Bay Technical Associates RM356 Manual De Usuario
Reference Guide for the Model RM356 Modem Router
Introduction
1-5
Basic Router Concepts
In general, the cost of providing network bandwidth is proportional to the data speed and the
distance over which the network extends. Large amounts of bandwidth are provided easily and
relatively inexpensively in a local area network (office, department, and similar situations).
However, providing the same high data speeds between two local networks that are physically
distant may be prohibitively expensive. Because of this expense, high-speed local area networks
(LANs) are usually interconnected by slower-speed links to form a wide area network (WAN).
distance over which the network extends. Large amounts of bandwidth are provided easily and
relatively inexpensively in a local area network (office, department, and similar situations).
However, providing the same high data speeds between two local networks that are physically
distant may be prohibitively expensive. Because of this expense, high-speed local area networks
(LANs) are usually interconnected by slower-speed links to form a wide area network (WAN).
In order to make the best use of the slower WAN links, a mechanism must be in place at each
location for selecting data meant only for another location and sending it by the best available link.
The function of selecting and forwarding this data is performed by a router.
location for selecting data meant only for another location and sending it by the best available link.
The function of selecting and forwarding this data is performed by a router.
What is a Router?
A router is a device that forwards traffic between networks based on network layer information in
the data and on routing tables maintained by the router. In these routing tables, a router builds up a
logical picture of the overall network by gathering and exchanging information with other routers
in the network. Using this information, it chooses the best path for forwarding network traffic.
the data and on routing tables maintained by the router. In these routing tables, a router builds up a
logical picture of the overall network by gathering and exchanging information with other routers
in the network. Using this information, it chooses the best path for forwarding network traffic.
Routers vary in performance and scale, number of routing protocols supported, and types of
physical WAN connections supported. The Model RM356 Modem Router is a small office router
that routes the IP protocol over a dial-up telephone connection.
physical WAN connections supported. The Model RM356 Modem Router is a small office router
that routes the IP protocol over a dial-up telephone connection.
Routing Information Protocol
One of the protocols used by a router to build and maintain a picture of the network is the Routing
Information Protocol (RIP). RIP is a distance vector protocol, meaning that all the decisions about
which path to use are based upon a logical distance between source and destination networks. This
distance is measured in “hops,” meaning the number of relaying routers in the path between the
source LAN router and the router of the destination LAN. For example, the LAN of router A is
considered to be 1 hop away. If router A can reach the network of router B by a direct WAN link to
the network of router B, the network of router B is two hops away. If another network must be
reached by calling router B and having router B forward the data, that network is n hops away,
where n is the number of routers traversed by the data to get to the network farthest away. When
there are multiple paths to a network, the path with the fewest hops is chosen and is regarded as the
best path, and all other information about how to get to that network is discarded.
Information Protocol (RIP). RIP is a distance vector protocol, meaning that all the decisions about
which path to use are based upon a logical distance between source and destination networks. This
distance is measured in “hops,” meaning the number of relaying routers in the path between the
source LAN router and the router of the destination LAN. For example, the LAN of router A is
considered to be 1 hop away. If router A can reach the network of router B by a direct WAN link to
the network of router B, the network of router B is two hops away. If another network must be
reached by calling router B and having router B forward the data, that network is n hops away,
where n is the number of routers traversed by the data to get to the network farthest away. When
there are multiple paths to a network, the path with the fewest hops is chosen and is regarded as the
best path, and all other information about how to get to that network is discarded.