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 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 Single connection only that no routing update is required

4 Static Route / Router(config)# ip 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

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 Router(config)# ip default-network

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

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

12 Problem : Count to Infinity Router A Router B 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 Router A Router B 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 Net Next Cost 1 A 1 2 direct 0 A skips this entry when telling B Or carries “next hop” in messages such that B can ignore (e.g. RIP)

15 Solution : Poison Reverse Claim infinity cost to the neighbor when direct links become invalid Router A Router B Net Next Cost 1 direct 0 2 direct 0 3 B 1 Net Next Cost 1 A 1 2 direct 0 3 direct 0 ∞ Net Next Cost 1 direct 0 2 direct 0 3 B ∞ A updates this entry by infinity Net Next Cost 1 A 1 2 direct 0 3 direct ∞

16 Problem : Routing Loops Packets never reach their destination but instead cycle repeatedly through the same group of network nodes Router B Router C Router D Router E Network 1 Net Next Cost 1 B 3 Router A 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 now inaccessible, 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 from the 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 Flush Invalid Update Holddown expire Holddown

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 A B C A C D B C D A B C D A B D

21 Link State Concerns Processing and memory requirements Bandwidth requirements Problem : Unsynchronized LSAs leading to inconsistent path decisions amongst routers A B C D 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 Lab1(config-router)# network

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

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/ Serial0/ Automatic network summarization is in effect Routing for Networks: Routing Information Sources: Gateway Distance Last Update :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 /24 [120/2] via , 00:00:21, Serial0/0 C /24 is directly connected, Serial0/0 R /24 [120/3] via , 00:00:21, Serial0/0 R /24 [120/1] via , 00:00:21, Serial0/0 C /24 is directly connected, FastEthernet0/0 R /24 [120/1] via , 00:00:21, Serial0/0 R /24 [120/2] via , 00:00:21, Serial0/0

27 Verifying Commands lab-a#debug ip rip 02:54:05: RIP: build update entries 02:54:05: network metric 2 02:54:05: network metric 3 02:54:05: network metric 4 02:54:05: network metric 1 02:54:05: network metric 2 02:54:05: network metric 3 02:54:05: RIP: sending v1 update to via Serial0/0 ( ) 02:54:05: RIP: build update entries 02:54:05: network metric 1 02:54:07: RIP: received v1 update from on Serial0/0 02:54:07: in 1 hops 02:54:07: in 2 hops 02:54:07: in 3 hops 02:54:07: in 1 hops 02:54:07: in 2 hops