Re: How do I determine subnet manually?

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verifone411

join:2008-05-08

Re: How do I determine subnet manually?

Thanks for the infomation. Sticking with the first class b number (does that change things since you decided to move the example to a class c?)

How do you know and how do you determine that...

/24 = 256 IPs = 254 Usable ? i know the diagrams say that.

Is it because the last 2 sets of octects represent 8 bits each for a total of 16. Each 16 bit placeholder can have 2 different values so that is why you raise it to the power of 2? to get 65536- 2=65534 usable?

permalink · 2008-05-08 18:46:15 ·

tschmidt
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Re: How do I determine subnet manually?

Each octet is 8-bits. A /24 address means 24-bits of address are reserved for network leaving 8 for host. This assumes you are talking about IPv4 with a 32-bit address range.

An Octet is FFh or 256 (in decimal notion) However, since the lowest address is reserved as network address and highest for broadcast that leaves 254 available host addresses.

Dotted Decimal was a convenient way to represent IP address when Class-full addressing was used since Class boundaries were also octet boundaries. With the advent of classless routing where split between network and host address can occur anywhere dotted decimal is a little like using Roman numerals to build a house.

If you stick with binary or hex it is a lot less confusing.

/tom

permalink · 2008-05-08 20:18:51 · Print ·

IamGimli join:2004-02-28 Canada ·Primus Talkbroadband ·B2B2C High-Speed I..	Re: How do I determine subnet manually? said by tschmidt : If you stick with binary or hex it is a lot less confusing. I understand binary but how is hexadecimal any less confusing than decimal to represent network addresses? It may make them a bit shorter to write but I don't see any difference in the confusion aspect.
	permalink · 2008-05-09 10:22:29 ·

tschmidt
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Re: How do I determine subnet manually?

said by IamGimli

:

I understand binary but how is hexadecimal any less confusing than decimal to represent network addresses? It may make them a bit shorter to write but I don't see any difference in the confusion aspect.

Dotted decimal represents a discontinuous counting method. If I add 1 to FFh I get 100h. If I add 1 to 0.255 (dotted decimal) I get 1.0. Life gets even more exciting if I start playing with masking lower order bits.

If I want to mask the 2 low order bits I have
1111 1100 b (binary)
FCh (hex)
252 Decimal

Perhaps I'm unique (after all this is not my day job) but I find it impossible to do arithmetic in dotted decimal.

/tom

permalink · 2008-05-09 12:52:12 · Print ·

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