Evidence-based analysis of DoIP and UDS diagnostic failures.
Port 13400 is the default destination engineers look for when narrowing Wireshark captures down to Diagnostic over IP traffic.
NRC 0x31 usually means the ECU received a service request whose parameters or preconditions did not fit the allowed range.
NRC 0x78 indicates that the ECU accepted the request but still needs time before returning the final response.
BMW ENET and similar DoIP workflows can fail either during routing activation itself or immediately after activation when the session never becomes operationally stable.
Routing Activation analysis starts with the response and TCP stream state. A rejection before UDS, a confirmation-required state, and later session instability are different branches that require different evidence.
A 0x8002 acknowledgement proves that the DoIP entity accepted the diagnostic message. It does not prove the request reached a vehicle bus or that an ECU received or answered it.
If you are new to automotive Ethernet captures, the first obstacle is turning raw packets into a usable diagnostic story.
DoIP Entity Status Request (payload type 0x4001) queries basic DoIP entity attributes. The resulting response describes gateway-level entity state but cannot prove downstream ECU reachability, forwarding, or root cause.