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Chabot College

Chabot College. ELEC 99.08 IP Routing Protocol Highlights . IP Routing Protocol Topics. Routing tables How routes are learned Default routes Metrics Administrative Distance Distance Vector / Link State RIP / IGRP Commands. Routing Table. Stored in RAM

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Chabot College

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  1. Chabot College ELEC 99.08 IP Routing Protocol Highlights

  2. IP Routing Protocol Topics • Routing tables • How routes are learned • Default routes • Metrics • Administrative Distance • Distance Vector / Link State • RIP / IGRP • Commands

  3. Routing Table • Stored in RAM • Basis for all path selection decisions • Includes destination network address - next hop pairs

  4. Routing Table Example hayward#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP D - EIGRP, EX - EIGRP external, O - OSPF N1 - OSPF NSSA external type 1, N2 - OSPF NSSA E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, L1 - IS-IS level-1,* - candidate default Gateway of last resort is not set R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0

  5. Routing Table Example hayward#show ip route R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0 Destination Network Address Next Hop

  6. How routes are learned 1. Interface configuration in the config file. Defines directly connected networks even when no dynamic routing is configured: hayward#show ip route 10.0.0.0/16 is subnetted C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 C 192.168.3.0/24 is directly connected, Ethernet0

  7. How routes are learned When dynamic routing is running, directly connected networks are listed in the routing table along with others: hayward#show ip route R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0

  8. How routes are learned 2. Static routes entered manually in the router config file. hayward#show ip route R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0

  9. How routes are learned 3. Routes learned from a dynamic routing protocol (e.g. RIP, IGRP, OSPF). hayward#show ip route R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0

  10. How routes are learned 4. Default route set manually. Shown with * Also: gateway of last resort oakland#show ip route Gateway of last resort is 10.2.0.1 to network 0.0.0.0 10.0.0.0/16 is subnetted, 2 subnets C 10.2.0.0 is directly connected, Serial1 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0 R* 0.0.0.0/0 [1/0] via 10.2.0.1

  11. Static Routes - Why? • Security • RIP may reveal too much of your network to others.A static route limits what you “show”. • Backup routes • A static route can be a backup to be used automatically if a dynamic route goes down • Bandwidth conservation • Dynamic routing uses network bandwidth; static routes do not. • Static routes are sufficient for stub networks

  12. Stub Networks • Only one path in & out of the network; no path selection decision: Only one path to this “stub” network A static route to the stub net will do. Here, there are path selection decisions. Dynamic routing needed.

  13. Default Routes - the Problem • For each packet, routing are decisions based on the routing table rules. • What happens to a packet if has a destination that is not included in the routing table?

  14. Default Routes - the Problem • What happens to a packet sent to 209.33.45.177 • It is dropped because there is no entry for that network in the routing table: oak#show ip route Gateway of last resort is not set R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0

  15. Default Routes - the Problem • But the routing table can’t hold entries for every network, including all those on the Internet! • So we need a route for internet traffic - the default. Gateway Our Network If packet has a destination not on our network, try sending it here

  16. Default Routes - Terms • default route (through) • default gateway (also known as) • gateway of last resort (to) • default network

  17. Metric • Specifies the cost of a route • Dynamic routing protocol chooses the route with the lowest cost • Metrics differ, depending on routing protocol:

  18. Administrative Distance • Specifies the trustworthiness of a route source • 0 - 255 Lower values = more trustworthy • The IOS chooses the route with lowest distance: IOS ignores these routes

  19. Distance Vector vs Link State • Distance Vector • Each router knows: • Direction (vector) • Distance (hops) • Example. Destination is: • out S0 • 3 hops away • Does not know exact map to destination. 3 hops

  20. Distance Vector vs Link State • Distance Vector • To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit • Which office could be Joe’s? 3

  21. Distance Vector vs Link State • Distance Vector • To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit • Which office could be Joe’s? 2 3

  22. Distance Vector vs Link State • Distance Vector • To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit • Which office could be Joe’s? 2 3 1

  23. Distance Vector vs Link State • Distance Vector • To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit • Which office could be Joe’s? 2 3 1 0

  24. Distance Vector vs Link State • Distance Vector • To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit • Which office could be Joe’s? 2 3 1 0 Joe

  25. Distance Vector vs Link State • Link State • Each router knows: • Overall map of network • Shortest path to destination

  26. Distance Vector vs Link State • Link State • To reach Joe’s office:Follow Campus Map.Take shortest path. Joe

  27. Distance Vector vs Link State • Distance Vector Updates (RIP example) • Each router gossips to its direct neighbor. • Gossip is sent every 30 seconds. • Takes time to pass the gossip to the end of the line. • When all routers have received the gossip they are “converged”. Until then, the routers posses conflicting knowledge. A tells B B tells C C tells D D tells E E tells F A B C D E F

  28. Down Distance Vector vs Link State • Link State • Each router sends information about its links to all other routers. • Changes in network topology trigger these link state advertisements. • Each router then develops a full map of the network. A tells all other routers when it learns of a change in the network A B C D E F When any other router detects a change, it also tells everyone.

