What could prevent a DHCP server from starting on a LAN interface that is also a bridge port?

A DHCP server that is configured to operate on a LAN interface that is part of a bridge can indeed face limitations due to the nature of bridging in networking. When an interface is added to a bridge, it becomes part of the bridge's logical interface, which means it cannot operate independently.

In bridging, the individual characteristics of the LAN interface, such as its ability to serve as the DHCP server, are often overridden by the behavior of the bridge itself. To put it simply, once an interface is assigned to a bridge, it does not have its own unique IP address and operates on the bridge's address instead. This means that the DHCP server cannot function on an interface that is just a bridge port because the DHCP service relies on having a unique IP address on the interface to offer leases to clients.

Understanding this principle is crucial for properly configuring networks that utilize bridging. A well-defined setup will ensure that DHCP services are allocated correctly, ideally configured directly on the bridge itself when dealing with bridges in networking.