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Mobile Internet with 4G router: problems with IP

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Bicurico:
Hi,

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.

Thanks,
Vitor

retiredfeline:

--- 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.

Bicurico:
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.

Regards,
Vitor

rob77:
there are 3 prefixes for local networks..

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

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

AndyBeez:
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 255.255.255.0

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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