Have several MX appliances, mix of 84 and 100's. Setting up backup internet connections on the 84 seemed straightforward, just edit WAN 2. I'm not seeing similar option on 100? is there a trick to it, i don't see where i can toggle one of the interfaces for WAN. Also, is there anything special about any settings for the failover or is it just plug and play
The MX100 has a dedicated management interface to access the local web page, but I think you can also access the local webpage when you have L3 access to the LAN IP of the MX. For that you'll have to set " Remote device status pages" to "Enabled" in Network-Wide > General.
The docs specify the following:
You can toggle the LAN2 port between LAN and Internet, through Uplink configuration under the Local status tab.