Travis HillNETWORK

COMPONENTS 101

A computer network or data network is a telecommunications network that allows computers to exchange data. In computer networks, networked computing devices pass data to each other along data connections. The connections (network links) between nodes are established using either cable media or wireless media. The best-known computer network is the Internet.

Internet based networks use many diff erent technologies and devices to gain access. In the following we will go over some of these basic devices.

WHAT IS A COMPUTER NETWORK?

Hub

Switch

Router

Gateway

Firewall

Wireless AP

NETWORK DEVICES

HUB SWITCH

A hub is typically the least expensive, least intelligent, and least complicated of the three. Its job is very simple – anything that comes in one port is sent out to the others.That’s it.If a message comes in for computer “A”, that message is sent out all the other ports, regardless of which one computer “A” is on:

And when computer “A” responds, its response also goes out to every other port on the hub:

Every computer connected to the hub “sees” everything that every other computer on the hub sees. The computers themselves decide if they are the targeted recipient of the message and when a message should be paid attention to or not.

The hub itself is blissfully ignorant of the data being transmitted. For years, simple hubs have been quick and easy ways to connect computers in small networks.

HUB SWITCH

A switch does essentially what a hub does, but more efficiently. By paying attention to the traffic that comes across it, it can “learn” where particular addresses are.Initially, a switch knows nothing and simply sends on incoming messages to all ports:

In addition to sending the response through to the originator, the switch has now learned something else – it now knows on which connection machine “A” is located.That means that subsequent messages destined for machine “A” need only be sent to that one port:

Even accepting that first message, however, the switch has learned something – it knows on which connection the sender of the message is located. Thus, when machine “A” responds to the message, the switches only need to send that message out to the one connection:

A router   i s the smar tes t and most comp l i ca ted o f t he bunch . Rou te rs come in a l l shapes and s i zes – f rom the sma l l , f ou r-po r t b roadband rou te rs tha t a re ve ry popu la r r i gh t now to the l a rge indus t r i a l s t reng th dev i ces tha t d r i ve the i n te rne t i t se l f.

A s imp le way to th ink o f a rou te r i s as a computer tha t can be p rog rammed to unders tand , poss ib ly man ipu la te , and rou te the da ta tha t i t ’ s be ing asked to hand le . Many rou ters t oday a re , i n fac t , l i t t l e computers ded ica ted to the task o f rou t ing ne twork t raffi c .

As fa r as s imp le t raffi c rou t ing i s concerned , a rou te r opera tes exac t l y as a sw i t ch , l ea rn ing the l oca t ion o f t he computers on i t s connec t i ons and rou t ing t raffi c on ly to those computers .

Consumer g rade rou te rs pe r fo rm a t m in imum two add i t i ona l and impor tan ttasks :  DHCP and  NAT.

DHCP – Dynamic Hos t Confi gura t ion Pro toco l – i s t he way dynamic IP add resses a re ass igned . A dev i ce asks fo r an IP address t o be ass igned to i t f rom “ups t ream” and a DHCP se rver responds w i th an IP add ress ass ignment . A rou te r connec ted to you r ISP-p rov ided in te rne t connec t ion w i l l t yp i ca l l y ask you r ISP ’ s se rver fo r an IP add ress ; th i s w i l l be your I P address on the in te rne t . You r l oca l computers , on the o ther hand , w i l l a sk the rou te r fo r an IP add ress and these add resses a re l oca l t o you r ne twork .

ROUTER

NAT – Network Address Trans la t i on – i s t he way tha t the rou te r   t rans la tes   t he IP addresses o f packet s tha t c ross the i n te rne t / l oca l ne twork boundary. When computer “A” sends a packet ou t , t he IP address tha t i t ’ s “f rom” i s t ha t o f computer “A” – 192 .168 .1 .2 i n the examp le above . When the rou te r passes tha t on to the i n te rne t , i t rep laces the l oca l I P add ress w i th the in te rne t I P address ass igned by the ISP. I t a l so keeps t rack , so tha t i f a response comes back f rom somewhere on the in te rne t , t he rou te r knows to do the t rans la t i on i n reverse – rep lace the in te rne t I P address w i th the l oca l I P address fo r mach ine “A” and then send tha t response packet on to mach ine “A” .

A s ide eff ec t o f NAT i s t ha t mach ines on the in te rne t canno t i n i t i a te commun ica t ions t o l oca l mach ines – they can on ly respond to commun ica t i ons in i t i a ted by those l oca l mach ines .

