Visualising Class C Subnets

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I’ve just started learning how to subnet and while there are plenty of resources to help with the calculations and understand the maths I tend to grasp things better if I have some visual representation.

To help, I put together the following table which – I hope – nicely illustrates the patterns of binary 0s and 1s in the 4th octet of a class C IP address and their correlation to the patterns of block sizes, network IDs, host IDs and broadcast addresses of the various subnets. The table is not intended to explain how to calculate subnets nor even to act as a cheat-sheet, but others may find the visual representation helpful.

Some examples of how this table may be useful:

1. Looking in the the 4th Octet of IP Address column and using a CIDR of /27 where only the first 3 bits of the 4th octet of the IP address are used for the network ID the pattern of 0s and 1s starts at 000 for the 1st subnet and then changes 7 times – 001, 010, 011,100, 101, 110 and 111 – each transition marking the beginning of a new subnet.

2. Similarly, the CIDR /27 column shows the 8 subnets each with a block size of 32 and 30 hosts, network IDs of .0, .32, .64, .96, .128, .160, .192 and .224 and broadcast addresses of .31, .63, .95, .127, .159, .191, .223 and .255.

3. Looking in row 125 of the IP # column gives the following for an IP address of 192.168.75.124:

192.168.75.124/25 is the 124th host ID on the 1st subnet that begins with a network ID of 192.168.75.0.

192.168.75.124/26 is the 60th host ID on the 2nd subnet that begins with a network ID of 192.168.75.64.

192.168.75.124/27 is the 28th host ID on the 4th subnet that begins with a network ID of 192.168.75.96.

192.168.75.124/28 is the 12th host ID on the 8th subnet that begins with a network ID of 192.168.75.112.

192.168.75.124/29 is the 4th host ID on the 16th subnet that begins with a network ID of 192.168.75.120.

192.168.75.124/30 is the network ID of the 32nd subnet.

As the table only uses CIDRs /25, /26, /27, /28, /29 and /30 only the first 6 bits of the 4th octet are significant in terms of the network ID. The 7th and 8th bits are used only for the host ID.

 

