Don't think of the Class C at all....if you have a /25, that means that, of the 32 bits in the address, the most significant 25 represent the network address. Dotted decimal notation is for human convenience, nothing more. The address is a string of binary digits coming over the wire, and it is read as a string by the device. The most significant 25 of the string will be the network, the remaining 7 bits will be the specific host within that network.
Having said all that-- Dotted decimal groups those 32 bits into 4 convenient sets of 8. A /25 means that the first 3 groups of 3 (for a total of 24) *plus the next bit* represent the network; the last 7 bits represent the host. Among the set of hosts which belong to any one of the /25 networks available, the first address is the network number, and the last address is the network's broadcast address. That's why you have 2^7 - 2 usable host addresses: 2^7 because you have 7 bits available; less 2 to account for the network address and broadcast address. Does that help? Annlee ""Hunt Lee"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > As for VLSM, I found an example in Jeff Doyle (TCP/IP Vol 1) on p290 that I > don't understand. > > 192.168.50.0 /25, and it states that the reason it has /25 is because it > needs to have 100 hosts => so 2^7-2=126 hosts (as 2^6 would be too zmall), > so it makes sense. > > What confuses me is that since 192.168.50.0 /25 is a Class C, it uses up /24 > for subnet bits: > > And if /25 - /24 = /1 > > But isn't the way the calculate the number of subnet: 2^n-2, and in this > case, 2^1-2 = 0, so does it mean it has no subnet? > Also, as for host address, how can I derive Jeff's answer as the host range > is 192.168.50.1-192.168.50.126? > > Thanks so much for your help in advance. > > Best Regards, > Hunt Lee > System Engineer > WebCentral Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35912&t=35827 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
