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IP Subnet Masks

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• 1 IP-Subnet-Mask numbers 

o 1.1 hat is a !ero subnet" #o$ has it %hanged"

o 1.& #ere is an e'amp(e: 

1.&.1 Mask tab(e 

1.&.1.1 Mask ) *&+

1.&.1.& Mask ) *&

1.&.1. Mask ) *&

1.&.1.+ Mask ) *&/

1.&.1. Mask ) *&0

1.&.1. Mask ) *&

1.&.1./ Mask ) *2

o 1. 3etmasks

o 1.+ as this In4ormation 5se4u("

[edit] IP-Subnet-Mask numbers

IP mask numbers are used to divide internet addresses into b(ocks ca((ed subnets. 6he mask number represents the number o4 1s in

the binar7 o4 the address that is 8masked9 against the address so that it ignores the (ast bits $hich are 4or the group o4 IP addresses inthe masked address.

6he 4irst address o4 a subnet b(ock a(( 2s; is ca((ed the net$ork address or net$ork I<. 6he (ast address a(( 1s; is the broadcast

address o4 the net$ork. 67pica((7 the net$ork address =1 or the broadcast address -1 is the gate$a7 to the internet. 6he 8s(ash8

notation ie *&+; is kno$n as %I<> 4ormat, $hi(e the more conventiona( &.&.&.2 notation is considered a subnet mask.

[edit] What is a zero subnet? How has it Changed?

5nder o(d IP subnetting ru(es, the a(( 2?s subnet $as reserved 4or the net$ork, and the a(( 1?s subnet $as reserved 4or the broadcast.

@ver time, it $as 4ound that the a(( 2?s subnet $asn?t rea((7 used and, i4 it cou(d be handed out as a useab(e net$ork, man7 IPaddresses cou(d be changed.

An e'amp(e o4 an IP address that is using a !ero subnet is 12.1.2.1 $ith a subnet mask o4 &.&.&.2. Bar(ier this $as a kind o4

net$ork id but toda7, this IP address is per4ect(7 (ega( $hen it comes to subnetting. 6hus, i4 I had an IP address o4 12.1.2.2 $ith a&.&.2.2 subnet mask is the net$ork I< and i4 $e subnet it, $e cou(d actua((7 get & va(id net$orks out o4 it b7 using the 2

subnet.

et bits Subnet mask tota!-addresses "er subnet

*&2 &.&.&+2.2 +2

*&1 &.&.&+0.2 &2+0

*&& &.&.&&.2 12&+

*& &.&.&+.2 1&

*&+ &.&.&.2 &

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*& &.&.&.1&0 1&0

*& &.&.&.1& +

*&/ &.&.&.&&+ &

*&0 &.&.&.&+2 1

*& &.&.&.&+0 0

*2 &.&.&.&& +

6he 4irst address o4 a subnet b(ock a(( 2s; is ca((ed the net$ork address or net$ork I<. 6he (ast address a(( 1s; is the broadcast

address o4 the net$ork. 67pica((7 the net$ork address =1 or the broadcast address -1 is the gate$a7 to the internet. 6his (eaves us

$ith tota( number o4 IP numbers - (e4t over 4or host address $ith in a sub net b(ock. 6hat8s $h7 7ou either get 1 IP +-) 1; or i4

7ou ask 4or one more 7ou get 0-);.

[edit] Here is an e#am"!e$

1&.10.1.2*& $ou(d inc(ude a(( address bet$een 1&.10.1.2 and 1&.10.1.1&/

$hi(e 1&.10.1.1&0*& $ou(d inc(ude 1&.10.1.1&0 and 1&.10.1.&

Ce(o$ is a mask tab(e that makes it eas7 to (ook up the mask 4or a group o4 IP addresses.

[edit] Mask tab!e

[edit] Mask % &'(

0-255

[edit] Mask % &')

0-127

128-255

[edit] Mask % &'*

0-63

64-127

128-191

192-255

[edit] Mask % &'+

0-31

32-63

64-95

96-127

128-159

160-191

192-223

224-255

[edit] Mask % &',

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0-15

16-31

32-47

48-63

64-79

80-95

96-111

112-127

128-143

144-159

160-175

176-191

192-207

208-223

224-239

240-255

[edit] Mask % &'

0-7

8-15

16-23

24-31

32-39

40-47

48-55

56-63

64-71

72-79

80-87

88-95

96-103

104-111

112-119

120-127

128-135

136-143

144-151

152-159

160-167

168-175

176-183

184-191

192-199

200-207

208-215

216-223

224-231

232-239

240-247

248-255

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[edit] Mask % &./

0-3

4-7

8-11

12-15

16-19

20-23

24-27

28-31

32-35

36-39

40-43

44-47

48-51

52-55

56-5960-63

64-67

68-71

72-75

76-79

80-83

84-87

88-91

92-95

96-99

100-103

104-107

108-111

112-115

116-119

120-123

124-127

128-131

132-135

136-139

140-143

144-147

148-151

152-155

156-159

160-163

164-167

168-171

172-175

176-179

180-183

184-187

188-191

192-195

196-199

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200-203

204-207

208-211

212-215

216-219

220-223

224-227

228-231

232-235

236-239

240-243

244-247

248-250

252-255

[edit] etmasks

Netmask Netmask (binary) CIDR Notes

255255255255 11111111111111111111111111111111 !32 "ost (sin#$e a%%r)

255255255254 11111111111111111111111111111110 !31 &n'sab$e

255255255252 11111111111111111111111111111100 !30 2 'sab$e

255255255248 11111111111111111111111111111000 !29 6 'sab$e

255255255240 11111111111111111111111111110000 !28 14 'sab$e

255255255224 11111111111111111111111111100000 !27 30 'sab$e

255255255192 11111111111111111111111111000000 !26 62 'sab$e

255255255128 11111111111111111111111110000000 !25 126 'sab$e

2552552550 11111111111111111111111100000000 !24 C$ass C 254 'sab$e

2552552540 11111111111111111111111000000000 !23 2 C$ass Cs

2552552520 11111111111111111111110000000000 !22 4 C$ass Cs

2552552480 11111111111111111111100000000000 !21 8 C$ass Cs

2552552400 11111111111111111111000000000000 !20 16 C$ass Cs

2552552240 11111111111111111110000000000000 !19 32 C$ass Cs

2552551920 11111111111111111100000000000000 !18 64 C$ass Cs

2552551280 11111111111111111000000000000000 !17 128 C$ass Cs

25525500 11111111111111110000000000000000 !16 C$ass *

 

25525400 11111111111111100000000000000000 !15 2 C$ass *s

25525200 11111111111111000000000000000000 !14 4 C$ass *s

25524800 11111111111110000000000000000000 !13 8 C$ass *s

25524000 11111111111100000000000000000000 !12 16 C$ass *s

25522400 11111111111000000000000000000000 !11 32 C$ass *s

25519200 11111111110000000000000000000000 !10 64 C$ass *s

25512800 11111111100000000000000000000000 !9 128 C$ass *s

255000 11111111000000000000000000000000 !8 C$ass +

254000 11111110000000000000000000000000 !7

252000 11111100000000000000000000000000 !6

248000 11111000000000000000000000000000 !5

240000 11110000000000000000000000000000 !4 C$ass , ('$ti.ast an%

reser/e%)

224000 11100000000000000000000000000000 !3

192000 11000000000000000000000000000000 !2

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128000 10000000000000000000000000000000 !1

0000 00000000000000000000000000000000 !0 I sa.e