The ypbind service is a daemon that remembers information (called a binding) consisting of the association of a domain name with a NIS server. Traditional NIS implementations rely on this daemon to detect a suitable NIS server in their NIS domain. Before being able to perform any NIS queries, an application first finds out from ypbind which server to use.
ypbind probes for servers by broadcasting to the local IP network. The first server to respond is assumed to be the potentially fastest one and will be used in all subsequent NIS queries. After a certain interval has elapsed, or if the server becomes unavailable, ypbind will probe for active servers again.
ypbind may create a security issue if it blindly trusts whomever answers, which could be an attacker. This issue is compounded if your network manages its password databases over NIS. To guard against this, NIS+ does not use ypbind by default, but rather picks up the server host name from a configuration file.