Appendix A IP Addresses and Subnetting
B222s User’s Guide
181
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:
Notation
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.
For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with subnet mask 255.255.255.128.
Table 75
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
255.255.255.248
Table 76
Maximum Host Numbers
SUBNET MASK
HOST ID SIZE
MAXIMUM NUMBER OF
HOSTS
8 bits
255.0.0.0
24 bits
2
24
– 2
16777214
16 bits
255.255.0.0
16 bits
2
16
– 2
65534
24 bits
255.255.255.0
8 bits
2
8
– 2
254
29 bits
255.255.255.248
3 bits
2
3
– 2
6
Summary of Contents for B222s
Page 4: ...Contents Overview B222s User s Guide 4 ...
Page 12: ...Table of Contents B222s User s Guide 12 ...
Page 13: ...13 PART I User s Guide ...
Page 14: ...14 ...
Page 28: ...28 ...
Page 78: ...Chapter 7 Routing B222s User s Guide 78 ...
Page 82: ...Chapter 8 DNS Route B222s User s Guide 82 ...
Page 102: ...Chapter 10 Network Address Translation NAT B222s User s Guide 102 ...
Page 114: ...Chapter 12 Firewall B222s User s Guide 114 ...
Page 120: ...Chapter 14 Parental Control B222s User s Guide 120 ...
Page 125: ...Chapter 15 VoIP B222s User s Guide 125 ...
Page 144: ...Chapter 15 VoIP B222s User s Guide 144 ...
Page 154: ...Chapter 17 Traffic Status B222s User s Guide 154 ...
Page 156: ...Chapter 18 User Account B222s User s Guide 156 ...
Page 170: ...Chapter 24 Backup Restore B222s User s Guide 170 ...
Page 172: ...Chapter 25 Diagnostic B222s User s Guide 172 ...
Page 218: ...Appendix B Setting Up Your Computer s IP Address B222s User s Guide 218 ...
Page 228: ...Appendix C Pop up Windows JavaScript and Java Permissions B222s User s Guide 228 ...
Page 252: ...Appendix E Common Services B222s User s Guide 252 ...