In the aftermath of my recent events I am going to write my observations.
Incoming long post
Prior to the powercut I had my asus rt-n66u and hg612 openreach modem connected and all was good. I've had this setup for over a year and never had any issues with either device. To setup the router I had to follow some basic instructions, which worked first time.
On Sept 12th I had 2 powercuts. I say two because when the power came back, within a minute it was off again, then back on.
After this happened I could no longer get on the internet. Both the router and modem said there was a connection. But I could not connect via my ethernet connected computers (I have 2 pc's and 1 laptop).
When trying to access the router via my pc the gateway ip to the router wouldnt connect me, and instead said that the ip and or port number had been changed. It suggested I use a wifi device to connect to the router and make changes. So I picked up my phone and typed in the same gateway ip and was able to access the router controls. The connection to the page was intermittant with sometimes the pages not fully loading up.
While looking at the router configuration page I noticed both the gateway and subnet had changed. The subnet mask changed from 255.255.255.0 to 255.255.255.255
I spent the rest of the day trying to figure out what that new subnet mask meant. Some people said its connected to having a static internet ip address. Others said it was a broadcast ip address that isp's use, while a couple of people said it puts the router on its own sub network and would be inaccessable.
In the LAN section of the router there is an opportunity to change the LAN IP address of the router, like the gateway ip. I tried changing this back to how I had it before. But it wouldnt change back. The option box on that screen was to change the subnet mask back to 255.255.255.0 , by pressing apply this did nothing. I should point out I was unable to access the router on pc even using this new gateway ip that appeared.
On my machines I have them setup as static lan ip addresses. So in an attempt to gain access to the router (and hopefully the internet), I set all ip settings to accept whatever was being given out by the router. I saved and closed the box and still no joy.
I should also mention that the cctv camera system I have setup is connected to the router so I'm able to view the cameras from all my computers. After the powercut the connections become intermittant. So something had changed in the routing of the router.
After trying a couple of power downs of the router and leaving it off for about 15 minutes only to find powering it back on the settings were still the same I was faced with the possibility of a factory reset OR I could use a backup rt n66u which I'd bought ages ago as a backup. It was still in the wrapping paper unopened.
I changed both the router AND also the hg612 to one I'd updated the firmware to the correct one.
Switching these 2 devices on, and setting them up exactly had I'd done before, again this 255.255.255.255 subnet was still there and so was this unusual gateway ip. So this really eliminated the possibility that the first router and OR modem had been damaged, if the new devices were doing the same thing.
After this I was kind of urged to get the smart hub 6 from bt as they didnt want to send any engineer out until I had their kit installed. So I managed to get a deal and paid just over £100 for it.
After setting the hub up I found it worked. I noticed that the subnet on the device was back to 255.255.255.0 and the gateway was also correct. It actually connected 7Mb's higher.
The conclusion.
During all this a number of other devices in my house went off and stopped functioning properly. Including the kitchen light, a microwave appeared to be broke and also my other pc which I turned on this morning had a bios issue and had loss time, the time it stopped at was when the powercut happened.
Now.. for the odd thing. Last night I noticed all the lights were giving off a low light. Like they didnt have full power. Then as I said in my last post the power went off again last night (Sept 13th) for 5 minutes and back on. When it came back on the lights were bright again. The kitchen light that had stopped working suddenly worked, as did the microwave.
I suspect what happened is when the power came back on the 12th, they set it to lower power (there are electrical digging going on according to roadworks website fixing low voltage cables), and this low power stopped some devices working properly, while others it stopped them working totally.
So my theory is, if I was to put my rt-n66u router back on, and the hg612 modem, I'm betting they would work correctly now.
Sorry for my long post but I thought it might be of value for other people having issues after a power cut. To help them go through things like I did.