S2S Download from site slow, but upload normal?

[Mikeyy]

Hi all,

I'm experiencing a weird behaviour on a MX67c (16.16.4) that is connecting back to our Datacenter (MX95, 10Gbit symmetrical).

The site with the MX67c has 100mbit symmetrical fiber.
Everything outside the s2s-tunnel back to the DC is getting the full 100mbit.
Iperf to a host in the datacenter is giving me the full 100mbit as well (tested both wireless & wired). Ping around 20ms constantly.

File upload to the datacenter is working perfectly fine, close to a 100mbit.

Now to the issue; Download is dog-slow, sub 10mbit. This is the issue I cannot get my head around? 

All my other sites, using a mix of Z3, Mx68, Mx75 don't have any issues at all with downloading files from the same host. Has anyone experienced something similar? What could be the problem?

All help is much appreciated!

[PhilipDAth]

Smells like an MTU issue.

On a test machine, run this to get a list of adaptor names:

netsh interface ipv4 show subinterface

 Then try lowering the MTU on that interface (change Ethernet to be your actual interface name):

netsh interface ipv4 set subinterface “Ethernet” mtu=1300

If it works, run the same command again but with " store=persistent " on the end to make the setting survive a reboot.

As you have symmetric circuits I don't think it will be an issue with asymmetric timings, but you can also try:

netsh int tcp set global timestamps=enable 

[Mikeyy]

Thanks for the reply Philip. It would seem strange, as all my other MXs' can connect to the DC without any issues what so ever?

[Mikeyy]

Just for a quick test, I did set the MTU to 1300, nothing changed in terms of slow speeds 😕 Any other idea other then RMA?

[PhilipDAth]

Did you try enabling timestamps?

[Mikeyy]

Meraki support has received a pcap, but they couldn't find anything wrong in it, so I'm a bit lost at the moment to be honest.