Class C Subnets Table

KEY Nn nth Network ID Bn nth Broadcast Address Hn nth Host of Subnet
IP # 4th Octet Of IP Address CIDR
dec binary /25 /26 /27 /28 /29 /30
128
(1)
64
(2)
32
(3)
16
(4)
8
(5)
4
(6)
2
(7)
1
(8)
1 .0 0 0 0 0 0 0 0 0 N1 N1 N1 N1 N1 N1
2 .1 0 0 0 0 0 0 0 1 H1 H1 H1 H1 H1 H1
3 .2 0 0 0 0 0 0 1 0 H2 H2 H2 H2 H2 H2
4 .3 0 0 0 0 0 0 1 1 H3 H3 H3 H3 H3 B1
5 .4 0 0 0 0 0 1 0 0 H4 H4 H4 H4 H4 N2
6 .5 0 0 0 0 0 1 0 1 H5 H5 H5 H5 H5 H1
7 .6 0 0 0 0 0 1 1 0 H6 H6 H6 H6 H6 H2
8 .7 0 0 0 0 0 1 1 1 H7 H7 H7 H7 B1 B2
9 .8 0 0 0 0 1 0 0 0 H8 H8 H8 H8 N2 N3
10 .9 0 0 0 0 1 0 0 1 H9 H9 H9 H9 H1 H1
11 .10 0 0 0 0 1 0 1 0 H10 H10 H10 H10 H2 H2
12 .11 0 0 0 0 1 0 1 1 H11 H11 H11 H11 H3 B3
13 .12 0 0 0 0 1 1 0 0 H12 H12 H12 H12 H4 N4
14 .13 0 0 0 0 1 1 0 1 H13 H13 H13 H13 H5 H1
15 .14 0 0 0 0 1 1 1 0 H14 H14 H14 H14 H6 H2
16 .15 0 0 0 0 1 1 1 1 H15 H15 H15 B1 B2 B4
17 .16 0 0 0 1 0 0 0 0 H16 H16 H16 N2 N3 N5
18 .17 0 0 0 1 0 0 0 1 H17 H17 H17 H1 H1 H1
19 .18 0 0 0 1 0 0 1 0 H18 H18 H18 H2 H2 H2
20 .19 0 0 0 1 0 0 1 1 H19 H19 H19 H3 H3 B5
21 .20 0 0 0 1 0 1 0 0 H20 H20 H20 H4 H4 N6
22 .21 0 0 0 1 0 1 0 1 H21 H21 H21 H5 H5 H1
23 .22 0 0 0 1 0 1 1 0 H22 H22 H22 H6 H6 H2
24 .23 0 0 0 1 0 1 1 1 H23 H23 H23 H7 B3 B6
25 .24 0 0 0 1 1 0 0 0 H24 H24 H24 H8 N4 N7
26 .25 0 0 0 1 1 0 0 1 H25 H25 H25 H9 H1 H1
27 .26 0 0 0 1 1 0 1 0 H26 H26 H26 H10 H2 H2
28 .27 0 0 0 1 1 0 1 1 H27 H27 H27 H11 H3 B7
29 .28 0 0 0 1 1 1 0 0 H28 H28 H28 H12 H4 N8
30 .29 0 0 0 1 1 1 0 1 H29 H29 H29 H13 H5 H1
31 .30 0 0 0 1 1 1 1 0 H30 H30 H30 H14 H6 H2
32 .31 0 0 0 1 1 1 1 1 H31 H31 B1 B2 B4 B8
33 .32 0 0 1 0 0 0 0 0 H32 H32 N2 N3 N5 N9
34 .33 0 0 1 0 0 0 0 1 H33 H33 H1 H1 H1 H1
35 .34 0 0 1 0 0 0 1 0 H34 H34 H2 H2 H2 H2
36 .35 0 0 1 0 0 0 1 1 H35 H35 H3 H3 H3 B9
37 .36 0 0 1 0 0 1 0 0 H36 H36 H4 H4 H4 N10
38 .37 0 0 1 0 0 1 0 1 H37 H37 H5 H5 H5 H1
39 .38 0 0 1 0 0 1 1 0 H38 H38 H6 H6 H6 H2
40 .39 0 0 1 0 0 1 1 1 H39 H39 H7 H7 B5 B10
41 .40 0 0 1 0 1 0 0 0 H40 H40 H8 H8 N6 N11
42 .41 0 0 1 0 1 0 0 1 H41 H41 H9 H9 H1 H1
43 .42 0 0 1 0 1 0 1 0 H42 H42 H10 H10 H2 H2
44 .43 0 0 1 0 1 0 1 1 H43 H43 H11 H11 H3 B11
