effective for the broadcast domain (or LAN) that it is connected to. The router also maintains a routing table that allows it to route data outside of the broadcast domain. Each ARP table contains an IP-MAC address pair (the MAC addresses in the graphic are represented by the acronym MAC, as the actual addresses are too long to fit in the graphic). The routing tables also track how the route was learned (in this case either directly connected [C] or learned by RIP [R]), the network IP address for reachable networks, the hop count or distance to those networks, and the interface the data must be sent out to get to the destination network. The Layer 2 switch can only recognize its own local MAC addresses and cannot handle Layer 3 IP addresses. When a host has data for a non-local IP address, it sends the frame to the closest router, also known as its default gateway. The host uses the MAC address of the router as the destination MAC address. A Layer 2 switch interconnects segments belonging to same logical network or subnetwork. If Host X needs to send a frame to a host on a different network or subnetwork, Host X sends the frame to the router that is also connected to the switch. The switch forwards the frame to the router based on the destination MAC address. The router examines the Layer 3 destination address of the packet to make the forwarding decision. Host X knows the IP address of the router because the IP configuration of the router also includes the IP address of the default gateway. Just as a Layer 2 switch keeps a table of known MAC addresses, the router keeps a table of IP addresses known as a routing table. There is a difference between these two types of addresses. MAC addresses are not logically organized, but IP addresses are organized in a hierarchical manner. A Layer 2 device can handle a reasonable number of unorganized MAC addresses, because it will only have to search its table for those addresses within its segment. Routers need to handle a greater volume of addresses. Therefore, routers need an organized addressing system that can group similar addresses together and treat them as a single network unit until the data reaches the destination segment. If IP addresses were not organized, the Internet simply would not work. An example would be like a library that contained millions of individual pages of printed material in a large pile. This material is useless because it is impossible to locate an individual document. If the pages are organized into books and each page is individually identified, and the books are also listed in a book index, it becomes a lot easier to locate and use the data. Another difference between switched and routed networks is switched networks do not block broadcasts. As a result, switches can be overwhelmed by broadcast storms. Routers block LAN broadcasts, so a broadcast storm only affects the broadcast domain from which it originated. Because routers block broadcasts, routers also provide a higher level of security and bandwidth control than switches. Interactive Media Activity Drag and Drop: Routing vs. Switching After completing this activity, the student will be able to identify the differences between routing and switching. Web Links Routing vs. Switching http://www.cs.cornell.edu/skeshav/ talks/infocom97panel/

Content 10.2 IP Routing Protocols 10.2.3 Routed versus routing Protocols used at the network layer that transfer data from one host to another across a router are called routed or routable protocols. Routed protocols transport data across a network. Routing protocols allow routers to choose the best path for data from source to destination. A routed protocol functions include the following:

Includes any network protocol suite that provides enough information in its network layer address to allow a router to forward it to the next device and ultimately to its destination.
Defines the format and use of the fields within a packet

The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are examples of routed protocols. Other examples include DECnet, AppleTalk, Banyan VINES, and Xerox Network Systems (XNS). Routers use routing protocols to exchange routing tables and share routing information. In other words, routing protocols enable routers to route routed protocols. A routing protocol functions includes the following:

Provides processes for sharing route information
Allows routers to communicate with other routers to update and maintain the routing tables

Examples of routing protocols that support the IP routed protocol include the Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Enhanced IGRP (EIGRP). Interactive Media Activity Checkbox: Routed vs. Routing Protocols After completing this activity, the student will be able to identify the differences between routed and routing protocols. Web Links Routing versus. Routed Protocols http://www.inetdaemon.com/tutorials/internet/ routing/routing_vs_routed.html

Content 10.2 IP Routing Protocols 10.2.4 Path determination Path determination occurs at the network layer. Path determination enables a router to compare the destination address to the available routes in its routing table, and to select the best path. The routers learn of these available routes through static routing or dynamic routing. Routes configured manually by the network administrator are static routes. Routes learned by others routers using a routing protocol are dynamic routes. The router uses path determination to decide which port an incoming packet should be sent out of to travel on to its destination. This process is also referred to as routing the packet. Each router that the packet encounters along the way is called a hop. The hop count is the distanced traveled. Path determination can be compared to a person driving a car from one location in a city to another. The driver has a map that shows the streets that can be taken to get to the destination, just as a router has a routing table. The driver travels from one intersection to another just as a packet travels from one router to another in each hop. At any intersection, the driver can route himself by choosing to turn left, turn right, or go straight ahead. In the same manner, a router decides which outbound port the packet should be sent. The decisions of a driver are influenced by factors such as traffic on a road, the speed limit of the road, the number of lanes on the road, whether or not there is a toll on the road, and whether or not the road is frequently closed. Sometimes it is faster to take a longer route on a smaller, less crowded back street instead of a highway with a lot of traffic. Similarly, routers can make decisions based on the load, bandwidth, delay, cost, and reliability of a network link. The following process is used during path determination for every packet that is routed:

The destination address is obtained from the packet.
The mask of the first entry in the routing table is applied to the destination address.
The masked destination and the routing table entry are compared.
If there is a match, the packet is forwarded to the port that is associated with that table entry.
If there is not a match, the next entry in the table is checked.
If the packet does not match any entries in the table, the router checks to see if a default route has been set.
If a default route has been set, the packet is forwarded to the associated port. A default route is a route that is configured by the network administrator as the route to use if there are no matches in the routing table.
If there is no default route, the packet is discarded. Usually a message is sent back to the sending device indicating that the destination was unreachable.

Interactive Media Activity Drag and Drop: Path Determination Flowchart After completing this activity, the