Networking and Security Basics
The Use of IP Addresses
Cisco RVS4000 Security Router with VPN Administrator Guide
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The Use of IP Addresses
IP stands for Internet Protocol. Every device in an IP-based network, including PCs,
print servers, and routers, requires an IP address to identify its location, or
address, on the network. This applies to both the Internet and LAN connections.
There are two ways of assigning IP addresses to your network devices.
A static IP address is a fixed IP address that you assign manually to a PC or other
device on the network. Since a static IP address remains valid until you disable it,
static IP addressing ensures that the device assigned it will always have that same
IP address until you change it. Static IP addresses are commonly used with
network devices such as server PCs or print servers.
If you use the router to share your cable or DSL Internet connection, contact your
ISP to find out if they have assigned a static IP address to your account. If so, you
will need that static IP address when configuring the router. You can get the
information from your ISP.
A dynamic IP address is automatically assigned to a device on the network. These
IP addresses are called dynamic because they are only temporarily assigned to
the PC or other device. After a certain time period, they expire and may change. If
a PC logs onto the network (or the Internet) and its dynamic IP address has
expired, the DHCP server will assign it a new dynamic IP address.
A DHCP server can either be a designated PC on the network or another network
device, such as the router. By default, the router’s Internet Connection Type is
Obtain an IP automatically
(DHCP).
The PC or network device that obtains an IP address is called the DHCP client.
DHCP frees you from the requirement to assign an IP address manually when a
new user is added to your network.
For DSL users, many ISPs may require you to log on with a user name and
password to gain access to the Internet. This is a dedicated, high-speed
connection type called Point to Point Protocol over Ethernet (PPPoE). PPPoE is
similar to a dial-up connection, but PPPoE does not dial a phone number when
establishing a connection. It also will provide the router with a dynamic IP address
to establish a connection to the Internet.
By default, a DHCP server (on the LAN side) is enabled on the router. If you already
have a DHCP server on your network, you MUST disable one of the two DHCP
servers. If you run more than one DHCP server on your network, you will
experience network errors, such as conflicting IP addresses. To disable DHCP on
the router, see the Basic Setup section in
Chapter 5, “Setting Up and
Configuring the Router.”
