What the IP register checker looks for
The IP address register is usually a spreadsheet: one line per device with its name, IP address, subnet mask, gateway, MAC address and VLAN. It is written early, copied between documents and edited by several people, so typing errors survive until commissioning. Checking the whole list at once is faster than finding the faults one by one on site.
Per device the checker verifies the format of the IP, mask and MAC, and flags addresses that cannot be assigned: the network or broadcast address of the subnet, loopback, multicast and 169.254.x.x link-local addresses. It checks that the gateway is inside the device's own subnet and is not the device itself.
Across the register it finds duplicate IP addresses, MAC addresses and device names; masks or gateways that differ inside one VLAN or network (the majority value is taken as intended); subnets that overlap, which means devices disagree about who is local; and one subnet spread over several VLANs, which cannot work without routing.
Paste the table directly from Excel (it is tab separated), or open a CSV file. The checker reads the column headings to find the columns, accepts IP/prefix notation such as 10.13.0.14/25, and gives the line number of every finding. The data stays in your browser.
Findings and their meaning
| Code | Severity | Meaning |
|---|---|---|
| DUP-IP | Error | The same IP address on two or more devices |
| DUP-MAC | Error | The same MAC address on two devices (often a copied line) |
| IP-NETBC | Error | Network or broadcast address given to a device |
| IP-SPECIAL | Error | Loopback, link-local (169.254.x.x), multicast or reserved address |
| GW-OUTSIDE | Error | Gateway outside the device's own subnet |
| SUBNET-OVERLAP | Error | Two different subnets cover the same addresses |
| MASK-MIX / GW-MIX | Warning | Mask or gateway differs from the rest of the VLAN or network |
| SUBNET-VLANS | Warning | One subnet appears in more than one VLAN |
| VLAN-SUBNETS | Info | A VLAN carries more than one subnet |
Frequently asked questions
Which columns does the checker need?
At least an IP address column. A subnet mask column (or IP/prefix notation) enables the mask, gateway and subnet checks; gateway, MAC, VLAN and network columns enable the rest. Column names such as Device, IP address, Subnet mask, Gateway, MAC address, VLAN are recognised.
Is my register uploaded anywhere?
No. The file is read and checked in your browser; nothing is sent to a server.
Why is an overlap an error and not a warning?
When two subnets overlap, a device on the wider subnet treats addresses as local that the device on the narrower subnet sends to its gateway. The result is the one-way fault that the SCADA Connectivity Assistant explains — it nearly always means one mask is wrong.