Information Technology Reference
In-Depth Information
Routers are configured to run routing protocols to determine the best paths to a destination.
Routers exchange information about destination networks and their interface status by using
these routing protocols. Routers can also be configured manually with static routes. Some IP
routing protocols are the following:
Routing Information Protocol (RIP)
Interior Gateway Routing Protocol (IGRP)
Open shortest Path First (OSPF)
Intermediate System-to-Intermediate System (IS-IS)
Enhanced Interior Gateway Routing Protocol (EIGRP)
Border Gateway Protocol (BGP)
These protocols are discussed in Chapter 7, Chapter 8, and Chapter 9.
LAN switches that are capable of running routing protocols are called Layer-3 switches. They
run the full routing protocols and can communicate with routers as peers. Layer-3 switches
off-load local traffic from wide-area network (WAN) routers by performing network-layer
forwarding within the local-area networks (LANs). Both routers and Layer-3 switches make
forwarding decisions based on IP addresses and not MAC addresses. Both participate in the
exchange of route information based on the dynamic routing protocol they participate in.
The Difference Between Layer-2 Switching and Routing
The most obvious difference between Layer-2 switching and routing is that switching occurs at
Layer 2 of the OSI reference model and routing occurs at Layer 3. Switches forward frames
based on MAC address information. Routers forward packets based on logical addresses (IP
address).
Throughout this topic, switching means bridging, unless you see the term Layer-3 switching.
NOTE
Routing Protocol Characteristics
This section discusses the different types and metrics of routing protocols.
Static Versus Dynamic Routing Protocols
Static routes are manually configured on a router; therefore, they cannot react based on network
outages. The one exception to this is when the static route points to the outbound interface: If
the interface goes down, the static route is removed from the routing table. The size of today's
 
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