Date: Tue, 24 Jan 2006 15:49:54 -0600 (CST) From: Mark Jacobson To: 810-023-01@uni.edu Subject: 9 bit subnet masking.. Hi 023 students, If you wanted to have more than 256 but fewer than 512 subnetworks at your organization, then your organization: 1. Has to be class A or class B, it could NOT be class C. Why? Default masks: A -- 255.0.0.0 B -- 255.255.0.0 C -- 255.255.255.0 2. You would need 9 bits to specify the network at your organization. Class A mask would be 255.255.128.0 11111111.11111111.10000000.00000000 255 255 128 0 Class B mask would be 255.255.255.128 11111111.11111111.11111111.10000000 255 255 255 128 n = network bit s = subnet or subnetwork bit h = host bit, such as a device like a PC or server or printer Either 8 n's, 9 s's and 15 h's nnnnnnnn.ssssssss.shhhhhhh.hhhhhhhh 11111111.11111111.10000000.00000000 -------- - 255 255 128 0 or 16 n's, 9 s's and 7 h's nnnnnnnn.nnnnnnnn.ssssssss.shhhhhhh 11111111.11111111.11111111.10000000 nnnnnnnn.nnnnnnnn.ssssssss.shhhhhhh -------- - 255 255 255 128 The subnetwork bits are underlined too. There are 9 (NINE) subnet specifying bits, to allow for up to 2 to the 9th or 512 different subnetworks. Eight is NOT enough, if you need MORE THAN 256 subnets! ------------------- 8 2 = 256 9 10 2 = 512 2 = 1,024 Nine bits are needed! Mark