[Gllug] subnetting

[Paul Cupis]

On Thursday 11 November 2004 19:16, "Paul Cupis" <paul at cupis.co.uk> 
wrote:
> I'll look around for some reference to this later.

Aha, found it:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml#subnetzero

Traditionally, it was strongly recommended that subnet zero and the 
all-ones subnet not be used for addressing. According to RFC 950, "It 
is useful to preserve and extend the interpretation of these special 
(network and broadcast) addresses in subnetted networks. This means the 
values of all zeros and all ones in the subnet field should not be 
assigned to actual (physical) subnets." This is the reason why network 
engineers required to calculate the number of subnets obtained by 
borrowing three bits would calculate 23-2 (6) and not 23 (8). The -2 
takes into account that subnet zero and the all-ones subnet are not 
used traditionally.

RFC 950
http://www.ietf.org/rfc/rfc0950.txt

Regards,

Paul Cupis
-- 
paul at cupis.co.uk

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