45 .44 0 0 1 0 1 1 0 0 H44 H44 H12 H12 H4 N12
46 .45 0 0 1 0 1 1 0 1 H45 H45 H13 H13 H5 H1
47 .46 0 0 1 0 1 1 1 0 H46 H46 H14 H14 H6 H2
48 .47 0 0 1 0 1 1 1 1 H47 H47 H15 B3 B6 B12
49 .48 0 0 1 1 0 0 0 0 H48 H48 H16 N4 N7 N13
50 .49 0 0 1 1 0 0 0 1 H49 H49 H17 H1 H1 H1
51 .50 0 0 1 1 0 0 1 0 H50 H50 H18 H2 H2 H2
52 .51 0 0 1 1 0 0 1 1 H51 H51 H19 H3 H3 B13
53 .52 0 0 1 1 0 1 0 0 H52 H52 H20 H4 H4 N14
54 .53 0 0 1 1 0 1 0 1 H53 H53 H21 H5 H5 H1
55 .54 0 0 1 1 0 1 1 0 H54 H54 H22 H6 H6 H2
56 .55 0 0 1 1 0 1 1 1 H55 H55 H23 H7 B7 B14
57 .56 0 0 1 1 1 0 0 0 H56 H56 H24 H8 N8 N15
58 .57 0 0 1 1 1 0 0 1 H57 H57 H25 H9 H1 H1
59 .58 0 0 1 1 1 0 1 0 H58 H58 H26 H10 H2 H2
60 .59 0 0 1 1 1 0 1 1 H59 H59 H27 H11 H3 B15
61 .60 0 0 1 1 1 1 0 0 H60 H60 H28 H12 H4 N16
62 .61 0 0 1 1 1 1 0 1 H61 H61 H29 H13 H5 H1
63 .62 0 0 1 1 1 1 1 0 H62 H62 H30 H14 H6 H2
64 .63 0 0 1 1 1 1 1 1 H63 B1 B2 B4 B8 B16
65 .64 0 1 0 0 0 0 0 0 H64 N2 N3 N5 N9 N17
66 .65 0 1 0 0 0 0 0 1 H65 H1 H1 H1 H1 H1
67 .66 0 1 0 0 0 0 1 0 H66 H2 H2 H2 H2 H2
68 .67 0 1 0 0 0 0 1 1 H67 H3 H3 H3 H3 B17
69 .68 0 1 0 0 0 1 0 0 H68 H4 H4 H4 H4 N18
70 .69 0 1 0 0 0 1 0 1 H69 H5 H5 H5 H5 H1
71 .70 0 1 0 0 0 1 1 0 H70 H6 H6 H6 H6 H2
72 .71 0 1 0 0 0 1 1 1 H71 H7 H7 H7 B9 B18
73 .72 0 1 0 0 1 0 0 0 H72 H8 H8 H8 N10 N19
74 .73 0 1 0 0 1 0 0 1 H73 H9 H9 H9 H1 H1
75 .74 0 1 0 0 1 0 1 0 H74 H10 H10 H10 H2 H2
76 .75 0 1 0 0 1 0 1 1 H75 H11 H11 H11 H3 B19
77 .76 0 1 0 0 1 1 0 0 H76 H12 H12 H12 H4 N20
78 .77 0 1 0 0 1 1 0 1 H77 H13 H13 H13 H5 H1
79 .78 0 1 0 0 1 1 1 0 H78 H14 H14 H14 H6 H2
80 .79 0 1 0 0 1 1 1 1 H79 H15 H15 B5 B10 B20
81 .80 0 1 0 1 0 0 0 0 H80 H16 H16 N6 N11 N21
82 .81 0 1 0 1 0 0 0 1 H81 H17 H17 H1 H1 H1
83 .82 0 1 0 1 0 0 1 0 H82 H18 H18 H2 H2 H2
84 .83 0 1 0 1 0 0 1 1 H83 H19 H19 H3 H3 B21
85 .84 0 1 0 1 0 1 0 0 H84 H20 H20 H4 H4 N22
86 .85 0 1 0 1 0 1 0 1 H85 H21 H21 H5 H5 H1
87 .86 0 1 0 1 0 1 1 0 H86 H22 H22 H6 H6 H2
88 .87 0 1 0 1 0 1 1 1 H87 H23 H23 H7 B11 B22
89 .88 0 1 0 1 1 0 0 0 H88 H24 H24 H8 N12 N23
90 .89 0 1 0 1 1 0 0 1 H89 H25 H25 H9 H1 H1
91 .90 0 1 0 1 1 0 1 0 H90 H26 H26 H10 H2 H2
92 .91 0 1 0 1 1 0 1 1 H91 H27 H27 H11 H3 B23
