MX250 2nd WAN port connection to Comcast flapping

[Einstein]

We have 2 internet connections. Our primary has been rock solid for years, yes years. 

Our WAN 2, which is backup and goes to Comcast seems to always be flapping. We have had many tickets with Comcast, modem swaps but the issue remains. 

Any insight from anyone? 

Our Comcast connection also runs our phone system, which goes through an Edgewater and never has issues. 

Could WAN port #2, or the SFP on the Meraki be the issue?

I have reset the SFP, with no change. 

Thank you in advance. 

[alemabrahao]

Which log messages are you receiving?

From what I understand, despite you observing this flapping, you've never had any problems, is that correct?

[Mloraditch]

The MX's port or the SFP could definitely be damaged somehow. Perhaps an electrical surge at some point? Have you asked Meraki support? I've not had issues in general with comcast handoffs through a wide variety of gear (Cienas, Junipers, Coax Modems, etc)
Do you have a spare SFP you can try? Do you see the issue if you connect the Comcast gear to another device?

[Einstein]

The issue is so sporadic. I doubt it's a Meraki issue. The only log I have on the Meraki side is that the link is down. Our Comcast connection comes into our building, goes into a splitter. One side goes to the Edgewater and the phone system (which is always ok). The other side goes to the Comcast modem where we always have issue. All the cables, the splitter, and the Comcast modem itself have all been replaced many times. I think we are on our 4th Comcast modem. On the Comcast portal, it reports the modem as down. The Meraki portal reports WAN2 as offline. We also have 2 analog lines that come off the Comcast modem (fax), it is down as well. Comcast points fingers to us, but they cannot get into their own modem? Their portal reports the connection as "experiencing issues". We are running 19.1.11 firmware on the MX.

I am just trying to cross "t's", dot "i's" as much as I can. We have an EXTREMELY long cable run from the road into the server room. ±.5 mile. Wilson 400 cable.

I will order another SFP see if that fixes it. 

Thank you everyone!

[Mloraditch]

If comcast side is reporting the modem down at the time you see the Meraki reporting things down, the issue is 100% comcast. The status of the modem relies on power and the coax cable, that's it. 

[Einstein]

Totally agree. It's all finger pointing. I am just a little tired of swapping out cable modems. All equipment is plugged into large APCs, so power is always clean and consistent.  I have said to them before, I believe it the cable run from the pole to the DMARC. I think we are getting surges through that which blow out the cable modem via the RG6 connection. With Comcast always 👉👉👈👈👉👉👈👈.......