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Monday, December 28, 2009

Day 31: Network Components and Operation

We have a three-layer hierarchical model:
  1. Access layer devices that connect hosts on a LAN to provide users with access (hubs, bridges and switches).
  2. Distribution layer devices that provide connectivity between LANs, obviously we find routers here.
  3. Core layer devices that provide high-speed connectivity between distribution layer devices.
A hub is an ethernet networking device with multiple ports that regenerates a signal it receives on one port to all other ports. The bandwith is shared by all devices and if two send at the same time we get collisions. Think of it as a multiport repeater.

The switch is a multiport networking device that looks at the destination physical address of a received frame on one port to forward the frame to the port where that host is connected. Communication is through temporary circuits, avoiding collisions.

A bridge is a two-port switch that can be used to divide a large, hub-based collision domain.

Routers look at the destination IP address of a received packet and forward the packet to its destination network. They also determine the best path for a packet to its destination network.

Interconnections are a physical component that provides a means for data to travel accross the network, this includes NICs, network media and connectors.
Remember that collaborations and databates are two of the most common network applications.
Batch applications are started and complete on their own without further interaction, Interactive apps are requested from a server by a user who then waits for a reply.
A physical topology defines the physical components of the network like cables, devices while the logical topology defines the data path of the network.
Passive attack refers to monitoring and gathering data, close-in is also gaining close proximity for a wireless tap. Active is trying to break or bypass security. Access attacks are exploiting known flaws (passwords, man-in-the-middle, trojan horses, etc.).
Always use SSH (or SSL and IPsec) because it encrypts all data, telnet sends it all in clear text.

About networks: a main office can have hundreds or thousands of people who depend on network access. Its a connected collection of devices that can communicate with each other and the purpose is to create a means to provide all workers with access to all information and components that are accessible by the network.
The purpose of network interconnections is to provide a means for data to travel from one point to another.
The main threath to a closed network is misuse by employees.

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