[Samba] Signed Dynamic DNS Updates with Internal DNS [SEC=UNCLASSIFIED]

Thamm, Russell russell.thamm at dsto.defence.gov.au
Thu Jan 28 06:15:04 UTC 2016

I just installed SAMBA 4 as the PDC on a new standalone Windows network (https://wiki.samba.org/index.php/Samba4/HOWTO#Samba_AD_management).
Everything appears to be working correctly except for signed dynamic updates.

Non-secure updates work fine. A, AAAA and PTR records are added to DNS when a PC joins the domain or I issue ipconfig /registerdns.

Using wireshark, I see the following when I issue "ipconfig /registerdns" (samba configured for signed updates):

An unsigned dynamic update request is rejected.
An apparently successful Tkey handshake occurs.
The client fails to request a signed dynamic update.

I interpret this as the client not being happy with the TKEY response. However, no errors are reported in the client's event log.

In the samba log I see (log level = 3):

Update not allowed for unsigned packet.
Tkey handshake completed
Terminating connection - 'dns_tcp_call_loop: tstream_read_pdu_blob_recv() - NT_STATUS_CONNECTION_DISCONNECTED

In the past I used Samba 4 to take over from 2003 server (https://wiki.samba.org/index.php/Samba4/HOWTO/Join_a_domain_as_a_DC). Here I used bind and eventually got signed dynamic updates working.

When I compare the Tkey transaction (internal DNS vs bind), I see that the Tkey response packet for internal DNS has an additional RR.
    Additional records
        1252-ms-7.1-247ed95d.4c1a5028-c4b1-11e5-f7a4-5065f335d668: type TSIG, class ANY
            Name: 1252-ms-7.1-247ed95d.4c1a5028-c4b1-11e5-f7a4-5065f335d668
            Type: TSIG (Transaction Signature) (250)
            Class: ANY (0x00ff)
            Time to live: 0
            Data length: 46
            Algorithm Name: gss-tsig
            [Expert Info (Warn/Malformed): Trying to fetch an absolute time value with length 6]
                [Trying to fetch an absolute time value with length 6]
                [Severity level: Warn]
                [Group: Malformed]
            Time Signed: Jan  1, 1970 15:39:44.000000000 ACST
            Fudge: 300
            MAC Size: 28
                [Expert Info (Warn/Undecoded): No dissector for algorithm:gss-tsig]
                    [No dissector for algorithm:gss-tsig]
                    [Severity level: Warn]
                    [Group: Undecoded]
            Original Id: 38945
            Error: No error (0)
            Other Len: 0

Could the apparently malformed "Time Signed" field be the problem. This is the only whiff of an error that I can detect.

I'd be grateful for any hints


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