ls4 socket types

7/31/2019 LS4 Socket Types

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SocketsClient-server paradigm


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Client-server paradigm

Typical network app has two pieces: clientandserver

applicationtransportnetworkdata linkphysical

applicationtransport

networkdata linkphysical

Client:

initiates contact with server (speaks

first)

typically requests service from server, for Web, client is implemented in

browser; for e-mail, in mail reader

Server:

provides requested service to client, via

replies e.g., Web server sends requested Web

page, mail server delivers e-mail

request

reply


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socket()

bind()

listen()

accept()

read()

write()

procees request

get a blocked client

Server Process

TCP UDP

socket()

connect()

write()

read()

Client Process

socket()

bind()

sendto()

recvfrom()

Client Process

1

2

3

socket()

bind()

recvfrom()

sendto()

Server Process


process request

UNIX

version


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socket()

bind()

listen()

accept()

recv()

send()

process request


Server Process

TCP UDP

socket()

connect()

send()

recv()

Client Process

socket()

bind()

sendto()

recvfrom()

Client Process

1

2

3

socket()

bind()

recvfrom()

sendto()

Server Process


process request

Winsock

or Unix

version


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IP (Raw) Socket

To use RAW sockets in Unix it is mandatory that one haveroot authority. To create a RAW socket write:s=socket(AF_INET,SOCK_RAW,[protocol])

Then you can send or receive over it. Raw sockets are usedto generate / receive packets of a type that the kerneldoesn't explicitly support.


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IP Raw Socket example

A familiar example is PING. Ping works by sending out an ICMPecho packet.

It formats an ICMP echo packet and sends it out over aSOCK_RAW, waiting for a response.


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Names and addresses

struct hostent *gethostbyname(char *hostname);

Converts textual name to a hostent structure

This structure contains all IPv4/IPv6 addresses of a host

/* Returns in Network Order */

unsigned long inet_addr(char *ipaddrstring);

Converts dotted decimal address to a 32 bit address

Similar functionality provided by inet_pton()

Deprecated. Better to use inet_aton()


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Byte ordering routines

How to interpret bits on the wire

Different computers store bytes in different order in memory

Network byte order (nbo) is big endian

Example: internal representation of 224


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ls4 socket types

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