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my goal is to set up VPN Server on the remote router and connect to it via WWW with a VPN Client. To avoid fixed public IP I use DynDNS service (no-ip) and it seems it is working (I see both in noip and router that the record is updated).

How can I check that the router is really accessible with its name via internet? I'm trying to ping both DNS name and its updated IP but it is not responding. But should it actually?

The Router is Robustel R3000. It is connected to WWW with 4G internet (Cellular, SIM)

UPD: added some pictures with router status

router status

noip record updated

router log - noip updated successfully

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  • First of all, does the router actually have a public IP address? Have you verified that its public address shows up on the router's own status screen? Especially for cellular connections, this could very well be different from the address reported by external services (see: CGNAT).
    – grawity_u1686
    Commented Jan 18, 2021 at 19:35
  • @user1686, in router status it shows not public IP but ip taken from provider NAT, you are right(Orange GN, sim card). But in the log of the router it shows that it updates noip record with public ip. I added some pictures. But the strange is, that I tested such a connection but with another cellular provider (Telekom DE) and it was working somehow
    – Ignat Talitskikh
    Commented Jan 19, 2021 at 7:22
  • But that's just the address seen by your DDNS provider, it doesn't mean the address is exclusively yours.
    – grawity_u1686
    Commented Jan 19, 2021 at 8:27
  • @user1686, thank you, now I got it. before I tested it with Telekom DE SIM Card and it gives me dynamic but public IP. now I have SIM Card from another provider (Orange GN) and it seems it has its own CGNAT and it gives IP from its own range. But NOIP gets IP of the Orange DNS. I have to use another SIM Card or Tariff or etc.
    – Ignat Talitskikh
    Commented Jan 19, 2021 at 9:02

2 Answers 2

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in router status it shows not public IP but ip taken from provider NAT, you are right(Orange GN, sim card).

Because you're behind provider NAT (aka CGNAT), there's a very high possibility that it's "1-to-many" NAT – i.e. the public IP address is shared between several customers and the ISP is unable to forward any inbound packets to any specific customer.

In such case, lack of ping response would be normal. (Maybe you're pinging the provider's CGNAT gateway and it's configured to not respond, or maybe you're pinging a "virtual" IP address that only exists in the NAT pool but has not been assigned to a physical device.)

Even if provider NAT weren't an issue, some cellular providers deliberately block all inbound connections if the customer hasn't ordered a static IP address.

But in the log of the router it shows that it updates noip record with public ip

The log message merely reports the public address that was seen by the DDNS service. External websites will always see you connecting from some public IP address – but that doesn't mean the address is exclusively yours.

But the strange is, that I tested such a connection but with another cellular provider (Telekom DE) and it was working somehow

Each ISP manages their network differently – it is possible that Telekom DE was using 1:1 CGNAT (which does allow incoming connections), and it's even possible that the provider wasn't using any CGNAT at all.

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  • that's it, @user1686. Thank you!
    – Ignat Talitskikh
    Commented Jan 19, 2021 at 9:06
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Yes. It should. If you say that you can access the web interface but cant ping, probably the SNMP protocol is disabled at the equipment. You should check if the protocol is enabled at the Robustel.

At the "Access Control Settings" you should have the option "Enable Remote Ping Respond". verify if the state is ON.

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  • That would be ICMP, not SNMP.
    – grawity_u1686
    Commented Jan 19, 2021 at 8:20

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