Dyndns with exposed host

Recently moved to Bamberg, got DSL with preconfigured router from Bambit just this week. I went for this option since there was no discount for the "no router" option and, also, I did not have a VDSL2 modem for the German networks.

The preconfigured FB 7530AX I received does not have bridge mode, however there is apparently a workaround whereas one would enter false credentials for DSL and then enable PPPoE passthrough. I can read the username from the web interface but the password is off-limits so, as much as I would like to terminate the PPP session on my own router, I am out of luck. Asking for the credentials right after ordering the preconfigured unit is doable, but I'd rather avoid it.

At the moment I have set my router as "exposed host" and it seems to work, but I can already anticipate an issue: when the forced disconnection occurs, my own router will not learn about it. To keep dyndns working I would need to shorten the polling interval enough to catch both planned and casual disconnection.

Are there other ways to go about it?

Doesn't the 7530 have its own ddns client?

The legal situation in Germany is simple, you are allowed to use your own (compatible-) modem and they have to supply the access credentials, all ISPs should have accommodations for that (in most cases on the contract info or their webinterface). Their network ends at the passive plug (first-TAE, rj-45, ...), everything behind that they may offer to rent out, but you don't have to take it.

By now, ISPs should have this implemented and hand out the credentials at least on request (GPON ftth credentials can be more difficult, but especially VDSL is simple).

My advice would be to leave the Fritz!Box untouched (respectively to use it until you have a replacement) and to get a cheap second hand VDSL modem - profile 17b (for deployments up to 100/40 MBit/s) compatible ones can be found for 5-20 EUR, just profile 35b (for deployments up to 250/40 MBit/s) capable modems tend to be a bit more expensive. In that case you can still use the Fritz!Box for your SIP (landline) phone needs, in IPoE mode behind your OpenWrt router.

Yes, it does though I'd have to check if it supports DuckDNS.
EDIT: it doesn't but apparently it can be extended.

Given that I have already chosen the "with modem" option and, crucially, that I did not have to pay extra for it nor would I have received a discount for skipping it, buying a new one simply to avoid a sw workaround is perhaps overkill.

That is assuming I could find it in that price range, ebay kleinanzeige doesn't have anything and amazon has more expensive stuff. Where would I find such a cheapo unit, then?

I am not worried about asking for the credentials, I know the legal situation... I am simply concerned it might look bad, after all I could have opted for "own modem" directly but I had not anticipated trouble in getting the credentials to apply the passthrough workaround.

EDIT: it seems the current configuration of ddns is already catching the forced disconnection even without an explicit notification from the 7530, good!

It turns out that dyndns can alread deal with this scenario, even if not as promptly like with a real modem.

        option ip_source 'web'
        option ip_url 'http://checkip.dyndns.org/'

The default value of check_interval (10 minutes) is more than enough to catch daily disconnections and probably also for random ones.

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@slh would an italian Zyxel VMG1312-B work here in Germany? I left it in my previous place because, well, the car was already full and I thought it was anyway the wrong annex. (EDIT: for one thing, the socket for DSL on the back on the 7530 seems like a normal ethernet port whereas on my Zyxel seems a phone socket)

Yes, to all intents and purposes, for VDSL the Annex does not matter, this is only an issue for ADSL lines. NB: Lacking a gigabit port, the VMG1312 will cap your downstream hard at the 100 mbit its fast ethernet port can deliver.

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Right, I forgot about that... I'll make some more tests in april when I go back to Italy, otherwise I'll probably stick with the 7530AX / exposed host configuration.

For VDSL ports, both rj-45 and rj-11 are common (and in rare cases TAE).

The VMG1312-B30A works reliably, but as takimata mentioned, its 100 MBit/s fast-ethernet ports may cost you ~5-6 MBit/s (as ISPs tend to establish link rates just over 100 MBit/s raw data rate for their 100/40 MBit/s contracts, if you're close to the DSLAM). That's not necessarily a reason not to use it, if you already own one for free (at least it gives you options).

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