The panel may show a healthy CompactLogix 5380 while RSLinx Classic cannot browse it; a ping that reports “Destination host unreachable” points first to an IP-path problem, not an RSLinx browse setting. Check the PC’s active network adapter and the controller’s actual Ethernet address before changing drivers. A direct USB connection can help you read or set the controller’s Ethernet configuration without relying on the suspect network path.
Check what “unreachable” means on the PC
Read the complete ping output, including the address after “Reply from.” Windows can report an unreachable destination from the PC’s own address; that is not a successful reply from the PLC. The key result is whether the destination answers, not whether the output contains the words “Reply from.”
- Record the exact PLC address you pinged and the address that generated any unreachable message.
- Check the PC’s active adapter for its IPv4 address, subnet mask, and gateway. Confirm you are checking the adapter connected to the PLC, not Wi-Fi, a VPN, or another Ethernet interface.
- Confirm the controller’s current address through USB, the BOOTP/DHCP utility, or an authorized network discovery method. Do not treat a remembered or assumed address as verified.
If ping fails, resolve the address and network path before spending time rebuilding an RSLinx browse. A successful ping is useful, but it does not prove that EtherNet/IP traffic or RSLinx communication works.
Separate address, subnet, and service symptoms
| What you see | What to check next |
|---|---|
| Ping reports the destination as unreachable, possibly from the PC’s own address. | Verify the PLC IP, PC adapter, subnet mask, physical link, and route. The PC may not have a valid path to that destination. |
| Ping times out without an unreachable message. | Verify the target address and link, then check whether ICMP is permitted. A timeout alone does not identify an RSLinx fault. |
| Ping succeeds but RSLinx does not browse or connect. | Test EtherNet/IP reachability, confirm the RSLinx driver and target address, then investigate PC security software or network filtering. |
| Neither known PLC address nor RSLinx access works. | Use USB or BOOTP/DHCP discovery to establish the actual controller address and whether it is configured for DHCP/BOOTP. |
The fast rule-out is simple: if the PC cannot reach the controller’s verified IP, changing RSLinx browse settings will not repair the IP path.
Understand why a direct cable can still fail
A direct Ethernet cable provides a physical connection; it does not automatically assign matching IP settings to both endpoints. The PC and PLC still need compatible addresses and subnet masks, and the PC must send traffic through the adapter connected to the controller. A wrong PLC address, an address conflict, or a PC adapter on a different subnet can prevent communication even when the cable is connected.
ICMP ping tests whether the IP destination responds to ping. EtherNet/IP communication uses a separate service path; the provided Windows check tests TCP port 44818. Thus, a successful ping with a failed port test narrows the problem to service reachability or filtering rather than basic ICMP reachability. A failed port test can also result from an incorrect target address or a path issue, so confirm the address first.
RSLinx Classic’s Ethernet Devices driver uses a specified target address; the EtherNet/IP driver is a separate driver choice. Neither driver can compensate for an unknown PLC IP or a PC adapter that cannot reach it.
Find and correct the CompactLogix 5380 address
- Connect to the controller over USB. In RSLinx Classic, use the USB connection to access the controller and inspect its Ethernet configuration.
- Record the active Ethernet address and subnet mask. Check whether the address is static or whether the controller is still set for DHCP/BOOTP. Do not assign an address based on a scan result until you identify the controller.
- If the existing address is wrong for the intended network, set the correct address and subnet using the appropriate controller configuration method. Use an address approved for that network; avoid duplicating an address already in use.
- Set the PC’s connected adapter to an address compatible with the controller’s configured subnet. Use the intended subnet mask for that network. Do not cycle through broad Class C, B, and A masks as a troubleshooting strategy; an incorrect mask can create ambiguous routing and conceal the underlying mismatch.
- Reconnect or renew the PC configuration as needed, then repeat ping against the verified PLC address.
If USB is unavailable, use the BOOTP/DHCP utility or an authorized packet capture or network discovery tool to identify the controller and its address. Tools such as Wireshark, Slitheris, and Nmap were suggested for discovery; use scanning only on networks you are authorized to inspect. Do not introduce a laptop DHCP server onto a company LAN as a shortcut: it can disrupt address assignment for other devices.
Test the network path before configuring RSLinx
- From Windows Command Prompt, ping the verified PLC IP. Read the destination and source addresses in the result; distinguish a response from the target from an unreachable message generated locally.
- From PowerShell, test the EtherNet/IP TCP port with
Test-NetConnection <IPaddress> -Port 44818. Replace<IPaddress>with the controller’s verified address. If the port test fails, recheck the address, adapter, route, and any filtering before treating RSLinx as the cause. - Optionally enter
http://<IPAddress>in a browser as an additional reachability check. A browser result depends on the controller’s web service and configuration; do not use a missing page alone to conclude that EtherNet/IP is unavailable.
Run these checks in order: IP and ping first, EtherNet/IP port second, optional browser check third. This separates a basic network problem from an RSLinx-specific browse or connection problem.
Configure the RSLinx driver for the verified target
- Open RSLinx Classic and go to
Communications > Configure Drivers. - For the Ethernet Devices driver, enter the verified PLC address in the host name field. Confirm the PC adapter can reach that address before testing the driver.
- If you use the EtherNet/IP driver instead, configure it for the network path where the controller is reachable. Do not assume switching driver types will resolve a wrong IP, an incompatible subnet, or a blocked service.
- Save the driver configuration and browse again. If the device still does not appear while ping and the port test succeed, check that the selected driver points to the correct interface or target and review PC firewall or network-filtering rules.
Verify the fix and avoid repeat troubleshooting
Confirm each layer independently: the PC has the intended adapter configuration, ping reaches the verified PLC address, the TCP port test succeeds, and RSLinx can browse or connect through the configured driver. Record the working PLC address, subnet mask, PC adapter, and RSLinx driver so the next connection attempt starts from known values.
- Do not interpret “Reply from” as proof that the PLC answered; check the responding address and the unreachable or timeout status.
- Do not change subnet masks experimentally to force connectivity. Match both endpoints to the network design and verify the actual controller settings.
- Do not start RSLinx troubleshooting while the PLC IP remains unknown or the PC cannot reach it.
- Do not add a DHCP service to a live company network to find an address. Prefer USB, the BOOTP/DHCP utility, or authorized discovery on an isolated or approved network.
- Do not treat browser access as a required test for EtherNet/IP; use the port test and RSLinx connection result for that path.
Frequently asked questions
What happens if ping says “Reply from” but the PLC is unreachable?
Check the address after “Reply from.” Windows may be reporting that the PC itself generated an unreachable message; that does not mean the PLC replied. Verify the PLC IP and PC adapter settings.
What happens if ping works but RSLinx still cannot find the CompactLogix?
Test TCP port 44818 with Test-NetConnection <IPaddress> -Port 44818. If it succeeds, verify the RSLinx driver’s target or interface and investigate filtering on the PC or network.
What happens if I do not know the CompactLogix 5380 IP address?
Connect over USB and inspect the Ethernet configuration, or use the BOOTP/DHCP utility or authorized network discovery. Check whether the controller is set for DHCP/BOOTP before assigning an address.
What happens if I enter the PLC IP in the RSLinx host name field?
That is the target entry for the Ethernet Devices driver, but it works only when the address is correct and the PC can reach it. Verify ping and TCP port 44818 before changing RSLinx settings again.
Stop changing IP settings when the controller address, subnet, or network assignment remains unclear; use USB or the approved network administrator process to resolve it. Escalate to official Rockwell Automation support with the controller model, observed address settings, ping output, port-test result, and RSLinx driver configuration if the network checks pass but communication still fails.