Specifications

Niagara Release 2.3
Revised: May 22, 2002 Niagara Networking & Connectivity Guide
Chapter 1 Understanding Networking and IP Addressing
Networking using IP
1–24
Note Some administrators have chosen to implement IP addressing on their private
networks using legitimate (such as 205.254.1.0) addresses that have not been
assigned to them. They use NAT to translate between the legitimate external address
and the illegitimate internal address. Depending on how the Internet connection
works, this may cause problems in the event of a failure in the connection. It is
always best to use private address ranges instead.
See Figure 1-4 for examples of private networks and routers using NAT to translate
between private and public IP addresses.
IP Routing and
Default Gateway
As discussed previously, any host on a network can communicate with another host
on the same network. But what if the host needs to communicate to host on another
network across the company or across the world?
If a host wants to communicate outside its network, the administrator sets a default
gateway on the host which is the IP address of a router used for communication with
other networks.
The router examines an IP packet from the host and compares the destination address
with a table of addresses it holds in memory. If it finds a match, it will forward the
packet to the address associated with the table entry. This address could be on another
network attached directly to the router, or the router could forward it to another router
that knows about the network of the destination address.
Routers can build these tables of destinations in a number of different ways. For
simple networks, the router could load a table during start-up that was manually
created by the administrator. However, more typically, routers use a broadcasting
protocol to advertise the networks they know about. Routers use other protocols to
discover the shortest path between networks (the least number of hops from router to
router). Routes are updated periodically to reflect changes in the availability of a
route.
Figure 1-4 illustrates a typical network architecture of routers and default gateways
in several networks.