Chapter Introduction
Routing is at the core of every data network, moving information across an internetwork from source to destination. Routers are the devices responsible for the transfer of packets from one network to the next.
As we learned in the previous chapter, routers learn about remote networks either dynamically using routing protocols or manually using static routes. In many cases routers use a combination of both dynamic routing protocols and static routes. This chapter focuses on static routing.
Static routes are very common and do not require the same amount of processing and overhead as we will see with dynamic routing protocols.
In this chapter, we will follow a sample topology as we configure static routes and learn troubleshooting techniques. In the process, we will examine several key IOS commands and the results they display. We will also introduce the routing table using both directly connected networks and static routes.
As you work through the Packet Tracer activities associated with these commands, take the time to experiment with the commands and examine the results. Reading the routing tables will soon become second nature.
Role of the Router
The router is a special-purpose computer that plays a key role in the operation of any data network. Routers are primarily responsible for interconnecting networks by:
Determining the best path to send packets
Forwarding packets toward their destination
Routers perform packet forwarding by learning about remote networks and maintaining routing information. The router is the junction or intersection that connects multiple IP networks. The routers primary forwarding decision is based on Layer 3 information, the destination IP address.
The router’s routing table is used to find the best match between the destination IP of a packet and a network address in the routing table. The routing table will ultimately determine the
exit interface to forward the packet and the router will encapsulate that packet in the appropriated data link frame for that outgoing interface.
Introducing the Topology
The figure shows the topology used in this chapter. The topology consists of three routers, labeled R1, R2, and R3. Routers R1 and R2 are connected through one WAN link, and routers R2 and R3 are connected through another WAN link. Each router is connected to a different Ethernet LAN, represented by a switch and a PC.
Each router in this example is a Cisco 1841. A Cisco 1841 router has the following interfaces:
Two FastEthernet interfaces: FastEthernet 0/0 and FastEthernet 0/1
Two serial interfaces: Serial 0/0/0 and Serial0/0/1
The interfaces on your routers may vary from those on the 1841, but you should be able to follow the commands in this chapter-with some slight modifications-and complete the hands-on labs. In addition, Packet Tracer activities are available throughout the discussion of static routing so that you can practice skills as they are presented. Lab 2.8.1, “Basic Static Route Configuration,” mirrors the topology, configurations, and commands discussed in this chapter.
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