4 Computer Networking - Virtualization

Virtualization

The basic idea behind virtualization is to use software to simulate the existence of hardware. Each of the simulated computer is called a virtual  machine VM. The operating system has no idea that it is running on a virtual machine than an actual machine.

Terms

Host/Bare metal - Actual physical machine on which one or more virtual machines run

Guest - Another term for a virtual machine running on a host

Guest operating system - An operating system that runs within a virtual machine.

Hypervisor - The virtualization operating system that creates and runs virtual machines. 2 types of hypervisors. Type 1 - runs on bare metal. Type 2 - runs within an OS which itself runs on bare metal.

Simulated computers always slower than actual computers.

Ctrl+Alt+End used by VM to send Ctrl+Alt+Delete to host OS.

3 Computer Networking - Understanding network hardware

Servers

What's important in a server?
1. Scalability
2. Reliability
3. Availability
4. Service and Support

Hot-swappable components - components in a server that can be changed without shutting down the server.

Server form factors

Form factor refers to the size, shape and packaging of a hardware device. Server computers usually come in three form factor:
1. Tower case
2. Rack mount
3. Blade servers

Network Interface Card

Every computer on the network requires a NIC to access the network. NIC is a Physical/Data Link layer device.

Network Cable

Coaxial -  also known as thinnet or BNC.

Twisted Pair - UTP (Unshielded twisted pair - 10BaseT)

Switch

Data Link layer device which can look into the packets that pass through it and examine their MAC address. This enables it  to route packets to the appropriate destination.

A Hub is a physical layer device, hence cannot do this.

Repeater

Boosts a network signal so that it can travel farther. Physical Layer device.

Bridge

A Bridge connects two networks so that they act if they're one network. It's a Data Link Layer device.

Router

Router itself is a node on a network. Routes packets. Network layer device.

NAS

Network  Attached storage

SAN

Storage Area network

Active Directory

Database that organises information about a network and allows users and computers to gain permission to access network resources.

2 Computer Networking - Protocols

Network protocol

Protocol - A set of rules that enable effective communication to occur.
Standard - An agreed upon definition of a protocol.
Protocols make it possible for various components of the network to communicate with each other.
Standards make it possible for different manufacturer's network components to work together.

Organisations involved in setting standards for networking are:
1. ANSI
2. IEEE
3. ISO
4. IETF
5. W3C

OSI

Open Systems Interconnection (OSI) model breaks the various aspects of a computer network into 7 distinct layers. These layers are kind of like the layers of an onion - each successive layer envelops the layer beneath it hiding it's details from the layers above.

OSI model is a framework into which various networking standards can fit.
OSI model specifies what aspects of a network's operation can be addressed by various network standards.

Seven layers in all. 1-3 are called lower layers and deal with mechanics of how information is sent from one computer to another over a network. 4-7 are upper layers and deal with how application  software can relate to the network through application programming interfaces.

1. Physical layer: addresses physical characteristics of the network like the type of cables used to connect devices, types of connectors used, how long the cables can be etc.
Devices - Repeater, Hub and NIC
Protocol - Ethernet

2. Data Link Layer: lowest layer at which meaning is assigned to the bits that are transmitted over network. Addresses issues like size of packets, means of addressing each packet so that it's delivered to the recipient, basic error detection and correction etc.
At the Data Link Layer, each device on the network has an address - Media Access Control (MAC), this is hard-wired into every network device by the manufacturer and is unique.
Use ipconfig /all (Physical address is the MAC).
One of the most important functions of the Data Link Layer is to provide a way for packets to be sent safely over the physical media without interference from other nodes attempting to send packets at the same time. Ways to do this are CSMA/CD (good up to a network size of 30, then divide into collision domains) and token passing.
Devices - Bridge (intelligent repeater), Switch
Protocol - Ethernet

3. Network Layer: handles the task of routing network messages from one computer to another. IP is a popular network layer protocol. Network layer provides two important functions - logical addressing and routing.
Logical addresses are created by Network layer protocols. They translate logical addresses to MAC addresses. Logical address consists of 2 parts - 1. Network address 2. Device address
Routing comes into play when one computer on a network wants to send packet to a computer on another network.
A protocol is considered routable if it uses addresses that include a network part and a host part.
Devices - Router
Protocol - IP, IPX

