New ISP - MX105 throttling speeds

Comes here often

New ISP - MX105 throttling speeds

Since changing to a PPPOE ISP yesterday, my MX105 seems to be throttling speeds and I have no idea why. I was with Virgin Media (VM) who use DHCP public IP addresses but my new ISP (BT) uses PPPOE. I should be getting 900Mbps down and 110 up but I’m only seeing 350 down and 0.35 up.


When with VM, I had their router in modem mode and used the MX as the router and firewall. Everything was fine with VM and I got full speeds. When I moved to BT, I connected the MX direct to the ONT – the router doesn’t have a modem/bypass function – you just go direct to the ONT.


When I noticed the reduced speeds direct to the ONT, I unplugged the MX from the ONT, reconnected BT’s router and plugged in a laptop and ran some speed test, all of which showed full speeds (900/110).


Any ideas on what may be causing the reduced speeds through the MX?


Many thanks!

6 Replies 6
Building a reputation

I'm a little unclear on the last part of your post. Have you run a speed test over the new BT connection without the MX and gotten the expected speeds?


Any chance the ports are auto negotiating to half duplex when connected to the ONT?

Yes, you are correct, running a speed test using just the BT router connected to the ONT shows the expected speeds.


I'll check the ports in the morning and report back.

Building a reputation

Hopefully it's just a speed/duplex issue, we've seen this a couple times with our MX's that connect to CenturyLink or AT&T ONT's. We've had to go manually set the ports to 100/full or 1gbps/full, depending on what the carrier specifies.

Head in the Cloud

Can you connect your laptop to the ONT and setup the PPOE settings and test the speeds your getting? This way rules out any hardware..

Eliot F | Simplifying IT with Cloud Solutions
Found this helpful? Give me some Kudos! (click on the little up-arrow below)

Hi Miles, just done as you said and surprisingly, I'm getting the same problem as with the MX - 260 down and 0.35 up.


As soon as I reconnect the BT router to the ONT, and do a speed test on a wired connection, I'm getting full speed.

Kind of a big deal
Kind of a big deal

Some thoughts of mine (I know nothing about BT ONT configuration):

  • Perhaps you are facing a speed/duplex mismatch.  I'd try locking the config at 1000/full for a test.
  • DHCP has a 1500 byte MTU.  PPPoE has a 1492 byte MTU.  Perhaps you are experiencing an MTU squeeze.  You can test this on windows by running:
    netsh interface ipv4 show subinterface 
    Note the name of the interface being used for Internet traffic (it will have lots of traffic on it).
    Then temporarily change the MTU to something like 1300.
    netsh interface ipv4 set subinterfaceLocal Area Connection 2mtu=1300
    If that resolves it, you'll need to request Meraki support to lower the MTU for you.
  • Perhaps BT use a VLAN tag for the Internet service, and you are falling into some default service with lower performance by not using the same VLAN tag.
Get notified when there are additional replies to this discussion.
Welcome to the Meraki Community!
To start contributing, simply sign in with your Cisco account. If you don't yet have a Cisco account, you can sign up.