LLDP allows you to know exactly on which port is a server (and reciprocally).
It is an industry standard protocol designed to supplant proprietary Link-Layer protocols such as EDP or CDP. The goal of LLDP is to provide an inter-vendor compatible mechanism to deliver Link-Layer notifications to adjacent network devices.
lldpd is an ISC-licensed implementation
of LLDP for various Unixes. It also supports some
proprietary protocols.