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Routing & Protocols

Routing & Protocols. Paul Traina cisco Engineering. xx. 2. Job Number Goes Here. Today's Talk. Terminology Routing Static Routes Interior Gateway Protocols Exterior Gateway Protocols Building an ISP network. Paul Traina / INET '95 Developing Countries Workshop. 3. Terminology.

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Routing & Protocols

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  1. Routing & Protocols

  2. Paul Trainacisco Engineering xx 2 Job Number Goes Here

  3. Today's Talk • Terminology • Routing • Static Routes • Interior Gateway Protocols • Exterior Gateway Protocols • Building an ISP network Paul Traina / INET '95 Developing Countries Workshop 3

  4. Terminology • network number • prefix • mask (or length) Paul Traina / INET '95 Developing Countries Workshop 4

  5. Static routes hand configured routing • tell the router which way to send packets • based upon final packet destination Paul Traina / INET '95 Developing Countries Workshop 5

  6. Static routes • ip route 10.0.0.0 255.0.0.0 serial 3 • ip route 131.108.0.0 255.255.0.0 171.65.3.4 S3 171.65.3.4 Paul Traina / INET '95 Developing Countries Workshop 6

  7. Terminology Interior Gateway Protocol (IGP) • RIP, IGRP, HELLO, OSPF • Primary goal is optimal connectivity • Strong distance metrics • May not have good administrative controls Paul Traina / INET '95 Developing Countries Workshop 7

  8. Terminology Distance vector protocols • listen to neighboring routers • install routes in table, lowest distance wins • advertise all routes in table • very simple • very stupid Paul Traina / INET '95 Developing Countries Workshop 8

  9. Terminology Distance vector protocols D A G E B A 2 B 2 C 2 D 1 E sup F 1 G 1 H 1 I1 H I F A 1 B 1 C 1 G sup H 1 C Paul Traina / INET '95 Developing Countries Workshop 9

  10. Terminology Link state protocols • information about adjacencies sent to all routers • each router builds a topology database • a "shortest path" algorithm is used to find best route • converge as quickly as databases can be updated Paul Traina / INET '95 Developing Countries Workshop 10

  11. Terminology Link state protocols D A 2 1 G E B 3 H I F C router 3 H, I router 1 A, B, C, G, H router 2 D, E, F, G, I A - 1 - G - 2 - D Paul Traina / INET '95 Developing Countries Workshop 11

  12. Interior Gateway Protocols Routing Information Protocol (RIP) • IP only • distance vector protocol • slow convergence • does not carry mask information • reasonably simple design & configuration • does not scale (maximum 15 hops) • poor metrics (hop-count) Paul Traina / INET '95 Developing Countries Workshop 12

  13. Interior Gateway Protocols Interior Gateway Routing Protocol (IGRP) • IP only • distance vector protocol • slow convergence (like RIP) • does not carry mask information (like RIP) • very simple design & configuration • powerful proprietary metric • load sharing across diverse links Paul Traina / INET '95 Developing Countries Workshop 13

  14. Interior Gateway Protocols The IGRP metric • always get optimal routing • metric vector, not single value • bandwidth • delay • hops • reliability • loading Paul Traina / INET '95 Developing Countries Workshop 14

  15. Interior Gateway Protocols Enhanced IGRP • multi-protocol (IP, IPX, Appletalk) • fast convergence (like OSPF) • very simple design & configuration (like IGRP) • IGRP metric • allows load sharing across diverse links Paul Traina / INET '95 Developing Countries Workshop 15

  16. Interior Gateway Protocols Enhanced IGRP • distance vector based protocol • NOT a Bellman-Ford protocolUses "dual" algorithm • alternative to OSPF & I-ISIS • can be bandwidth intensive on slow links Paul Traina / INET '95 Developing Countries Workshop 16

  17. Interior Gateway Protocols Integrated IS-IS (I-ISIS) • multi-protocol (CLNP, IP, IPX, ...) • link state protocol • fast convergence • design and architecture moderately complex • configuration may be simple Paul Traina / INET '95 Developing Countries Workshop 17

  18. Interior Gateway Protocols Open Shortest Path First (OSPF) • IS - IS = 0 Paul Traina / INET '95 Developing Countries Workshop 18

  19. Interior Gateway Protocols Open Shortest Path First (OSPF) • IP only • link state protocol • fast convergence • design and architecture very complex • configuration can be simple Paul Traina / INET '95 Developing Countries Workshop 19

  20. Interior Gateway Protocols Which to use? • Your interior network is actually VERY simple. • Your IGP should only carry your routes and your direct customers' Paul Traina / INET '95 Developing Countries Workshop 20

  21. Interior Gateway Protcols Problems with "classic" protocols • slow convergence • count to infinity • no mask information • no CIDR • no VLSM • no subnet 0 Paul Traina / INET '95 Developing Countries Workshop 21

  22. Interior Gateway Protocols Slow convergence • advertisement period • entire routing table dumped every n seconds • timeout period • usually 3 times advertisement period • RIP values are normally 30 and 90 seconds! Paul Traina / INET '95 Developing Countries Workshop 22

  23. 1 4 2 3 A B C 1 4 2 3 A B C 1 4 2 3 A B C Interior Gateway Protocols Count to infinty problem 1 (1 hop) 1 (2 hops) 1 (3 hops) route cleared 1 (3 hops) 1 (4 hops) 1 (3 hops) Paul Traina / INET '95 Developing Countries Workshop 23

