Example

197 . 217 . 244 . 51 1100 0101 . 1101 1001 . 1111 0100 . 0011 0011

/26 - subnet mask 1111 1111 . 1111 1111 . 1111 1111 . 1100 0000

bitwise AND logic is: 0 AND 0 = 0 1 AND 0 = 0 0 AND 1 = 0 1 AND 1 = 1

Network 1100 0101 . 1101 1001 . 1111 0100 . 0000 0000 197 . 217 . 244 . 0

Broadcast 1100 0101 . 1101 1001 . 1111 0100 . 0011 1111 197 . 217 . 244 . 63

first host = NET + 1 197 . 217 . 244 . 1

last host = BRD - 1 197 . 217 . 244 . 62

next subnet 197 .217 . 244 .64

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Practice

Target ip address

decimal	181	12	23	148
binary	1011 0101	0000 1100	0001 0111	1001 0100

/19 - subnet mask

decimal	8	16	24	32
binary	1111 1111	1111 1111	1110 0000	0000 0000

Network

binary	1011 0101	0000 1100	0000 0000	0000 0000
decimal	181	12	0	0

Broadcast

binary	1011 0101	0000 1100	0001 1111	1111 1111
decimal	181	12	31	255

First host = NET + 1

Last host = BRD - 1

next subnet = BRD + 1

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Patterns to Recognize

• Common IP Octet Values in Binary:
• • 0 = 00000000 (all zeros)
• • 128 = 10000000 (just the first bit)
• • 192 = 11000000 (first two bits)
• • 224 = 11100000 (first three bits)
• • 240 = 11110000 (first four bits)
• • 248 = 11111000 (first five bits)
• • 252 = 11111100 (first six bits)
• • 254 = 11111110 (first seven bits)
• • 255 = 11111111 (all ones)

Speed Tips

• 1. The Half-Way Method
• • 128 is half of 256 (the range of one octet)
• • If a number is ≥ 128, the first bit is 1
• • Subtract 128 and repeat with 64, 32, etc.
• 2. Common Patterns
• • 255 = all 1s (8 bits on)
• • 0 = all 0s (8 bits off)
• • Powers of 2 = only one bit on
• 3. Subnet Mask Shortcuts
• • /24 = 255.255.255.0 (3 full octets)
• • /16 = 255.255.0.0 (2 full octets)
• • /8 = 255.0.0.0 (1 full octet)
• 4. Quick Check Method
• • Even numbers end in 0
• • Odd numbers end in 1
• • Numbers ≥ 128 start with 1

172 1010 1100