Routing Protocols and Configuration

1. Routing Protocols and Configuration Instructor: Te-Lung Liu Program Associate Researcher NCHC, South Region Office

2. Outline • Static Route • Default Route • Dynamic Route • Routing Metrics • Routing Protocols • Distance Vector • Link State • Configure Dynamic Routing Protocols • Verifying Commands

3. Single connection only that no routing update is required Static Route • Static route knowledge is administered manually by a network administrator who enters it into a router's configuration. • The administrator must manually update this static route entry whenever an internetwork topology change requires an update "stub" network

4. Router(config)# ip route 199.13.2.0 255.255.255.0 199.13.1.2 Static Route • specified for "stub" network connection Router(config)#ip route network [mask] address [adm_distance] Administrative distance (0~255) is a rating of the trustworthiness of a routing information source. The higher the number, the lower the trustworthiness rating 199.13.2.1 199.13.1.2 199.13.2.0 / 255.255.255.0 199.13.1.1

5. Default Route • If the next hop is not explicitly listed in the routing table, send it to default router Router(config)#ip default-network network-number Network number must exist in routing table Company or Campus Internet 10.0.0.0 192.168.1.0 Router(config)# ip default-network 192.168.1.0

6. Dynamic Route • The route knowledge is automatically updated by a routing process whenever new information is received from the internetwork. • Changes in dynamic knowledge are exchanged between routers as part of the update process.

7. Routing Metrics • bandwidth -- the data capacity of a link; (normally, a 10 Mbps Ethernet link is preferable to a 64 kbps leased line) • delay -- the length of time required to move a packet along each link from source to destination • load -- the amount of activity on a network resource such as a router or link • reliability -- usually refers to the error rate of each network link • hop count -- the number of routers a packet must travel through before reaching its destination • ticks -- the delay on a data link using IBM PC clock ticks (approximately 55 milliseconds). • cost -- an arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator

8. Routing Protocols • Distance Vector • Routing table is exchanged with the neighbor routers • Ex. RIP,IGRP • Link State • Link state is multicast to all routers in the same AS • Full view of network topology • Faster convergence • Ex. OSPF

9. Distance Vector • Each router periodically send its routing table to its neighbors. • When the topology in a distance-vector protocol network changes, routing table updates must occur. • Count to Infinity and Routing Loop Problem • Split Horizon and Hold-down Timers

10. 3 5 4 2 1 Router B Router C Router A Net Next Cost 4 direct 0 5 direct 0 Net Next Cost 1 direct 0 2 direct 0 Net Next Cost 2 direct 0 3 direct 0 4 direct 0 Net Next Cost 2 B 1 3 B 1 4 direct 0 5 direct 0 Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 4 direct 0 5 C 1

11. 3 5 4 2 1 Router B Router C Router A Net Next Cost 2 B 1 3 B 1 4 direct 0 5 direct 0 Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 4 direct 0 5 C 1 Net Next Cost 1 B 2 2 B 1 3 B 1 4 direct 0 5 direct 0 Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1 5 B 2 Net Next Cost 1 A 1 2 direct 0 3 direct 0 4 direct 0 5 C 1

12. Problem : Count to Infinity 3 2 1 Router B Router A Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 removed Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 A 2

13. Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 A 2 Net Next Cost 1 direct 0 2 direct 0 3 B 3 Net Next Cost 1 A 1 2 direct 0 3 A 2 Net Next Cost 1 direct 0 2 direct 0 3 B 3 Net Next Cost 1 A 1 2 direct 0 3 A 4 : :

14. Solution : Split Horizon • Not update the neighbor entries that comes from itself 3 2 1 Router B Router A Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 A skips this entry when telling B removed Or carries “next hop” in messages such that B can ignore (e.g. RIP) Net Next Cost 1 direct 0 2 direct 0 Net Next Cost 1 A 1 2 direct 0

15. Solution : Poison Reverse Claim infinity cost to neighbors when direct links become invalid, quickly outdating routing info. 3 2 1 Router B Router A Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 A updates this entry by infinity claim from B ∞ Net Next Cost 1 A 1 2 direct 0 3 direct ∞ Net Next Cost 1 direct 0 2 direct 0 3 B ∞ 15

16. Problem : Routing Loops • Packets never reach their destination but instead cycle repeatedly through the same group of network nodes Net Next Cost 1 B 3 Router B Router E Router D Router A Network 1 Router C With split horizon, B will not be updated by A However, C will. Then it passes to D, B, A, C ...... => Count to infinity still occurs!

