© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Designing IP Addressing and Selecting Routing Protocols Designing a Routing Protocol Deployment

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Routing Protocols in the Enterprise Architecture

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Redistribution Redistribution on routing protocols and domain boundaries occurs on the router.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Redistribution Direction Redistribution of routing protocols (boundary router) One-way redistribution in one direction (for example, from enterprise edge to campus core) Two-way redistribution in both directions

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Redistribution in the Enterprise Network Redistribution: From selected building access protocols Between campus core and WAN routers From static routes to enterprise IGP Static routes or BGP routes into enterprise IGP

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Filtering Filtering upon redistribution: Avoids routing loops Avoids suboptimal routing Prevents certain routes from entering routing domain

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Summarization

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Route Summarization

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Recommended Practice: Summarize at the Distribution Layer It is important to force summarization at the distribution layer toward the core. After link failure, for return path traffic, an OSPF or EIGRP reroute is required.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Recommended Practice: Summarize at the Distribution Layer It is important to force summarization at the distribution layer toward the core. After link failure, for return path traffic, an OSPF or EIGRP reroute is required. Summaries limit the number of peers an EIGRP router must query or the number of LSAs an OSPF peer must process.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Recommended Practice: Summarize at the Distribution Layer It is important to force summarization at the distribution layer toward the core. After link failure, for return path traffic, an OSPF or EIGRP reroute is required. Summaries limit the number of peers an EIGRP router must query or the number of LSAs an OSPF peer must process. Summaries allow faster reroutes.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Recommended Practice: Passive Interfaces for IGP at Access Layer Limit unnecessary peering Without passive interface: –With four VLANs per wiring closet –12 adjacencies total –Memory and CPU requirements increased with no real benefit –Creates overhead for IGP

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Summary Large networks may implement multiple protocols for different modules of the Cisco Enterprise Architecture. Advanced routing features such as redistribution, filtering, and summarization allow multiple routing protocols to coexist and provide greater scalability. –Redistribution between different routing protocols passes routing knowledge from one protocol to another. –Route filtering prevents advertisement of certain routes through the routing domain. –Route summarization and an IP hierarchy reduce routing traffic and unnecessary route recomputation.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v