Zyxel VGMG1312-B10b and 3G backup

Peter Tselios
Peter Tselios Posts: 9
edited August 2021 in Home Router
Hello,
I have a problem with the under subject router.
I have configured a backup 3G modem and I see that the 3G modem:
1. Is recognized
2. Has signal
3. Can connect to the 3g network of the mobile carrier.

However,  when I try to browse the Internet ,nothing happens. DNS is not working,  browsing is not working, nothing works! When I connect the 3g modem on the PC, everything is fine.
I believe that the issue is not on the 3g modem,  since it works just fine, but something is configured wrong I  my router. Obviously, I can share any information needed.

Any idea how to troubleshoot this and fix it?

All Replies

  • tonygibbs16
    tonygibbs16 Posts: 384  Master Member
    edited July 2021
    Hello Peter,

    Regarding DNS not working, is the router set up to use DNS servers that only come from DSL provider? Does it work if you use Google Public DNS servers 8.8.8.8 and 8.8.4.4 in the router?
          - on the 3G backup screen? see section 5.3 of ftp://ftp.zyxel.com/VMG8324-B10A/user_guide/VMG8324-B10A_V1.00.pdf

    Kind regards,
        Tony
  • I have my own DNS server.
    But even from the router's troubleshooting page I cannot ping or traceroute or use the provider's dns servers.
    I will try to get some screenshot tonight.
  • Just to return after the fix of the typo in the title.
    The 3G Backup settings are the following:

    • Cellular Backup: Enabled
    • Ping Check: Enabled (20sec, Gateway, 5sec)
    • Authentication: Auto
    • Dial String/APN: Those provided by my ISP
    • Connection: Nailed Up
    • Obtain an IP Address Automatically
    • Obtain DNS Info Dynamically
    The connection does starts when I unplug the cable for example and I see that I get IP/DNS information from the mobile carrier. However, I cannot ping/traceroute/nslookup any server neither from the LAN clients, nor the router.









  • tonygibbs16
    tonygibbs16 Posts: 384  Master Member
    Hello Peter,

    Regarding the nslookup failures from LAN clients, are the LAN clients querying your own DNS server?

    If yes, then can your DNS server get to root servers via the 3G connection?

    Can you get a Wireshark log on your LAN client of an nslookup? What does it look like?

    If you told an LAN client to use your VMG1312-B10D router (e.g. 192.168.1.1) as the DNS server, then does the nslookup work with 3G connection?

    Kind regards,
         Tony
  • To answer your last question.
    All my clients ask the local DNS server and the router.
    The local DNS cannot access the root servers.
    I will take a tcpdump tonight or tomorrow morning.
  • And I had a breakthrough.
    Not the type O wanted but eventually I made it working. Now I will try to see if it's possible to use a newer Huawei stick

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