Cisco PIX 500 Series Configuration Manual page 1037

Appendix D Addresses, Protocols, and Ports
Determining the Subnet Mask
To determine the subnet mask based on how many hosts you want, see
Table D-1
Hosts
16,777,216
65,536
32,768
16,384
8192
4096
2048
1024
512
256
128
64
32
16
8
4
Do not use
1
1. The first and last number of a subnet are reserved, except for /32, which identifies a single host.
Determining the Address to Use with the Subnet Mask
The following sections describe how to determine the network address to use with a subnet mask for a
Class C-size and a Class B-size network. This section includes the following topics:
•
•
Class C-Size Network Address
For a network between 2 and 254 hosts, the fourth octet falls on a multiple of the number of host
addresses, starting with 0. For example, the 8-host subnets (/29) of 192.168.0.x are as follows:
Subnet with Mask /29 (255.255.255.248) Address Range
192.168.0.0
192.168.0.8
OL-12172-03
Hosts, Bits, and Dotted-Decimal Masks
1
/Bits Mask
/8
/16
/17
/18
/19
/20
/21
/22
/23
/24
/25
/26
/27
/28
/29
/30
/31
/32
Class C-Size Network Address, page D-3
Class B-Size Network Address, page D-4
Dotted-Decimal Mask
255.0.0.0 Class A Network
255.255.0.0 Class B Network
255.255.128.0
255.255.192.0
255.255.224.0
255.255.240.0
255.255.248.0
255.255.252.0
255.255.254.0
255.255.255.0 Class C Network
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
255.255.255.254
255.255.255.255 Single Host Address
1
192.168.0.0 to 192.168.0.7
192.168.0.8 to 192.168.0.15
Cisco Security Appliance Command Line Configuration Guide
IPv4 Addresses and Subnet Masks
Table D-1.
D-3