In reply to a post by meditator:

I've not, however, been able to see a default MTU value in the Registry, as it's now apparent that, in Win XP Home edition, no such data is shown there.

But ANY version of Windows, not just XP Home, will only have an MTU registry entry if the default value has ever been changed. Thus if ANY version of Windows has no MTU registry entry then it will have the default value of 1500.

In reply to a post by jcym:

In reply to a post by meditator:

I've not, however, been able to see a default MTU value in the Registry, as it's now apparent that, in Win XP Home edition, no such data is shown there.

But ANY version of Windows, not just XP Home, will only have an MTU registry entry if the default value has ever been changed. Thus if ANY version of Windows has no MTU registry entry then it will have the default value of 1500.

And it follows that possibly the MTU path discovery wouldn't be there unless changed either ?

Not a bad thing, when you think about it, otherwise the registry would become very bloated with entries full of default values.

correct, there is a LOT of registry entries that do not exist by default. The code in windows will use a default value when they dont exist.

of the top of my head there is 20-30 registry keys inside tcp/parameters that do not exist by default but are configurable. Of course that is just one tiny part of the registry.