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Checkpoint Next Generation Security Administration by Syngress

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Appendix A

Class C Subnet Mask Cheat Sheet

This cheat sheet can come in handy when working with network addresses and subnet masks. A standard netmask is written 255.255.255.0 which is equivalent to the aggregate /24. Using aggregates has become popular because computer people tend to be lazy and it only requires three keystrokes.

Table A.1

Netmasks and Aggregates

Netmasks and Aggregates
Subnet Mask255.255.255.0Hex Mask0xffffff00
Subnet Bits/Aggregate24Host Bits8
Number of Subnets1Hosts per Subnet254
Network AddressHost IP RangeBroadcast Addresses
.0.1 - .254.255
Subnet Mask255.255.255.128Hex Mask0xffffff80
Subnet Bits/Aggregate25Host Bits7
Number of Subnets2Hosts per Subnet126
Network AddressHost IP RangeBroadcast Addresses
.0.1 - .126.127
.128.129 - .254

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