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Appendix B IP Addresses and Subnetting
NBG5715 User’s Guide
191
Subnet Planning
The following table is a summary for subnet planning on a network with a 24-bit network number.
The following table is a summary for subnet planning on a network with a 16-bit network number.
7
192
193
222
223
8
224
225
254
255
Table 82
Eight Subnets (continued)
SUBNET
SUBNET
ADDRESS
FIRST ADDRESS
LAST
ADDRESS
BROADCAST
ADDRESS
Table 83
24-bit Network Number Subnet Planning
NO. “BORROWED”
HOST BITS
SUBNET MASK
NO. SUBNETS
NO. HOSTS PER
SUBNET
1
255.255.255.128 (/25)
2
126
2
255.255.255.192 (/26)
4
62
3
255.255.255.224 (/27)
8
30
4
255.255.255.240 (/28)
16
14
5
255.255.255.248 (/29)
32
6
6
255.255.255.252 (/30)
64
2
7
255.255.255.254 (/31)
128
1
Table 84
16-bit Network Number Subnet Planning
NO. “BORROWED”
HOST BITS
SUBNET MASK
NO. SUBNETS
NO. HOSTS PER
SUBNET
1
255.255.128.0 (/17)
2
32766
2
255.255.192.0 (/18)
4
16382
3
255.255.224.0 (/19)
8
8190
4
255.255.240.0 (/)
16
4094
5
255.255.248.0 (/21)
32
2046
6
255.255.252.0 (/22)
64
1022
7
255.255.254.0 (/23)
128
510
8
255.255.255.0 (/24)
256
254
9
255.255.255.128 (/25)
512
126
10
255.255.255.192 (/26)
1024
62
11
255.255.255.224 (/27)
2048
30
12
255.255.255.240 (/28)
4096
14
13
255.255.255.248 (/29)
8192
6
14
255.255.255.252 (/30)
16384
2
15
255.255.255.254 (/31)
32768
1
Page 192 / 252
Appendix B IP Addresses and Subnetting
NBG5715 User’s Guide
192
Configuring IP Addresses
Where you obtain your network number depends on your particular situation. If the ISP or your
network administrator assigns you a block of registered IP addresses, follow their instructions in
selecting the IP addresses and the subnet mask.
If the ISP did not explicitly give you an IP network number, then most likely you have a single user
account and the ISP will assign you a dynamic IP address when the connection is established. If this
is the case, it is recommended that you select a network number from 192.168.0.0 to
192.168.255.0. The Internet Assigned Number Authority (IANA) reserved this block of addresses
specifically for private use; please do not use any other number unless you are told otherwise. You
must also enable Network Address Translation (NAT) on the NBG5715.
Once you have decided on the network number, pick an IP address for your NBG5715 that is easy to
remember (for instance, 192.168.1.1) but make sure that no other device on your network is using
that IP address.
The subnet mask specifies the network number portion of an IP address. Your NBG5715 will
compute the subnet mask automatically based on the IP address that you entered. You don't need
to change the subnet mask computed by the NBG5715 unless you are instructed to do otherwise.
Private IP Addresses
Every machine on the Internet must have a unique address. If your networks are isolated from the
Internet (running only between two branch offices, for example) you can assign any IP addresses to
the hosts without problems. However, the Internet Assigned Numbers Authority (IANA) has
reserved the following three blocks of IP addresses specifically for private networks:
• 10.0.0.0
— 10.255.255.255
• 172.16.0.0
— 172.31.255.255
192.168.0.0 — 192.168.255.255
You can obtain your IP address from the IANA, from an ISP, or it can be assigned from a private
network. If you belong to a small organization and your Internet access is through an ISP, the ISP
can provide you with the Internet addresses for your local networks. On the other hand, if you are
part of a much larger organization, you should consult your network administrator for the
appropriate IP addresses.
Regardless of your particular situation, do not create an arbitrary IP address; always follow the
guidelines above. For more information on address assignment, please refer to RFC 1597, Address
Allocation for Private Internets and RFC 1466, Guidelines for Management of IP Address Space.
IP Address Conflicts
Each device on a network must have a unique IP address. Devices with duplicate IP addresses on
the same network will not be able to access the Internet or other resources. The devices may also
be unreachable through the network.
Conflicting Computer IP Addresses Example
More than one device can not use the same IP address. In the following example computer
A
has a
static (or fixed) IP address that is the same as the IP address that a DHCP server assigns to
Page 193 / 252
Appendix B IP Addresses and Subnetting
NBG5715 User’s Guide
193
computer
B
which is a DHCP client. Neither can access the Internet. This problem can be solved by
assigning a different static IP address to computer
A
or setting computer
A
to obtain an IP address
automatically.
Figure 126
Conflicting Computer IP Addresses Example
Conflicting Router IP Addresses Example
Since a router connects different networks, it must have interfaces using different network
numbers. For example, if a router is set between a LAN and the Internet (WAN), the router’s LAN
and WAN addresses must be on different subnets. In the following example, the LAN and WAN are
on the same subnet. The LAN computers cannot access the Internet because the router cannot
route between networks.
Figure 127
Conflicting Router IP Addresses Example
Conflicting Computer and Router IP Addresses Example
More than one device can not use the same IP address. In the following example, the computer and
the router’s LAN port both use 192.168.1.1 as the IP address. The computer cannot access the
Internet. This problem can be solved by assigning a different IP address to the computer or the
router’s LAN port.
Page 194 / 252
Appendix B IP Addresses and Subnetting
NBG5715 User’s Guide
194
Figure 128
Conflicting Computer and Router IP Addresses Example
Page 195 / 252
NBG5715 User’s Guide
195
A
PPENDIX
C
Setting Up Your Computer’s IP Address
Note: Your specific NBG5715 may not support all of the operating systems described in
this appendix. See the product specifications for more information about which
operating systems are supported.
This appendix shows you how to configure the IP settings on your computer in order for it to be
able to communicate with the other devices on your network. Windows Vista/XP/2000, Mac OS 9/
OS X, and all versions of UNIX/LINUX include the software components you need to use TCP/IP on
your computer.
If you manually assign IP information instead of using a dynamic IP, make sure that your network’s
computers have IP addresses that place them in the same subnet.
In this appendix, you can set up an IP address for:
Windows XP/NT/2000
on
page 195
Windows Vista
on
page 199
Windows 7
on
page 203
Mac OS X: 10.3 and 10.4
on
page 207
Mac OS X: 10.5 and 10.6
on
page 210
Linux: Ubuntu 8 (GNOME)
on
page 213
Linux: openSUSE 10.3 (KDE)
on
page 217
Windows XP/NT/2000
The following example uses the default Windows XP display theme but can also apply to Windows
2000 and Windows NT.
1
Click
Start
>
Control Panel
.

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