4. Transport Layer: concerned with transportation of information from one computer to another. TCP is a popular transport layer protocol. The main purpose of transport layer is to ensure packets are transported reliably without errors - does this by establishing connections between network devices, acknowledging receipt of packets and resending packets that aren't received or corrupted. Also divides a large packet into smaller packets that can be sent efficiently.
A connectionless protocol is User Datagram Protocol (UDP) - used when efficiency and speed is important and reliability isn't.
Netstat command gives status of TCP and UDP connections. Netstat /N for numeric network addresses.
Devices -
Protocol - TCP, UDP

5. Session Layer: establishes sessions (conversations) between networked devices. A session is an exchange of connection oriented transmissions between 2 network devices. Each transmission is handled by transport layer protocol. Session itself is managed by Session layer. Session layer allows 3 transmission modes - Simplex, half-duplex, full-duplex.
Devices -
Protocol -

6. Presentation Layer: handles how data is represented to applications. e.g. ASCII to EBCDIC conversion. Compress/uncompress data for faster transmission. Encrypt/Decrypt data.
Devices -
Protocol -

7. Application Layer: deals with the techniques that application programs use to communicate with the network. This layer represents the programming interfaces that application programs use to request network services. e.g. DNS, FTP, SMTP, NFS, Telnet etc.
Devices -
Protocols - DNS, FTP, SMTP etc.

Ethernet (IEEE 802.3) is the most popular protocol for Physical and Data Link layer. Ethernet comes in 3 speed versions:
1. Standard Ethernet - 10 Mbps
2. Fast Ethernet - 100 Mbps
3. Gigabit Ethernet - 1000 Mbps

TCP/IP

4 layers:

1. Application layer

2. Transport layer

3. Network layer

4. Network interface layer

TCP isn't used for broadcast, UDP is used for it.

Application layer protocol that uses TCP is HTTP, FTP etc.

Application layer protocol that uses UDP is DNS.

1 Computer Networking - Introduction

What is a network?

A network is 2 or more connected computers for information exchange or resource sharing. These can be connected with electric cables, fibre optic cables or wireless network.

Building blocks of a network

Client computers: Used  by end users to access the resources of the network.

Server computers: These computers provide shared resources and network services to client computers. Run a specialised network operating system such as Windows Server along with special software like MS-Exchange, Apache Web Server etc.

Network Interface:This interface (sometime called a network port) is installed on a computer to enable it to communicate over a network. In old times, you needed to install a network interface card on a computer, nowadays all computers come with it installed (NIC).

Cable: for physically connecting computers. Twisted pair cable most common. It's official name is 10BaseT.

Switch: Each computer is connected to a central switch which connects to the rest of the network. Each switch has a certain number of ports, typically 8 or 16.

Wireless networks: Radio transmitters used for networking. Less secure than cabled networks.

Network software: Network operating system (NOS) and configuration of servers and clients.

Benefits of network

Sharing information - e-mail, chat, video conference etc.
Sharing resources - file server, printers etc.
Sharing applications - special applications which can be accessed simultaneously through workstations

Dedicated servers and peers

Dedicated server: A server that does the job of a server alone. Such a network is called a client-server network
Peer-to-peer network: Same computer can be both server and client. Built in all operating systems since Windows 95.

Networks Big and Small

LAN: networks within same office or building
WAN: spans city, region or country. Geographic distance is the criteria here.
MAN: Typically connects LANs within the same city.

Network Topology

Topology refers to the shape of how computers and other network components are connected to each other.

Node: is a term used to refer to a device connected to a network

Packet: Message sent over network from one node to another. Each packet contains address of sending and receiving nodes along with data.

Types of topology

Bus: Nodes are strung together in a line. Every node can see every packet sent on a cable.

Star: Each network node is connected to a central device - a hub or a switch. Only networks that use switches have a true star topology. (Hub - does not know about computers connected to each of its ports, so when a node sends a packet for another node, hub sends it to all of its ports. Switch however sends the packet only to the intended recipient).

Expanding stars: More complex topology. Backbone (bus that connects the switches is called a backbone) and daisy-chaining (switch connected to another switch as if it were one of the nodes in the star).

Ring: Packets are sent around the circle from computer to computer.

Mesh: Has multiple connections between each node on the network.