Your SlideShare is downloading. ×
2008118090324 hk
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Saving this for later?

Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime - even offline.

Text the download link to your phone

Standard text messaging rates apply

2008118090324 hk

202
views

Published on

Published in: Technology, Business

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
202
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
15
Comments
0
Likes
1
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Distance Vector RoutingDistance Vector RoutingProtocolsProtocolsVivek KumarVivek KumarTechnical TrainerTechnical Trainer
  • 2. Meaning of distance Vector (1/2)Meaning of distance Vector (1/2)• A router using a distance vector routingA router using a distance vector routingprotocol does not have the knowledge ofprotocol does not have the knowledge ofthe entire path to a destination network.the entire path to a destination network.• The router only knowsThe router only knows– The direction or interface in which packetsThe direction or interface in which packetsshould be forwarded andshould be forwarded and– The distance or how far it is to the destinationThe distance or how far it is to the destinationnetworknetwork
  • 3. Meaning of distance Vector (2/2)Meaning of distance Vector (2/2)
  • 4. Operation of distance vector (1/4)Operation of distance vector (1/4)• Some distance vector routing protocolsSome distance vector routing protocolscall for the router to periodically broadcastcall for the router to periodically broadcastthe entire routing table to each of itsthe entire routing table to each of itsneighbors.neighbors.• This method is inefficient because theThis method is inefficient because theupdates not only consume bandwidth butupdates not only consume bandwidth butalso consume router CPU resources toalso consume router CPU resources toprocess the updates.process the updates.
  • 5. Operation of distance vector (2/4)Operation of distance vector (2/4)• Periodic UpdatesPeriodic Updates are sent at regular intervals (30are sent at regular intervals (30seconds for RIP and 90 seconds for IGRP).seconds for RIP and 90 seconds for IGRP).– Even if the topology has not changed in several days,Even if the topology has not changed in several days,periodic updates continue to be sent to all neighbors.periodic updates continue to be sent to all neighbors.– Neighbors are routers that share a link and areNeighbors are routers that share a link and areconfigured to use the same routing protocol.configured to use the same routing protocol.– The router is only aware of the network addresses ofThe router is only aware of the network addresses ofits own interfaces and the remote network addresses itits own interfaces and the remote network addresses itcan reach through its neighborscan reach through its neighbors
  • 6. Operation of distance vector (3/4)Operation of distance vector (3/4)• Broadcast UpdatesBroadcast Updates are sent toare sent to255.255.255.255.255.255.255.255.– Neighboring routers that are configured withNeighboring routers that are configured withthe same routing protocol will process thethe same routing protocol will process theupdates.updates.– All other devices will also process the updateAll other devices will also process the updateup to Layer 3 before discarding it.up to Layer 3 before discarding it.– Some distance vector routing protocols useSome distance vector routing protocols usemulticast addresses instead of broadcastmulticast addresses instead of broadcastaddresses.addresses.
  • 7. Operation of distance vector (4/4)Operation of distance vector (4/4)• Entire Routing Table UpdatesEntire Routing Table Updates are sent,are sent,periodically to all neighbors.periodically to all neighbors.– Neighbors receiving these updates mustNeighbors receiving these updates mustprocess the entire update to find pertinentprocess the entire update to find pertinentinformation and discard the rest.information and discard the rest.– Some distance vector routing protocols likeSome distance vector routing protocols likeEIGRP do not send periodic routing tableEIGRP do not send periodic routing tableupdates.updates.
  • 8. Routing AlgorithmRouting Algorithm• The algorithm used for the routing protocolsThe algorithm used for the routing protocolsdefines the following processes:defines the following processes:– Mechanism for sending and receiving routingMechanism for sending and receiving routinginformation.information.– Mechanism for calculating the best paths andMechanism for calculating the best paths andinstalling routes in the routing table.installing routes in the routing table.– Mechanism for detecting and reacting toMechanism for detecting and reacting totopology changes.topology changes.