  29. RIP • Distance-Vector • Updates: every 30 seconds • Metric: Hops • Default administrative distance: 120 • Convergence: slow • Versions 1 & 2

  30. IGRP • Distance-Vector • Updates: every 90 seconds • Metric: bandwidth & delay (defaults)Can also include load, reliability • Default administrative distance: 100 • Convergence: faster than RIP

  31. Configuring Dynamic Routing 1. Specify the routing protocol. • Ordinarily, all routers must run the same protocol. 2. Specify all directly connected networks on which the router will send and receive route updates (also called advertisements). • Network are specified by major network numbers, not subnets. Example - here the network is 10.0.0.0: 10.2.0.2/16 10.3.0.1/16

  32. Commands • Configuring RIP Sets RIP to send/receive updates on these directly connected networks Enables RIP routing oak(config)#router rip oak(config-router)#network 10.0.0.0 oak(config-router)#network 192.168.3.0 oak(config-router)#^Z

  33. Commands • Configuring RIP version 2 - same as RIP but • adds version 2 statement • version should be the same for all routers Enables RIP routing Sets RIP version 2 oak(config)#router rip oak(config-router)#version 2 oak(config-router)#network 10.0.0.0 oak(config-router)#network 192.168.4.0 oak(config-router)#^Z

  34. Commands • Configuring IGRP - same as RIP, but • includes an autonomous system number • AS must be same for all routers Autonomous System # Enables IGRP routing oak(config)#router igrp 40 oak(config-router)#network 10.0.0.0 oak(config-router)#network 192.168.3.0 oak(config-router)#^Z

  35. Commands • Configuring a static route - outgoing interface Route to network via this outgoing interface Destination network & mask fre(config)#ip route 192.168.1.0 255.255.255.0 s0 fre(config)#^Z

  36. Commands • Configuring a static route - next hop Destination network & mask fre(config)#ip route 192.168.1.0 255.255.255.0 s0 fre(config)#ip route 192.168.1.0 255.255.255.0 10.1.0.2 fre(config)#^Z Route to network via this next hop address. Use this format to improve clarity of routing tables.

  37. Comands • Specifying next hop • It is the ip address of nearest interface of the neighbor router along the route. • From Router B, this is the next hop to LAN A: B LAN A LAN C LAN D

  38. Comands • From Router B, what is the next hop to • the 192.168.3.0 net? • 10.2.0.2 10.1.0.2 10.1.0.1 10.2.0.2 10.3.0.2 10.2.0.1 10.3.0.1 B 192.168.1.0 Net 192.168.3.0 Net 192.168.4.0 Net

  39. Comands • From Router B, what is the next hop to • the 192.168.4.0 net? • 10.2.0.2 • The next hop is always on the neighbor router! 10.1.0.2 10.1.0.1 10.2.0.2 10.3.0.2 10.2.0.1 10.3.0.1 B 192.168.1.0 Net 192.168.3.0 Net 192.168.4.0 Net

  40. Comands • From Router B, what are the only two possible next hop addreses? • 10.1.0.1 • 10.2.0.2 10.1.0.2 10.1.0.1 10.1.0.1 10.2.0.2 10.2.0.2 10.3.0.2 10.2.0.1 10.3.0.1 B 192.168.1.0 Net 192.168.3.0 Net 192.168.4.0 Net

  41. Commands • Static route - administrative distance parameter • Optional oak(config)#ip route 10.1.0.0 255.255.0.0 s0 121 oak(config)#^Z Administrative Distance

  42. Commands • Static route - administrative distance • If unspecified, default distance is 0for outgoing interface format. • These routes will show as S but will be listed as directly connected in the routing table. oak(config)#ip route 10.1.0.0 255.255.0.0 s0

  43. Commands • Static route - administrative distance • If unspecified, default distance is 1for next hop format. • These routes will show as S (static) in the routing table. oak(config)#ip route 10.1.0.0 255.255.0.0 10.3.0.1

  44. Commands • Configuring a default route (default network)method 1 - set a default route to the wildcard network & subnet of 0.0.0.0 0.0.0.0 Wildcard network & mask hay(config)#ip route 0.0.0.0 0.0.0.0 192.168.0.1 hay(config)#^Z Route to default network via this “next hop” address - the address of the direct neighbor interface. See http://www.cisco.com/warp/public/105/default.html

  45. Commands • method 1 - RIP will automatically redistribute the default route to the wildcard network & subnet of 0.0.0.0 0.0.0.0 to other routers: oakland#show ip route Gateway of last resort is 10.2.0.1 to network 0.0.0.0 10.0.0.0/16 is subnetted, 2 subnets C 10.2.0.0 is directly connected, Serial1 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1 R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0 R* 0.0.0.0/0 [1/0] via 10.2.0.1 Distributed from hayward to oakland by RIP

  46. Commands • Configuring a default route (default network)method 2: (presented in the curriculum) ip default-network xxx.xxx.xxx.xxx Send default traffic here hay(config)#ip default-network 192.168.0.0 hay(config)#^Z See http://www.cisco.com/warp/public/105/default.html

  47. Commands • Default network must be • defined on each routeror • redistributed by RIP to other routers

  48. Commands • Redistribution methods: • 0.0.0.0: • With IOS Version 12.0, RIP automatically distributes a route to 0.0.0.0 to other routers. • With IOS Version 12.1 or later, you must add the default-information originate command: hay(config)#router rip hay(config-router)#default-information originate • ip default-network: To force RIP to redistribute the default route, you must add the redistribute static command: hay(config)#router rip hay(config-router)#redistribute static

  49. Commands • show ip route • displays routing table [Administrative Distance/Metric] oakland#show ip route Gateway of last resort is 10.2.0.1 to network 192.168.1.0 R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:11, Serial0 10.0.0.0/16 is subnetted, 3 subnets C 10.2.0.0 is directly connected, Serial1 C 10.3.0.0 is directly connected, Serial0 R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1 R* 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1 S 192.168.2.0/24 [1/0] via 10.2.0.1 C 192.168.3.0/24 is directly connected, Ethernet0 RouteSource

  50. Commands • show ip protocols oak(config)#show ip protocols Routing Protocol is "rip" Sending updates every 30 seconds, next due in 2 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Routing for Networks: 10.0.0.0 192.168.4.0 Update Distance: (default is 120)

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