MAC address are similar result in similar ip address

[zillah]

By using "a-change MAC address V5.0", I did a test within same LAN, I have got two laptop A and B with Nortel Acess Point.

These laptop are getting IP address form Nortel AP automatically. Type of ip address is 10.70.72.x/24.

IP address for laptop A is 10.70.72.93/25 , and MAC is 00-91-4C-2A-2B-2C.

IP address for laptop B is 10.70.72.141/25, and MAC is 01-80-4C-29-22-29.

I changed the MAC address for laptop B to be same to laptop A (i.e. form 01-80-4C-29-22-29 to 00-91-4C-2A-2B-2C ).

When I changed the MAC address , ip address for B has been changed to be same to the ip address for A as well,,,,,Why ? What is concept ? does it related to ARP protocol ?

I have not received notification message telling me that the are conflict in the ip addresses.

If laptop A tries to access the net first , then Laptop B can not access.

And if laptop B tries to access the net first , then laptop A can not access the net.

I tried to change ip addresses for one of the laptop , and keep MAC address similar for both of them, by configure laptop A manually with existing any ip address within the same LAN (i.e 10.70.72.141/25 has not been assigned to other PC within LAN) ),,,,,result still same I can not

 

[hawkstar]

The MAC address for each and every network card in the world is unique, so I don't understand what you are trying to achieve by altering them. So change it back to how it was.

You say that the Nortel has IP address of 10.70.72.x/24 but that Laptops have address of 10.70.72.93/25 & 10.70.72.141/25 - if this is correct then the subnet mask is wrong - it needs to be either /24 or /25 for all.

 

[zillah]

The MAC address for each and every network card in the world is unique,

Off topic:
The author for these two books disagre with you

1- "Data Communications and Networking"by Behrouz A. Forouzan, Ed3, Chapter 20, page 512 :

A MAC address is a local address. Its jurisdiction is a local network. It should be unique locally, but not necessarily universally

2- He mentioned in another book “TCP/!P Protocol Suite” , E3, Chapter 7,
Section 7.3 RARP, page173 :

The machine can get its physical address (by reading its NIC, for example), which is unique locally

.

so I don't understand what you are trying to achieve by altering them.

One of my friend he is doing his senior project "Wireless and Network Security", therefor he tried to simulate spoofing for the MAc address.

You say that the Nortel has IP address of 10.70.72.x/24 but that Laptops have address of 10.70.72.93/25 & 10.70.72.141/25 -

It was typo, all of them should be /24

 

[jjw]

IF there is a DHCP server in charge of handing out IP addresses then...

Until the IP address has been assigned by the DHCP server, the MAC address is all that is available to identify a connected device.


1) The PC broadcasts its MAC address requesting an IP address
2) The DHCP server responds with network configuration including the an IP address.
3) The PC uses this information to automatically configure the network interface

The DHCP server uses the MAC address to keep track of what devices have what IP address.

JJW