The most dangerous green light in monitoring is a firewall ping sensor, all by itself. It proves the box has power. Your users need three other proofs.
The video puts firewall status on the PRTG dashboard, and the temptation is to stop at a Ping sensor. Resist it. A firewall is not one thing - it is a box, two or more traffic paths, and a handful of services (VPN, DHCP, DNS, sometimes mail). Each can fail while the others shine green. Honest firewall status in PRTG means three layers of sensors: alive, flowing, serving.
Ping proves the firewall's interface answers - power on, cable in, stack alive. Add the SNMP uptime where available: an uptime that reset an hour ago tells you the box rebooted, which explains a morning of strange reports better than any user interview. Necessary - and almost never sufficient.
Put an SNMP Traffic sensor on the WAN port and one on the LAN port. Now you can see the patterns that mean something: WAN traffic at zero in office hours is an internet outage, not a quiet day. LAN traffic huge with WAN flat points inward - a local loop or a chattering device. Errors climbing on one interface is a cable or duplex problem introducing itself politely, days before it becomes an outage.
For every service the outside world or the office depends on, add its check: a Port sensor for the VPN port, an HTTP sensor for a published portal, DNS if the firewall is the office resolver. These sensors fail in the exact shape users experience - "VPN won't connect" is a down port sensor that spoke first. Match each port sensor to a service someone will actually miss; an elegant dashboard of ports nobody uses is decoration.
Only then say "the firewall is up" out loud. Announcing at step 1 is how IT says it twice.
Every sensor in this guide is created live in the video - installation, discovery, CPU and RAM, bandwidth and firewall status.
Watch Full VideoMore than you fear: ping, port sensors for VPN and published services, and an HTTP sensor for any web interface you choose to expose to the LAN. You lose traffic graphs and uptime from that box - put the traffic sensors on the switch port it plugs into instead.
The one matched to the pain your office feels first. For most offices that is the VPN port sensor or the WAN traffic sensor - the two failures that generate phone calls. Start there, then complete the three layers.
PRTG notifications can trigger scripts, and some teams auto-restart services this way - but be careful: automatic action on a security device, triggered by one failed check, can turn a glitch into an outage. Alert a human first; automate only what you have watched fail safely many times.