Wednesday, February 08, 2006  

[For a very special audience only...]

[This post requires some networking background/knowledge to understand. If not, it probably won't make much sense to you.]

If you've ever taken any networking courses or read any networking book, you'd most likely have come across subnetting. The reasons why the host portion cannot have all 1's or all 0's are obvious and easy to understand.

However, why does this rule apply to the subnet portion? Most (if not all) textbooks also say that all 1's and all 0's cannot be used for the subnet portion, but after thinking long and hard, I realised there's really no reason why it cannot be done. If implemented correctly, the networking devices should not confused the all 1's and all 0's subnets for network address or broadcast addresses, since you cannot have all 1's and 0's for the host portion.

Did some digging around online, found this site that taught subnetting. Nothing new about the information presented, except the last bit at the bottom of the page.
"Historically, subnets composed of all ones or all zeros were reserved. Therefore the minimum number of subnet bits allowed was two, which allotted for two usable subnets (01 and 10 in binary, subnets 1 and 2 in decimal) and two reserved subnet addresses (00 and 11 in binary, subnets 0 and 3 in decimal). However, RFC 1878 abolished this practice because the reserved subnets were generally not being used for any special purpose and was considered wasteful. Thus the minimum number of subnet bits is now one, allowing for two usable subnets (0 and 1 in binary, and decimal). This info can be helpful for students preparing for the MCSE 70-216 exam."
Mystery solved.

^^^ by Locksley @ 12:37 PM. 0 comments.
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