assoc_group_id in dcesrv_bind()

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Dear all,

I'm comparing the Samba4alpha5 active directory with the Windows active directory.

I found the Windows AD processed the four NETLOGON processes: 
NetrServerReqChallenge, NetrServerAuthenticate3, NetrLogonGetDomainInfo, and NetrLogonSamLogonWithFlags.
However, the Samba4 AD processed only NetrServerReqChallenge and NetrServerAuthenticate3.

A function dcesrv_bind() on a file "rpc_server/dcerpc_server.c" contains the following check:

	if (call->pkt.u.bind.assoc_group_id != 0) {
	      return dcesrv_bind_nak(call, 0);
	}

This "assoc_group_id" marked non-zero values in most cases.
If this part is commented out, the Samba4 AD can enter NetrLogonGetDomainInfo process.

In addition, dcesrv_bind() sets a constant value "0x12345678" to assoc_group_id for dcesrvauth_bind_ack().

Now, I would like to know why the assoc_group_id is assumed as a constant value in the code.
Is there a document showing behaviour of assoc_group_id in DCERPC handling?

Best regards

Takeshi Higashizaki