The ne t eff ec t i s tha t the rou te r then a l so ac t s as a fi rewa l l :

ROUTER

A b r idge dev i ce fi l t e rs da ta t raffi c a t a ne twork boundary. B r idges reduce the amount o f t raffi c on a l oca l a rea ne twork (L AN) by d iv id ing i t i n to two segments .

Br idges opera te a t the da ta l i nk l ayer (Layer 2 ) o f the OS I mode l . B r idges in spec t i ncoming t raffi c and dec ide whether to fo rward o r d i sca rd i t . An E thernet b r idge , fo r examp le , i n spec t s each incoming E thernet f rame - i nc lud ing the sou rce and des t ina t ion MAC addresses , and somet imes the f rame s i ze - i n mak ing ind iv idua l fo rward ing dec i s i ons .

Br idges se rve a s im i l a r func t i on as network sw i t ches tha t a l so opera te a t Layer 2 . Trad i t i ona l b r idges , t hough , suppor t one ne twork boundary (access ib le th rough a ha rdware po r t ) , whereas sw i t ches usua l l y off er fou r o r more ha rdware po r t s . Sw i t ches a re somet imes ca l l ed "mu l t i - po r t b r idges" fo r t h i s reason .

BRIDGE

A network ga teway i s an i n te rne twork ing sys tem capab le o f j o in ing together two ne tworks tha t use d iff eren t base p ro toco l s . A network ga teway can be imp lemented comp le te ly i n so f tware , comp le te ly i n ha rdware , o r as a comb ina t i on o f bo th . Depend ing on the t ypes o f p ro toco l s they suppor t , ne twork ga teways can opera te a t any l eve l o f t he OS I mode l .

Because a network ga teway , by defi n i t i on , appears a t t he edge o f a ne twork , re la ted capab i l i t i es l i ke fi rewa l l s t end to be i n teg ra ted w i th i t . On home networks , a b roadband rou ter t yp i ca l l y se rves as the ne twork ga teway a l though o rd ina ry computers can a l so be confi gured to

per fo rm equ iva len t func t i ons.

GATEWAY

In comput ing, a fi rewal l i s a so ftware or hardware -based network secur i ty sys tem that contro l s the incoming and outgo ing network t raffi c based on app l ied ru le se t . A fi rewal l es tab l i shes a barr ie r between a t rus ted, secure in te rna l network and another network (e .g . , the In te rnet ) that i s not assumed to be secure and t rus ted

Many persona l computer operat ing sys tems inc lude software -based fi rewal l s to protec t aga ins t threats f rom the pub l i c In te rnet . Many routers that pass data between networks conta in fi rewal l components and, converse ly , many fi rewal l s can per form bas ic rout ing funct ions .

FIREWALL

Wire less access points (APs or WAPs) are specia l ly confi gured devices on wire less local area networks (WLANs) . Access points act as a centra l t ransmitter and rece iver of wire less radio s ignals inc luding Wi-Fi . APs are most commonly used to support publ ic Internet hotspots and a lso on internal bus iness networks to extend the i r Wi -Fi s ignal range.

Access points on home or smal l bus iness networks are smal l , dedicated hardware devices featur ing a bui l t - in network adapter , antenna, and radio t ransmitter. Wire less routers for home networks inc lude bui l t - in access point funct ional i ty as part of the device. Standalone WAP devices a lso exist for both home and business use.

Although Wi-Fi connect ions can funct ion wi thout access points in so -cal led ad hoc Wi-Fi or peer- to -peer mode, access points support Wi-Fi infrastructure mode. Infrastructure mode br idges the wire less local sub network wi th a wired Ethernet sub network and a lso scales the wire less network to support more c l ients . O lder access points a l lowed a maximum of only 10 or 20 c l ients , but modern APs support up to 255 c l ients

WIRELESS ACCESS POINT

COMPUTER NETWORK

http://compnetworking.about.com/cs/wireless/g/bldef_ap.htm

http://compnetworking.about.com/od/networkdesign/g/network-gateway.htm

http://askleo.com/whats_the_diff erence_between_a_hub_a_switch_and_a_router/

http://compnetworking.about.com/cs/internetworking/g/bldef_bridge.htm

http://en.wikipedia.org/wiki/Computer_network

REFERENCES