MX 100 setup (with Meraki APs) only works if port speed is 100mb!!!

[me_shad]

So basically my colleague set this up as a small Meraki setup for an open internet. I was checking it remotely today and noticed

- Internet port is configured as manual - Given an IP and gateway is set as the ISP ADSL Router IP (LAN port of ADSL modem)

- In MX, Single LAN and no routes added, LAN port of meraki MX is connected to c9300 in an access port vlan 100

- 3 Meraki APs connected to same access vlan 100 (not trunk)

- DHCP is enabled in MX and AP's are getting an IP and internet from that DHCP scope

All ports are giga, but setup only works and APs turn online once we keep it as 100mb (or auto under c9300 port config), i dont know the reason yet but assuming something with the MX setup only. I can also see under the c9300 port settings as half-duplex and 100mb.

I need to resolve without interruption or a very minimum one.............Any help!!!

[alemabrahao]

Ensure that the AP is connected with a high-quality cable. Especially with Cat5e, some cables only negotiate 100MBit and others go to 1Gig.There have been instances where port speed issues were resolved by downgrading the switch firmware.

Solved: Port speed issues with MS 12.10 - The Meraki Community

You can try swapping the AP connected at 100mbit with one of the known working at 1000mbit using the same cable. 

[me_shad]

Thanks for the fast reply man.......but cable is not the problem, we did swap a few cat6 cables which is new and working fine over a Giga port..

[alemabrahao]

I suggest you open a support case.

[PhilipDAth]

>or auto under c9300 port config

You mention a C9300 (which is a switch) but the rest of the post is about an MX100.  Is the C9300 plugged into MX port 2?  Is it the connection between the MX and the C930 which has the issue?

If so, ask the C9300 to do a cable test.  What does that report?  Not that this is likely to cause a disruption in traffic for several seconds (because this is an uplink port running at 100Mb/s) so choose when you want to do this.

[me_shad]

Yes absolutely - the connection between MX and c9300 has the issue. And strangely, the setup is working fine with 100mb, if I change the port setting from auto to 1000 speed in c9300, it breaks. Same applies if I change the port settings in Meraki MX. I might have missed this, when we connected locally to MX, i can see the port setting of port 2 is 100mb, full duplex. We changed to 1000mb, the system breaks and eventually lost wifi (AP's in the cloud go offline)

[Brash]

If the connection is only working at 100Mbps half-duplex, it's almost definitely a layer 1 issue.

Cable/SFP's would be the first thing to rule out.

Beyond that, you could try connecting each port to a different device (during a maintenance window of course) and seeing if either one will negotiate 1Gbps.

Just to clarify, when testing you're changing both sides to 1Gbps (or auto), not just one side?

[Mustafa_Taqi]

I Agree with @Brash . It looks like a Layer 1 issue. Have you tried different ports on the Cisco c9300 and on the MX100? 

[cmr]

Go to the MX100's local status page and check that the LAN port hasn't been forced to 100Mb, as opposed to being on autonegotiate, this would cause these problems.