Inter Device Expandable Network Protocol?
You are mixing few layers of the networking stack.


Physical layer - I2C, SPI, Ethernet PHY Physical implementation details (Bus length, impedance)
Media access layer - I2C frame format, SPI Chip select pins, Ethernet MAC layer
Network management - Clients connecting and disconnecting, DHCP etc.


Those protocols vary from a very simple to the very complex and the choice really depend on your requirements and constraints.

The concept of layers allows you to choose an optimal solution for each part of the network stack. You can, theoretically, run a DHCP like service over an I2C link.