New beta firmware with new modem code if any wants to see if it sorts issues out on VDSL. It also limits MTU to 1500

https://www.draytek.co.uk/download/support/files/v166_0203_beta_126010_15.zip

Just run up a 166UK, updated to 4.2.3, connected on a BT Business G.fast service in Router mode. Works fine. It can take three or four minutes to sync. It is a comparable speed to the ZTLink MT992 modem, BT Business Smart Hub combination supplied by BT, 117 down compared to 103, 20 up in both cases, but no 4G Assure capability with the 166.

One strange thing was that it only wants to DNS in IPv6 so I had to enable in <Internet Access><IPv6>.

New beta firmware with new modem code if any wants to see if it sorts issues out on VDSL. It also limits MTU to 1500
That's a bit naughty, to comply with the Openreach specification the MTU should be 1508.
Sounds like an EU version that one of Draytek's developers hasn't tweaked properly.

SIN498 which states:- (I believe) "The modem shall support an Ethernet frame size of between 68 and 1534 bytes. For clarity, this figure includes 4 bytes for the C-VLAN, and excludes bits allocated to pre-amble, Inter-Frame Gap, and Frame Check Sequence at the user network interface (UNI). Support for frame sizes above 1534 bytes (inclusive of C-VLAN) is not guaranteed."

So Draytec are well within the rights to use a MTU of 1500 if thats the case. Also this firmware is for the UK version as it was sent by Draytec to me for my UK 166

When I asked DrayTek UK about buying the 166 (just before the UK version was released) I was advised not to buy the EU version as it had a max MTU=1500, & although it would work it wouldn't support Jumbo frames and so didn't meet Openreach's spec. (because it needs a min. MTU=1508). Sure enough the UK version arrived with a max MTU=1520 in the firmware. It's a shame they're blocking owners of the EU versions from flashing the UK firmware though, perhaps they could add a higher max. MTU to the next release of EU firmware? (I know a few people who bought them last year from Germany). Of course if someone should find a workaround to cross-flash UK firmware to an EU model I hope they will let us all know how they did it!

UK versions dont have to support jumbo frames from reading the sine, and the gain from doing so is tiny. If the original Openreach modems for VDSL2 were only had a MTU of 1500 and many ISP modems are limited to 1500 as well, then a MTU is fine as most routers will only do 1492 in the UK anyway (there are a few that will do 1500). Oddly enough the HG612 with a MTU of 1500 still supported Jumbo frames. Not sure how but its mentioned on Kitz. I bought a UK model and with a MTU of 1520 had packet fragmentation, hence we were advised to lower the MTU to 1492 or 1500, maybe the UK variant works better at 1500.

Netgears modem was limited to 1500 and worked fine, so for the tiny gain I'm not worried, also that was on the list of modems you could use in the UK so 1508 is not needed, Maybe the MTU is larger for G.Fast but maybe 1500 is just more stable all round. I mean people are happily using HG612's with a fixed MTU as I mentioned of 1500 still and they seem happy enough (on VDSL) as to flashing EU versions to UK firmware I think its the board that is coded not to accept UK firmware, rather like routers cant take other firmware of the same brand, so if you want one get a UK one.

Anyway did this version help in any way? Its ment to fix throughput issues and the spikes on VDSL.