ZyXEL VSG-1200 User Manual download pdf (Page 267)

VSG-1200 User’s Guide

Appendix H IP Subnetting 267

For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with mask 255.255.255.128.

The following table shows all possible subnet masks for a class “C” address using both

notations.

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.

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

have two separate 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.

Table 99 Alternative Subnet Mask Notation

SUBNET MASK IP ADDRESS SUBNET MASK “1” BITS LAST OCTET BIT VALUE

255.255.255.0 /24 0000 0000

255.255.255.128 /25 1000 0000

255.255.255.192 /26 1100 0000

255.255.255.224 /27 1110 0000

255.255.255.240 /28 1111 0000

255.255.255.248 /29 1111 1000

255.255.255.252 /30 1111 1100

Table 100 Two Subnets Example

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

Note: In the following charts, shaded/bolded last octet bit values indicate host

ID bits “borrowed” to form 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.

1 2 ... 262 263 264 265 266 267 268 269 270 271 272 ... 279 280

No comments

ZyXEL VSG-1200 User Manual Page 267