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2762N corrupted modem software? (resolved)

  • orbitalzone
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09 Oct 2020 14:19 #97390 by orbitalzone
2762N corrupted modem software? (resolved) was created by orbitalzone
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?

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09 Oct 2020 15:14 #97391 by admin3
Replied by admin3 on topic Re: 2762N corrupted modem software?
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



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  • orbitalzone
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09 Oct 2020 15:38 #97394 by orbitalzone
Replied by orbitalzone on topic Re: 2762N corrupted modem software?
Hi, thank you very much, I will give that a try and see what happens.

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10 Oct 2020 09:22 #97402 by orbitalzone
Replied by orbitalzone on topic Re: 2762N corrupted modem software?
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.
:D

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10 Oct 2020 09:58 #97403 by adrianh54
Replied by adrianh54 on topic Re: 2762N corrupted modem software?

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.
:D




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.

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10 Oct 2020 12:08 #97405 by orbitalzone
Replied by orbitalzone on topic Re: 2762N corrupted modem software?
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.

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