Specifications

Chapter A Networking Concepts
Network Address Translation
A-10
Cisco 1700 Series Router Software Configuration Guide
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on the minimum and maximum number of B channels reserved by any dialer pool.
A channel reserved by a dialer pool remains idle until traffic is directed to the
pool.
When you use dialer profiles to configure dial-on-demand routing (DDR), the
physical interface is configured only for encapsulation and for the dialer pools to
which the interface belongs. All other characteristics used for making calls are
defined in the dialer map.
Network Address Translation
Network Address Translation (NAT) provides a mechanism for a privately
addressed network to access registered networks, such as the Internet, without
requiring a registered subnet address. This mechanism eliminates the need for
host renumbering and allows the same IP address range to be used in multiple
intranets.
NAT is configured on the router at the border of an inside network (a network that
uses nonregistered IP addresses) and an outside network (a network that uses a
globally unique IP address; in this case, the Internet). NAT translates the inside
local addresses (the nonregistered IP addresses assigned to hosts on the inside
network) into globally unique IP addresses before sending packets to the outside
network.
With NAT, the inside network continues to use its existing private or obsolete
addresses. These addresses are converted into legal addresses before packets are
forwarded onto the outside network. The translation function is compatible with
standard routing; the feature is required only on the router connecting the inside
network to the outside domain.
Translations can be static or dynamic. A static address translation establishes a
one-to-one mapping between the inside network and the outside domain.
Dynamic address translations are defined by describing the local addresses to be
translated and the pool of addresses from which to allocate outside addresses.
Allocation occurs in numerical order, and multiple pools of contiguous address
blocks can be defined.
NAT eliminates the need to readdress all hosts that require external access, saving
time and money. It also conserves addresses through application port-level
multiplexing. With NAT, internal hosts can share a single registered IP address for