Settings: Draytek Vigor 120 modem and Asus RT-AC66U Wireless AC Router on o2 Broadband
Help needed with correct settings please!
I am fairly sure I am on o2 old network with dynamic IP. o2 support have been fairly useless in assisting and have given be conflicting information on the connection type.
I had satisfactory and stable internet connection until doing a firmware update on the router yesterday. Now my internet connection is very flaky – downloads start at full speed but then rapidly decline to low or zero speed and websites take a long time to load or require constant refreshes. The firmware update may be coincidental with the problem.
I have reset everything and firmware updated everything without success. I suspect the problem lies with the modem settings. I have connected PC directly to the modem on LAN for testing the connection and still have the same connection problems as on wireless.
I have read and followed without complete success the support guide at http://www.draytek.co.uk/support/kb_vigor100_setup.html
I have the following settings:

Modem: (Draytek 120 Annex A v2/Firmware: 3.2.6/ADSL Firmware: 332201_A Hardware: Annex A)
Internet Access type is set to MPoA (o2 support advised it should be on PPPoA which doesn’t seem right)
Encapsulation: 1483 Bridged IP LLC
VPI: 0
VCI: 101
Modulation: I have tried without success
- “ADSL2+(G.992.5)” following the Draytek set up guide
- “ADSL2+ Annex M” following o2 support advice
- Multimode
MAC address set to Default MAC address

Router: (Asus RT-AC66U Wireless AC/Firmware 3.0.0.4.374_726-g10636ee/in wireless router mode)
WAN Settings:
WAN Connection type: Automatic IP (other choices are PPPoE/StaticIP/PPTP/L2TP)
WAN enabled/NAT enabled/UnP enabled/Connect to DNS Automatically enabled

There is also a menu for “Special Requirements from ISP” which has Host Name left blank, MAC clone left blank and DHCP query mode set to Normal rather than Aggressive.

When setting up the router there is a quick Internet Setup screen which I am fairly sure I had working correctly before and it automatically detected my connection type. It does not work now in that it does not detect the connection type, I suspect because the modem is not set up correctly. The screen has options for Automatic IP (DHCP), PPPoE, and Static IP.
Any help with varying these settings would be much appreciated!

Second question if your patience isn’t exhausted – if I want to use OpenDNS servers where should I be inputting the settings; on the wireless router or in the IPv4 settings for the connection type in Widows?

hi ... few points to note

If is the 120 you have update & it makes the problem ... make sure you have to correct firmware
the 120 v2 modem will state under the V2 ... then you have the correct firmware
the v1 will not have any v2 sign under by its label

i am not with O2 but i think have seen few posts where for few users VCI 100 worked ... so try again annex M or 2+ or multi with vci 100

At asus now try avoid the detect internet connection and go straight to the set up page
I think this is the link to take you direct at asus main page and navigate to wan settings
http://192.168.1.1/index.asp
at asus leave auto IP (if you are sure you got dynamic IP) but set manually PPPOE, dns let to normal and if still no connection try disable NAT

Second question it depence what you want

setting DNS at asus router will use all the rest devices in your home ... i think is better
If you set at the specific pc via ipv4 as you mentioned ... then only this pc will benefit the change of the dns ... not the others

EDIT
http://community.o2.co.uk/t5/Home-Broadband-Home-Phone/how-do-you-setup-draytek-vigor-120/m-p/234333/highlight/true#M56861
http://forums.overclockers.co.uk/showthread.php?p=18384906

Thanks for very helpful reply.

I am sure that the modem is v2 (it's on the label) - just not sure whether I have the right firmware when there are so many versions. I have v3.2.6/ADSL Firmware: 332201.

I have seen suggestions that I should use another ADSL version for UK ISP's with long line connections like mine.

I will check out other firmware but would be grateful for other suggestions - after a day of frustration :x I've gone back to using my Linksys WAG160N in bridged mode as my modem and it works perfectly and syncs perfectly with my Asus router.

Thanks for the DNS tip too!