Trust No One® said:
Hi all,
I'm after a script or utility that will allow me to export all the subnet
objects in an AD domain, and subsequently import them into another AD
domain.
You can off course do this with an ADSI (custom?) script but the question
implies a need to import a LARGE number of IP Subnets which should almost
never be required.
So far I've had little success.
Has anyone come across such a thing? Several hundred subnets are involved
so I'd hate to have to type them all in!
You can SUMMARIZE adjacent subnets by decreasing the subnet mask (1-bit
summarizes 2, 2 bits summarize 4, 3-8, 4-16, in powers of two.)
I use the term "Step Size" when discussing and teaching either such
summaries
or subnet "sizes". So subnets come in step sizes of 4, 8, 16 etc -- and
subnets
can be summarized in step sizes of 2, 4, 8, 16 etc.
When ISPs combine subnets like this it is usually referred to as
"Supernetting"
-- i.e., creating one larger 'supernetwork' from multiple smaller
subnetworks.
The rule is actually that the LOWEST subnet summarized must be on a multiple
of the "Step Size", and the entire step size MUST be included, i.e., they
must
be adjacent, contiguous, begin at a multiple of the step size, and continue
to
JUST below the NEXT multiple (which would be the next network or supernet.)
Example:
Actual current (sub)networks in Chicago office:
192.168.200.0/24 --- 192.168.207.0/24
Effective summary of these subnets by reducing the mask:
192.168.200.0/21
21 bits is 3 LESS than 24 so it will summarize those 8 subnets, starting at
200, and going up to 207 which is just before the NEXT multiple of 8, 208.
One might wonder, "But what if my subnets are not contiguous? What are
the chances of that happening?"
Actually the chances should be excellent since good (sub)network design
attempts to do this sort of thing whenver possible in a location that uses
multiple subnets, and AGAIN at "district" and "regional" network locations.
The idea is to be able to write the FEWEST number of Routes (then it
is called "route summarization") either by a human or even by smart
router.
This leads to both human and computer/network efficiencies, since the
routing tables and route updates between routers are smaller.
