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

Reply to
Dusty
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The consensus and associated conspiracy theory is that it's because some companies are too cheap to buy sufficient MAC addresses: 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 ??

Reply to
Jeff Liebermann

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.

Reply to
Dusty

formatting link

Reply to
Dusty

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.

Reply to
Jeff Liebermann

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

Reply to
Dusty

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.

Reply to
GlowingBlueMist

That is a good idea.

Reply to
Dusty

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.

Reply to
Char Jackson

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?

Reply to
Dusty

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