1. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-1 Implement an IPv4-Based Redistribution Solution Operating a Network Using Multiple IP Routing Protocols

2. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-2 Complex Routing Scenarios  Networks can be dispersed –Politically –Geographically –As a result of acquisitions—company mergers  Careful design and traffic optimization are required –Redistribution –Routing traffic filtering –Summarization

3. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-3 Using Multiple Routing Protocols  Temporarily during conversion or migration only  Application-specific protocols – One size does not always fit all  Political boundaries – Groups that do not work well with others  Mismatch between devices – Multivendor interoperability – Host-based routers

4. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-4 Using Multiple IP Routing Protocols

5. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-5 Redistribution  Routes learned by some other means are selectively redistributed into a routing protocol from one of three sources: –Another routing protocol –Static routes –Directly connected routes  Routing loop prevention: –Only routes used by the router itself are redistributed  Double redistribution inside the same router is not allowed

6. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-6 Redistributing Route Information

7. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-7 Using Seed Metrics  The initial, or seed, metric for a route is derived from the directly connected router interface.  Once a compatible metric is established, the metric will increase in increments just like any other route.  Use the default-metric command to establish the seed metric for the route or specify the metric when redistributing. router eigrp 110 network 10.0.0.0 redistribute rip default-metric 1000 100 250 100 1500 R1#

8. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-8 Default Seed Metrics ProtocolDefault Seed Metric RIPInifinity EIGRPInfinity OSPF 20 for all except BGP, which is 1 BGP BGP metric is set to IGP metric value

9. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-9 Redistribution with Seed Metric

10. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-10 One-Point Redistribution  One-point redistribution –One-way; default route or static routes needed –Two-way

11. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-11 One-Way and Two-Way Multipoint Redistribution  Multipoint redistribution –One-way –Two-way

12. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-12 Redistribution Techniques

13. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-13 Redistribution Implementation Considerations  Problems: –Routing loop  Suboptimal path selection –Incompatible routing information –Inconsistent convergence time  Solutions: –Administrative distance –Route maps –Distribution lists –Manipulation of metrics

14. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-14 One-Way Redistribution Issue

15. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-15 One-Way Multipoint Redistribution Issue

16. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-16 Two-Way Multipoint Redistribution Issue

17. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-17 Summary  Big, complex networks must be adjusted based on factors like political borders, geographical borders, and mergers with other companies. In such complex scenarios, running multiple IP routing protocols is common.  Using a routing protocol to advertise routes that are learned by some other means, such as by another routing protocol, static routes, or directly connected routes, is called redistribution.  When a router advertises a link directly connected to one of its interfaces, the initial, or seed, metric that is used is derived from the characteristics of that interface. During redistribution the default metric is used; when redistributing routes into RIP and EIGRP, the default metric must be specified.

18. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-18 Summary (Cont.)  Redistribution can be one-point (one-way or two-way) or multipoint (one-way or two-way). One-point redistribution, whether one-way or two-way, is always safe, because it represents the only exit from one routing protocol to another. In contrast, multipoint redistribution is likely to introduce routing loops, so careful design and configuration must be applied.  The key issues that arise when you are using redistribution are routing feedback (routing loops), incompatible routing information, and inconsistent convergence time. Solutions to these issues include correct design in terms of the administrative distance, manipulation of metrics, and filtering using route maps and distribution lists.

19. © 2009 Cisco Systems, Inc. All rights reserved. ROUTE v1.0—4-19