6sn7
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Raspberry Pi 3 B MAC Address Suddenly Changed

Sun Mar 11, 2018 7:32 pm

Hello,

I have a Raspberry Pi 3 B running jessie 8
It has been stable, survived a few power interruptions over the years and always came back up with no issues. This time when power was disrupted the following symptoms occurred:

The MAC address changed on the wired NIC (eth0).
A different IP address was issued from my router and I can ssh into it with the new address.
I can still ping the original IP address but get connection refused if I attempt to ssh to it.

What would cause the MAC address to change, and why would I still be able to ping the old IP address?

ifconfig reports no address on wlan0 and I don't use wireless on this system.

Thanks.

pcmanbob
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Re: Raspberry Pi 3 B MAC Address Suddenly Changed

Sun Mar 11, 2018 8:15 pm

Hi.

As the MAC is hard coded in to the pi at the factory it cant change unless you have some software that can spoof a new MAC.

You have not said how you IP was set.

DHCP from router
Static IP on pi
reserved IP on router

if the IP was assigned by the DHCP in the router a lose of power to the router will mean all devices get a new IP address but the MAC will be the same.
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n67
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Re: Raspberry Pi 3 B MAC Address Suddenly Changed

Sun Mar 11, 2018 8:19 pm

As the MAC is hard coded in to the pi at the factory it cant change unless you have some software that can spoof a new MAC.
No, you're wrong. I've seen this happen.

Power failures/aborts can cause just about anything to happen.
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mahjongg
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Re: Raspberry Pi 3 B MAC Address Suddenly Changed

Sun Mar 11, 2018 9:05 pm

A power failure cannot change the contents of a ROM, corrupting anything in RAM including a whole OS yes, ROM no...

6sn7
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Re: Raspberry Pi 3 B MAC Address Suddenly Changed

Mon Mar 12, 2018 10:47 am

Thanks for the replies.
The Pi is set up for DHCP.

When I power up the pi, my router leases two IP addresses; one for the original MAC, and yet another IP address for the new MAC address.

While the pi is shut down, or the Ethernet cable is disconnected from the pi, I cannot ping either of the addresses as expected.
As soon as the pi boots and the network is connected, I can ping both addresses. Can ssh into it using the IP address associated with the new MAC address, but cannot ssh into the IP address associated with the original MAC address. I have never seen this happen before and have several Pi systems.

Other than the above, the Pi seems to be functioning normally.

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DougieLawson
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Re: Raspberry Pi 3 B MAC Address Suddenly Changed

Mon Mar 12, 2018 11:51 am

Undo your changes in /etc/network/interfaces
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