ZyXEL P-663HN-51 Manuel d'utilisateur télécharger pdf (Page 255)

Appendix C IP Addresses and Subnetting

P-663HN-51 User’s Guide

255

By convention, subnet masks always consist of a continuous sequence of ones

beginning from the leftmost bit of the mask, followed by a continuous sequence of

zeros, for a total number of 32 bits.

Subnet masks can be referred to by the size of the network number part (the bits

with a “1” value). For example, an “8-bit mask” means that the first 8 bits of the

mask are ones and the remaining 24 bits are zeroes.

Subnet masks are expressed in dotted decimal notation just like IP addresses. The

following examples show the binary and decimal notation for 8-bit, 16-bit, 24-bit

and 29-bit subnet masks.

Network Size

The size of the network number determines the maximum number of possible

hosts you can have on your network. The larger the number of network number

bits, the smaller the number of remaining host ID bits.

An IP address with host IDs of all zeros is the IP address of the network

(192.168.1.0 with a 24-bit subnet mask, for example). An IP address with host

IDs of all ones is the broadcast address for that network (192.168.1.255 with a

24-bit subnet mask, for example).

As these two IP addresses cannot be used for individual hosts, calculate the

maximum number of possible hosts in a network as follows:

Table 80 Subnet Masks

BINARY

DECIMAL

1ST

OCTET

2ND

OCTET

3RD

OCTET

4TH

OCTET

8-bit mask 11111111 00000000 00000000 00000000 255.0.0.0

16-bit

mask

11111111 11111111 00000000 00000000 255.255.0.0

24-bit

mask

11111111 11111111 11111111 00000000 255.255.255.0

29-bit

mask

11111111 11111111 11111111 11111000 255.255.255.24

Table 81 Maximum Host Numbers

SUBNET MASK HOST ID SIZE

MAXIMUM NUMBER OF

HOSTS

8 bits 255.0.0.0 24 bits 2

– 2 16777214

16 bits 255.255.0.0 16 bits 2

– 2 65534

24 bits 255.255.255.0 8 bits 2

– 2 254

29 bits 255.255.255.2

3 bits 2

– 2 6

1 2 ... 250 251 252 253 254 255 256 257 258 259 260 ... 299 300

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