• Configuring route summarization on an interface
  • Verifying IP route summarization
  • Disabling automatic route summarization
  • Running IGRP and RIP concurrently
  • Disabling the validation of source IP addresses
  • Enabling or disabling split horizon
  • Connecting RIP to a WAN
    • To enable RIP, use the following commands beginning in global configuration mode: Lab Activity Lab Exercise: Configuring RIP This lab is to setup an IP addressing scheme using class B networks and configure the RIP dynamic routing protocol on routers. Lab Activity e-Lab Activity: RIP In this lab, the students will take a look at the router topology before starting the lab. Web Links Configuring RIP http://www.cisco.com/en/US/products/sw/
    iosswrel/ps1831/ products_configuration_guide_
    chapter09186a00800d97f7.html#xtocid2
    Content 7.2 RIP 7.2.3 Using the ip classless command Sometimes a router receives packets destined for an unknown subnet of a network that has directly connected subnets. In order for the Cisco IOS software to forward these packets to the best supernet route possible, use the ip classless global configuration command. A supernet route is a route that covers a greater range of subnets with a single entry. For example, an enterprise uses the entire subnet 10.10.0.0 /16, then a supernet route for 10.10.10.0 /24 would be 10.10.0.0 /16. The ip classless command is enabled by default in Cisco IOS Software Release 11.3 and later. To disable this feature, use the no form of this command.When this feature is disabled any packets received that are destined for a subnet that numerically falls within the router’s subnetwork addressing scheme will be discarded. IP classless only affects the operation of the forwarding processes in IOS. IP classless does not affect the way the routing table is built. This is the essence of classful routing. If one part of a major network is known, but the subnet toward which the packet is destined within that major network is unknown, the packet is dropped. The most confusing aspect of this rule is that the router only uses the default route if the major network destination does not exist in the routing table. A router by default assumes that all subnets of a directly connected network should be present in the routing table. If a packet is received with an unknown destination address within an unknown subnet of a directly attached network, the router assumes that the subnet does not exist. So the router will drop the packet even if there is a default route. Configuring ip classless on the router resolves this problem by allowing the router to ignore the classful boundaries of the networks in its routing table and simply route to the default route. Lab Activity e-Lab Activity: Using Classless IP Routing In this lab, the student will configure the router to use classless routing when forwarding packets. Web Links ip classless Global Configuration Command http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/ products_command_reference_ chapter09186a0080087387.html#1018036
    Content 7.2 RIP 7.2.4 Common RIP configuration issues RIP routers must rely on neighboring routers for network information that is not known first hand. A common term used to describe this functionality is Routing By Rumor. RIP uses a distance vector routing algorithm. All distance vector routing protocols have issues that are primarily created by slow convergence. Convergence is when all routers in the same internetwork have the same routing information.Among these issues are routing loops and counting to infinity. These result in inconsistencies due to routing update messages with out of date routes being propagated around the internetwork. To reduce routing loops and counting to infinity, RIP uses the following techniques: Some of these methods may require some configuration, while others do not require or rarely require configuration. RIP permits a maximum hop count of 15. Any destination greater that 15 hops away is tagged as unreachable. RIP’s maximum hop count greatly restricts its use in large internetworks but prevents a problem called “counting to infinity” from causing endless network routing loops. The split horizon rule is based on the theory that it is not useful to send information about a route back in the direction from which it came. In some network configurations, it may be necessary to disable split horizon. The following command is used to disable split horizon: GAD(config-if)#no ip split-horizon The holddown timer is another mechanism that may need some changes. Holddown timers help prevent counting to infinity but also increase convergence time. The default holddown for RIP is 180 seconds. This will prevent any inferior route from being updated but may also prevent a valid alternative route from being installed. The holddown timer can be decreased to speed up convergence but should be done with caution. The ideal setting would be to set the timer just longer that the longest possible update time for the internetwork. In the example in Figure , the loop consists of four routers. If each router has an update time of 30 seconds, the longest loop would be 120 seconds. Therefore, the holddown timer should be set to slightly more than 120 seconds. To change the holddown timer: Router(config-router)#timers basic update invalid holddown flush [sleeptime] One additional item that affects convergence time, and is configurable, is the update interval. The default RIP update interval in Cisco IOS is 30 seconds. This can be configured for longer intervals to conserve bandwidth, or for shorter intervals to decrease convergence time. To change the update internal: GAD(config-router)#update-timer seconds Another issue with routing protocols is the unwanted advertisement of routing updates out a particular interface. When a network command is issued for a given network, RIP will immediately begin sending advertisements out all interfaces within the specified network address range. To control the set of interfaces that will exchange routing updates, the network administrator can disable the sending of routing updates on specified interfaces by configuring the passive-interface command. Because RIP is a broadcast protocol, the network administrator may have to configure RIP to exchange routing information in a non-broadcast network such as Frame Relay. In this type of network, RIP needs to be told of other neighboring RIP routers. To do this use the command displayed in Figure . By default, the Cisco IOS software receives RIP Version 1 and Version 2 packets, but sends only Version 1 packets. The network administrator can configure the router to only receive and send Version 1 packets or the administrator can configure the router to send only Version 2 packets. To configure the router to send and receive packets from only one version, use the commands in Figure . To control how packets received from an interface are processed, use the commands in Figure . Web Links Configuring RIP