The engineer's laptop and a protection IED have addresses in the same range, yet ping fails. Checking the addressing from both sides shows why, and which laptop address works.
| Laptop | 10.13.0.200, mask 255.255.255.0, no gateway |
| IED | 10.13.0.14, mask 255.255.255.128, gateway 10.13.0.1 |
| Connection | Laptop on a spare port of the station-bus switch, same VLAN |
| Symptom | Ping times out; the IED's web page does not open |
The laptop was set up from an old drawing that showed the station bus as a /24. The IED configuration uses /25.
The laptop applies its own mask (/24) to its own address and to the IED's address.
The IED applies its own mask (/25). Its subnet 10.13.0.0/25 covers 10.13.0.0–10.13.0.127.
The ping request reaches the IED. The reply is addressed to the router, not to the laptop. Unless the router sends it back onto the same LAN, it is lost — so ping fails although the cable, switch and VLAN are fine.
This is why the check must be done from both sides. Looking only at the laptop, everything seems correct.
Put the laptop in the IED's subnet with the IED's mask. The assistant proposes an address near the top of the usable range (lastHost − 9), away from the IEDs at the bottom and the gateway.
Check the IP address register first that 10.13.0.117 is not already used.
With the new address the assistant reports 'Can talk directly'. Next, test the protocol: IEC 61850 MMS on TCP 102. If ping works but the engineering tool cannot connect, check the Windows firewall and the IED's client-connection limit.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Laptop sees IED as local (/24) | Both sides agree | Local | ✓ PASS |
| IED sees laptop as local (/25) | Both sides agree | Via gateway | ✗ FAIL |
| After change: 10.13.0.117/25 | Same subnet both ways | Direct | ✓ PASS |
Key insight: Each device judges 'local' with its own mask. Two devices only talk directly when both agree.
Every input in this example is editable in the live calculator — no signup needed.
Open SCADA Connectivity Assistant calculator →No. The laptop already sends directly; the problem is the IED's reply going to its gateway. Only matching the mask (or a router that sends the reply back) fixes it.
The /25 is part of the station-bus design; other devices and the gateway rely on it. Change the laptop, not the protection IED.