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VSG-1200 User’s Guide
266
Appendix H IP Subnetting
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.
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.
Subnetting
With subnetting, the class arrangement of an IP address is ignored. For example, a class C
address no longer has to have 24 bits of network number and 8 bits of host ID. With
subnetting, some of the host ID bits are converted into network number bits. By convention,
subnet masks always consist of a continuous sequence of ones beginning from the left most bit
of the mask, followed by a continuous sequence of zeros, for a total number of 32 bits.
Since the mask is always a continuous number of ones beginning from the left, followed by a
continuous number of zeros for the remainder of the 32 bit mask, you can simply specify the
number of ones instead of writing the value of each octet. This is usually specified by writing
a “/” followed by the number of bits in the mask after the address.
Table 97
Allowed IP Address Range By Class
CLASS
ALLOWED RANGE OF FIRST OCTET
(BINARY)
ALLOWED RANGE OF FIRST OCTET
(DECIMAL)
Class A
0
0000000 to
0
1111111
0 to 127
Class B
10
000000 to
10
111111
128 to 191
Class C
110
00000 to
110
11111
192 to 223
Class D
1110
0000 to
1110
1111
224 to 239
Table 98
“Natural” Masks
CLASS
NATURAL MASK
A
255.0.0.0
B
255.255.0.0
C
255.255.255.0
Summary of Contents for VSG-1200
Page 1: ...VSG 1200 Vantage Service Gateway User s Guide Version 1 08 1 2006 ...
Page 8: ...VSG 1200 User s Guide 8 Customer Support ...
Page 22: ...VSG 1200 User s Guide 22 List of Figures ...
Page 26: ...VSG 1200 User s Guide 26 List of Tables ...
Page 40: ...VSG 1200 User s Guide 40 Chapter 2 Hardware Installation and Connection ...
Page 45: ...VSG 1200 User s Guide Chapter 3 The Web Configurator 45 Figure 13 System Setting System ...
Page 52: ...VSG 1200 User s Guide 52 Chapter 3 The Web Configurator ...
Page 64: ...VSG 1200 User s Guide 64 Chapter 4 LAN WAN and Server Setup ...
Page 74: ...VSG 1200 User s Guide 74 Chapter 6 Authentication Figure 29 System Setting Authentication ...
Page 102: ...VSG 1200 User s Guide 102 Chapter 9 Dynamic Subscriber Accounts ...
Page 128: ...VSG 1200 User s Guide 128 Chapter 13 Subscriber Information Window ...
Page 136: ...VSG 1200 User s Guide 136 Chapter 14 Account Printout ...
Page 140: ...VSG 1200 User s Guide 140 Chapter 15 User Agreement Page ...
Page 144: ...VSG 1200 User s Guide 144 Chapter 16 Bandwidth Management ...
Page 158: ...VSG 1200 User s Guide 158 Chapter 19 LAN Devices ...
Page 162: ...VSG 1200 User s Guide 162 Chapter 20 Static Route ...
Page 170: ...VSG 1200 User s Guide 170 Chapter 21 Syslog and Session Trace ...
Page 174: ...VSG 1200 User s Guide 174 Chapter 22 SNMP ...
Page 198: ...VSG 1200 User s Guide 198 Chapter 25 Secure Socket Layer ...
Page 206: ...VSG 1200 User s Guide 206 Chapter 26 The SMT ...
Page 214: ...VSG 1200 User s Guide 214 Chapter 27 LAN and WAN Setup Using the SMT ...
Page 226: ...VSG 1200 User s Guide 226 Chapter 28 Configuration and Firmware Maintenance ...
Page 236: ...VSG 1200 User s Guide 236 Appendix B IP Address Assignment Conflicts ...
Page 238: ...VSG 1200 User s Guide 238 Appendix C Subscriber Login ...
Page 242: ...VSG 1200 User s Guide 242 Appendix D Vendor Specific Attributes ...
Page 252: ...VSG 1200 User s Guide 252 Appendix F Cable Types and Cable Pin Assignments ...
Page 264: ...VSG 1200 User s Guide 264 Appendix G Setting up Your Computer s IP Address ...
Page 272: ...VSG 1200 User s Guide 272 Appendix H IP Subnetting ...