Cisco Networking Academy Chapter 7: Static Routing PDF

Chapter 7: Static Routing Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1  Chapter 7 7.1 Static Routing Implementation 7.2 Configure Static and Default Routes 7.4 Configure Summary and Floating Static Routes...

Chapter 7: Static Routing Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1  Chapter 7 7.1 Static Routing Implementation 7.2 Configure Static and Default Routes 7.4 Configure Summary and Floating Static Routes 7.5 Troubleshoot Static and Default Route Issues 7.6 Summary Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2  Chapter 7: Objectives  Explain the advantages and disadvantages of static routing.  Explain the purpose of different types of static routes.  Configure IPv4 static routes by specifying a next-hop address.  Configure an IPv4 default routes. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3  Chapter 7: Objectives (cont.)  Configure an IPv4 summary network address to reduce the number of routing table updates.  Configure a floating static route to provide a backup connection.  Explain how a router processes packets when a static route is configured.  Troubleshoot common static and default route configuration issues. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4  Static Routing Reach Remote Networks A router can learn about remote networks in one of two ways: Manually - Remote networks are manually entered into the route table using static routes. Dynamically - Remote routes are automatically learned using a dynamic routing protocol. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5  Static Routing Why Use Static Routing? Static routing provides some advantages over dynamic routing, including:  Static routes are not advertised over the network, resulting in better security.  Static routes use less bandwidth than dynamic routing protocols, no CPU cycles are used to calculate and communicate routes.  The path a static route uses to send data is known. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6  Static Routing Why Use Static Routing? (cont.) Static routing has the following disadvantages:  Initial configuration and maintenance is time- consuming.  Configuration is error-prone, especially in large networks.  Administrator intervention is required to maintain changing route information.  Does not scale well with growing networks; maintenance becomes cumbersome.  Requires complete knowledge of the whole network for proper implementation. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7  Static Routing When to Use Static Routes Static routing has three primary uses:  Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly.  Routing to and from stub networks. A stub network is a network accessed by a single route, and the router has no other neighbors.  Using a single default route to represent a path to any network that does not have a more specific match with another route in the routing table. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8  Types of Static Routes Static Route Applications Static Routes are often used to:  Connect to a specific network.  Provide a Gateway of Last Resort for a stub network.  Reduce the number of routes advertised by summarizing several contiguous networks as one static route.  Create a backup route in case a primary route link fails. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9  Types of Static Routes Standard Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10  Types of Static Routes Default Static Route  A default static route is a route that matches all packets.  A default route identifies the gateway IP address to which the router sends all IP packets that it does not have a learned or static route.  A default static route is simply a static route with 0.0.0.0/0 as the destination IPv4 address. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11  Types of Static Routes Summary Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12  Types of Static Routes Floating Static Route  Floating static routes are static routes that are used to provide a backup path to a primary static or dynamic route, in the event of a link failure.  The floating static route is only used when the primary route is not available.  To accomplish this, the floating static route is configured with a higher administrative distance than the primary route. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13  Configure IPv4 Static Routes ip route Command Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14  Configure IPv4 Static Routes Next-Hop Options The next hop can be identified by an IP address, exit interface, or both. How the destination is specified creates one of the three following route types:  Next-hop route – ( recursive ) Only the next-hop IP address is specified.  Directly attached (connected) static route - Only the router exit interface is specified.  Fully specified static route - The next-hop IP address and exit interface are specified. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 15  Configure IPv4 Static Routes Configure a Next-Hop Static Route When a packet is destined for the 192.168.2.0/24 network, R1: 1. Looks for a match in the routing table and finds that it has to forward the packets to the next-hop IPv4 address 172.16.2.2. 2. R1 must now determine how to reach 172.16.2.2; therefore, it searches a second time for a 172.16.2.2 match. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 16  Configure IPv4 Static Routes Configure Directly Connected Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 17  Configure IPv4 Static Routes Configure a Fully Specified Static Route In a fully specified static route:  Both the output interface and the next-hop IP address are specified.  This form of static route is used when the output interface is a multi-access interface and it is necessary to explicitly identify the next hop.  The next hop must be directly connected to the specified exit interface. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 18  Configure IPv4 Static Routes Verify a Static Route Along with ping and traceroute, useful commands to verify static routes include:  show ip route  show ip route static  show ip route network Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19  Configure IPv4 Default Routes Default Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 20  Configure IPv4 Default Routes Configure a Default Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 21  Configure IPv4 Default Routes Verify a Default Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 22  Configure IPv4 Summary Routes Route Summarization Route summarization, also known as route aggregation, is the process of advertising a contiguous set of addresses as a single address with a less-specific, shorter subnet mask. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 23  Configure IPv4 Summary Routes Calculate a Summary Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 24  Configure IPv4 Summary Routes Summary Static Route Example Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 25  Configure Floating Static Routes Floating Static Routes Floating static routes are static routes that have an administrative distance greater than the administrative distance of another static route or dynamic routes:  The administrative distance of a static route can be increased to make the route less desirable than that of another static route or a route learned through a dynamic routing protocol.  In this way, the static route “floats” and is not used when the route with the better administrative distance is active.  However, if the preferred route is lost, the floating static route can take over, and traffic can be sent through this alternate route. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 26  Configure Floating Static Routes Configure a Floating Static Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 27  Configure Floating Static Routes Test the Floating Static Route To test a floating static route:  Use a show ip route command to verify that the routing table is using the default static route.  Use a traceroute command to follow the traffic flow out the primary route.  Disconnect the primary link or shutdown the primary exit interface.  Use a show ip route command to verify that the routing table is using the floating static route.  Use a traceroute command to follow the traffic flow out the backup route. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 28  Troubleshoot Static and Default Route Issues Static Routes and Packet Forwarding Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 29  Troubleshoot IPv4 Static and Default Route Configuration Troubleshoot a Missing Route Common IOS troubleshooting commands include:  ping  traceroute  show ip route  show ip interface brief  show cdp neighbors detail Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 30  Chapter 7: Summary  Static routes can be configured with a next-hop IP address, which is commonly the IP address of the next- hop router.  When a next-hop IP address is used, the routing table process must resolve this address to an exit interface.  On point-to-point serial links, it is usually more efficient to configure the static route with an exit interface.  On multi-access networks, such as Ethernet, both a next- hop IP address and an exit interface can be configured on the static route.  Static routes have a default administrative distance of "1". Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 31  Chapter 7: Summary (cont.)  A static route is only entered in the routing table if the next-hop IP address can be resolved through an exit interface.  Whether the static route is configured with a next-hop IP address or exit interface, if the exit interface that is used to forward that packet is not in the routing table, the static route is not included in the routing table.  In many cases, several static routes can be configured as a single summary route. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 32  Chapter 7: Summary (cont.)  The ultimate summary route is a default route, configured with a 0.0.0.0 network address and a 0.0.0.0 subnet mask.  If there is not a more specific match in the routing table, the routing table uses the default route to forward the packet to another router.  A floating static route can be configured to back up a main link by manipulating its administrative value. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 33 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 34