All the following are possible solutions for preventing routing loops.
1. Split Horizon - Based on the principle that it is not useful to send the information about a route back in the direction from which the information originally came.
2. Poison Reverse - A router that discovers an inaccessible route sets a table entry in a consistent state (infinite metric) while the network converges.
3. Hold-down Timers - Holddown timers prevent regular update messages from reinstating a route that has gone bad. Here, if a route fails, the router waits a certain amount of time before accepting any other routing information about that route.
4. Triggered Updates - Normally, new routing tables are sent to neigbhoring routers at regular intervals (IP RIP every 30 sec / and IPX RIP every 60 sec). A triggered update is an update sent immediately in response to some change in the routing table. Triggered updates along with Hold-down timers can be used effectively to counter routing loops.
IP route summarization is used to make networks more flexible and efficient. Although some routing protocols such as RIPv1 and IGRP summarize only at the boundaries of major network numbers, others support route summarization (aggregation) at any bit boundary. Variable-length subnet masks enable routing protocols to summarize on bit boundaries. The following are the advantages to summarizing addresses into a hierarchy:
1. Reduces the amount of information stored in routing tables - Without summarization, a router needs to process every single route in the network. With summarization, routers can condense network addresses down to a single link advertisement, resulting in a reduction in both the resource load on the router and the overall network complexity. Route summarization is most effective in large networks.
2. Allocates an existing pool of addresses more economically - The available IP addresses are limited. Route summarization ensures that IP addresses are utilized efficiently.
3. Makes the routing process more efficient - With less overhead, routers are faster and more efficient.
4. Lowers the network convergence time - The network convergence time would reduce with route summarization.
Policy-based routing is applied to incoming packets. All packets received on an interface with policy-based routing enabled are considered for policy-based routing. The router passes the packets through enhanced packet filters called route maps. Based on the criteria defined in the route maps, packets are forwarded/routed to the appropriate next hop.
1. show policy -map control-plane: Verifies the applied policy map, the class maps in the order in which they will be applied, the match conditions of the class maps, and the policies that are applied to the traffic that is matched
2. show class-map: Displays all configured class maps on the router
3. show access-list: Displays all configured ACLs on the router
4. show policy-map: Displays all configured policy maps on the router