93 .92 0 1 0 1 1 1 0 0 H92 H28 H28 H12 H4 N24
94 .93 0 1 0 1 1 1 0 1 H93 H29 H29 H13 H5 H1
95 .94 0 1 0 1 1 1 1 0 H94 H30 H30 H14 H6 H2
96 .95 0 1 0 1 1 1 1 1 H95 H31 B3 B6 B12 B24
97 .96 0 1 1 0 0 0 0 0 H96 H32 N4 N7 N13 N25
98 .97 0 1 1 0 0 0 0 1 H97 H33 H1 H1 H1 H1
99 .98 0 1 1 0 0 0 1 0 H98 H34 H2 H2 H2 H2
100 .99 0 1 1 0 0 0 1 1 H99 H35 H3 H3 H3 B25
101 .100 0 1 1 0 0 1 0 0 H100 H36 H4 H4 H4 N26
102 .101 0 1 1 0 0 1 0 1 H101 H37 H5 H5 H5 H1
103 .102 0 1 1 0 0 1 1 0 H102 H38 H6 H6 H6 H2
104 .103 0 1 1 0 0 1 1 1 H103 H39 H7 H7 B13 B26
105 .104 0 1 1 0 1 0 0 0 H104 H40 H8 H8 N14 N27
106 .105 0 1 1 0 1 0 0 1 H105 H41 H9 H9 H1 H1
107 .106 0 1 1 0 1 0 1 0 H106 H42 H10 H10 H2 H2
108 .107 0 1 1 0 1 0 1 1 H107 H43 H11 H11 H3 B27
109 .108 0 1 1 0 1 1 0 0 H108 H44 H12 H12 H4 N28
110 .109 0 1 1 0 1 1 0 1 H109 H45 H13 H13 H5 H1
111 .110 0 1 1 0 1 1 1 0 H110 H46 H14 H14 H6 H2
112 .111 0 1 1 0 1 1 1 1 H111 H47 H15 B7 B14 B28
113 .112 0 1 1 1 0 0 0 0 H112 H48 H16 N8 N15 N29
114 .113 0 1 1 1 0 0 0 1 H113 H49 H17 H1 H1 H1
115 .114 0 1 1 1 0 0 1 0 H114 H50 H18 H2 H2 H2
116 .115 0 1 1 1 0 0 1 1 H115 H51 H19 H3 H3 B29
117 .116 0 1 1 1 0 1 0 0 H116 H52 H20 H4 H4 N30
118 .117 0 1 1 1 0 1 0 1 H117 H53 H21 H5 H5 H1
119 .118 0 1 1 1 0 1 1 0 H118 H54 H22 H6 H6 H2
120 .119 0 1 1 1 0 1 1 1 H119 H55 H23 H7 B15 B30
121 .120 0 1 1 1 1 0 0 0 H120 H56 H24 H8 N16 N31
122 .121 0 1 1 1 1 0 0 1 H121 H57 H25 H9 H1 H1
123 .122 0 1 1 1 1 0 1 0 H122 H58 H26 H10 H2 H2
124 .123 0 1 1 1 1 0 1 1 H123 H59 H27 H11 H3 B31
125 .124 0 1 1 1 1 1 0 0 H124 H60 H28 H12 H4 N32
126 .125 0 1 1 1 1 1 0 1 H125 H61 H29 H13 H5 H1
127 .126 0 1 1 1 1 1 1 0 H126 H62 H30 H14 H6 H2
128 .127 0 1 1 1 1 1 1 1 B1 B2 B4 B8 B16 B32
129 .128 1 0 0 0 0 0 0 0 N2 N3 N5 N9 N17 N33
130 .129 1 0 0 0 0 0 0 1 H1 H1 H1 H1 H1 H1
131 .130 1 0 0 0 0 0 1 0 H2 H2 H2 H2 H2 H2
132 .131 1 0 0 0 0 0 1 1 H3 H3 H3 H3 H3 B33
133 .132 1 0 0 0 0 1 0 0 H4 H4 H4 H4 H4 N34
134 .133 1 0 0 0 0 1 0 1 H5 H5 H5 H5 H5 H1
135 .134 1 0 0 0 0 1 1 0 H6 H6 H6 H6 H6 H2
136 .135 1 0 0 0 0 1 1 1 H7 H7 H7 H7 B17 B34
137 .136 1 0 0 0 1 0 0 0 H8 H8 H8 H8 N18 N35
