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Re: DHCP!




Nelson Guedes Paulo Junior wrote:


Hi,

I've copied my hard drive to another hard drive using dd. The machines
are almost the same, but the first one was from another person. After


I have seen problems doing this using dd. If the hard disk is IDENTICAL it usually has no problem. However, if they are not identical, the drive copied to becomes exactly like the one copied from. CHS and LBA become the same regardless of the actual physical size of the drive. The partition table and the drive physical information are overwritten.

Better and more flexibility are achieved by using one of the backup/restore applications available such as mondoarchive that copies the data but does not overwrite the drive physical configuration.

the copy, I've noticed that the machine was working in the network, wich
seems impossible because I have a DHCP server witch atribute IP address per
MAC address.


Not so impossible. DHCP assigns an address to an adapter. If the config is set to only allow handing out addresses to known and listed devices and to prevent handing out addresses to unknown MAC addresses, then yes it should not happen. (see comments below)
The common config is to set the MAC address/IP address pairs for those such as servers that are wanted to have static IP, and to allow most others to get addresses in the range allowed.


After that I've noticed that the file ifcfg-eth0 on my system had the followwing
line:

HWADDR=xx:xx:xx:xx:xx:xx


This line specifies the specific device to be used. It does not AFAIK physically change the MAC address, only ties that MAC address to the eth0 device. Using the redhat-config-network tool will write this line with the MAC address ot the adapter that is installed.

And the MAC in there, was the MAC of the NIC of the first machine, not
the one I'm running now.

My question is, it's not a security flaw let someone change the MAC that
way???


It can be a flaw if the line physically changes the MAC address reported to and used on the network. See my comment above. NOTE: This file is written by and can only be modified by the root user on that PC.

With a reread of your comments above it seems the physical MAC address may be overlaid by the MAC address from the ifcfg-eth0 file. That can provide a security risk, but must be evaluated in its impact.

It also can be of benefit in cases like you describe where the network is set for IP mapping to MAC and different hardware would have a different MAC and thus not allowed to connect via DHCP. A copy of the config file would allow that one to connect anyway it seems.





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