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SMB Login failure 3x weight measured

SMB. protocol version mismatch between client and server

SMB connection failed: protocol error
Events
199
Pts per check
4.2
Pts missed
829.2
Teams hit
2/13

Authority mappings

Which work roles, knowledge units, and EWU courses this error pattern touches. Hover for context, click to drill in.

DCWF roles: CE-463 Host Analyst CS-462 Control Systems Security Specialist CS-521 Cyber Defense Infrastructure Support Specialist CS-531 Cyber Defense Incident Responder IT-411 Technical Support Specialist IT-451 System Administrator
Knowledge Units: CD-ISC IT Systems Components CD-NDF Network Defense CD-OSA Operating Systems Administration CD-OSC Operating Systems Concepts CD-OSH Operating Systems Hardening
EWU courses: CSCD240-S26 CSCD210 CSCD212 CSCD240 CSCD327 CSCD379 CSCD380 CSCD381 CSCD434 CSCD470 CSCD496

What the message means

The SMB handshake failed because client and server can't agree on a protocol version. Modern Samba defaults to SMB3 but some scoring engines or older clients only speak SMB1 (NT1). The fix is to widen your min protocol.

Why the service is down

Commands in order

  1. 1. 1. Check current min/max protocol
    testparm -s 2>/dev/null | grep -iE 'min protocol|max protocol|server min'
    Expect
    server min protocol = NT1 or SMB2
    Interpret and next
    If nothing printed, defaults are in effect (Samba 4.11+ defaults to SMB2).
  2. 2. 2. Lower min protocol for compatibility
    # edit /etc/samba/smb.conf, under [global]: server min protocol = NT1 client min protocol = NT1
    Expect
    File saved without syntax error
    Interpret and next
    Re-run testparm. If errors: remove the new lines, check spelling.
  3. 3. 3. Restart Samba and retest
    systemctl restart smbd smbclient -L //localhost -U keons
    Expect
    Share list appears without 'protocol error'
    Interpret and next
    Still fails = try removing `smb encrypt`/`smb signing` strict settings, or check `ntlm auth = yes`.

Decision tree

Answer each question to route to the right fix.

Q: Does testparm -s show a min protocol?
Yes: Lower it to NT1 temporarily.
No: Add `server min protocol = NT1` and `ntlm auth = ntlmv1-permitted` under [global].

External references

Other patterns on this service