Received packet ... with invalid Message-Authenticator! (Shared secret is incorrect.)

FreeRADIUS 'invalid Message-Authenticator' — shared secret

The log line:

Dropping packet without response because of error:
Received packet from 192.168.10.5 with invalid Message-Authenticator!
(Shared secret is incorrect.)

What it actually means: the RADIUS request failed its integrity check. The NAS (switch/AP/controller) signed the packet with one shared secret; FreeRADIUS verified it with another. They disagree, so the server drops the packet without replying at all — which is why the NAS side shows timeouts, not rejects, and why clients just spin.

Nothing about the user, their password, EAP, or your policies is involved. This failure happens before all of that.

The three ways this happens

1. The secrets are actually different

Someone typo’d, someone pasted with a trailing newline, or one side still has last year’s secret. Both input fields show dots, so you can’t compare by looking.

Fix: re-type (never paste) the secret on the NAS and in the matching client {} block in clients.conf, restart or SIGHUP radiusd, retest. If the NAS firmware is old, keep the secret under 32 characters — some devices truncate silently.

2. The packet matched a different client block than you think

FreeRADIUS selects the client {} entry by the packet’s source IP, and more-specific definitions coexist with broad ones. A stray client 0.0.0.0/0 (often added “temporarily” for testing) or an overlapping subnet entry means the secret being checked isn’t from the block you keep editing.

Fix: run radiusd -X, find the incoming packet, and read which client FreeRADIUS says it is. Then grep clients.conf (and sites-enabled/, and any SQL-backed client store) for overlapping definitions.

3. NAT is rewriting the source address

If the NAS sits behind NAT or a load balancer, packets arrive from the translated address — which matches a different (or no) client entry. You fixed the right secret on the right client block; the packets just aren’t attributed to it.

Fix: compare the source IP in the debug line with the NAS’s real address. If they differ, add a client entry for the NAT address, or fix routing so RADIUS traffic keeps its source.

The NPS equivalent

Windows NPS reports the identical disease as Event 6273, Reason Code 262 — “The supplied message is incomplete. The signature was not verified.” Same fix, different console.