  • 9. Routing protocol characteristicsRouting protocol characteristics(1/3)(1/3)• Time to ConvergenceTime to Convergence - Time to convergence- Time to convergencedefines how quickly the routers in thedefines how quickly the routers in thenetwork topology share routing informationnetwork topology share routing informationand reach a state of consistent knowledge.and reach a state of consistent knowledge.– The faster the convergence, the more preferableThe faster the convergence, the more preferablethe protocol.the protocol.– Routing loops can occur when inconsistentRouting loops can occur when inconsistentrouting tables are not updated due to slowrouting tables are not updated due to slowconvergence in a changing network.convergence in a changing network.
  • 10. Routing protocol characteristicsRouting protocol characteristics(2/3)(2/3)• ScalabilityScalability - Scalability defines how large a- Scalability defines how large anetwork can become based on the routingnetwork can become based on the routingprotocol that is deployed.protocol that is deployed.– The larger the network is, the more scalable the routingThe larger the network is, the more scalable the routingprotocol needs to be.protocol needs to be.• Classless (Use of VLSM) or ClassfulClassless (Use of VLSM) or Classful - Classless- Classlessrouting protocols include the subnet mask in therouting protocols include the subnet mask in theupdates.updates.– This feature supports the use of Variable Length SubnetThis feature supports the use of Variable Length SubnetMasking (VLSM) and better route summarization.Masking (VLSM) and better route summarization.– Classful routing protocols do not include the subnetClassful routing protocols do not include the subnetmask and cannot support VLSM.mask and cannot support VLSM.
  • 11. Routing protocol characteristicsRouting protocol characteristics(3/3)(3/3)• Resource UsageResource Usage - Resource usage includes the- Resource usage includes therequirements of a routing protocol such as memoryrequirements of a routing protocol such as memoryspace, CPU utilization, and link bandwidthspace, CPU utilization, and link bandwidthutilizationutilization– Higher resource requirements necessitate more powerfulHigher resource requirements necessitate more powerfulhardware to support the routing protocol operation inhardware to support the routing protocol operation inaddition to the packet forwarding processes.addition to the packet forwarding processes.• Implementation and MaintenanceImplementation and Maintenance - Implementation- Implementationand maintenance describes the level of knowledgeand maintenance describes the level of knowledgethat is required for a network administrator tothat is required for a network administrator toimplement and maintain the network based on theimplement and maintain the network based on therouting protocol deployed.routing protocol deployed.
  • 12. Distance Vector Routing Protocols
  • 13. Comparison of Routing ProtocolComparison of Routing Protocol
  • 14. Periodic updatesPeriodic updates :RIP(1/3):RIP(1/3)• The term periodic updates refers to the factThe term periodic updates refers to the factthat a router sends the complete routingthat a router sends the complete routingtable to its neighbors at a predefinedtable to its neighbors at a predefinedinterval.interval.– For RIP, these updates are sent every 30For RIP, these updates are sent every 30seconds as a broadcast (255.255.255.255)seconds as a broadcast (255.255.255.255)whether or not there has been a topologywhether or not there has been a topologychange.change.– This 30-second interval is a route update timerThis 30-second interval is a route update timerthat also aids in tracking the age of routingthat also aids in tracking the age of routinginformation in the routing table.information in the routing table.
  • 15. Periodic updates:RIPPeriodic updates:RIP (2/3)(2/3)• The age of routing information in a routing table isThe age of routing information in a routing table isrefreshed each time an update is received.refreshed each time an update is received.• This way information in the routing table can beThis way information in the routing table can bemaintained when there is a topology change.maintained when there is a topology change.• Changes may occur for several reasons,Changes may occur for several reasons,including:including:– Failure of a linkFailure of a link– Introduction of a new linkIntroduction of a new link– Failure of a routerFailure of a router– Change of link parametersChange of link parameters
