We are attempting to use the SFP ports on our MX400 as WAN uplinks(support has updated the beta firmware to support this). However, the MX400 doesn't seem to be able to reach the cloud once the firmware/configuration has been downloaded to the MX400.
We are using the MX400 in one arm concentrator mode if that makes any difference.
Does anyone out there have any experience with this?
Definitely something you should contact Support about - recommendation is to connect the copper uplink as normal, and verify that it's online first, then it should fetch its config, and allow you to cut over, but they can verify that it's in the right state internally first before you do it.
It's usually easier if you start in NAT mode incidentally, as that way you can connect copper on the secondary WAN connection, and then verify the fiber connection is still working - less risk of it going offline on you.
I concur, connecting via copper to get cloud sync is definitely the best way to go (have the SFP+ modules in) so that the cloud sees them. After that, it's a functionality that has to be turned on by the support team, you'll need to call them.