Common registration failures and root causes

When Registration Goes Wrong

Registration failures are among the most common issues in 5G networks and can stem from authentication problems, subscription misconfigurations, or transport failures. Systematic troubleshooting requires understanding where in the registration flow the failure occurred and reading the associated 5GMM cause code in the Registration Reject message. The cause code maps directly to the root cause: code 3 means illegal UE, code 11 means PLMN not allowed, code 12 means tracking area not allowed, and code 20 means MAC failure during authentication.