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Routing Protocol Comparison

Routing Protocol Comparison. AfNOG Workshops Philip Smith. Static and Dynamic Routing. Static Routing is a simplistic approach Shortcomings Cumbersome to configure Cannot adapt to addition of new links or nodes Cannot adapt to link or node failures Does not scale to large networks

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Routing Protocol Comparison

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  1. Routing Protocol Comparison AfNOG Workshops Philip Smith

  2. Static and Dynamic Routing • Static Routing is a simplistic approach • Shortcomings • Cumbersome to configure • Cannot adapt to addition of new links or nodes • Cannot adapt to link or node failures • Does not scale to large networks • Solution is to use Dynamic Routing

  3. Desirable Characteristics • Automatically detect and adapt to topology changes • Provide optimal routing • Scalability • Robustness • Simplicity • Rapid convergence • Some control of routing choices • E.g. which links we prefer to use

  4. Convergence – why do I care? • Convergence is when all the routers have the same routing information • When a network is not converged there is network downtime • Packets don’t get to where they are supposed to go • Black holes (packets “disappear”) • Routing Loops (packets go back and fore between the same devices) • Occurs when there is a change in status of router or the links

  5. Interior Gateway Protocols • RIP • “Routing Information Protocol” – “Rest In Peace”  • Lots of scaling problems • RIPv1 is classful, and officially obsolete • EIGRP • “Enhanced Interior Gateway Routing Protocol” • Cisco-only routing protocol • IS-IS • “Intermediate System to Intermediate System” • Forerunner of OSPF • Multiprotocol (OSPF supports IP only)

  6. Why not use RIP? • RIP is a Distance Vector Algorithm • Listen to neighbouring routes • Install all routes in routing table • Lowest hop count wins • Advertise all routes in table • Very simple, very stupid • Metric is hop count only • Infinity of 16 (not large enough) • Slow convergence (routing loops) • Poor robustness

  7. OSPF • Open Shortest Path First • “Open” means it is not proprietary (IETF standard) • Uses “Shortest Path First” algorithm • Dynamic IGP, Link State Protocol • Use this in your network • Encourages good network design • Easy to learn • Has fast convergence • Scales very well

  8. Link State Algorithm • Each router contains a database containing a map of the whole topology • Links • Their state (including cost) • All routers have the same information • All routers calculate the best path to every destination • Any link state changes are flooded across the network • “Global spread of local knowledge”

  9. Summary • Comparison of static routes, RIP and OSPF • Dynamic Routing Protocol should be used in any ISP network • Static routes don’t scale • RIP doesn’t scale (and is obsolete) • OSPF will be covered in more detail shortly

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