Ethernet slow to initialize on startup

Network Utility.app (included on your Mac) can show you the actual connection speed and error counters for any Network connection.

if not present in

/Applications/Utilities

it can be found in:

/System/Library/CoreServices/Applications

Your connection should be at the expected speed, and there should be no more than a handful of initial errors, and no continuing pattern of errors.

.

Your packets bound for the Internet will be sent to the TopMost Interface in system Preferences > Network. If Wi-Fi or FireWire is at the top, but not in use, this can delay the initialization of your active network interface. Be sure the one you want is at the top.

What sometimes happens is that the network settings are still burdened with some long-forgotten settings, still in use long after they are needed. these are incorporated in the "Location" file.

To walk away from all old settings, use

system preferences > Network > Ethernet > (assist me) > (assistant)

to set it up again from scratch. NB> It is very important that you create a New, named "Location" file, and not rely on "automatic".

every troubleshooting procedure, including the

(assist me) > (diagnostics)

... option available on these settings suggests that you cycle the power on your Router as a routine diagnostic step.

It can't hurt.