  24. Interior Gateway Protocols Count to infinity: split-horizon • Don't feed selected route back to source • no feedback on source interface • no feedback to source neighbor Paul Traina / INET '95 Developing Countries Workshop 24

  25. 1 4 2 3 A B C 1 (1 hop) 1 (2 hops) 1 4 2 3 A B C 1 route cleared 4 2 3 A B C route cleared Interior Gateway Protocols Count to infinity: split-horizon 1 (3 hops) 1 (3 hops) route cleared Paul Traina / INET '95 Developing Countries Workshop 25

  26. Interior Gateway Protocols Count to infinity: hold-down • Split horizon not sufficient! • Holddown period • interval during which "less attractive" updates are ignored Paul Traina / INET '95 Developing Countries Workshop 26

  27. Interior Gateway Protocols Count to infinity: hold-down Paul Traina / INET '95 Developing Countries Workshop 27

  28. Interior Gateway Protocols The universal rule • You will always trade bandwidth for speed of convergence Paul Traina / INET '95 Developing Countries Workshop 28

  29. Interior Gateway Protocols OSPF configuration • myth • OSPF is hard to use • reality: • router ospf 1network 192.111.107.0 0.0.0.255 area 0 Paul Traina / INET '95 Developing Countries Workshop 29

  30. Interior Gateway Protocols OSPF operation • every OSPF router sends out 'hello' packets • hello packets used to determine if neighbor is up • hello packets are small easy to process packets • hello packets are sent periodically (usually short interval) Paul Traina / INET '95 Developing Countries Workshop 30

  31. Interior Gateway Protocols OSPF operation • once an adjacency is established, trade information with your neighbor • topology information is packaged in a "link state announcement" • announcements are sent ONCE, and only updated if there's a change • (or every 45mins...) Paul Traina / INET '95 Developing Countries Workshop 31

  32. Interior Gateway Protocols OSPF operation • change occurs • broadcast change • run SPF algorithm • install output into forwarding table Paul Traina / INET '95 Developing Countries Workshop 32

  33. Interior Gateway Protocols making OSPF scale • each link transition causes a broadcast and SPF run • OSPF can group routers to appear as one single router • OSPF areas Paul Traina / INET '95 Developing Countries Workshop 33

  34. Interior Gateway Protocols OSPF areas (before) Paul Traina / INET '95 Developing Countries Workshop 34

  35. Interior Gateway Protocols OSPF areas (after) Paul Traina / INET '95 Developing Countries Workshop 35

  36. Interior Gateway Protocols OSPF areas - partitioning Paul Traina / INET '95 Developing Countries Workshop 36

  37. Interior Gateway Protocols OSPF areas - partition repair Paul Traina / INET '95 Developing Countries Workshop 37

  38. Interior Gateway Protocols OSPF areas • rule of thumb:no more than 150 routers/area • reality:no more than 500 routers/area • backbone "area" is an area • proper use of areas reduce bandwidth & CPU utilization Paul Traina / INET '95 Developing Countries Workshop 38

  39. Interior Gateway Protocols EIGRP operation • design goals were • make it as fast as OSPF & IS-IS • make it trivial to configure • easy migration from IGRP Paul Traina / INET '95 Developing Countries Workshop 39

  40. Interior Gateway Protocols EIGRP operation • router eigrp 1network 192.108.0.0 mask 255.255.0.0 Paul Traina / INET '95 Developing Countries Workshop 40

  41. Interior Gateway Protocols EIGRP operation - caveats • nothing is for free • EIGRP works best on high speed links • EIGRP doesn't scale well in high-meshed frame-relay networks • star networks OK Paul Traina / INET '95 Developing Countries Workshop 41

  42. 150.196 150.196.4.0 .1.0 .3.0 131.108.3.0 .2.0 131.108 Interior Gateway Protocols summarization • classful routing protocols naturally summarize to network numbers at boundaries Paul Traina / INET '95 Developing Countries Workshop 42

  43. Interior Gateway Protocols summarization • classless routing protocols summarize at arbitrary bit boundaries 131.108.0.0/16 131.108.4.32/29 131.108.3.64/27 131.108.4.0/24 Paul Traina / INET '95 Developing Countries Workshop 43

  44. Interior Gateway Protocols route filtering • pseudo-security (bad idea!) • low bandwidth links • eliminate unnecessary information Paul Traina / INET '95 Developing Countries Workshop 44

  45. 131.108/16 150.136/16 44/8 0/0 Interior Gateway Protocols route filtering B C A Paul Traina / INET '95 Developing Countries Workshop 45

  46. Interior Gateway Protocols redistribution • you run OSPF • your neighbor runs RIP OSPF RIP Paul Traina / INET '95 Developing Countries Workshop 46

  47. Interior Gateway Protocols redistribution • run RIP on their interface • router ripnetwork 192.111.107.0 • configure OSPF to redistribute RIP • router ospf 1network 135.111.104.0 0.0.0.255 area 0redistribute rip metric 10 Paul Traina / INET '95 Developing Countries Workshop 47

  48. Interior Gateway Protocols redistribution • bi-directional redistribution MUST be filtered! Paul Traina / INET '95 Developing Countries Workshop 48

  49. Interior Gateway Protocols redistribution • router ripnetwork 192.111.107.0 • router ospf 1network 135.111.104.0 0.0.0.255 area 0redistribute rip metric 10distribute-list 1 out rip • access-list 1 permit 192.111.107.0 0.0.0.255 Paul Traina / INET '95 Developing Countries Workshop 49

  50. Exterior routing xx 50 Job Number Goes Here

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