Frustrating Mac address

Whenever I run a program to check machines & IP addresses on my
network, I notice that my tablet IP address keeps changing. I went
into my router settings and assigned a specific IP address to each
Mac address. The IP address still changed. Finally I noticed that
every time the tablet reboots, it gets a new Mac address.

Why does this happen?

Should this be able to happen?

I thought Mac addresses were permanent?

I only have five devices on the network, and wanted them to
go from 192.168.1.2 to 192.168.1.6 instead of jumping all
around like the tablet getting 192.168.1.16 sometimes, then
192.168.1.28 another time, or any number in between.

This is a Chinese tablet, called Dragon Touch. It's inexpensive but
it's good, except for the Mac address problem.

There doesn't seem to be a way to specify a permanent Mac address
in the settings.

Could having the Mac address keep changing be good for security?

Curious & frustrating

 

The consensus and associated conspiracy theory is that it's because
some companies are too cheap to buy sufficient MAC addresses:
<https://code.google.com/p/android/issues/detail?id=23330>
<https://code.google.com/p/android/issues/detail?id=23330#c9>
<http://standards.ieee.org/develop/regauth/oui36/index.html>
Judging from the code fragment, it seems to be intentional. Using a
random MAC address within a small MAC address space, allows
considerable MAC address reuse and saves the manufactory about $645
for 4096 addresses or about $0.16/address. If you're shipping 10
million devices, that's $1.6 million saved, so this not spare change.
In the distant past

That also suggests it's intentional.

That's a minor reason compared to the cost. If you include anonymity
and stealth as part of "security", then yes. There are numerous apps
for PC, MAC, OS/X, and various devices for changing the MAC address.
The idea is that it makes the device more difficult to identify. I
guess the Dragon Touch people decided to make it a feature.

Strictly speaking, there's nothing really wrong with random MAC
addresses, except that filtering by MAC address won't work, the log
files will be a mess, the ARP table on the router might overflow if
rebooted too often, ethernet switches might complain, and various
authentication schemes for VPN's might fail.

Do your MAC addresses begin with 00:90:4C ??
<http://forums.androidcentral.com/ve...7-wifi-mac-address-changes-every-reboot.html>

 

When I did a factory reset, then reinstalled VPN One Click it wouldn't
show that I still had ten months left on the subscription. I had to work
with tech support quite a bit to get the problem worked out.

They start with 00:08:22

Thank you Jeff
When the alien overlords take over earth, you will be protected.

 

There are various methods of VPN authentication. It has to be
something on your machine that does NOT change. Usually, it's the MAC
address, sometimes the IP address, and in desperation, a login and
password. Yeah, I can see a problem.

I found this work around for a different phone, but which seems to be
usable, if your tablet is rooted. You get to pick your own MAC
address, which has its limitations and dangers. The MAC address does
NOT go through the router to the internet and is used only on your
LAN. The only exceptions I can think of is the VPN authentication
problems. With a limited number of machines on your LAN, chances of a
duplicate MAC address is minimal.
<http://forum.xda-developers.com/showpost.php?p=32222083&postcount=8>

 

There seem to be a jillion ideas on how to root a tablet, which,
so far, haven't worked on this one.

 

With only having 5 devices on a network and only 1 of them doing what
you describe, with the proper router you could still control it.

Set your DHCP limit to only assign 5 possible address values, 2-6.
Then assign every machine a "fixed" address except the problem device
using the routers ability to lock an IP address to a specific MAC
address. Reboot all devices so the new address values get assigned to
each of the non-problem devices by the router. The problem tablet
should now be forced to take the last available DHCP address every time
as the others would already be "busy" according to the router.

 

That is a good idea.

 

That's a creative solution, but it looks like there could be a potential
issue with the tablet.

Turn the tablet on and it gets its one and only available IP address via
DHCP. The other 5 addresses are reserved, so it gets what's left. Per the
router, the DHCP lease is good for X mins/hrs/days. Now, partway through the
lease period, the tablet is turned off, then sometime later but still within
the original lease period it's turned on again. It'll request an IP via DHCP
but now there are no DHCP addresses available. You have to wait for the
existing lease to time out and expire.

I suppose a workaround would be to set a very short DHCP lease period, with
the knowledge that doing so will affect all 6 of the OP's network devices,
since the lease setting is global. What would be a good lease duration? 10
minutes, so everything renews every 5 minutes? Just thinking out loud. For
me, my DHCP lease period is currently 24 hours, but I've seen NAT routers
that default to 7 days. Such a long period clearly wouldn't work for the OP
and his crazy tablet.

 

There doesn't seem to be a way to set DHCP lease time on this router.
It shows when the lease began, and when it ends.

I've enclosed a link for the router Manuel if you want to see if you can
find a way, if I missed it.

The other routers can change lease time, but the way the network is
set up, this router needs to cover the center of the house, while the
others cover the ends, unless I wire in a switch, then use the WAP in
the middle and put this router at the end, but the WAP is old and tends
to overheat so I only plug it in when needed. If I get another WAP it
will be an outdoor one for long range.

I wonder if the long range WAP will cover the whole house if I put it at the
end, about 6ft above the roof?