Network+ Tutorial Oct 28 08 _01

[Q355]

What is ARP ?

It is Address Resolution Protocol

It is on Layer 3 ( network Layer )

Address Resolution , means , resolve/translate/mapping Address "A" to Address "B". In this case , ARP is translate IP address to MAC Address .

Why we need to Resolve/Translate IP Address to MAC Address ?

As we know , all the data , ultimately , need to reach NIC before the data move into workstation In the other words , the data need to be transfered through NIC before it reach our workstation .

In order to reach NIC , we need to have MAC Address .

MAC Address is NIC’s address . If the data need to send to NIC “A” , we must know the NIC “A” MAC Address .

So, in order to reach NIC , we need to “transform” the IP Address become MAC Address then the data only can reach the NIC .

Which mechanism help us to translate IP Address to MAC Address ?

ARP . It translate IP address to MAC Address .

How ARP Work ?

Say , Host#1 need to communicate with Host#2 . It will broadcast the IP Address ( from layer 3 , IP address is at layer 3 ) and ask every host on the network which host own this IP Address . Once Host#2 receive this broadcast ( we call it as ARP Request ) , the Host#2 will reply to Host#1 and tell the Host#1 , this IP Address is belong to him , at the same time , Host#2 will attach its MAC Address and return back to Host#1 .

Once Host#1 receive the information from Host#2 ( this information contain host#2 IP Address & MAC Address ) , host#1 will cache ( temporary store ) this information in its ARP table .

We also call ARP Cache as ARP Table . This cache/table contain the info of IP Address mapping MAC Address.

Once Host#1 getting the Host#2’s MAC Address , Host#1 will forward the data to Host#2’s NIC .

Which command Utility can display the ARP Cache ?

Arp –a will display Internet Address ( IP Address ) + Physical Address ( MAC Address ) + type of cache.

Type of Cache , means , whether it is static or dynamic.

Static, means , update the ARP table/cache manually.

Dynamic , means , update the ARP table/cache automatically

You need to run the command of “arp –a “ to see the actual output of this command in order to understand above explanation.


[Q356]

If we cannot connect/access to Internet , there could be few factors :-

1. Connectivity problem among the network devices ( Hardware Problem )
The connectivity could be connector ( RJ45 ) , cable ( UTP cable ) , port ( hub/switch’s port )
, switch / NIC / Router firmware “hang” .

Just reset or power off and power on the switch / hub / router / NIC will reset the firmware
issue.


2. Configuration problem ( SOFTWARE Setting Problem ) . The Network Properties setting
incorrect ( wrong setting ) or incomplete (one of the setting never set , left empty ) .


What is Network Device ?

NIC , Switch , Hub , Router , Printer etc

What is Network Properties ? ( in window based system , also call it as TCP/IP Properties )

Subnet Mask ; Workstation IP Addrsss ; Default Gateway Address , DNS Server Address.