Rapid changes in my Dynamic IP Address

  • 4 November 2022
  • 31 replies
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Recently the dynamic public IP address assigned to me by T-Mobile Home Internet service started behaving differently.  The IP address (reported by google when doing a google search for “what is my ip address”) changes very rapidly,  about once per second, sometimes even faster.

This is very strange.  All the dynamic IP addresses I’ve had assigned in the past by other internet service providers (cable, dsl, etc.) did change over time,  but the changes were only once or twice per day,  not once per second.

The problem with the rapid changes is that some websites detect IP address changes and consider this a security risk.  For example if I’m trying to log in to a website,  I will enter my username and then enter my password, but when I click “login” button the website will take me immediately back to a blank login page.  Or when I try to log in to webmail at my domain hosting provider it will post an error message saying “your IP address has changed...” and won’t let me log in.   Again, some websites are sensitive to the rapid IP address changes,  others are not.

I did not experience these problems when I first started using T-Mobile Home Internet service (early part of this year) on the specific websites that are currently having problems,  so the rapidly changing public/dynamic IP address seems to be a recent issue.

Since my public dynamic IP address is assigned by the T-Mobile system,  that’s where the problem exists.  It is not a problem with my computers, home network, etc.

I made a screen capture video showing the rapidly changing IP addresses - I hope the T-mobile engineers (I have a support ticket submitted) can view this video to help understand what’s going on.  Anyone can view the video, here’s the link:

Demonstration of Rapidly Changing Public IP Address

 

 


31 replies

No, I am not with TM… just another customer impacted by this issue who happens to be pretty familiar with networking.  

 

Mike

ugh… well, add IRS.GOV to the list of sites that do not play nice with the rapid changing IP address for logins. https://sa.www4.irs.gov/ola/

I have to switch over to my slow DSL line that at least retains a public side IP address for days.  Otherwise the IRS site during login just says “A technical problem has occurred. Please try your request again later.”

I’ve been struggling with this IP-4 address “switching” every couple seconds as well.  I found that getting a VPN seems to have solved all my issues.  I now seem to have a “static” IP-4 and am able to login to sites, FTP etc.  I’m using Nord but I’m sure any VPN service will work.

Yep, using a VPN is a workaround for the T-mobile NAT issue (Your IP address is not really changing, just the t-mobile NAT’s (network address translation) it differently for every new connection to a different destination IP).  if your IP was actually changing, the VPN would be disconnected every time it changed.

 

By using a VPN you are using the VPN providers to be your exit point for all  your traffic that goes out to the internet, and they do not have a NAT issue.

 

Mike

Software engineer of 20 years here, you can demonstrate this easily with a single powershell script aimed at the Rest service provided by no-ip that you can trigger when your ip change. It is changing as many as 10+ times second, but they appear to be from a set pool, just random order. 
 

i suspect this is prevent abuse of people hosting services behind dynamic ips, because I was flustered as well. It forces segmentation into business and consumer, but is a pain for DNS adblockers, which is why I even am as far down this rabbit hole as I am. It makes sense though from t-mobile standpoint though. But it completely breaks DNS ad blockers so my business just lost a ton of money invested in AdGuard. T-mobile, you are breaking those of us using services that rely on ip for identities and id 

 

also, this breaks authorization and proxies. All on all a horrible solution. Just watch egress, that’s it. 

Yep, this is a mess,  I do not think it is intentional, rather a misconfiguration of NAT64 device, or faulty firmware for said device that has been rolled out to Minneapolis region first.  Again, your IP address is NOT really changing..  However at the NAT device within T-mobiles Minneapolis core, a new source IP address is being utilized for the NAT translation for every new outbound connection.  Another possible reason would be that they have deployed a set of NAT64 devices behind a load balancer, and your traffic is being “load balanced” to a different NAT64 device with each new connection.  In any case, traffic from your real IP address, if it needs to be NAT’ed, but be NAT’ed to the same outbound side source address for every new connection, otherwise it breaks a great many sites on the internet and renders the internet gateway unusable.

 

It is easy to confirm that NAT is taking place, by using your t-mobile phone hotspot, and look at the the IP addresses that have been assigned by DHCP to your phone. (The internet gateway does not appear to let you see this information).   Go to any of a number of hosts that display your IP and note that the IP address the site reports, is not the IP address assigned to your phone.   Go to a different site that reports your IP address, note that it is different, and also note that your phone’s IP address has not changed.

 

Mike

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