MS/TP Duplicate MAC
Two or more nodes on the same MS/TP trunk have the same MAC address. This breaks token passing, causes unpredictable responses, and leads to timeouts and CRC errors.
Common Causes
- New device added with default MAC (e.g., 0) already in use
- Copy-paste configuration without changing MAC
- Multiple trunks merged without MAC reassignment
- No documentation of MAC assignments; accidental reuse
Fix Steps
- Run MS/TP MAC scan or use diagnostic tool to list all addresses on trunk.
- Identify duplicates; physically locate devices (by device instance if known).
- Assign unique MAC (0–127) to one of the conflicting devices; document change.
- Power-cycle the trunk; allow token ring to reform with correct addresses.
- Maintain a MAC assignment log to prevent future duplicates.