Appendix C IP Addresses and Subnetting
ZyWALL 2WG User’s Guide
731
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 261
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 262
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 263
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
Summary of Contents for ZYWALL 2 WG
Page 2: ......
Page 8: ...Safety Warnings ZyWALL 2WG User s Guide 8 ...
Page 42: ...List of Figures ZyWALL 2WG User s Guide 42 ...
Page 50: ...List of Tables ZyWALL 2WG User s Guide 50 ...
Page 52: ...52 ...
Page 80: ...Chapter 2 Introducing the Web Configurator ZyWALL 2WG User s Guide 80 ...
Page 100: ...Chapter 3 Wizard Setup ZyWALL 2WG User s Guide 100 ...
Page 140: ...Chapter 4 Tutorial ZyWALL 2WG User s Guide 140 ...
Page 146: ...146 ...
Page 158: ...Chapter 6 LAN Screens ZyWALL 2WG User s Guide 158 ...
Page 171: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 171 Figure 108 NETWORK WAN General ...
Page 200: ...Chapter 8 WAN Screens ZyWALL 2WG User s Guide 200 ...
Page 238: ...238 ...
Page 300: ...Chapter 13 Content Filtering Reports ZyWALL 2WG User s Guide 300 ...
Page 348: ...Chapter 14 IPSec VPN ZyWALL 2WG User s Guide 348 ...
Page 378: ...Chapter 15 Certificates ZyWALL 2WG User s Guide 378 ...
Page 384: ...384 ...
Page 426: ...Chapter 20 Bandwidth Management ZyWALL 2WG User s Guide 426 ...
Page 479: ...479 PART V Logs and Maintenance Logs Screens 481 Maintenance 511 ...
Page 480: ...480 ...
Page 485: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 485 Figure 304 LOGS Log Settings ...
Page 510: ...Chapter 26 Logs Screens ZyWALL 2WG User s Guide 510 ...
Page 530: ...530 ...
Page 558: ...Chapter 30 WAN and Dial Backup Setup ZyWALL 2WG User s Guide 558 ...
Page 564: ...Chapter 31 LAN Setup ZyWALL 2WG User s Guide 564 ...
Page 570: ...Chapter 32 Internet Access ZyWALL 2WG User s Guide 570 ...
Page 574: ...Chapter 33 DMZ Setup ZyWALL 2WG User s Guide 574 ...
Page 578: ...Chapter 34 Route Setup ZyWALL 2WG User s Guide 578 ...
Page 582: ...Chapter 35 Wireless Setup ZyWALL 2WG User s Guide 582 ...
Page 594: ...Chapter 37 IP Static Route Setup ZyWALL 2WG User s Guide 594 ...
Page 614: ...Chapter 38 Network Address Translation NAT ZyWALL 2WG User s Guide 614 ...
Page 632: ...Chapter 40 Filter Configuration ZyWALL 2WG User s Guide 632 ...
Page 668: ...Chapter 44 System Maintenance Menus 8 to 10 ZyWALL 2WG User s Guide 668 ...
Page 672: ...Chapter 45 Remote Management ZyWALL 2WG User s Guide 672 ...
Page 680: ...Chapter 46 IP Policy Routing ZyWALL 2WG User s Guide 680 ...
Page 686: ...686 ...
Page 692: ...Chapter 48 Troubleshooting ZyWALL 2WG User s Guide 692 ...
Page 702: ...Chapter 49 Product Specifications ZyWALL 2WG User s Guide 702 ...
Page 704: ...704 ...
Page 712: ...Appendix A Pop up Windows JavaScripts and Java Permissions ZyWALL 2WG User s Guide 712 ...
Page 740: ...Appendix D Common Services ZyWALL 2WG User s Guide 740 ...
Page 768: ...Appendix G Legal Information ZyWALL 2WG User s Guide 768 ...
Page 774: ...Appendix H Customer Support ZyWALL 2WG User s Guide 774 ...