The hideous beast known as Elisa VDSL Kotiboksi
It was a sunny Thursday morning, when a co-worker paged me over Slack, letting me know the brand-spanking new VDSL line had been installed just a few minutes ago. Despite knowing the glorious speeds of 50M/10M Interwebs I would have available at the office, I dreaded of how the VDSL was installed: Elisa used to cater to consumers and companies alike until they bought another competing operator, which later became a subsidiary (Saunalahti). After this structural change, Elisa mostly dropped all consumer products and primarily focused on companies, while Saunalahti was the cheaper consumer brand, which later also began to cater companies as well.
After arriving at the office, having been informed the internet was down and everything was about to blow up because of it, I took a long glance at where our trusty Cisco 877 ADSL/service router once was, the CD light blinking, desperately trying to indicate the ADSL connection would be back any time soon. Alas, it was for naught as the PoTS cable had already been moved to the newfangled VDSL modem/router/monstrosity.
"Our internet is down" chimed in the co-worker who had paged me earlier on Slack. "Yes, and I know exactly why..." I replied while pointing towards the aura of death oozing from the black box of doom. Only lights that were lit on the device were power, two wifi indicators (dual-band, only redeeming feature on this device) and the bright green "Internet"-light, showing that it indeed had cats ready to flow through the tubes. Had it been connected to the router that serves as our office firewall/wifi hotspot/NAT, the internet might have worked, apart from a few port forwards for VPN and SSH.
I drew a long sigh, sat down at my desk, grabbed my laptop from my shoulder bag and set it on the docking station, booting up Ubuntu and preparing for the worst... but not without coffee. I sensed that the need of a pencil to push the reset button on the back and thus moved the modem to my desk for better access. Oh how well did I know beforehand what sort of adventure I would be embarking on.
The box in question is a ZyXEL VMG3926-B10A, and despite the very specific model number, this model does not exist, according to ZyXEL support. The reasoning behind this is, the model is meant to be sold only to ISPs, who then forward this pestering pustule to their customers. Some rumours say this model has an almost identical consumer model, but that's enough of that.
Due to our network infrastructure, we only need the thing to spew unlimited interwebs to our router and other devices. The instructions for bridging are quite short (seriously, they read "please see this other model for instructions") and when followed, you will not get the external internet unless you unplug all cables that are connected to your internal addressing space. This was quite a facepalm when our router would ask for an IP, get a response from itself and then assign the same IP to itself on the WAN port. Going around what guide suggests and forcing the WAN connection on the modem to be bridged resulted in the same issue: the ethernet switch has no separation between ports, regardless of what the web interface says or has configured.
This has taken me more time than what I would expect of a device that actually works and am quite cross with the damn thing by now. I decided to give up on the dream of having a management connection to the device from LAN and it probably advertises all sorts of fun bits to the outside internet.
our router would ask for an IP, get a response from itself and then assign the same IP to itself on the WAN port
Why would a modem/router in bridge mode ask for an IP on the WAN port?
Also, good job masking your internal IP that nobody outside your network can connect to anyway.
At consumer quality, if the thing's properly in bridge mode it's only passing packets along. It might still function as a working (wan) switch but it won't have an IP address of its own.
There is also the Elisa Viihde combined TV receiver / modem / WLAN router, a device that I have never personally owned though I have once had the diabolical misfortune of configuring one.
In summary, I lost my faith in humanity when I realized that you need to log in to Oma Elisa to configure the device, which then fetches all your settings from Elisa's server. Provided, of course, that it can access the Internet.