1 3-Oct-15 Distance Vector Routing CCNA Exploration Semester 2 Chapter 4

2 3-Oct-15 Topics Characteristics of distance vector routing protocols Distance vector routing protocols in use today How they discover routes How they maintain routing tables Routing loops

3 3-Oct-15 RIP v1 RIP v2 IGRP EIGRP Routing protocols InteriorExterior Distance vectorLink state OSPF IS-IS EGP BGP

4 3-Oct-15 Distance vector knowledge A distance vector protocol learns: The distance to a network, measured in hops or in some other way The direction of the network: which port should be used to reach it It puts the routes in the routing table It does not know any more details of the route or the other routers along the way

5 3-Oct-15 Distance vector Network is 3 hops away using port fa0/0 Network is 2 hops away using port fa0/1

6 3-Oct-15 Link state knowledge A link state routing protocol finds out about all the routers in the system and the networks they link to. It builds up a complete picture of the topology It can then work out the best path to any network It puts these best paths in the routing table

7 3-Oct-15 Link state I know all the routers and paths in this system of networks.

8 3-Oct-15 Metrics RIP v1 and 2hop count, maximum 15 IGRP and EIGRPbandwidth, delay, load, reliability

9 3-Oct-15 Distance vector Exchange complete routing tables with immediate neighbours Do this at regular intervals Adjust the metric, e.g. add 1 to the hop count, or add number based on bandwidth and delay of link.

10 3-Oct-15 Adjust the metric is 2 hops away is 3 hops away Send update

11 3-Oct-15 Sending updates RIP v1 Whole routing table Broadcast every 30 sec RIP v2Whole routing table Multicast every 30 sec IGRPWhole routing table Broadcast every 90 sec EIGRPInitial learning process then small updates when topology changes

12 3-Oct-15 RIP v1 RIP v2 IGRP Routing protocols Distance vectorLink state OSPF IS-IS EIGRP Slow to converge Easy to configure Small networks Little use of resources Fast to converge Harder to configure Large networks Much use of resources

13 3-Oct-15 Distance vector updates Routers start up. R1 adds directly connected networks to table. NetworkInterfaceHop Fa0/ S0/0/

14 3-Oct-15 Distance vector updates Exchange of routing table information

15 3-Oct-15 Distance vector updates R1 has learned about from R2. It does not know about NetworkInterfaceHop Fa0/ S0/0/ S0/0/

16 3-Oct-15 Distance vector updates Exchange of routing table information

17 3-Oct-15 Distance vector updates R1 has learned about from R2. R2 previously learned about it from R3. NetworkInterfaceHop Fa0/ S0/0/ S0/0/ S0/0/

18 3-Oct-15 Update timer R [120/1] via , 00:00:04, Serial0/0 Show ip route gives number of seconds since last update. Routing Protocol is “rip” Sending updates every 30 seconds, next due in 3 seconds Show ip protocols says when next update is due. Update timer default is 30 seconds

19 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 26 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:04, Serial0/0 R [120/2] via , 00:00:04, Serial0/0 Routing table contains two RIP routes

20 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/2] via , 00:00:30, Serial0/0 30 seconds – update Route to refreshed Route to not included

21 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/2] via , 00:01:00, Serial0/0 60 seconds – update Route to refreshed Route to not included

22 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/2] via , 00:01:30, Serial0/0 90 seconds – update Route to refreshed Route to not included

23 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/2] via , 00:02:00, Serial0/0 120 seconds – update Route to refreshed Route to not included

24 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/2] via , 00:02:30, Serial0/0 150 seconds – update Route to refreshed Route to not included

25 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/16] via , 00:03:00, Serial0/0 180 seconds – update Route to refreshed Route to not included

26 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 R [120/16] via , 00:03:30, Serial0/0 210 seconds – update Route to refreshed Route to not included

27 3-Oct-15 RIP timers Routing Protocol is “rip” Sending updates every 30 seconds, next due in 30 seconds Invalid after 180 seconds, hold down 180, flushed after 240 R [120/1] via , 00:00:00, Serial0/0 240 seconds – update Route to refreshed Route to not included Route has been removed.

28 3-Oct-15 RIP_JITTER RIP updates can become synchronised This is a problem if routers are linked by hubs because the updates will collide RIP_JITTER is a random variable that makes updates vary a little from the default 30 seconds

29 3-Oct-15 Triggered updates These are to speed up convergence Interface goes up/down, route added/removed Router detects change, sends update to neighbour at once without waiting for timer Neighbour passes on update at once.

30 3-Oct-15 EIGRP Does not send regular updates Does not send its whole routing table Sends only information about changes Sends only to routers that need the information Non-periodic, partial, bounded.

31 3-Oct-15 Routing loop A packet is sent from router to router in a loop until it is eventually dropped when its TTL field drops to 0 Caused by incorrect or out of date information in routing tables Very bad for network – uses up bandwidth and processing power in routers

32 3-Oct-15 Avoiding routing loops Defining a maximum metric to prevent count to infinity Holddown timers Split horizon Route poisoning or poison reverse Triggered updates

33 3-Oct-15 Maximum metric Routers exchanging wrong information can report higher and higher values of the metric. RIP sets a maximum metric. The hop count can go up to 15. If it reaches 16 then the route is regarded as unreachable.

34 3-Oct-15 Holddown timers Router receives update saying that a network is down. Router marks the network as possibly down and starts holddown timer. Update with a better metric for that network arrives: network is reinstated and holddown timer removed. Update with the same or worse metric for that network arrives: update is ignored. Timer runs out : network removed from table. Packets still forwarded to network while timer runs.

35 3-Oct-15 Split horizon Router receives information about a route through an interface. It will not send out information about the same route through that interface. Route to in 3 hops Route to in 4 hops

36 3-Oct-15 Route poisoning A router detects that a route has gone down. It marks that route as unreachable in its routing table. (16 hops for RIP) It sends out updates that show the route as unreachable. Neighbour routers pass on these “poison” updates.

37 3-Oct-15 Poison reverse This is an exception to split horizon. If a router receives an update marking a route as unreachable then it will send this information back to the router that sent it.

38 3-Oct-15 RIP v1 and RIP v2 RIP v1 Classful, does not send subnet mask in updates so does not support VLSM Sends updates as broadcasts No authentication No manual route summarisation RIP v2 Classless, includes the subnet mask in routing updates, so supports VLSM. Sends updates as multicasts Authentication for security Supports manual route summarization.

39 3-Oct-15 RIP v2 or EIGRP? RIP runs on any make of router, EIGRP only on Cisco routers. EIGRP is suitable for large networks EIGRP uses a more efficient metric and may choose faster routes. EIGRP converges faster than RIP EIGRP uses less bandwidth but it needs more processing power and RAM RIP is simpler to configure

40 3-Oct-15 The End