© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Designing IP Addressing and Selecting Routing Protocols Reviewing Enterprise Routing Protocols

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Distance Vector and Link-State Comparison Distance vector protocol characteristics: Slow convergence Easy implementation and maintenance Limited scalability Link-state protocol characteristics: Fast convergence Good scalability Less routing traffic overhead More knowledge needed for implementation and maintenance

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Distance Vector Routing Routing updates are periodic: Include whole routing tables Use gratuitous updates (except RIPv2)

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Link-State Routing Triggered updates: Include data on link states of changing links Use multicast propagation

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Interior vs. Exterior Routing Protocols Interior Gateway Protocols (IGPs): Routing inside autonomous systems Fast convergence and easy configuration Low administrator influence on routing decisions Exterior gateway protocols (EGPs): Routing between autonomous systems Slow convergence and more complex configuration High administrator influence on routing decisions

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Interior vs. Exterior Routing Protocols

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Hierarchical vs. Flat Routing Protocols Flat routing protocols propagate all routing information throughout the network: –Classful routing protocols –Not appropriate for large networks –RIPv1, IGRP, RIPv2 (classless) Hierarchical routing protocols divide large networks into smaller areas: –Classless routing protocols –Limited route propagation between areas –EIGRP, OSPF, IS-IS

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Flat and Hierarchical Networks Comparing flat and hierarchical networks: Hierarchical structure means less routing traffic overhead. Summarization is the key.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Routing Protocol Convergence A converged network is a stable network with all needed routing information. Network convergence takes place: –Initially on network startup –On topological changes Enterprise routing protocols should have short convergence times.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Routing Protocol Convergence Comparison ProtocolConvergence Time to Router E RIPHolddown + 1 or 2 update intervals EIGRPMatter of seconds OSPFMatter of seconds

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Enhanced IGRP (EIGRP) Advanced distance vector protocol based on IGRP with some link-state protocol features Supports VLSM

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v EIGRP Characteristics Implemented By Fast convergenceDiffusing Update Algorithm (DUAL) Improved scalabilityManual summarization, fast convergence Use of VLSMSubnet mask in updates Reduced bandwidth usageNo periodic updates Multiple network layer protocol supportIPv4, IPv6 (Protocol Dependent Modules for IPX, AppleTalk)

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Open Shortest Path First (OSPF) Developed in 1988 by IETF, version 2 is described in RFC OSPF was devised for use in large, scalable networks where RIP failed: –Improved speed of convergence –Network reachability (no hop-count limitations) –Support for VLSM –Improved path calculation

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: OSPF Multiarea Network

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v OSPF CharacteristicsImplemented By Fast convergenceLink-state updates (triggered), SPF calculation Very good scalabilityMultiple-area design Use of VLSMSubnet mask in updates Reduced bandwidth usageNo periodic updates OSPF Characteristics

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Integrated IS-IS Link-state protocol –Supports IPv4, IPv6, and OSI CLNP –Support for VLSM –Based on Level 2 backbone to which Level 1 areas are attached Typically deployed in service provider environments, with enterprise network administrators having limited knowledge of IS-IS

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Border Gateway Protocol (BGP) BGP is an exterior gateway protocol (EGP) used in Internet routing. BGP is a path vector protocol with enhancements: –Suited for strategic routing policies used between autonomous systems –Allows administrators to adjust parameters to influence routing

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v BGP Network Implementation BGP is primarily used for inter-AS system routing.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Internal BGP BGP can run between routers within one autonomous system. IBGP neighbors need not be directly connected (use static routes or an IGP to convey reachability information). Other IBGP uses: –Intra-autonomous system policy implementations –QoS Policy Propagation on BGP (QPPB) –MPLS VPNs (using multiprotocol IBGP)

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Recommended Enterprise Routing Protocol Comparison Enterprise Characteristics EIGRPOSPF Fast convergence Yes Very good scalability Yes Use of VLSM Yes Multiple network layer protocol support YesNo Mixed vendor devices NoYes

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Summary Protocols with hierarchical and link-state attributes support the fastest network convergence. EIGRP and OSPF are the recommend IGPs for the enterprise. –EIGRP is a Cisco proprietary protocol for routing IPv4, IPv6, IPX, and AppleTalk traffic. –OSPF is a standardized protocol for routing IPv4, developed to replace RIP in larger, more diverse media networks. It also can support IPv6. –BGP is a representative EGP. It is primarily used to interconnect autonomous systems or to connect enterprises to an ISP.

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