EtherNet/IP (CIP) connection faults — module fault, timeout

EtherNet/IP (CIP over Ethernet — Rockwell/Allen-Bradley default) showing module fault, connection timeout, or I/O not coming up in Logix is usually IP/subnet, RPI, duplicate IP, EDS/AOP or switch/multicast — rarely a faulty module.

Common causes

1. Wrong IP / subnet — device on another subnet, wrong gateway, DHCP changed the IP.
2. Duplicate IP — two devices share an IP → intermittent.
3. RPI too small / overload — a low RPI floods the CPU/switch.
4. EDS / AOP — missing the correct EDS or Add-On Profile version for the module.
5. Switch & multicast — an unmanaged/non-IGMP switch floods multicast; or blocks ports.

Step-by-step diagnosis

1. Ping & IP Ping the device; verify IP/subnet/gateway are correct, no duplicate IP in the range.
2. Read the module fault In Logix, read the connection error code (e.g. 16#0204 timeout) for direction.
3. Check the RPI Set a sensible RPI (not too small); check total packet load on CPU/switch.
4. EDS / AOP Install the right EDS/AOP for the module + firmware; firmware mismatch often causes connection faults.
5. Switch & multicast Use a managed switch with IGMP snooping; check VLAN/ports; avoid unmanaged on large networks.
6. Capture traffic Wireshark + CIP dissector to view the connection request/response, separating config from physical faults.

When to call an expert

EtherNet/IP multicast/RPI/EDS faults eat hours without CIP experience. DeepDebug is strong on Rockwell + CIP capture, supports remotely and localizes fast.