I have a problem with slow speed on a BT FTTC VDSL broadband connection that appears to be due to the config of the USG-3P and would be very grateful if anyone hear can shed any light on it. I have read all of the similar posts both on this forum and the internet in general and can't seem to find a solution. My apologies if the post is long but I've tried everything that I can think of to no avail.
In brief, we have two sites both served by BT Business FTTC broadband. Site A which has been working happily for some years has a USG Pro getting a PPPoE connection from a Draytek 167. Site B has a USG-3P getting broadband through a Draytek 130. Until recently this was running happily through Talk Talk (LLU) over DHCP. We have just changed the broadband service to BT FTTC VDSL PPPoE and we are now experiencing very slow speed (40% of available) and frequent drop outs.
When Site B is connected using the BT supplied Super Hub the connection is reliable and fast so no line fault.
When site B is connected to the USG either through putting the Super Hub into Bridge Mode or by using the Draytek we get a terrible service.
I have tested the equipment by taking it to Site A and found that the Draytek 130 is working perfectly well when inserted into Site A's network (i.e. replaced the Draytek 167 with the 130). Similarly by connecting the USG-3P to the Site A Draytek 167 we get the same poor performance and so clearly the USG-3P is the culprit.
I have performed a ping test that shows that the maximum unfragmented packet size is 1464 and have accordingly set the MTU to 1492.
I have disabled IPv6 in case that was causing the problem.
I compared the config of the USG-3P with the USG Pro and noticed that the USG Pro had MSS set to 1328 (seems low ??). Anyway I set the USG-3P MSS to 1328 and BINGO! it worked perfectly at full speed. Feeling very pleased with myself, I re-installed the USG-3P at Site B and the old problems resurfaced. When brought back to Site A with everything unchanged it again still had slow speed (the config.boot has not been overwritten by either the network controller or the config.JSON). I have been unable to replicate my brief period of success.
Any advice would be gratefully received.
Thank you,
Richard.
