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Cisco S3 C5 Routing Protocols. Network Design Characteristics Reliable – provides mechanisms for error detection and correction Connectivity – incorporate.

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Presentation on theme: "Cisco S3 C5 Routing Protocols. Network Design Characteristics Reliable – provides mechanisms for error detection and correction Connectivity – incorporate."— Presentation transcript:

1 Cisco S3 C5 Routing Protocols

2 Network Design Characteristics Reliable – provides mechanisms for error detection and correction Connectivity – incorporate variety of hard ware and software Easy to use – don’t need to know structure Easy to modify – can evolve and adapt Easy to implement – follow standards & allow for variety of configurations

3 Path Determination Frame received on router interface and data link layer frame is removed and discarded Network layer handled by appropriate network layer process Network protocol header examined to determine destination Refers to routing table to determine which port to send packet back out

4 IP Routing Table Consists of destination network address and next hop pairs When no match is found, datagram is sent to default router; drops packet if no default router Routers communicate to build tables and update at intervals or by event Routing updates can help build detailed picture of network topology

5 Routing Metrics Hop Count Bandwidth Delay Load Reliability (administrative number) Ticks Cost

6 Routed and Routing Routed Protocols –IP, IPX, Appletalk, Vines, DecNet Routing Protocols –IGRPEIGRP –RIPOSPF –EGPBGP OSI routing Advanced Peer-to-Peer

7 Multi-protocol Routing Route multiple routed protocols – IP, IPX, AppleTalk, etc. Can use multiple routing protocols – RIP, IGRP Routers pass traffic from all routed protocols over inter-network

8 Routing Protocol Differences Goals of protocol designer affect operation of resulting routing protocol Various types of routing protocols – each protocol has different effect on network and router resources Routing protocols use variety of metrics to identify best routes Two broad classes – Exterior and Interior

9 Routing Protocol Goals Optimal Route – select best route – depends on metrics and metric weightings Simplicity and Efficiency – important when there are limited resources Robustness – perform correctly in difficult circumstances – high loads Rapid convergence – all routers see same topology Flexibility – adapt to variety of network circumstances

10 Routing Loops Maximum defined by protocol –IGRP has 255 maximum; defaults to 100; usually set for 50

11 Static vs Dynamic Static –Uses a protocol route that network administrator enters into router Dynamic Route –Uses route that network routing protocol adjusts automatically for topology or traffic changes Supplement with static routes and router of last resort – gateway router

12 Routing Classes Distance vector – metrics – IGRP and RIP Link State – SPF – re-creates exact topology – OSPF, IS-IS and NLSP Hybrid – combines aspects of distance vector and hybrid -- EIGRP

13 Configuring Protocols Each routing protocol must be configured separately –Create the routing process with a router command –Configure protocol specifics Both RIP and IGRP must have list of networks specified before routing activities begin IGRP requires an autonomous system AS number

14 Choosing a Routing Protocol Network size and complexity Network traffic levels Security needs Reliability needs Network delay characteristics Organization policies Organization tolerance for change

15 Distance Vector Metrics Reliability 1 to 255 Load1 to 255 Bandwidth1200 bps to 10 Gbps Delay1 to 224 Default values related to weightings for IGRP give most importance to bandwidth making it superior to RIP which uses hop count

16 How IGRP Works Used only on autonomous systems If network is not sub-netted, it does not advertise interior routes and subnet information is not included in IGRP updates System routes to other major networks in AS do not include sub-netting information Exterior routes are considered when identifying gateway of last resort Sends up-date every 90 seconds Maximum hop count is 255

17 Router Commands Router (config)#router igrp Router (config-router)# network Sample Router Statement –Router(config)# router igrp 46 – timers basic – network – no metric holddown – metric maximum-hop 50

18 Routing Problems Holddown – used when router learns that a network is a greater distance than previously known or a network is down – advertisements from other routers are ignored – helps avoid routing loop Holddown period is greater than period of time necessary to update entire network

19 Routing Problems Split Horizons provide extra protocol stability; Keeps router from sending information about a route back in the direction from which it came; defeats loops between adjacent routers Poison Reverse – intended to defeat larger routing loops; increase in metrics indicate loops. Poison reverse updates sent to remove route and place it in holddown – sends metric of infinity – helps speed convergence


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