blocks. Each block is one route. There is also an asterisk (*) next to one of the block entries. This corresponds to the active route that is used for new traffic.
Content 7.2 RIP 7.2.9 Load balancing across multiple paths Load-balancing describes the ability of a router to transmit packets to a destination IP address over more than one path. Load balancing is a concept that allows a router to take advantage of multiple best paths to a given destination. The paths are derived either statically or with dynamic protocols, such as RIP, EIGRP, OSPF, and IGRP.When a router learns multiple routes to a specific network, the route with the lowest administrative distance is installed in the routing table. Sometimes the router must select a route from among many, learned via the same routing process with the same administrative distance. In this case, the router chooses the path with the lowest cost or metric to the destination. Each routing process calculates its cost differently and the costs may need to be manually configured in order to achieve load balancing. If the router receives and installs multiple paths with the same administrative distance and cost to a destination, load-balancing can occur. There can be up to six equal cost routes (a limit imposed by Cisco IOS on the routing table), but some Interior Gateway Protocols (IGPs) have their own limitation. EIGRP allows up to four equal cost routes. By default, most IP routing protocols install a maximum of four parallel routes in a routing table. Static routes always install six routes. The exception is BGP, which by default allows only one path to a destination. The range of maximum paths is one to six paths. To change the maximum number of parallel paths allowed, use the following command in router configuration mode: Router(config-router)#maximum-paths [number] IGRP can load balance up to six unequal links. RIP networks must have the same hop count to load balance, whereas IGRP uses bandwidth to determine how to load balance. Three ways to get to Network X: Router E chooses the second path above, E-C-A with a metric of 20 as it is a lower cost than 30 and 45. When routing IP, the Cisco IOS offers two methods of load balancing, per-packet and per-destination load balancing. If process switching is enabled, the router will alternate paths on a per-packet basis. If fast switching is enabled, only one of the alternate routes will be cached for the destination address, so all packets in the packet stream bound for a specific host will take the same path. Packets bound for a different host on the same network may use an alternate route, traffic is load balanced on a per-destination basis. Lab Activity Lab Exercise: Load Balancing Across Multiple Paths This lab is to configure Load balance across multiple paths. Lab Activity e-Lab Activity: Load Balancing Across Multiple Paths In this lab, the students will load balance across multiple paths and observe load balancing. Interactive Media Activity Drag and Drop: Administrative Distances After completing this activity, the student will be able to administrative distances. Web Links How Does Load Balancing Work? http://www.cisco.com/en/US/tech/ tk826/tk365/
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Content 7.2 RIP 7.2.10 Integrating static routes with RIP Static routes are user-defined routes that force packets moving between a source and a destination to take a specific path. Static routes become very important if the Cisco IOS software does not learn a route to a particular destination. They are also useful for specifying a “gateway of last resort”, commonly referred to as a default route. If a packet is destined for a subnet that is not explicitly listed in the routing table, the packet is forwarded to the default route. A router running RIP can receive a default route via an update from another router running RIP. Another option is for the router to generate the default route itself. The static routes can be removed using the no ip route global configuration command. The administrator can override a static route with dynamic routing information by adjusting the administrative distance values. Each dynamic routing protocol has a default administrative distance (AD). A static route can be defined as less desirable than a dynamically learned route, as long as the AD of the static route is higher than that of the dynamic route. Static routes that point out an interface will be advertised via the RIP router that owns the static route, and propagated throughout the internetwork. This is because static routes that point to an interface are considered in the routing table to be connected and thus lose their static nature in the update. If a static route is assigned to an interface that is not defined in the RIP process, via a network command, RIP will not advertise the route unless a redistribute static command is specified in the RIP process. When an interface goes down, all static routes pointing out that interface are removed from the IP routing table. Likewise, when the software can no longer find a valid next hop for the address specified in the static route, then the static route is removed from the IP routing table. In Figure a static route has been configured on the GAD router to take the place of the RIP route in the event that the RIP routing process fails. This is referred to as a floating static route. The floating static route was configured by defining an AD on the static route (130) greater than the default AD of RIP (120). The BHM router would also need to be configured with a default route. To configure a static route, use the Figure command in global configuration mode. Lab Activity e-Lab Activity: Integrating Static Routes with RIP In this lab, the students will enable RIP to propagate static routes.
Content 7.3 IGRP 7.3.1 IGRP features IGRP is a distance vector Interior Gateway Protocol (IGP). Distance vector routing protocols mathematically compare routes by measuring distances. This measurement is known as the distance vector. Routers using distance vector protocols must send all or a portion of their routing table in a routing update message at regular intervals to each of their neighboring routers. As routing information spreads throughout the network, routers perform the following functions: IGRP is a distance vector routing protocol developed by Cisco. IGRP sends routing updates at 90 second intervals, advertising networks for a particular autonomous system. Key design characteristics of IGRP are a follows: By default, the IGRP routing protocol uses bandwidth and delay as metrics. Additionally, IGRP can be configured to use a combination of variables to determine a composite metric. Those variables include: Interactive Media Activity Checkbox: RIP versus IGRP After completing this activity, the student will be able to understand RIP and IGRP. Web Links Specifying a Next Hop IP Address for Static Routes http://www.cisco.com/en/US/tech/tk826/ tk365/technologies_tech_ note09186a00800ef7b2.shtml
Content 7.3 IGRP 7.3.2 IGRP metrics The show ip protocols command displays parameters, filters, and network information concerning the routing protocols in use on the router. The algorithm used to calculate the routing metric for IGRP is shown in the graphic. It defines the value of the K1-K5 metrics and provides information concerning the maximum hop count. The metric K1