How many ethernet ports are too many?

Some network protocols need to keep track of which physical port is which in a topology. PTP is one of those. Defined in IEEE 1588, it specifies a field called portNumber. It is an unsigned 16-bit integer. This means the limit for a single network switch is 65536 ethernet ports. Now, one could argue that 8 bits, 256 ports, is enough. But it doesn’t hurt to future proof and the next logical step is 16 bits. Surely no one will ever make a switch with that many ports!

But if someone makes a switch with over 4096 ports, and that switch also needs to comply with IEC 62439-3:2021, it is up to the network engineering team to ensure no more than 4096 ports are used.

Since the four most significant bits of the portNumber must be “0000” for all clocks in the network, the number of ports per device is reduced to 4 096. The network engineering team is responsible for enforcing it. – IEC 62439-3:2021

Let’s pray that this will be enough.