138 .137 1 0 0 0 1 0 0 1 H9 H9 H9 H9 H1 H1
139 .138 1 0 0 0 1 0 1 0 H10 H10 H10 H10 H2 H2
140 .139 1 0 0 0 1 0 1 1 H11 H11 H11 H11 H3 B35
141 .140 1 0 0 0 1 1 0 0 H12 H12 H12 H12 H4 N36
142 .141 1 0 0 0 1 1 0 1 H13 H13 H13 H13 H5 H1
143 .142 1 0 0 0 1 1 1 0 H14 H14 H14 H14 H6 H2
144 .143 1 0 0 0 1 1 1 1 H15 H15 H15 B9 B18 B36
145 .144 1 0 0 1 0 0 0 0 H16 H16 H16 N10 N19 N37
146 .145 1 0 0 1 0 0 0 1 H17 H17 H17 H1 H1 H1
147 .146 1 0 0 1 0 0 1 0 H18 H18 H18 H2 H2 H2
148 .147 1 0 0 1 0 0 1 1 H19 H19 H19 H3 H3 B37
149 .148 1 0 0 1 0 1 0 0 H20 H20 H20 H4 H4 N38
150 .149 1 0 0 1 0 1 0 1 H21 H21 H21 H5 H5 H1
151 .150 1 0 0 1 0 1 1 0 H22 H22 H22 H6 H6 H2
152 .151 1 0 0 1 0 1 1 1 H23 H23 H23 H7 B19 B38
153 .152 1 0 0 1 1 0 0 0 H24 H24 H24 H8 N20 N39
154 .153 1 0 0 1 1 0 0 1 H25 H25 H25 H9 H1 H1
155 .154 1 0 0 1 1 0 1 0 H26 H26 H26 H10 H2 H2
156 .155 1 0 0 1 1 0 1 1 H27 H27 H27 H11 H3 B39
157 .156 1 0 0 1 1 1 0 0 H28 H28 H28 H12 H4 N40
158 .157 1 0 0 1 1 1 0 1 H29 H29 H29 H13 H5 H1
159 .158 1 0 0 1 1 1 1 0 H30 H30 H30 H14 H6 H2
160 .159 1 0 0 1 1 1 1 1 H31 H31 B5 B10 B20 B40
161 .160 1 0 1 0 0 0 0 0 H32 H32 N6 N11 N21 N41
162 .161 1 0 1 0 0 0 0 1 H33 H33 H1 H1 H1 H1
163 .162 1 0 1 0 0 0 1 0 H34 H34 H2 H2 H2 H2
164 .163 1 0 1 0 0 0 1 1 H35 H35 H3 H3 H3 B41
165 .164 1 0 1 0 0 1 0 0 H36 H36 H4 H4 H4 N42
166 .165 1 0 1 0 0 1 0 1 H37 H37 H5 H5 H5 H1
167 .166 1 0 1 0 0 1 1 0 H38 H38 H6 H6 H6 H2
168 .167 1 0 1 0 0 1 1 1 H39 H39 H7 H7 B21 B42
169 .168 1 0 1 0 1 0 0 0 H40 H40 H8 H8 N22 N43
170 .169 1 0 1 0 1 0 0 1 H41 H41 H9 H9 H1 H1
171 .170 1 0 1 0 1 0 1 0 H42 H42 H10 H10 H2 H2
172 .171 1 0 1 0 1 0 1 1 H43 H43 H11 H11 H3 B43
173 .172 1 0 1 0 1 1 0 0 H44 H44 H12 H12 H4 N44
174 .173 1 0 1 0 1 1 0 1 H45 H45 H13 H13 H5 H1
175 .174 1 0 1 0 1 1 1 0 H46 H46 H14 H14 H6 H2
176 .175 1 0 1 0 1 1 1 1 H47 H47 H15 B11 B22 B44
177 .176 1 0 1 1 0 0 0 0 H48 H48 H16 N12 N23 N45
178 .177 1 0 1 1 0 0 0 1 H49 H49 H17 H1 H1 H1
179 .178 1 0 1 1 0 0 1 0 H50 H50 H18 H2 H2 H2
180 .179 1 0 1 1 0 0 1 1 H51 H51 H19 H3 H3 B45
181 .180 1 0 1 1 0 1 0 0 H52 H52 H20 H4 H4 N46
182 .181 1 0 1 1 0 1 0 1 H53 H53 H21 H5 H5 H1
183 .182 1 0 1 1 0 1 1 0 H54 H54 H22 H6 H6 H2
