

0x598e 00002

410

146010

210


Ethernet frame




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p p g

Application data

58


Ethernet frame


No Application Data

in this frame


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Different Views of NetworkingDifferent Views of NetworkingDifferent Views of NetworkingDifferent Views of Networking Different Layers of the protocol stack have a different view of the

network. This is HTTPs and TCPs view of the network.

Argon

128.143.137.144

HTTP

Neon

128.143.71.21

HTTP

59

c en

TCP client

server

TCP server

IP Network

server

TCP server


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Network View of Ethernet Ethernets view of the network

Argon

(128.143.137.144)

Router137

61

(128.143.137.1)

Ethernet Network

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Sess1bc Networking Review