219

Figure 6-22  Subnets Planned on a Spreadsheet

	Corporate Net	HQ	Sales		HR		Legal		WAN1	WAN2		WAN3	Unused
	172.16.0.0/22	172.16.0.0/23	172.16.2.0/24		172.16.3.0/26		172.16.3.64/27	172.16.3.128/30		172.16.3.132/30		172.16.3.136/30
	172.16.0.1	172.16.0.1
		172.16.1.255
			172.16.2.0
			172.16.2.255
					172.16.3.0
					172.16.3.63
							172.16.3.64
							172.16.3.127
								172.16.3.128
								172.16.3.131
										172.16.3.132
										172.16.3.135
												172.16.3.136
												172.16.3.139
													172.16.3.140
	172.16.3.255												172.16.3.255
Figure 6-23  Additional Subnetting of the HQ Location
					HQ		HQ1		HQ2
				172.16.0.0/23		172.16.0.0/24			172.16.1.0/24
				172.16.0.1		172.16.0.0
						172.16.0.255
									172.16.1.0
				172.16.1.255					172.16.1.255

As previously presented, the creation of new, smaller networks from a given address block is done by extending the length of the prefix, that is, adding 1s to the subnet mask. Doing this allocates more bits to the network portion of the address to provide more patterns for the new subnet. For each bit you borrow, you double the number of networks you have. For example, if you use 1 bit, you have the potential to divide that block into two smaller networks.