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Archive for January 16th, 2008

MAC or Media Access Control is the other name for Ethernet Card Address. Ethernet was originally developed by Xerox then further developed by Xerox-DEC-Intel. Before the name was Alohanet. The name was taken from Palo Alto Research Center Aloha Network.

Ethernet was named by Robert Metcalfe. Maybe, Ethernet means carry data everywhere throughout the network.

MAC address is the true name for a computer in a LAN. It’s usually expressed with 12 digits hexadecimal number. (Example: 00:0d:88:b3:72:f3)

When you are connected to a LAN, your IP number will be translated to MAC address by a protocol called ARP (Address Resolution Protocol).

Let’s say, you use computer A with IP 192.168.0.2.

Computer B has an IP 192.168.0.3.

When you send a package to computer B, there are few steps run behind the scene. But these steps are based on LAN configurations. I’m sure that almost all LAN use star topology now.

The first generation of star topology use HUB to connect the all computers. Now, we use SWITCH.

Using HUB
When computer A (192.168.0.2) sends a package to computer B (192.168.0.3), first it will send a broadcast message to all computers in that LAN. Same like, when send a package to Alan, in front of the door, you scream, ‘Hey, who is ALAN?’. If Alan is there, he will say, ‘I’m Alan’ then you deliver the package to him.

Using SWITCH
When computer A (192.168.0.2) sends a package to computer B (192.168.0.3), it will send directly to computer B. Because Switch has everybody’s MAC address in its memory. So, you don’t have to scream.

What is the purpose MAC address for Administrator?

If you read my article about DHCP server,

http://taufanlubis.wordpress.com/2007/10/14/dhcp-server/

…..
…..

lease 192.168.0.199 {

starts 5 2007/10/05 22:37:02;

ends 5 2007/10/05 23:37:02;

tstp 5 2007/10/05 23:37:02;

binding state free;

hardware ethernet 00:0d:88:b3:72:f3;

}

….
….

You see that IP 192.168.0.199 is only used for MAC 00:0d:88:b3:72:f3. Mean, it won’t work if somebody try to use this IP address with another PC. Off course it’s very easy to hack because in Linux you can change your MAC address easily. If you know, :).

taufanlubis@toshiba:~$ ifconfig | grep Ethernet

eth0 Link encap:Ethernet HWaddr 00:A0:XX:XX:XX:XX

eth1 Link encap:Ethernet HWaddr 00:1B:XX:XX:XX:XX

eth0:avah Link encap:Ethernet HWaddr 00:A0:XX:XX:XX:XX

taufanlubis@toshiba:~$

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A Domain Name Server (DNS) for NAT networking could not be determined. Please, check your /etc/resolv.conf for nameserver entries. Either add one manually (man resolv.conf) or ensure that your host is correctly connected to an ISP. If you ignore this warning the guest will not be able to perform nameserver lookups and it will probably observe delays if trying so.

This error occurs when your Virtual Box’s guest try access internet but the main Operating System’s DNS hasn’t been set yet. To fix it, just add your Internet Service Provider (ISP)’s IP to your DNS.

In Ubuntu, the DNS file is /etc/resolv.conf.

Open System > Administration > Network > DNS and add your ISP’s IP to ‘DNS server List Box‘ then refresh the connection.

 

 

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