Basic notions of networking
Network (computing)#
Set of computers linked together (cable or wireless). These computers can remotely:
- Share resources (modem, hard drive, CD-Rom drive, applications, etc.)
- Exchange data: documents, chats etc.
Network cables or ethernet cable#
- UTP-CAT5 (Unshielded Twist Pair Category 5): 100 megabit/second
- UTP-CAT6 (Unshielded Twist Pair Category 6): 1gigabit/second
- straight ethernet cables: connects a computer to a switch
- crossed ethernet cables: connects 2 computers together
Network card#
Hardware that provides access to the network. This is where the data passes. The network card provides a MAC address to the computer in question in order to identify it on the network (physical address). A network card attaches to the computer’s PCI port.
Concentrator (Hub)#
Hardware that allows data exchange. It receives data through one port, and sends what it receives to other ports. It has a receive interface (one port) and a broadcast interface (several other ports through which other computers are connected).
Switch
Hardware that allows data exchange. It transmits data to other computers based on their MAC addresses
Router#
Hardware that allows data exchange. It is the border between the local network (Ethernet or WIFI cables) and the Interent network (cable plugged into the telephone jack).
Gateway#
System that connects two different networks. It could be on a machine with software. Example 2 networks which do not use the same protocol.
LAN (Local Area Network) or WLAN (Wireless Local Area Network)#
Network limited to a geographical space such as a building for example, wired or wireless. It’s a local network.
WAN (Wide Area Network)#
Extended network. A WAN and a set of LANs linked together.
Network topology#
Bus#
Star#
Router, switch or hub is located in the center of the network and all computers are connected to it. If they want to communicate with each other they must necessarily go through the router.
Mesh#
or mesh, all the computers are linked together by cables.
Ring, hybrid#
IP address#
Address to communicate with the computer. It relates to the network. This is the only way to identify machines on the Internet.
We distinguish:
IPv4#
4 numbers between 1 and 255, separated by periods.
An IPv4 address is made up of 32 bits separated into 4 portions by dots. (1byte = 1byte = 8bits). An IP address is therefore made up of 4 bytes, or 4 bytes or 32 bits. Example: 192.168.0.10
IPv6#
8 groups of 2 bytes represented in hexadecimal. Example 1fff:0011:0a88:85a3:6500:0320:ac1f:8001
Subnet mask#
An additional part of the address where to find a machine connected to the network.
MAC address#
Address relative to the network card. Unique identifier assigned to the network card. Example: 01:22:64:31:78:AC
Subnet#
It’s a network within a network. Multiple subnets can be part of the same network.
Network mask#
Subnet name. Example: 255.255.255.0
Protocol#
Subnet language to communicate with another subnet (in the network).
For 2 machines to communicate with each other in a network they must:
- Use the same protocol
- Belong to the same subnet
- Know their IP addressFor 2 machines from a different subnetwork to communicate with each other, a gateway is required.
Network architecture#
- client/server
- peer to peer: file sharing
Classes#
Set of IP addresses. Each IP address belongs to a main class (range). Each class has a default subnet mask. As soon as we give an IP address to the network card, the operating system directly assigns a default subnet mask according to the class to which the IP address belongs. There are 5 classes of IP addresses: A, B, C, D, E.
Class A#
IP addresses are between 1.0.0.0 and 127.255.255.255.
Default subnet mask: 255.0.0.0
IP addresses between 127.0.0.0 and 127.255.255.255 are used for specific tests.
Example: 110.168.0.10
Here 110 is the network ID. We are in the 110 network
168.0.10 is the host ID or the address of the network card
Thanks to the distribution of bytes between network ID and host ID, 16,777,214 IP addresses per network are available and 126 networks.
Class B#
IP addresses between 128.0.0.0 and 191.255.255.255.
Default subnet mask: 255.255.0.0.
Example: 170.40.0.6
Here 170.40 is the network ID. We are in the 170.40 network
0.6 is the host ID. Address 0.6 belongs to network 170.40
65,534 computers per network.
Class C#
IP address between 192.0.0.0 and 223.255.255.255.
The default subnet mask is 255.255.255.0.
254 IP addresses per network, and 2,097,152 networks.
Sending data in the network:
Unicast: in this case, data is sent to a single computer;
Multicast: data is sent to a group of computers;
The broadcast: we send data to all the computers on the network.
For class C: address 255 is a broadcast type address (hence 254 possible IP addresses per network in class C and not 255 since this address cannot be taken by a host)
For class B: address 255.255 is the broadcast address
For class A: the address 255.255.255 is the broadcast address
Private class#
Scope of IP addresses in a class (A,B,C) reserved for particular use or by convention.
Example:
- the scope 169.254.0.0 - 169.254.255.255 belongs to the private class reserved by Microsoft in class B.
- scope 192.168.0.0 - 192.168.255.255 belongs to a private class in class C. It will require NAT service to access the Internet.
- the scope 172.16.0.0 to 172.31.255.255 belongs to a private class of class B.
- the scope 10.0.0.0 to 10.255.255.255 belongs to a private class of class A.
NB: In general, ISPs offer addresses belonging to private classes.