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• Internet is a way to send data through successive intermediary links in spite of numerous different network technologies on these links.
• Internet is a way to send data world wide, from one interface to another through various intermediary interfaces (routers)
• Internet Datagramm are then encapsulated and extracted in/from frames of the intermediary technologies
• Each internet internet interface correspond to a unique world wide adress called Internet Protocole Address or IP Adress. Generally for IPv4, it consists in a 4 Bytes number (ex. 157.169.23.34)
• to facilitate routing, IP adress are organized hierarchicaly in set of adresses.
• Routing table on each router provided a way to know which interface to use to send data to a give IP adress.
• In such a hierarchy, every set of IP adresses consists in : a netid part and a hostid part : <netdid>|<hostid>
• a subnet is a subset of adresses in this hierarchy : <netid>|<subnetid>|<hostid>
• a network mask allows to specify the number of bits of the netid. All the bits corresponding to the netid are equal to 1 and the other to 0. Thus for 167.145.134.32/18 (the means 18 bits to code the netid), the mask is 255.255.192.0.
• For each network, size of subnetid + size of hostid = 32 - size of netid. Be careful, <netid>|0..0 and <netid>|1..1 are use respectively to indentify the corresponding network and the broadcast adress (to send data to all the interfaces of the <netid> network at the same time).
• So, for each network coded on k bits, a maximum of 2^(32-k-1) adresses are available for hosts.

• How many interfaces has your PC ? (use ipconfig or ifconfig commands according to your OS : linus, MacOS, Windows)
• What is the IP adress for Wifi ? What is the mask of the corresponding network ? What is the list of IP adresses on this network ?

• In a building there is only one connection for all the apartements. The ISDN supplier provides a set of public IP adresses : 145.134.235.32/26.
• If I want to provide one public IP adress per appartment, how many appartment can I have in my building ? (answer : 62)
• There are 6 appartments in this building. For each appartement I want to provide a subnet. How many bits must I fix for that ? (3)
• Can I fix a subnet with 0..0 or 1..1 ? Why ?
• What are the different adresses of these networks ? their network mask ?
• What maximum of host adresses can I set in each appartment ? (6)
• The router of the building is connected to ISDN optic fiber on the interface A (MAC address :

* Because one internet interface can be used to send and receive multiple data simultaneously (from and for multiple software applications on a same interface of a smartphone, a PC, a TV …), transport potocols are just above IP to dispatch these communications.

• On each