Very Slow OneDrive/SharePoint Download Speeds (600-800kb/s)

I have a fibre leased line (100Mbit over 1Gbit bearer) provided by ITS.

The gateway is a DrayTek 2927, connected via Gigabit Ethernet to a Cisco C1117-4P (managed by ITS), connected via fibre to an ADVA FSP 150-GE102Pro.

When I run a speed test, it always gives me ~94Mbit up and down - should I be getting the full 100Mbit? When I run a speed test on my 500/70 FTTP service at home, I get 500Mbit down or more and about 68Mbit up.

We are based in North Wales, but our Microsoft 365 Admin Center reckons we're based in Hatton (south of Birmingham), whereas an IP WHOIS Lookup on our IP range has an address of Hatton in Chester (CH3).

Everything works fine, apart from downloading anything from OneDrive/SharePoint. Whether I'm downloading via the OneDrive app on Windows or via the browser, the download rate is always 600kb/s to 800kb/s. I am also getting the same speeds using a standalone Linux server (on-premise) that's connected to the same network as our Windows PCs. The upload rate is about 5mb/s, it's just the download rate that's suffering.

Microsoft so far have suggested it's a problem with our network, but I've troubleshooted this issue with everything turned off: Firewalls, QoS, etc.

It doesn't matter if I use 1.1.1.1 DNS or the ISP DNS servers either.

Any advice would be greatly appreciated.

When you send or receive data over an internet connection there are packet overheads. The overheads are additional bits which have to be transmitted and so use some of the band width. 94Mbps will be about the maximum usable data that you can send or receive on a 100Mbps connection.

OK, but then why does my FTTP service at home achieve the full rate on the speed test?

Also, the MTU on the DrayTek WAN is set to 1500. Would decreasing it resolve the issue with OneDrive/SharePoint?

Set the IP address on your laptop to the same public IP and gateway as you have entered into the DrayTek, plug it into the Cisco managed router in place of the DrayTek device, and test again.

In reply to a post by davidenco:

OK, but then why does my FTTP service at home achieve the full rate on the speed test?

Possibly because your home FTTP provider accounts for packet overhead when calculating your actual allowed bandwidth vs advertised bandwidth, whereas your leased line provider doesn't.

A few minutes ago, I tried downloading a large file from our OneDrive for Business service, and it downloaded at 10MB/s - the full download rate of the connection. A few seconds later, I tried downloading the same file, and the download rate did not exceed 800KB/s.

To rule out it being a Windows thing, I tried downloading the same file via one of our Linux servers, which is connected to the same leased line connection as my computer, only to see the same slow download rate.

So I tried to VPN into my home router and download the file via that connection instead, and it downloaded at the full 10MB/s rate. I tried to download the file via the VPN a few more times, and every time it downloaded at the full rate.

Disconnecting from the VPN and downloading the same file via the leased line, and it is still downloading at up to 800KB/s.

Does this suggest the IP traffic originating from our leased line is being throttled?

What service do you use? Is it a hosted MS 365 type of thing?
If so you will be connecting to your nearest entry point to the MS Azure world.

I cannot help specifically but can only report many issues getting a stable connection for MS Teams going via ZScaler.

Could you just do the test that involves bypassing the DrayTek router entirely? There's still too many things in play to make any sort of guess where the issue might be.

if the op has the chance - maybe connect to the ont directly .....

Re getting pegged at 94 Mbps, suggests a 100BaseT connection with a standard MTU of 1500 and Ethernet frame size of 1518 bytes.

Ideally the WAN connection and LAN connections should be set to larger jumbo frames (typically an MTU of 9000 bytes) to getting better maximum throughput close to 99% of the port raw bitrate, due to less framing overheads.