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Interior Routing Protocols Discussion and Group Project Planning for Networking Course

Welcome to Day 13 of the course! Today's agenda includes the discussion of interior routing protocols such as RIP, HELLO, and OSPF. We will delve into their mechanics, advantages, and use cases. Additionally, we will introduce Assignment 3, covering chapters 11-15, due March 23, and discuss group project deliverables and timelines. The midterm exam is due today, so ensure all submissions are complete. Be prepared to choose your group project by March 23, focusing on important aspects like protocol definition and technical specifications.

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Interior Routing Protocols Discussion and Group Project Planning for Networking Course

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  1. COS 420 Day 13

  2. Agenda • Assignment 3 Posted • Covers chapters 11-15 • Due March 23 • 2 Days till Daytona Beach Bike Week • Midterm Exam is Due Today • Today we will discuss Interior Routing protocols (Rip, HELLO, OSPF)

  3. Group Project Initial Discussion • Deliverables • Programs requirements • Protocol Definition • Working Network Application • Client Server (or) • Peer to Peer • Paper • User Manual • Protocol specification • Program requirements • Implementation Technical Specifications • Presentation • Journal? • More Discussion after Break, be ready to pick a group project by March 23

  4. Project 2 Grading • Meeting Timelines 10% • Deliverables • Program requirements Due March 30 15% • Protocol Definition Due April 13 15% • Working Network Application Due May 4 25% • Final Paper Due May 1 25% • User Manual • Protocol • Program requirements • Technical Specifications • Presentation Due May 4 10%

  5. PART XVI ROUTING: INSIDE AN AUTONOMOUS SYSTEM (RIP, OSPF, HELLO)

  6. Static Vs. Dynamic Interior Routes • Static routes • Initialized at startup • Never change • Typical for host • Sometimes used for router • Dynamic router • Initialized at startup • Updated by route propagation protocols • Typical for router • Sometimes used in host

  7. Illustration Of Topology In WhichStatic Routing Is Optimal

  8. Illustration Of Topology In WhichDynamic Routing Is Needed

  9. Exchanging Routing InformationWithin An Autonomous System • Mechanisms called interior gateway protocols, IGPs • Choice of IGP is made by autonomous system • Note: if AS connects to rest of the world, a router in the AS must use an EGP to advertise network reachability to other autonomous systems.

  10. Example Of Two Autonomous SystemsAnd the Routing Protocols Used

  11. Example IGPs • RIP • HELLO • OSPF • Many Others

  12. Routing InformationProtocol (RIP) • Implemented by UNIX program routed • Uses hop count metric • Distance-vector protocol • Relies on broadcast (very chatty!) • Assumes low-delay local area network • Uses split horizon and poison reverse techniques to solve inconsistencies • Current standard is RIP2

  13. Two Forms Of RIP • Active • Form used by routers • Broadcasts routing updates periodically • Uses incoming messages to update routes • Passive • Form used by hosts • Uses incoming messages to update routes • Does not send updates

  14. Illustration Of HostsUsing Passive RIP

  15. RIP Operation • Each router sends update every 30 seconds • Update contains pairs of (destination address, distance in hops) • Distance of 16 is infinity (i.e., no route)

  16. Slow Convergence Problem(Slow Count To Infinity)

  17. Fixing Slow Convergence • Use technique know as Split-horizon update • Cannot announce routes to networks from same interface you got route information from • Use technique know as Poison-reverse update • If a router notices a connection is down, advertise an infinity cost to that network

  18. Rip Update Format • Uses family field to support multiple protocols • IP address sent in octets 3 - 6 of address field • Message travels in UDP datagram (uses UDP LEN)

  19. Rip commands • 1 • Request for partial or full routing informatoin • 2 • Response containing network-distance pairs from sender’s routing table • 9 • Update request • 10 • Update response • 11 • Update acknowledge

  20. Changes To RIP In Version 2 • Update includes subnet mask • Authentication supported • Explicit next-hop information • Messages can be multicast (optional) • IP multicast address is 224.0.0.9

  21. RIP2 Update Format • Packet format is backward compatible • Infinity still limited to 16 • RIP2 can be broadcast • Route Tag identifies originator

  22. Measures Of DistanceThat Have Been Used • Hops • Zero-origin • One-origin (e.g., RIP) • Delay • Throughput • Jitter

  23. HELLO: A Protocol ThatUsed Delay • Developed by Dave Mills • Measured delay in milliseconds • Used by NSFNET fuzzballs • A specially configured PDP11 computer made by DEC (16-bit) • http://starfish.osfn.org/rcs/pdp-11/Fuzzball/fuzz.txt • Now historic

  24. How HELLO Worked • Participants kept track of delay between pairs of routers • HELLO propagated delay information across net • Route chosen to minimize total delay

  25. Route Oscillation • Effective delay depends on traffic (delay increases as traffic increases) • Using delay as metric means routing traffic where delay is low • Increased traffic raises delay, which means route changes • Routes tend to oscillate

  26. Why HELLO Worked • HELLO used only on NSFNET backbone • All paths had equal throughput • Route changes damped to avoid oscillation

  27. Open Shortest Path First (OSPF) • Developed by IETF in response to vendors’ proprietary protocols • RFC 2328 OSPF Ver. 2 • Uses SPF (link-state) algorithm • More powerful than most predecessors • Permits hierarchical topology • More complex to install and manage

  28. OSPF Features • Type of service routing • Load balancing across multiple paths • Networks partitioned into subsets called areas • Message authentication • Network-specific, subnet-specific, host-specific, and CIDR routes • Designated router optimization for shared networks • Virtual network topology abstracts away details • Can import external routing information

  29. OSPF Message Header

  30. OSPF Message Types

  31. OSPF HELLO Message Format Field descriptions on Page 311

  32. OSPF Database Description Message Format Field descriptions on Page 289 & 290

  33. Values In The LINK Field

  34. OSPF Link Status Request Message Format

  35. OSPF Link Status Update Message Format

  36. Header Used In OSPF Link Status Advertisements • Four possible formats follow • Links from a router to given area • Links from a router to physical net • Links from a router to physical nets of a subnetted IP network • Links from a router to nets at other sites

  37. Discussion Question • What are the tradeoffs connected with the issue of routing in the presence of partial information?

  38. Summary • Interior Gateway Protocols (IGPs) used within an AS • Popular IGPs include • RIP (distance vector algorithm) • OSPF (link-state algorithm)

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