ES-2048 User’s Guide

Table 86 Alternative Subnet Mask Notation (continued)

SUBNET MASK

SUBNET MASK “1” BITS

LAST OCTET BIT VALUE

DECIMAL

 

 

 

 

255.255.255.240

/28

1111 0000

240

 

 

 

 

255.255.255.248

/29

1111 1000

248

 

 

 

 

255.255.255.252

/30

1111 1100

252

 

 

 

 

The first mask shown is the class “C” natural mask. Normally if no mask is specified it is understood that the natural mask is being used.

Example: Two Subnets

As an example, you have a class “C” address 192.168.1.0 with subnet mask of 255.255.255.0.

Table 87 Two Subnets Example

IP/SUBNET MASK

NETWORK NUMBER

HOST ID

 

 

 

IP Address

192.168.1.

0

 

 

 

IP Address (Binary)

11000000.10101000.00000001.

00000000

 

 

 

Subnet Mask

255.255.255.

0

 

 

 

Subnet Mask (Binary)

11111111.11111111.11111111.

00000000

 

 

 

The first three octets of the address make up the network number (class “C”).

To make two networks, divide the network 192.168.1.0 into two separate subnets by converting one of the host ID bits of the IP address to a network number bit. The “borrowed” host ID bit can be either “0” or “1” thus giving two subnets; 192.168.1.0 with mask 255.255.255.128 and 192.168.1.128 with mask 255.255.255.128.

Note: In the following charts, shaded/bolded last octet bit values indicate host ID bits “borrowed” to make network ID bits. The number of “borrowed” host ID bits determines the number of subnets you can have. The remaining number of host ID bits (after “borrowing”) determines the number of hosts you can have on each subnet.

Table 88 Subnet 1

IP/SUBNET MASK

NETWORK NUMBER

LAST OCTET BIT

VALUE

 

 

 

 

 

IP Address

192.168.1.

0

 

 

 

IP Address (Binary)

11000000.10101000.00000001.

00000000

 

 

 

Subnet Mask

255.255.255.

128

 

 

 

Subnet Mask (Binary)

11111111.11111111.11111111.

10000000

 

 

 

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