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Mobile Internet with 4G router: problems with IP

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I have a SIM card for 4G internet access at my secondary residence, which I use in my 4G router (Huawei). Everything was working fine, but the provider (NOS) must have had a noticable increase in traffic over the last months, so I changed the SIM card with one of the competition (Vodafone). These are pre-paid cards, costing 30 Euro for 30 days. I know there are cheaper deals, but they come with a 2 year fidelity contract, which I am not interested in, because I expect fiber to be available in some not so far away future.

So my problem is that with the new Vodafone SIM, ocasionally, the internet does not work. I know that because all the surveilance cameras get offline. After 2-3 days, they become active again, without any intervention.

Today I was there when it happend. Unfortunately I did not have much time, but what I discovered is that the router changed the DHCP settings from 192.168.3.X to 192.168.4.X! Also, it seems that the WAN I got assigned is actually from 192.168.3.X subnet. This explains why the DHCP server started to hand out IP's in a different subnet than the one I originally configured.

Is this even possible? I know that mobile internet providers use NAT instead of giving an individual IP address, but can they be using private IP addresses instead of public ones?

I think that this is what renders my network useless: because I am using mainly fixed IP addresses (settop boxes, access points, etc.), if the router/gateway is in a different subnet, nothing works.

Also, I think it gets back to normal after a few days, when the lease of the WAN IP terminates and I get assigned a WAN IP in the a different range, which causes the router to switch the DHCP server back to giving out 192.168.3.X addresses, as it should.

But this is weird: how does the router "remember" the former IP settings? And how does it adjust the settings automatically?

Any ideas on what is going on? I don't want to have to reconfigure all devices in my network and I have no guarantees that Vodafone is not using any other subnet within 192.168.X.X.



--- Quote from: Bicurico on August 06, 2022, 09:56:06 pm ---Is this even possible? I know that mobile internet providers use NAT instead of giving an individual IP address, but can they be using private IP addresses instead of public ones?

--- End quote ---

Yes, it's done. I just turned off WiFi on my mobile and used 4G mobile, and I've got a 10.x.y.z address. Nothing says that a mobile provider has to give you a public IP. Vodafone use of the 192.168.x.y range is risking collision with routers, but then maybe they didn't expect people to use routers, unlike fixed broadband.

After spending some time with the 4G router, I ended up doing a factory reset. After reconfiguring everything, my network and the internet access seem to work normally again.

In the end I did not fully understand what caused this reoccurring issue. I just hope it won't happen again.

And yes, Vodafone is also using a 10.x.x.x IP for 4G, so I must have had some other weird issue.


there are 3 prefixes for local networks..

most commonly used are the 192.168/16 and 10/8 , just use something from 172.16/12 and you'll be fine ;)

Not convinced... I would assume the class C 192.168.n.n/16 network is defined by the DHCP server on your router. The 4G link is the gateway address - which is often a class A or B range on 4G masts. I suspect some other glitch. Insure the DHCP server on the router is nailed down (fixed) to 192.168.3.n/24 - That's subnet

I should add, make sure all devices on your LAN get IP their from the router's DHCP server and, their own onboard DHCP servers are disabled. A possible conflict can occur when there are two DHCP servers on the same LAN - the router might get an IP from the rogue DHCP server!


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