  • 16. Periodic updates:RIPPeriodic updates:RIP (3/3)(3/3)
  • 17. RIP TimersRIP Timers (1/3)(1/3)• In addition to the update timer, the IOS implementsIn addition to the update timer, the IOS implementsthree additional timers for RIP:three additional timers for RIP:• Invalid TimerInvalid Timer. If an update has not been received to. If an update has not been received torefresh an existing route after 180 seconds (therefresh an existing route after 180 seconds (thedefault), the route is marked as invalid by settingdefault), the route is marked as invalid by settingthe metric to 16.the metric to 16.– The route is retained in the routing table until the flushThe route is retained in the routing table until the flushtimer expires.timer expires.• Flush TimerFlush Timer. By default, the flush timer is set for. By default, the flush timer is set for240 seconds, which is 60 seconds longer than the240 seconds, which is 60 seconds longer than theinvalid timer. When the flush timer expires, theinvalid timer. When the flush timer expires, theroute is removed from the routing table.route is removed from the routing table.
  • 18. RIP TimersRIP Timers (2/3)(2/3)• Holddown Timer. This timer stabilizesHolddown Timer. This timer stabilizesrouting information and helps preventrouting information and helps preventrouting loops during periods when therouting loops during periods when thetopology is converging on new information.topology is converging on new information.– Once a route is marked as unreachable, itOnce a route is marked as unreachable, itmust stay in holddown long enough for allmust stay in holddown long enough for allrouters in the topology to learn about therouters in the topology to learn about theunreachable network.unreachable network.– By default, the holddown timer is set for 180By default, the holddown timer is set for 180seconds.seconds.
  • 19. RIP TimersRIP Timers (3/3)(3/3)
  • 20. Bounded Updates :EIGRP(1/2)Bounded Updates :EIGRP(1/2)• Unlike other distance vector routing protocols,Unlike other distance vector routing protocols,EIGRP does not send periodic updates.EIGRP does not send periodic updates.• Instead, EIGRP sends bounded updates about aInstead, EIGRP sends bounded updates about aroute when a path changes or the metric for thatroute when a path changes or the metric for thatroute changes.route changes.• When a new route becomes available or when aWhen a new route becomes available or when aroute needs to be removedroute needs to be removed,, EIGRP sends anEIGRP sends anupdate only about that network instead of theupdate only about that network instead of theentire table.entire table.• This information is sent only to those routers thatThis information is sent only to those routers thatneed it.need it.
  • 21. Bounded Updates :EIGRP(2/2)Bounded Updates :EIGRP(2/2)• EIGRP uses updates that are:EIGRP uses updates that are:– Non-periodic because they are not sent out onNon-periodic because they are not sent out ona regular basis.a regular basis.– Partial updates sent only when there is aPartial updates sent only when there is achange in topology that influences routingchange in topology that influences routinginformation.information.– Bounded, meaning the propagation of partialBounded, meaning the propagation of partialupdates are automatically bounded so thatupdates are automatically bounded so thatonly those routers that need the informationonly those routers that need the informationare updated.are updated.
  • 22. Triggered UpdateTriggered Update (1/3)(1/3)• To speed up the convergence when there is aTo speed up the convergence when there is atopology change,topology change, RIP uses triggered updatesRIP uses triggered updates..• A triggered update is a routing table update thatA triggered update is a routing table update thatis sent immediately in response to a routingis sent immediately in response to a routingchangechange..• Triggered updates do not wait for update timersTriggered updates do not wait for update timersto expire.to expire.– The detecting router immediately sends an updateThe detecting router immediately sends an updatemessage to adjacent routers.message to adjacent routers.– The receiving routers, in turn, generate triggeredThe receiving routers, in turn, generate triggeredupdates that notify their neighbors of the change.updates that notify their neighbors of the change.
  • 23. Triggered UpdateTriggered Update (2/3)(2/3)• Triggered updates are sent when one ofTriggered updates are sent when one ofthe following occurs:the following occurs:– An interface changes state (up or down)An interface changes state (up or down)– A route has entered (or exited) theA route has entered (or exited) the"unreachable" state"unreachable" state– A route is installed in the routing tableA route is installed in the routing table
