Cisco TelePresence Administrator's Manual page 128

Device authentication
About device authentication
Ports
See Device authentication port reference [p.399] for a list of ports used when communicating with the AD
system.
SPNEGO
SPNEGO (Simple and Protected GSSAPI Negotiation Mechanism) is a mechanism used by client
applications when they seek to authenticate with a remote server. It allows the client and server to identify
which authentication protocols they both support and decide which protocol to use.
By default the VCS uses SPNEGO when communicating with an AD Domain Controller. It can only be
enabled or disabled through the CLI by using the command xConfiguration Authentication ADS
SPNEGO.
Cisco VCS Administrator Guide (X8.1.1) Page 128 of 507