To ensure proper operation of your Flux Node please be sure to setup your networking appropriately. Below we will cover single and multi-node network requirements.
Single Node
It is recommended to use UPnP, this requires a router that supports the UPnP protocol.
The widely accepted solution is to use a pfSense firewall/router.
https://www.pfsense.org/
The other option for a Single node setup is to place the node in the router's DMZ (demilitarized zone), effectively exposing all traffic to your Node. The Flux node has a firewall (UFW) that is installed and configured during the node setup process with multitoolbox. This firewall will handle opening the proper ports for the node to have access to the internet.
Port forwarding is no longer recommended after Flux OS version 4.0.0. Please see the release notes below.
Flux OS Release Notes v4.0.0 - https://github.com/RunOnFlux/flux/releases/tag/v4.0.0
UPnP Setup for Single Node
UPnP stands for universal plug and play which essentially allows devices on your network to request ports to be opened by your router for incoming traffic. UPNP can be an easier solution if your router is supported and sticks to proper upnp standards.
To setup upnp on your router you will first need to set your node to a static or or dhcp reservation so your local IP for you node always stays the same. Next you will need to remove any port forwarding that you have setup for you node (if any). Finally you will want to enable upnp and reboot your router before proceeding to the next step.
To enable upnp on your Flux node you will need to run multitoolbox option 14 and select an API port for your node. I typically suggest starting from the lowest port and working your way up. The lowest port is 16127.
Multi-Node Configuration
The maximum number of Flux nodes supported on a single external IP address is 8.
UPnP is REQUIRED to run more than a single node on the same external IP address. Port Forwarding or DMZ will NOT work properly on most consumer grade routers.
The UPnP setup is exactly the same as a single node setup except when you run multitoolbox option 14 you will want to choose a different API port for each node. Also, please be sure to set each node to a static or dhcp reservation in your router settings.