Hi, I have two 2762N modem routers (UK version) that have an issue as a result of a faulty BT phoneline:
I have FTTC, BT landline and Plusnet FTTC broadband and use a 2762N very reliably until recently my phoneline went very noisy and no calls could be made/received and the broadband connection became unusuable. Openreach found a shorted wire in the green roadside cabinet, once repaired my phoneline worked and broadband synched at 80/20 as it used to but many websites failed to load (some were fine though)
My second 2762N backup showed the same issues, no amount of rebooting, resetting configs would cure this issue, bare in mind they both worked perfectly before the line fault. I connected an Openreach fibre modem to the WAN port of the 2762N and have fast reliable internet again. Both devices were on 3.9.2_BT so I upgraded one to 3.9.4_BT, did a full reset, setup config for Plusnet VDSL and still get the same issue. It really appears both modems somehow got corrupted/damaged due to the line fault. I've tested using 4 different PCs, all hard wired, Draytek connects directly to VDSL socket on the master socket (fitted by BT when I got fibre)

It appears the line fault corrupted the modems in both devices, is that possible and could it be fixed?

If some sites load and some don't, that's usually down to MTU. Try reducing it a bit or use the path MTU detection. Maybe Openreach had to change some equipment and that's caused the different behaviour.

Guide here: https://www.draytek.co.uk/support/guides/kb-vigor-mtu-2

Hi, thank you very much, I will give that a try and see what happens.

Great news, lowering the MTU to 1492 resolved the issue... it had been at 1500 and had always worked without issue but as you said, the repaired line had perhaps had a change of kit and the MTU was more critical. Thanks once again for helping and I've learnt a bit more about these things.

orbitalzone wrote:
Great news, lowering the MTU to 1492 resolved the issue... it had been at 1500 and had always worked without issue but as you said, the repaired line had perhaps had a change of kit and the MTU was more critical. Thanks once again for helping and I've learnt a bit more about these things.

That is something to look out for if you factory reset, the router will default to 1500 MTU , PPOE works at 1492 or less.

My modem and router can use an MTU of 1508 , try it and the line is unusable.

Ah yes that might explain it then! - I did a factory reset, then rebuilt the settings from scratch but didn't notice the MTU may have changed itself. I ran the MTU test and it said 1492, so I'll leave at that and see how it goes.