For a while we have been running remote users VPN to network using L2TP/IPSec with Preshared key via the Windows 10 Built in Vpn.

Fibre connection to the router are 100Mbs/100Mbs or 150Mbs/150Mbs.

In the last few days we have seen a massive drop in transfer speeds. This happens on Vigor 2927 and 2952 devices. They NOT been updated or had any config changes for months. Restarting makes no difference.

The users connect fine and initally speeds seem fine. BUT file transfers in both directions timeout after a few seconds.

Whilst connected to the VPN on a client machine connected via a FTTP (300Mbs/3-00Mbs) and running a speedtest sites, we see an inital High transfer for a few seconds upto 50Mbs then the transfer speed drops to .3Mbs this si the same for Up and Down. this is the same across Google speed test, speedtest.net, speedtest.net.uk, broadbandspeedchecker.co.uk.

If we change to PPTP to test the connection we get 30 - 40Mbs consistantly up and down. But as this is not secure it is not suitable for day to day use.

Connection to a NON Vigor router over L2TP/IPSec with Preshared Key works as expected and we can get 30 - 40 Mbs.

This issue has manifested across 5 client machines in different locations so far all running upto date windows 10 pro.

The only change we are aware of is Windows 10 updates. BUT this does not explain why non-vigor routers are not affected.

Does anyone else have similar issues or know any solution.

Thanks

Update: I have also tested with the Draytek Smart Vpn client 5.4.1 and the same issue.

Performance through LtTP/IPSec with Preshared Key is terrible.

Please, anyone outhere who can do a speed test via Vpn to vigor router over L2TP/IPSec with Preshared Key, please post your results.

I just tried testing over my VPN using Netflix's speedtest .

Given there's an FTTC connection at each end, this is limited by the upload speed. I got about 7.6Mbps each way (which is the upload speed of the slower of the two connections).

Although it's not much of a throughput test, at least the answer is within expected values (and isn't 0.3Mbps...)

(Routers are ancient 2860n and even more ancient 2830n)

Thanks for the test.

Draytek support logged in this afternoon and was able to replicate from their connection. (Many thanks to them for their prompt support)

Turns out the default UDP DoS threshold was too low so increased to 5000 and seems to be ok again.

Odd though that this has only recently become an issue as no chnages made to router for a while.

Will monitor and report back.

pcjazzit wrote:
Turns out the default UDP DoS threshold was too low so increased to 5000 and seems to be ok again.

Both my 2830 and 2860 are set to 2500 (I believe the default is 2000).