184 .183 1 0 1 1 0 1 1 1 H55 H55 H23 H7 B23 B46
185 .184 1 0 1 1 1 0 0 0 H56 H56 H24 H8 N24 N47
186 .185 1 0 1 1 1 0 0 1 H57 H57 H25 H9 H1 H1
187 .186 1 0 1 1 1 0 1 0 H58 H58 H26 H10 H2 H2
188 .187 1 0 1 1 1 0 1 1 H59 H59 H27 H11 H3 B47
189 .188 1 0 1 1 1 1 0 0 H60 H60 H28 H12 H4 N48
190 .189 1 0 1 1 1 1 0 1 H61 H61 H29 H13 H5 H1
191 .190 1 0 1 1 1 1 1 0 H62 H62 H30 H14 H6 H2
192 .191 1 0 1 1 1 1 1 1 H63 B3 B6 B12 B24 B48
193 .192 1 1 0 0 0 0 0 0 H64 N4 N7 N13 N25 N49
194 .193 1 1 0 0 0 0 0 1 H65 H1 H1 H1 H1 H1
195 .194 1 1 0 0 0 0 1 0 H66 H2 H2 H2 H2 H2
196 .195 1 1 0 0 0 0 1 1 H67 H3 H3 H3 H3 B49
197 .196 1 1 0 0 0 1 0 0 H68 H4 H4 H4 H4 N50
198 .197 1 1 0 0 0 1 0 1 H69 H5 H5 H5 H5 H1
199 .198 1 1 0 0 0 1 1 0 H70 H6 H6 H6 H6 H2
200 .199 1 1 0 0 0 1 1 1 H71 H7 H7 H7 B25 B50
201 .200 1 1 0 0 1 0 0 0 H72 H8 H8 H8 N26 N51
202 .201 1 1 0 0 1 0 0 1 H73 H9 H9 H9 H1 H1
203 .202 1 1 0 0 1 0 1 0 H74 H10 H10 H10 H2 H2
204 .203 1 1 0 0 1 0 1 1 H75 H11 H11 H11 H3 B51
205 .204 1 1 0 0 1 1 0 0 H76 H12 H12 H12 H4 N52
206 .205 1 1 0 0 1 1 0 1 H77 H13 H13 H13 H5 H1
207 .206 1 1 0 0 1 1 1 0 H78 H14 H14 H14 H6 H2
208 .207 1 1 0 0 1 1 1 1 H79 H15 H15 B13 B26 B52
209 .208 1 1 0 1 0 0 0 0 H80 H16 H16 N14 N27 N53
210 .209 1 1 0 1 0 0 0 1 H81 H17 H17 H1 H1 H1
211 .210 1 1 0 1 0 0 1 0 H82 H18 H18 H2 H2 H2
212 .211 1 1 0 1 0 0 1 1 H83 H19 H19 H3 H3 B53
213 .212 1 1 0 1 0 1 0 0 H84 H20 H20 H4 H4 N54
214 .213 1 1 0 1 0 1 0 1 H85 H21 H21 H5 H5 H1
215 .214 1 1 0 1 0 1 1 0 H86 H22 H22 H6 H6 H2
216 .215 1 1 0 1 0 1 1 1 H87 H23 H23 H7 B27 B54
217 .216 1 1 0 1 1 0 0 0 H88 H24 H24 H8 N28 N55
218 .217 1 1 0 1 1 0 0 1 H89 H25 H25 H9 H1 H1
219 .218 1 1 0 1 1 0 1 0 H90 H26 H26 H10 H2 H2
220 .219 1 1 0 1 1 0 1 1 H91 H27 H27 H11 H3 B55
221 .220 1 1 0 1 1 1 0 0 H92 H28 H28 H12 H4 N56
222 .221 1 1 0 1 1 1 0 1 H93 H29 H29 H13 H5 H1
223 .222 1 1 0 1 1 1 1 0 H94 H30 H30 H14 H6 H2
224 .223 1 1 0 1 1 1 1 1 H95 H31 B7 B14 B28 B56
225 .224 1 1 1 0 0 0 0 0 H96 H32 N8 N15 N29 N57
226 .225 1 1 1 0 0 0 0 1 H97 H33 H1 H1 H1 H1
227 .226 1 1 1 0 0 0 1 0 H98 H34 H2 H2 H2 H2
228 .227 1 1 1 0 0 0 1 1 H99 H35 H3 H3 H3 B57