17. Solution : Hold-down Timer • When a router receives an update from a neighbor indicating that a previously accessible network is nowinaccessible, the router marks the route as inaccessible and starts a hold-down timer. • If at any time before the hold-down timer expires an update is received fromthe same neighbor indicating that the network is again accessible, the router marks the network as accessible and removes the hold-down timer. • If an update arrives from a different neighboring router with a better metric than originally recorded for the network, the router marks the network as accessible and removes the hold-down timer • If at any time before the hold-down timer expires an update is received from a different neighboring router with a poorer metric, the update is ignored.

18. RIP timer • Update timer 30 secs • Invalid timer 90 secs • Holddown timer 180 secs • Flush timer 270 secs Holddown Update Invalid Holddown expire Flush

19. Link State • Link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. • Each router sends its link-state advertisements (LSAs) to all routers in the same AS/Area • Routers can maintain the network topology with all LSAs and then use shortest-path algorithm to determine the route. • Whenever a link-state topology changes, the routers that first become aware of the change send information to other routers or to a designated router that all other routers can use for updates.

20. B B B B D D D D A A A A C C C C

21. B D A C Link State • Concerns • Processing and memory requirements • Bandwidth requirements • Problem : • Unsynchronized LSAs leading to inconsistent path decisions amongst routers Network is down and up again soon

22. Configure Dynamic Routing Protocols • Dynamic routing protocol setting - enter router configuration mode • Enter router config mode Router(config)#router protocol [keyword] • specify the networks to be routed Router(config-router)#network network-number • RIP Lab1(config)# router rip Lab1(config-router)# network 200.177.1.0 Lab1(config-router)# network 210.3.1.0

23. Configure Dynamic Routing Protocols • IGRP • AS number is used as keyword Lab1(config)# router igrp 100 Lab1(config-router)# network 200.177.1.0 Lab1(config-router)# network 210.3.1.0

24. IGRP v.s RIP • Both are Distance Vector algorithms • RIP : hop count only • IGRP :bandwidth, delay, load, reliability • Maximum hop • RIP : 15 • IGRP : 255 • Updating Timer • RIP : 30sec • IGRP : 90 sec • Administrative Distance • RIP : 120 • IGRP : 100

25. Verifying Commands lab-a#show ip protocols Routing Protocol is "rip" Sending updates every 30 seconds, next due in 0 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain FastEthernet0/0 1 1 2 Serial0/0 1 1 2 Automatic network summarization is in effect Routing for Networks: 192.168.1.0 192.168.10.0 Routing Information Sources: Gateway Distance Last Update 192.168.10.2 120 00:00:15 Distance: (default is 120)

26. Verifying Commands lab-a#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set R 192.168.30.0/24 [120/2] via 192.168.10.2, 00:00:21, Serial0/0 C 192.168.10.0/24 is directly connected, Serial0/0 R 192.168.4.0/24 [120/3] via 192.168.10.2, 00:00:21, Serial0/0 R 192.168.20.0/24 [120/1] via 192.168.10.2, 00:00:21, Serial0/0 C 192.168.1.0/24 is directly connected, FastEthernet0/0 R 192.168.2.0/24 [120/1] via 192.168.10.2, 00:00:21, Serial0/0 R 192.168.3.0/24 [120/2] via 192.168.10.2, 00:00:21, Serial0/0

27. Verifying Commands lab-a#debug ip rip 02:54:05: RIP: build update entries 02:54:05: network 192.168.2.0 metric 2 02:54:05: network 192.168.3.0 metric 3 02:54:05: network 192.168.4.0 metric 4 02:54:05: network 192.168.10.0 metric 1 02:54:05: network 192.168.20.0 metric 2 02:54:05: network 192.168.30.0 metric 3 02:54:05: RIP: sending v1 update to 255.255.255.255 via Serial0/0 (192.168.10.1) 02:54:05: RIP: build update entries 02:54:05: network 192.168.1.0 metric 1 02:54:07: RIP: received v1 update from 192.168.10.2 on Serial0/0 02:54:07: 192.168.2.0 in 1 hops 02:54:07: 192.168.3.0 in 2 hops 02:54:07: 192.168.4.0 in 3 hops 02:54:07: 192.168.20.0 in 1 hops 02:54:07: 192.168.30.0 in 2 hops