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IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E Americas Headquarters Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA http://www.cisco.com Tel: 408 526-4000 800 553-NETS (6387) Fax: 408 527-0883 THE SPECIFICATIONS AND INFORMATION REGARDING THE PRODUCTS IN THIS MANUAL ARE SUBJECT TO CHANGE WITHOUT NOTICE. ALL STATEMENTS, INFORMATION, AND RECOMMENDATIONS IN THIS MANUAL ARE BELIEVED TO BE ACCURATE BUT ARE PRESENTED WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. USERS MUST TAKE FULL RESPONSIBILITY FOR THEIR APPLICATION OF ANY PRODUCTS. THE SOFTWARE LICENSE AND LIMITED WARRANTY FOR THE ACCOMPANYING PRODUCT ARE SET FORTH IN THE INFORMATION PACKET THAT SHIPPED WITH THE PRODUCT AND ARE INCORPORATED HEREIN BY THIS REFERENCE. IF YOU ARE UNABLE TO LOCATE THE SOFTWARE LICENSE OR LIMITED WARRANTY, CONTACT YOUR CISCO REPRESENTATIVE FOR A COPY. The Cisco implementation of TCP header compression is an adaptation of a program developed by the University of California, Berkeley (UCB) as part of UCB's public domain version of the UNIX operating system. All rights reserved. Copyright © 1981, Regents of the University of California. NOTWITHSTANDING ANY OTHER WARRANTY HEREIN, ALL DOCUMENT FILES AND SOFTWARE OF THESE SUPPLIERS ARE PROVIDED “AS IS" WITH ALL FAULTS. CISCO AND THE ABOVE-NAMED SUPPLIERS DISCLAIM ALL WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING, WITHOUT LIMITATION, THOSE OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OR ARISING FROM A COURSE OF DEALING, USAGE, OR TRADE PRACTICE. IN NO EVENT SHALL CISCO OR ITS SUPPLIERS BE LIABLE FOR ANY INDIRECT, SPECIAL, CONSEQUENTIAL, OR INCIDENTAL DAMAGES, INCLUDING, WITHOUT LIMITATION, LOST PROFITS OR LOSS OR DAMAGE TO DATA ARISING OUT OF THE USE OR INABILITY TO USE THIS MANUAL, EVEN IF CISCO OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: http:// www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R) © 2016 Cisco Systems, Inc. All rights reserved. CONTENTS CHAPTER 1 Basic IP Routing 1 Finding Feature Information 1 Information About Basic IP Routing 1 Variable-Length Subnet Masks 1 Static Routes 2 Default Routes 3 Default Network 4 Gateway of Last Resort 4 Maximum Number of Paths 5 Multi-Interface Load Splitting 5 Routing Information Redistribution 5 Supported Metric Translations 6 Protocol Differences in Implementing the no redistribute Command 6 Sources of Routing Information Filtering 7 Authentication Key Management and Supported Protocols 7 How to Configure Basic IP Routing 8 Redistributing Routing Information 8 Defining Conditions for Redistributing Routes 8 Redistributing Routes from One Routing Domain to Another 11 Removing Options for Redistribution Routes 12 Configuring Routing Information Filtering 13 Controlling the Advertising of Routes in Routing Updates 13 Controlling the Processing of Routing Updates 14 Filtering Sources of Routing Information 14 Managing Authentication Keys 14 Monitoring and Maintaining the IP Network 15 Clearing Routes from the IP Routing Table 15 Displaying System and Network Statistics 16 IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E iii Contents Configuration Examples for Basic IP Routing 16 Example: Variable-Length Subnet Mask 16 Example: Overriding Static Routes with Dynamic Protocols 17 Example: IP Default Gateway as a Static IP Next Hop When IP Routing Is Disabled 17 Examples: Administrative Distances 18 Example: Static Routing Redistribution 18 Examples: EIGRP Redistribution 19 Example: Mutual Redistribution Between EIGRP and RIP 19 Example: Mutual Redistribution Between EIGRP and BGP 20 Examples: OSPF Routing and Route Redistribution 21 Examples: Basic OSPF Configuration 21 Example: Internal Device ABR and ASBRs Configuration 23 Example: Complex OSPF Configuration 25 Example: Default Metric Values Redistribution 27 Examples: Redistribution With and Without Route Maps 27 Examples: Key Management 29 Additional References 30 Feature Information for Basic IP Routing 30 CHAPTER 2 Fast-Switched Policy