Transcript Ethernet
Distance Vector Routing CCNA Exploration Semester 2 Chapter 4 28-Mar-16 1 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 28-Mar-16 2 Routing protocols Interior Distance vector RIP v1 RIP v2 IGRP EIGRP 28-Mar-16 Exterior Link state OSPF IS-IS EGP BGP 3 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 28-Mar-16 4 Distance vector Network 192.168.48.0 is 3 hops away using port fa0/0 28-Mar-16 Network 192.168.22.0 is 2 hops away using port fa0/1 5 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 28-Mar-16 6 Link state 28-Mar-16 I know all the routers and paths in this system of networks. 7 Metrics RIP v1 and 2 IGRP and EIGRP bandwidth, delay, load, reliability 28-Mar-16 hop count, maximum 15 8 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. 28-Mar-16 9 Adjust the metric 192.168.13.0 is 2 hops away 192.168.13.0 is 3 hops away Send update 28-Mar-16 10 Sending updates RIP v1 Whole routing table Broadcast every 30 sec RIP v2 Whole routing table Multicast every 30 sec IGRP Whole routing table Broadcast every 90 sec EIGRP Initial learning process then small updates when topology changes 28-Mar-16 11 Routing protocols Distance vector RIP v1 RIP v2 IGRP EIGRP Slow to converge Easy to configure Small networks Little use of resources 28-Mar-16 Link state OSPF IS-IS Fast to converge Harder to configure Large networks Much use of resources 12 Distance vector updates 10.1.0.0 10.2.0.0 Routers start up. R1 adds directly connected networks to table. 28-Mar-16 10.3.0.0 10.4.0.0 Network Interface Hop 10.1.0.0 10.2.0.0 Fa0/0 S0/0/0 0 0 13 Distance vector updates 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 Exchange of routing table information. 28-Mar-16 14 Distance vector updates 10.1.0.0 10.2.0.0 R1 has learned about 10.3.0.0 from R2. It does not know about 10.4.0.0 28-Mar-16 10.3.0.0 10.4.0.0 Network Interface Hop 10.1.0.0 10.2.0.0 Fa0/0 S0/0/0 0 0 10.3.0.0 S0/0/0 1 15 Distance vector updates 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 Exchange of routing table information. 28-Mar-16 16 Distance vector updates 10.1.0.0 10.2.0.0 R1 has learned about 10.4.0.0 from R2. R2 previously learned about it from R3. 28-Mar-16 10.3.0.0 10.4.0.0 Network Interface Hop 10.1.0.0 10.2.0.0 Fa0/0 S0/0/0 0 0 10.3.0.0 S0/0/0 1 10.4.0.0 S0/0/0 2 17 Update timer R 10.3.0.0 [120/1] via 10.2.0.2, 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 28-Mar-16 18 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 Routing table contains two RIP routes R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:04, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:00:04, Serial0/0 28-Mar-16 19 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 30 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:00:30, Serial0/0 28-Mar-16 20 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 60 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:01:00, Serial0/0 28-Mar-16 21 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 90 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:01:30, Serial0/0 28-Mar-16 22 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 240 120 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:02:00, Serial0/0 28-Mar-16 23 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 240 150 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/2] via 10.2.0.2, 00:02:30, Serial0/0 28-Mar-16 24 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 240 180 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/16] via 10.2.0.2, 00:03:00, Serial0/0 28-Mar-16 25 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 240 210 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 R 10.4.0.0 [120/16] via 10.2.0.2, 00:03:30, Serial0/0 28-Mar-16 26 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 240 240 seconds – update Route to 10.3.0.0 refreshed Route to 10.4.0.0 not included R 10.3.0.0 [120/1] via 10.2.0.2, 00:00:00, Serial0/0 Route has been removed. 28-Mar-16 27 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 28-Mar-16 28 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. 28-Mar-16 29 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. 28-Mar-16 30 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 28-Mar-16 31 Avoiding routing loops Defining a maximum metric to prevent count to infinity Holddown timers Split horizon Route poisoning or poison reverse Triggered updates 28-Mar-16 32 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. 28-Mar-16 33 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. 28-Mar-16 34 Split horizon Route to 10.1.1.0 in 3 hops Route to 10.1.1.0 in 4 hops Router receives information about a route through an interface. It will not send out information about the same route through that interface. 28-Mar-16 35 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. 28-Mar-16 36 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. 28-Mar-16 37 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 28-Mar-16 RIP v2 Classless, includes the subnet mask in routing updates, so supports VLSM. Sends updates as multicasts Authentication for security Supports manual route summarization. 38 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 28-Mar-16 39 The End 28-Mar-16 40