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Prestige 2602R Series User’s Guide

293 Appendix C IP Subnetting

Note: Host IDs of all zeros or all ones are not allowed.

Therefore:

A class “C” network (8 host bits) can have 2

–2 or 254 hosts.

A class “B” address (16 host bits) can have 2

–2 or 65534 hosts.

A class “A” address (24 host bits) can have 2

–2 hosts (approximately 16 million hosts).

Since the first octet of a class “A” IP address must contain a “0”, the first octet of a class “A”

address can have a value of 0 to 127.

Similarly the first octet of a class “B” must begin with “10”, therefore the first octet of a class

“B” address has a valid range of 128 to 191. The first octet of a class “C” address begins with

“110”, and therefore has a range of 192 to 223.

Table 85 Allowed IP Address Range By Class

CLASS

ALLOWED RANGE OF FIRST OCTET

(BINARY)

ALLOWED RANGE OF FIRST OCTET

(DECIMAL)

Class A 00000000 to 01111111 0 to 127

Class B 10000000 to 10111111 128 to 191

Class C 11000000 to 11011111 192 to 223

Class D 11100000 to 11101111 224 to 239

Subnet Masks

A subnet mask is used to determine which bits are part of the network number, and which bits

are part of the host ID (using a logical AND operation). A subnet mask has 32 is a “1” then

the corresponding bit in the IP address is part of the network number. If a bit in the subnet

mask is “0” then the corresponding bit in the IP address is part of the host ID.

Subnet masks are expressed in dotted decimal notation just as IP addresses are. The “natural”

masks for class A, B and C IP addresses are as follows.

Table 86 “Natural” Masks

CLASS NATURAL MASK

A 255.0.0.0

B 255.255.0.0

C 255.255.255.0

1 2 ... 288 289 290 291 292 293 294 295 296 297 298 ... 348 349

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ZyXEL Communications P-2602R-63 Betriebsanweisung Seite 293