NTLM Authentication: Client would send information/details required for authentication in the next REGISTER Requests to the skype for business server, skype for business server in turn talks to AD Server and validates the submitted information/details.If the Validation succeeds then, skype for business server would consider user authentication as valid/genuine and signs the user. Once it gets the Kerberos ticket, it submits that to Server in next REGISTER request, and server would authenticate the user and signs the user.(In Kerberos method, there is an interaction between clients and AD Servers, this is the primary reason why Kerberos Authentication isn't available for Remote Sign in) Kerberos authentication: Client would reach out to AD Server and gets authentication ticket (Kerberos ticket) for accessing service on Skype for Business Server. If Client is signing in Externally, then only 2 authentication methods will be available will be available.

If Client is signing in Internally, then all Authentication methods will be available.

In response to this REGISTER request, Skype for Business Server would send the list of Authentication mechanisms available for Authentication in 401 Unauthorized.

Firstly, Client sends an Unauthenticated REGISTER Request to the Skype for Business Server.

TLS connectivity Checks, in order for Client to be able to trust the presented certificate, client should have the Root CA Cert of the Certification authority that has issued the certificate to the server in its Certificate Trusted Root Store.

Port Connectivity Checks, TCP 3 Way Handshake.

Skype for Business Client is hardcoded to query certain DNS records to locate the Skype for business server information, which is required for Automatic Client sign in, below are the list of DNS records that client would query in order for Server discovery:Īt the End of this step, if we have DNS Records configured, skype for business client will get the FQDN/IP Address & Port combination of Skype for business server where it can reach to login. The entire Skype for Business Client Sign in process divided into below 5 steps:

How do i sign up for skype for business