19216811.liveAppendix A IP Addresses and Subnetting
NBG6515 User’s Guide
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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 NBG.
Once you have decided on the network number, pick an IP address for your NBG 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 NBG 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 NBG 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