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Networking and protocols

Simple introduction to Internet protocol stack and networking basics
by

Álvaro Ramos

on 6 November 2015

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Transcript of Networking and protocols

Basic networking protocols
Networking and protocols
Communication Protocols
Internet protocol suite
IP addresses and Ports
How it works
TCP/IP Tools
LAN Commons
A
communications protocol

is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications.
We don't usually memorize IP's... we connect to
www.google.com
,
www.prezi.com
, etc. so we need some service to translate from names to IP Addresses:
ping:
ask for a response from the host with a given name or address: used to test connection with another host.
Server processes within a host, by
ports
Hosts are identified by
IP addresses
DNS: Domain name service
Name:
www.google.com
IP Address:
173.194.34.49
DNS
Server
Example: open
www.google.com
web page from a browser

We type
www.google.com
in the browser navigation bar...
The browser knows that web servers are commonly listening at port
80
so it uses this value by default.
but the browser does not know the IP address of the Google web server
so it leaves the OS resolve this problem.
It asks the operating system to connect to the port
80
of the host with name
www.google.com
this is written as
www.google.com:80
Connect to
www.google.com:80
The browser asks the OS to connect to
www.google.com:80
The DNS process in the OS resolves to
173.194.34.49
Ports
are integers represented by 16 bits:
0 to 65535
IP addresses
are made of 4 bytes:
10.2.0.185, 192.168.1.1, 80.50.245.201
The OS opens a random port in the local host to start the bidirectional communications
Connect to
www.google.com:80
The OS opens a
random port
in the local host to start the bidirectional communications
Through this local port a connection packet is send to the remote IP (
173.194.34.49
) with destination port
80
Firefox
2546
192.168.1.14
Firefox
2546
192.168.1.14
Router
Router
Router
Router
Router
80
173.194.34.49
Web
Server
173.194.34.49
192.168.1.14
80
2546
(HTTP)
GET /index.html HTTP/1.1
IP and TCP headers
Firefox
2546
192.168.1.14
Router
Router
Router
Router
Router
80
173.194.34.49
Web
Server
192.168.1.14
2546
HTTP/1.1 302 Found
Location: http://www.google.es/
Cache-Control: private .......
IP and TCP headers
173.194.34.49
80
netstat:
shows information about active connections and listening processes
TCP, UDP
IP
Ethernet (802.3), Wifi(802.11),
...
telnet:


opens a TCP/IP connection to a given ip address (or host name) and port in plain text.
ifconfig(linux/FreeBSD/UNIX)/ipconfig (WIN):


lists the network interfaces of the local host and their configuration
HTTP, SMTP,
IMAP, ...
Every time a character is typed by the user, the corresponding byte is sent. Every time a byte is received the corresponding ASCII character is printed in the terminal.
Ethernet and Wifi
Cards have a MAC

or HW address (made of
6 bytes
) that identify them in this medium:
00:25:d3:e0:87:16
DHCP
Device IP address is configured automatically (given by a DHCP Server)
DHCP Client process
May I have an IP address?
MAC address
00:25:d3:e2:87:18
IP ????
DHCP
Server
Machine with MAC
00:25:d3:e2:87:18
please take
192.168.0.11
Subnets
Computers in the same subnet usually contact each other directly
192 .168.1.
11
255
.
255
.
255
.
0
192 .168.1.
34
255
.
255
.
255
.
0
Defined by a subnet mask: i.e.
255.255.255.
0
Packet sent directly
Subnets II
192.168.1.
12
255.255.255.
0
If not in the same subnet send to router/gateway
Dest. :
85.48.162
.3
255.255.255.
0
85.48.162
.3
Send to router directly
Router
...
Full transcript