229 .228 1 1 1 0 0 1 0 0 H100 H36 H4 H4 H4 N58
230 .229 1 1 1 0 0 1 0 1 H101 H37 H5 H5 H5 H1
231 .230 1 1 1 0 0 1 1 0 H102 H38 H6 H6 H6 H2
232 .231 1 1 1 0 0 1 1 1 H103 H39 H7 H7 B29 B58
233 .232 1 1 1 0 1 0 0 0 H104 H40 H8 H8 N30 N59
234 .233 1 1 1 0 1 0 0 1 H105 H41 H9 H9 H1 H1
235 .234 1 1 1 0 1 0 1 0 H106 H42 H10 H10 H2 H2
236 .235 1 1 1 0 1 0 1 1 H107 H43 H11 H11 H3 B59
237 .236 1 1 1 0 1 1 0 0 H108 H44 H12 H12 H4 N60
238 .237 1 1 1 0 1 1 0 1 H109 H45 H13 H13 H5 H1
239 .238 1 1 1 0 1 1 1 0 H110 H46 H14 H14 H6 H2
240 .239 1 1 1 0 1 1 1 1 H111 H47 H15 B15 B30 B60
241 .240 1 1 1 1 0 0 0 0 H112 H48 H16 N16 N31 N61
242 .241 1 1 1 1 0 0 0 1 H113 H49 H17 H1 H1 H1
243 .242 1 1 1 1 0 0 1 0 H114 H50 H18 H2 H2 H2
244 .243 1 1 1 1 0 0 1 1 H115 H51 H19 H3 H3 B61
245 .244 1 1 1 1 0 1 0 0 H116 H52 H20 H4 H4 N62
246 .245 1 1 1 1 0 1 0 1 H117 H53 H21 H5 H5 H1
247 .246 1 1 1 1 0 1 1 0 H118 H54 H22 H6 H6 H2
248 .247 1 1 1 1 0 1 1 1 H119 H55 H23 H7 B31 B62
249 .248 1 1 1 1 1 0 0 0 H120 H56 H24 H8 N32 N63
250 .249 1 1 1 1 1 0 0 1 H121 H57 H25 H9 H1 H1
251 .250 1 1 1 1 1 0 1 0 H122 H58 H26 H10 H2 H2
252 .251 1 1 1 1 1 0 1 1 H123 H59 H27 H11 H3 B63
253 .252 1 1 1 1 1 1 0 0 H124 H60 H28 H12 H4 N64
254 .253 1 1 1 1 1 1 0 1 H125 H61 H29 H13 H5 H1
255 .254 1 1 1 1 1 1 1 0 H126 H62 H30 H14 H6 H2
256 .255 1 1 1 1 1 1 1 1 B2 B4 B8 B16 B32 B64
KEY Nn nth Network ID Bn nth Broadcast Address Hn nth Host of Subnet

 

Summary of Class C Subnets Table

CIDR Masked Bits [1s] (x) Unmasked Bits [0s] (y) Mask [4th Octet] Block Size1
[256 – Mask]
# Subnets
[2x]
# Hosts Per Subnet2
[2y – 2]
25 1 7 .128 128 2 126
26 2 6 .192 64 4 62
27 3 5 .224 32 8 30
28 4 4 .240 16 16 14
29 5 3 .248 8 32 6
30 6 2 .252 4 64 2

1 Block Size can also be calculated as 2y
2 # Hosts Per Subnet can also be calculated as Block Size – 2

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A native Brit exiled in Japan, Steve spends too much of his time struggling with the Japanese language, dreaming of fish & chips and writing the occasional blog post he hopes others will find helpful.

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