Appendix C IP Addresses and Subnetting
ZyWALL 2 Plus User’s Guide
647
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.
The following table shows some possible subnet masks using both notations.
Table 228
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 229
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
Table 230
Alternative Subnet Mask Notation
SUBNET MASK
ALTERNATIVE
NOTATION
LAST OCTET
(BINARY)
LAST OCTET
(DECIMAL)
255.255.255.0
/24
0000 0000
0
255.255.255.128
/25
1000 0000
128
Содержание ADSL 2+ Security Gateway
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Страница 88: ...Chapter 3 Wizard Setup ZyWALL 2 Plus User s Guide 88 ...
Страница 131: ...131 PART II Network LAN Screens 133 Bridge Screens 145 WAN Screens 151 DMZ Screens 171 Wireless LAN 181 ...
Страница 132: ...132 ...
Страница 144: ...Chapter 6 LAN Screens ZyWALL 2 Plus User s Guide 144 ...
Страница 180: ...Chapter 9 DMZ Screens ZyWALL 2 Plus User s Guide 180 ...
Страница 190: ...190 ...
Страница 209: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 209 Figure 138 SECURITY FIREWALL Rule Summary Edit ...
Страница 221: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 221 Figure 149 My Service Firewall Rule Example Rule Summary Completed ...
Страница 222: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 222 ...
Страница 252: ...Chapter 13 Content Filtering Reports ZyWALL 2 Plus User s Guide 252 ...
Страница 265: ...Chapter 14 IPSec VPN ZyWALL 2 Plus User s Guide 265 Figure 178 SECURITY VPN VPN Rules IKE Edit Gateway Policy ...
Страница 274: ...Chapter 14 IPSec VPN ZyWALL 2 Plus User s Guide 274 Figure 181 SECURITY VPN VPN Rules IKE Edit Network Policy ...
Страница 306: ...Chapter 15 Certificates ZyWALL 2 Plus User s Guide 306 Figure 203 SECURITY CERTIFICATES My Certificates Create Basic ...
Страница 328: ...Chapter 16 Authentication Server ZyWALL 2 Plus User s Guide 328 ...
Страница 330: ...330 ...
Страница 346: ...Chapter 17 Network Address Translation NAT ZyWALL 2 Plus User s Guide 346 ...
Страница 350: ...Chapter 18 Static Route ZyWALL 2 Plus User s Guide 350 ...
Страница 398: ...Chapter 21 Remote Management ZyWALL 2 Plus User s Guide 398 ...
Страница 416: ...Chapter 24 ALG Screen ZyWALL 2 Plus User s Guide 416 ...
Страница 417: ...417 PART V Logs and Maintenance Logs Screens 419 Maintenance 447 ...
Страница 418: ...418 ...
Страница 423: ...Chapter 25 Logs Screens ZyWALL 2 Plus User s Guide 423 Figure 274 LOGS Log Settings ...
Страница 466: ...466 ...
Страница 474: ...Chapter 27 Introducing the SMT ZyWALL 2 Plus User s Guide 474 ...
Страница 496: ...Chapter 30 LAN Setup ZyWALL 2 Plus User s Guide 496 ...
Страница 504: ...Chapter 32 DMZ Setup ZyWALL 2 Plus User s Guide 504 ...
Страница 508: ...Chapter 33 Wireless Setup ZyWALL 2 Plus User s Guide 508 ...
Страница 556: ...Chapter 38 Filter Configuration ZyWALL 2 Plus User s Guide 556 ...
Страница 570: ...Chapter 40 System Information Diagnosis ZyWALL 2 Plus User s Guide 570 ...
Страница 586: ...Chapter 41 Firmware and Configuration File Maintenance ZyWALL 2 Plus User s Guide 586 ...
Страница 594: ...Chapter 42 System Maintenance Menus 8 to 10 ZyWALL 2 Plus User s Guide 594 ...
Страница 598: ...Chapter 43 Remote Management ZyWALL 2 Plus User s Guide 598 ...
Страница 603: ...603 PART VII Troubleshooting and Specifications Troubleshooting 605 Product Specifications 613 ...
Страница 604: ...604 ...
Страница 612: ...Chapter 45 Troubleshooting ZyWALL 2 Plus User s Guide 612 ...
Страница 620: ...620 ...
Страница 644: ...Appendix B Pop up Windows JavaScripts and Java Permissions ZyWALL 2 Plus User s Guide 644 ...
Страница 668: ...Appendix E Importing Certificates ZyWALL 2 Plus User s Guide 668 ...
Страница 672: ...Appendix F Legal Information ZyWALL 2 Plus User s Guide 672 ...
Страница 678: ...Appendix G Customer Support ZyWALL 2 Plus User s Guide 678 ...