Option 82 or subnet: who wins?

Simon Hobson dhcp1 at thehobsons.co.uk
Sat Mar 14 16:37:38 UTC 2009


David McGaughey wrote:
>Guess that I am confused about what "global" means for a class.  If 
>it means all class definitions are global, then by definition, it 
>should not matter in what other context they are defined.

It's "a bit complicated" !

Whilst various constructs are 'global' in as much as (say) a host 
statement defined anywhere will be available anywhere else, that's 
not to say that locality of definition is irrelevant. I assume 
classes are the same, but certainly for host statements, they are 
available anywhere but can inherit properties from where they are 
defined. For example, if you define a host inside one subnet 
definition, but that host is booting from a different subnet, then it 
will inherit some properties from the subnet where the host statement 
is defined and some from where it's current lease derives from - the 
result can be a host that gets given a router option for the wrong 
subnet !

That's why the standard advice is to always define such things in the 
global scope - if you don't then "interesting" things can happen.


And no I don't know why things are how they are - I'm sure parsers 
are non-trivial to implement.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.



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