LAN

(Local area network)     Typical network inside an office or inside a building

MAN

(Metropolitan area network)       A network that connects several LANs in a city.

WAN

(Wide area network)      A network that spans over long distance. Internet is an example of WAN.

Network device

Function

Network interface card (NIC)

Puts the data into packets and transmits packet onto the network. To install the NIC card you must have available IRQ in the computer.

Hub & Transceivers

You should know what a hub is. Extends collision domain. Transceiver converts one media to another.

MAU

Multi-station access unit. Acts as a hub in Token ring networks.

Repeater

Repeaters are used to extend segment beyond the limitation of the maximum allowed cable length. Boost the signal between two cable segments. Repeaters can connect segments with different physical media such as UTP and Coaxial cable. Repeaters can't connect different network architecture such as Ethernet and token ring.  Extends collision domain.

Bridge

Used to segment a network and reduce network traffic by examining the source and destination hardware address of the packet. Only Translation bridges can connect dissimilar network architectures like Ethernet and token ring.

Router

Used to route  packets to remote networks by examining the packet\'s network source and destination address. Routers reduce broadcast storms because they don\'t route broadcast packets. Routers can connect dissimilar network architectures. The destination address of the packet must match an entry in the routing table of the router; otherwise, the packet is discarded.

Brouter

A combination of Router and a Bridge. Used on networks that have both routable and non-routable protocols.

Gateway

Used to connect networks with different protocols like TCP/IP network and IPX/SPX networks.

Proxy server

Used to isolate internal network computers from the internet. When users on the network want to access the Internet, they first access the Proxy server and the proxy server accesses the internet and retrieves the requested web page or document. The user then gets a copy of that page from the proxy server. Only IP address of the proxy server goes out to the internet. Proxy server will also cache frequently used sites to speed up future access. Can also be configured to restrict access to certain sites.

Firewall

Used to prevent unauthorized access from the external network such as internet to your local network. Microsoft Proxy server has the ability to act as a firewall.

OSI layer

What the layer is responsible for

Corresponding devices

Corresponding protocols

1   Physical

     Bits

Data is sent across physical media like wires and hubs. Responsible for encoding scheme (like Manchester encoding)

Hubs, Repeaters, Amplifiers, Gateway , Transceivers, Media, NIC hardware

None

2   Datalink

     Frames

Packets placed into frames at this layer. CRC is added at this layer. If CRC fails at the receiving computer, this layer will request retransmission. Mac addresses are resolved at this layer. Divided into the LLC and MAC sublayer.

Bridges, Switches, NIC drivers, Gateway, BRouter

 ARP, RARP, Frame Relay, ISDN, PPP

3   Network

     Packets

Logical addressing, routing of message, determining the best route.

Routers, Gateway, BRouter, Layer 3 Switch

Routing - RIP, IGRP, EIGRP, OSPF

Routed – IPX, IP

ARP, RARP, Proxy ARP

4   Transport

     Segments

Sequencing, Error free delivery, checkpoints. Sliding window is at this layer.

Gateway, Software, Computers

TCP, UDP, SPX

5   Session

     Data

Responsible for opening, using and closing the session. Also places checkpoints in the data flow, so that if the transmission fails, only the data after the last checkpoint needs to be retransmitted.

Gateway, Software, Computers

Network File System (NFS), SQL, RPC, SCP,ASP

6  Presentation

    Data

Translating data into understandable format for transmission. Data compression and encryption takes place at this layer. Redirector works at this layer.

Gateway, Software, Computers

JPEG, MIDI, MPEG, (All kind of music, pictures and movie formats}

7 Application

   Data

Interface between the user and the computer. API incorporated in this layer.

Gateway, Software, Computers

SNMP, FTP, TELNET, WWW, HTTP, DNS

Class

IP addresses

Default subnet mask

Comment  (always reserve 2 IP’s for internal use and broadcasting)

A

1-126

255.0.0.0

10.*.*.* reserved for private networks.

B

128-191

255.255.0.0

network address 127.0.0.1 is local host loop back. It is reserved for testing purposes as a loop-back address. 172 private use.

C

192-223

255.255.255.0

192.168.*.* reserved for private use.

D

224-239

Used for multicast broadcasts

E

240-255

Reserved for future use.  IP .255 is reserved for broadcasting.

Remote communication protocol

Functionality

Serial Line Internet Protocol (SLIP)

Supports only TCP/IP protocol. Does not support compression or encryption. Provides no mechanism for error checking.

