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Reviewing Enterprise Routing Protocols

Designing IP Addressing and Selecting Routing Protocols

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-1

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-2

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-3

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-4

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-5

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

Example: Interior vs. Exterior Routing Protocols

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-6

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-7

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-8

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-9

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

Routing Protocol Convergence Comparison

Protocol RIP EIGRP OSPF

Convergence Time to Router E Holddown + 1 or 2 update intervals Matter of seconds Matter of seconds

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-10

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-11

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

EIGRP Characteristics
EIGRP Characteristics Fast convergence Improved scalability Use of VLSM Reduced bandwidth usage Multiple network layer protocol support Implemented By Diffusing Update Algorithm (DUAL) Manual summarization, fast convergence Subnet mask in updates No periodic updates IPv4, IPv6 (Protocol Dependent Modules for IPX, AppleTalk)

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-12

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

Open Shortest Path First (OSPF)
Developed in 1988 by IETF, version 2 is described in RFC 2328. 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 v2.0—5-13

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

Example: OSPF Multiarea Network

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-14

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

OSPF Characteristics
OSPF Characteristics Fast convergence Very good scalability Use of VLSM Reduced bandwidth usage Implemented By Link-state updates (triggered), SPF calculation Multiple-area design Subnet mask in updates No periodic updates

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-15

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-16

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-17

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

BGP Network Implementation

BGP is primarily used for inter-AS system routing.
2007 Cisco Systems, Inc. All rights reserved. DESGN v2.0—5-18

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-19

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

Recommended Enterprise Routing Protocol Comparison
Enterprise Characteristics Fast convergence Very good scalability Use of VLSM Multiple network layer protocol support Mixed vendor devices EIGRP Yes Yes Yes Yes No OSPF Yes Yes Yes No Yes

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-20

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

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 v2.0—5-21

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be

2007 Cisco Systems, Inc. All rights reserved.

DESGN v2.0—5-22

The PDF files and any printed representation for this material are the property of Cisco Systems, Inc., for the sole use by Cisco employees for personal study. The files or printed representations may not be


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