NAS 5G UE to AMF 3GPP TS 24.501

5G NAS - Authentication Failure

Authentication Failure is the UE's NAS message indicating that it could not validate or complete the network authentication challenge.

Message Fact Sheet

Protocol	nas	Network	5g
Spec	3GPP TS 24.501	Spec Section	8.2.4
Direction	UE to AMF	Message Type	5GMM signaling

Full message name	5G NAS - Authentication Failure
Protocol	NAS
Technology	5G
Direction	UE to AMF
Interface	N1
Signaling bearer / channel	NAS signaling / Dedicated NAS message, commonly via UL Information Transfer
Typical trigger	Sent when the UE cannot validate the network's authentication challenge or encounters a challenge-related failure condition.
Main purpose	Lets the UE explicitly signal that authentication of the network failed or could not be completed.
Main specification	3GPP TS 24.501, 8.2.4
Release added	Release 15
Procedures where used	5G Initial Registration, 5G Authentication Procedure
Related timers	T3560
Related cause values	5GMM cause

What is Authentication Failure in simple terms?

Authentication Failure is the UE's NAS message indicating that it could not validate or complete the network authentication challenge.

Lets the UE explicitly signal that authentication of the network failed or could not be completed.

Why this message matters

Authentication Failure is the UE telling the network that it could not complete the authentication challenge successfully.

Where this message appears in the call flow

5G Authentication Procedure

Call flow position: UE-side negative outcome within the authentication challenge-response exchange.

Typical state: UE could not successfully validate or use the received challenge.

Preconditions:

Authentication Request has been received.

Next likely message: Authentication Reject or another network decision

Call flow position

Previous message(s): Authentication Request

Next message(s): Authentication Reject, New Authentication Request

Message direction and transport

Sender and receiver: UE to AMF

Interface: N1

Domain: Core-side mobility management failure reporting

Signaling bearer: NAS signaling

Logical channel: Dedicated NAS message, commonly via UL Information Transfer

Transport / encapsulation: NAS 5GS message carried end-to-end between UE and AMF

Security context: Typically part of a failed authentication branch before full NAS security activation.

Message Structure Overview

Authentication Failure is a UE-originated failure report, so the cause value is the first field engineers inspect.

Structure Syntax

This message is not typically analyzed as ASN.1 on the wire. Engineers usually inspect it as a NAS or protocol field decode rather than an ASN.1 tree.

Authentication Failure is a NAS 24.501 message, not an ASN.1 message.

Decoded Message Dump

Authentication Failure
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Plain NAS
  Message Type: Authentication Failure
  5GMM Cause: MAC failure

How to read this dump

The 5GMM cause is usually the main engineering entry point.

Important Information Elements

IE	Required	Description
`5GMM cause`	Yes	Explains why the UE could not complete the authentication procedure.
`Authentication failure parameter`	Optional	Optional failure detail, such as synchronization-related information.

Detailed field explanation

`5GMM cause`

Explains why the UE could not complete the authentication procedure.

Presence: Required

`Authentication failure parameter`

Optional failure detail, such as synchronization-related information.

Presence: Optional

What to check in logs and traces

Check the returned 5GMM cause first.
Correlate the failure with the exact Authentication Request challenge values.
Inspect whether the message includes an additional failure parameter.

Common Issues and Troubleshooting

The UE never answers authentication successfully and sends Authentication Failure.

Likely cause: The UE could not validate AUTN, detected MAC failure, or hit a synchronization-related problem.

What to inspect: Check the 5GMM cause, optional failure parameter, and the preceding challenge.

Next step: Troubleshoot subscriber credentials, synchronization context, and network authentication data.

Detailed explanation

5G NAS - Authentication Failure Explained

Authentication Failure is the UE’s negative response during the authentication procedure. Instead of proving identity successfully, the UE tells the network that it could not validate or complete the challenge.

For beginners, the simple meaning is: the UE could not accept the network’s authentication challenge.
For engineers, this is one of the most useful failure messages in the 5GMM authentication branch because it points to challenge-validation problems rather than generic registration failure.

What is Authentication Failure in simple terms?

The network sent an authentication challenge. The UE could not process or validate it correctly, so it reports the problem back.

Why Authentication Failure matters

This message matters because it tells you the failure is happening inside the authentication branch, often because of:

challenge validation problems
synchronization issues
credential or subscriber-data mismatch

That is much more specific than simply saying “registration failed.”

Where Authentication Failure appears in the call flow

UE                              gNB / AMF
|<-- Authentication Request -----|
|--- Authentication Failure ---->|
|<-- Reject or retry decision ---|

Transport characteristics

Direction: UE to AMF
Interface: N1
Transport on access side: usually via UL Information Transfer
Security expectation: normally part of a pre-security failure branch

What Authentication Failure means operationally

Operationally, this message means the UE did not accept the challenge as valid. That is different from a missing response or a network-side reject.

The key engineering question becomes: why did the UE reject the challenge?

Important Information Elements

IE	Why it matters
`5GMM cause`	Gives the primary reason the UE could not complete authentication.
`Authentication failure parameter`	Adds failure detail in some scenarios, including synchronization-related cases.

Example message dump

Authentication Failure
  Extended Protocol Discriminator: 5G Mobility Management
  Security Header Type: Plain NAS
  Message Type: Authentication Failure
  5GMM Cause: MAC failure

How to read this dump

Read the 5GMM cause first.
Then go back to the preceding Authentication Request.
If additional failure parameters are present, decode them before concluding the root cause.

What to check in logs

inspect the exact cause reported by the UE
compare it with the preceding challenge values
check whether the network retries authentication or stops the procedure
correlate with subscriber and authentication-backend context

FAQ

What is Authentication Failure in 5G?

It is the UE's message indicating that it could not validate or complete the network's authentication challenge.

Summary

Authentication Failure is the UE's NAS message indicating that it could not validate or complete the network authentication challenge.

Advanced Engineer Notes

This is different from Authentication Reject. Authentication Failure is UE-originated and usually points to validation of the network challenge itself.

Related message pages

Related Procedures

Related Tools

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.