Cisco 7604 Configuration Guide - Page 689
Determining the Subnet Mask, Determining the Address to Use with the Subnet Mask, Hosts, Bits Mask
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Appendix E Addresses, Protocols, and Ports IPv4 Addresses and Subnet Masks You can also supernet multiple Class C networks into a larger network by using part of the third octet for the extended network prefix. For example, 192.168.0.0/20. This section includes the following topics: • Determining the Subnet Mask, page E-3 • Determining the Address to Use with the Subnet Mask, page E-3 Determining the Subnet Mask To determine the subnet mask based on how many hosts you want, see Table E-1. Table E-1 Hosts, Bits, and Dotted-Decimal Masks Hosts1 /Bits Mask Dotted-Decimal Mask 16,777,216 /8 255.0.0.0 Class A Network 65,536 /16 255.255.0.0 Class B Network 32,768 /17 255.255.128.0 16,384 /18 255.255.192.0 8192 /19 255.255.224.0 4096 /20 255.255.240.0 2048 /21 255.255.248.0 1024 /22 255.255.252.0 512 /23 255.255.254.0 256 /24 255.255.255.0 Class C Network 128 /25 255.255.255.128 64 /26 255.255.255.192 32 /27 255.255.255.224 16 /28 255.255.255.240 8 /29 255.255.255.248 4 /30 255.255.255.252 Do not use /31 255.255.255.254 1 /32 255.255.255.255 Single Host Address 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, page E-4 • Class B-Size Network Address, page E-4 OL-20748-01 Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM E-3
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