Why are Sure Signal so troublesome?

[FrithHillHouse]

For one of my clients they have a large property in an area with weak to no signal so we needed a solution.

My client has two internet connections on site:

1 - Backup service via BT Broadband using a standard BT Router

Sure Signal works perfectly with this service but this backup is only in one room so not suitable for the entire property.

2 - Main Service via KCOM. This is a bonded service and uses Draytek Routers and APs throughout the property.

Sure Signal with this service simply won't work. I've tried the following:

1. Sure Signal directly connected to Router
2. MAC address mapped to static IP
3. IP opened up in the DMZ
4. MTU lowered to 1460
5. Confirmed both Sure Signals are registered, active and users added

And yet the Sure Signal still just flashes away.

We've spoken to tech support a few times, make a change and then are told we need to wait 6 hours or it to sync or something. 

I don't get why these Sure Signals are so mystical and hard to troubleshoot. I even looked at the premium versions of the Sure Signal but the cost is ridiculous. 

I'm looking into using WiFi Calling but would rather just get the Sure Signal working.

Any other ideas?

[gsmsecure]

MTU needs increasing..

SureSignal cannot cope below 1492..

[Retired-Tom]

@FrithHillHouse Please complete our Sure Signal troubleshooting guide and post the results below in this thread.

[FrithHillHouse]

Weirdly dropping the MTU was the last thing I tried and it worked! 

So it seems the MTU on the draytek needs to be lowered. 

My post still stands, I don't get why these boxes are so troublesome to support. The 6 hour wait time makes them a nightmare to support as an IT consultant, you can't sit there for 6 hours waiting.

[gsmsecure]

What's it set to?

I could be that it's so low, it is being ignored and allow through at the max packet size for the device.

MTU should be adaptive which is where SureSignal fails in that the clown that designed it failed to allow for varying packet sizes and this is what I told Vodafone three and half years ago with promises to fix it..

Try increasing it to see if it still works but suspect the Draytek is ignoring the setting for SureSignal vpn data and allowing full size through.

It could also be as they are bonded that the packet was being split again and data arriving at different timing over the shared connections.

Might also be worth a tracert to see how packets are being transported..

I would not be able to use SureSignal here if not for good old Draytek.