I have found a problem when configuring a Draytek 2860 for remote management.

It seems that when QoS is configured, it stops remote management and you will not be able to gain access to the router remotely.
we have tried different firmware, different modem codes, switch off access for list for remote management, even setting port 80/443 for remote access ports, nothing seemed to work.

it was only when we switched off QoS that access came back to us. I had heard of problems with using specific ports would cause issue, we have also heard that having QoS and prioritisation for VoIP SIP/RTP would cause issues with bad packets.

but never deny access!

this is only a heads up for all other having the issue.

(p.s. I have had an issue outstanding with Draytek for months now with no apparent fix.... a force NAT/Route issue!)