Point -to- Point Protocol  (PPP)

PPP supports IPX/SPX, TCP/IP , NetBEUI, AppleTalk. Supports compression and error checking. Functions at physical and Datalink layer and virtually turns a modem into a NIC card.    Phases: Link Establishment, Network Protocol, & Link Termination.  Passwords are sent clear text.  (CHAP is 3 way handshake encrypted passwords.)

Point -to- Point Tunneling Protocol (PPTP)

Allows establishing a secure encrypted communication over TCP/IP network. PPTP is used to establish virtual private network over the internet.

CHAP Authentication

3 Way Handshake

4 Step Process

1. Client requests logon permission

2. Server sends challenge request

3. Client sends answer to challenge request

4. Server provides authentication based upon challenge answer

Application

Default port number

FTP

21                                           port 1023 and up is open to public

HTTP

80

TELNET

23

POP3       sends mail

110

SMTP     holds mail for the pop3

25                                               

TFTP

69

IEEE 802 Specifications

802.1

Internetworking 

802.1Q

VLAN

802.2

Logical link control

802.3

Ethernet (CSMA/CD)

802.4

Token bus LAN

802.5

Token Ring BUS

802.6

Metropolitan Area network (MAN)

802.7

Broadband

802.8

Fiber optic

802.9

Integrated voice/Data

802.10

Network Security

802.11

Wireless Networks  A, B, G

802.12

Demand Priority. Like 100VG-Any LAN

802.13

802.14

Cable TV

802.15

Wireless Personal Area Networks

802.16

Broadband Wireless (MAN’s)

802.17

Resilient Packet Ring

Type of cable

Connector

Comment

Maximum length

Transmission speed

Interference

UTP

Category 5e  10baseT

RJ-45

Usually used for star topology. Most networks require minimum category 3 cable. For speed of 100Mbps use cat 5 cable

100 meters=328 feet

10-100Mbps

High

STP

Category 5e 10baseT

RJ-45 or special connectors.

Usually used on IBM token ring and Apple\'s Apple Talk

100 meters=328 feet

16-500Mbps

Low

Thinnet
(RG 58 A/U)

Coaxial  10base5

BNC

Requires terminators at both ends of 50 Ohms. Used on BUS topology on simple peer-to-peer networks

185 meters=607 feet

10 Mbps

Low

Thicknet
(RG 11)

Coaxial  10base2

Transceiver, Transceiver cable,  AUI port, DB15

Not used to connect computer to computer. Can be use as a backbone  to link several networks together

500 meters=1640 feet

10 Mbps

Low

Fiber Optic

Glass or plastic

Category 6

Special connectors

ST and SC

Used to connect networks over a great distance. Can use laser to send the light pulses.

2 Kilometers and more.

100 Mbps-2 Gbps or faster

None

RAID

Description

Comments

0

Disk Striping without parity.

Minimum 2 disks. No fault tolerance. Improves read/write speed.

1

Disk Mirroring and Disk Duplexing

Minimum 2 disks. For disk duplexing minimum 2 disks and 2 controllers. GOOD FAULT TOLERANCE. Can be more than 2 disks.

2

Disk Striping with Error correction code

3

Disk striping with error correction code stored as parity

4

Disk striping with large blocks allocation.

5

Disk Striping with Parity

Minimum 3 maximum 32 disks. Fault tolerant, less expensive than disk mirroring. If more than one disk fails, data can\'t be recovered.

NBTSTAT -R

Flushes out the DNS Cache

WINIPCFG

To see TCP/IP configuration of your computer. Will display your IP address, subnet mask, default gateway, hardware MAC address.

Used from command prompt on windows 95/98. Very useful if your computer is obtaining It\'s IP address from DHCP server and you need to find out what IP address has been assigned to you.

IPCONFIG

Same function as WINIPCFG, used on NT computers

Only used on NT machines. For more detailed information use with a switch
IPCONFIG /ALL

NETSTAT

Will display your current TCP/IP session including addresses of hosts connected to your computer and port numbers.

Can be used when you want to find out who\'s communicating with your computer. Looking at port number will reveal what service being used. Can be useful if you suspect that someone is connected to your computer without authorization.

TRACERT

Will display a report that lists all routers and networks that the packet must travel to get to it\'s destination and the time in milliseconds that packet takes to travel between routers.

Very useful when trying to find a bottleneck in your network.

PING

Used to verify connection between your computer and remote host. You can ping a host using it\'s IP address or it\'s host name.

This is the first utility you should use when you have connection problem. If you can ping a host by IP address but can\'t by it\'s name then you have a problem with name resolution.

ARP

Will display hardware addresses of local hosts on the network. Entries will remain in ARP cache for 10 minutes on windows NT

Can use this command if you suspect invalid ARP entries in ARP cache.