Routing 33 Finding Feature Information 33 Prerequisites for Fast-Switched Policy Routing 33 Information About Fast-Switched Policy Routing 34 Fast-Switched Policy Routing 34 Additional References 34 Feature Information for Fast-Switched Policy Routing 35 CHAPTER 3 Policy-Based Routing 37 Finding Feature Information 37 Prerequisites for Policy-Based Routing 37 Information About Policy-Based Routing 38 Policy-Based Routing 38 How to Configure Policy-Based Routing 39 Configuring Policy-Based Routing 39 Configuration Examples for Policy-Based Routing 41 IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E iv Contents Additional References 41 Feature Information for Policy-Based Routing 42 CHAPTER 4 IPv6 Policy-Based Routing 43 Finding Feature Information 43 Information About IPv6 Policy-Based Routing 43 Policy-Based Routing Overview 43 How Policy-Based Routing Works 44 Packet Matching 44 Packet Forwarding Using Set Statements 45 When to Use Policy-Based Routing 46 How to Enable IPv6 Policy-Based Routing 46 Enabling IPv6 PBR on an Interface 46 Enabling Local PBR for IPv6 49 Verifying the Configuration and Operation of PBR for IPv6 50 Troubleshooting PBR for IPv6 51 Configuration Examples for IPv6 Policy-Based Routing 52 Example: Enabling PBR on an Interface 52 Example: Enabling Local PBR for IPv6 52 Example: show ipv6 policy Command Output 52 Example: Verifying Route-Map Information 52 Additional References for IPv6 Policy-Based Routing 53 Feature Information for IPv6 Policy-Based Routing 53 IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E v Contents IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E vi CHAPTER 1 Basic IP Routing This module describes how to configure basic IP routing. The Internet Protocol (IP) is a network layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network layer protocol in the Internet protocol suite. • Finding Feature Information, page 1 • Information About Basic IP Routing, page 1 • How to Configure Basic IP Routing, page 8 • Configuration Examples for Basic IP Routing, page 16 • Additional References, page 30 • Feature Information for Basic IP Routing, page 30 Finding Feature Information Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Information About Basic IP Routing Variable-Length Subnet Masks Enhanced Interior Gateway Routing Protocol (EIGRP), Intermediate System-to-Intermediate System (IS-IS), Open Shortest Path First (OSPF), Routing Information Protocol (RIP) Version 2, and static routes support variable-length subnet masks (VLSMs). With VLSMs, you can use different masks for the same network number on different interfaces, which allows you to conserve IP addresses and more efficiently use available IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E 1 Basic IP Routing Static Routes address space. However, using VLSMs also presents address assignment challenges for the network administrator and ongoing administrative challenges. Refer to RFC 1219 for detailed information about VLSMs and how to correctly assign addresses. Note Consider your decision to use VLSMs carefully. You can easily make mistakes in address assignments and you will generally find that the network is more difficult to monitor using VLSMs. The best way to implement VLSMs is to keep your existing addressing plan in place and gradually migrate some networks to VLSMs to recover address space. Static Routes Static routes are user-defined routes that cause packets moving between a source and a destination to take a specified path. Static routes can be important if the device cannot build a route to a particular destination. They are also useful for specifying a gateway of last resort to which all unroutable packets will be sent. To configure a static route, use the ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent | track number] [tag tag] global configuration command. Static routes remains in the device configuration until you remove them (using the no ip route global configuration command).
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