  • 24. Triggered UpdateTriggered Update (3/3)(3/3)• However, there are two problems with triggeredHowever, there are two problems with triggeredupdates:updates:– Packets containing the update message can bePackets containing the update message can bedropped or corrupted by some link in the network.dropped or corrupted by some link in the network.– The triggered updates do not happen instantaneously. ItThe triggered updates do not happen instantaneously. Itis possible that a router that has not yet received theis possible that a router that has not yet received thetriggered update will issue a regular update at just thetriggered update will issue a regular update at just thewrong time, causing the bad route to be reinserted in awrong time, causing the bad route to be reinserted in aneighbor that had already received the triggeredneighbor that had already received the triggeredupdate.update.
  • 25. Routing Loop (1/6)Routing Loop (1/6)• A routing loop is a condition in which aA routing loop is a condition in which apacket is continuously transmitted within apacket is continuously transmitted within aseries of routers without ever reaching itsseries of routers without ever reaching itsintended destination network.intended destination network.• A routing loop can occur when two orA routing loop can occur when two ormore routers have routing information thatmore routers have routing information thatincorrectly indicates that a valid path to anincorrectly indicates that a valid path to anunreachable destination exists.unreachable destination exists.
  • 26. Routing Loop (2/6)Routing Loop (2/6)• The loop may be a result of:The loop may be a result of:– Incorrectly configured static routesIncorrectly configured static routes– Incorrectly configured route redistributionIncorrectly configured route redistribution(redistribution is a process of handing the routing(redistribution is a process of handing the routinginformation from one routing protocol to anotherinformation from one routing protocol to anotherrouting protocol)routing protocol)– Inconsistent routing tables not being updatedInconsistent routing tables not being updateddue to slow convergence in a changing networkdue to slow convergence in a changing network– Incorrectly configured or installed discard routesIncorrectly configured or installed discard routes
  • 27. Routing Loop (3/6)Routing Loop (3/6)
  • 28. Routing Loop (4/6)Routing Loop (4/6)
  • 29. Routing Loop (5/6)Routing Loop (5/6)
  • 30. Routing Loop (6/6)Routing Loop (6/6)
  • 31. Count to infinity (1/5)Count to infinity (1/5)• Count to infinity is a condition that existsCount to infinity is a condition that existswhen inaccurate routing updates increasewhen inaccurate routing updates increasethe metric value to "infinity" for a networkthe metric value to "infinity" for a networkthat is no longer reachable.that is no longer reachable.
  • 32. Count to infinity (2/5)Count to infinity (2/5)
  • 33. Count to infinity (3/5)Count to infinity (3/5)
  • 34. Count to infinity (4/5)Count to infinity (4/5)
  • 35. Count to infinity (5/5)Count to infinity (5/5)
  • 36. Setting a Maximum (1/2)Setting a Maximum (1/2)• To eventually stop the incrementing of theTo eventually stop the incrementing of themetric, "infinity" is defined by setting ametric, "infinity" is defined by setting amaximum metric value.maximum metric value.• For example, RIP defines infinity as 16For example, RIP defines infinity as 16hops - an "unreachable" metric.hops - an "unreachable" metric.• Once the routers "count to infinity," theyOnce the routers "count to infinity," theymark the route as unreachable.mark the route as unreachable.
  • 37. Setting a Maximum (2/2)Setting a Maximum (2/2)
  • 38. Preventing routing loop withPreventing routing loop withholddown timerholddown timer (1/5)(1/5)• Holddown timers are used to prevent regularHolddown timers are used to prevent regularupdate messages from inappropriately reinstatingupdate messages from inappropriately reinstatinga route that may have gone bad.a route that may have gone bad.• Holddown timers instruct routers to hold anyHolddown timers instruct routers to hold anychanges that might affect routes for a specifiedchanges that might affect routes for a specifiedperiod of time.period of time.• If a route is identified as down or possibly down,If a route is identified as down or possibly down,any other information for that route containing theany other information for that route containing thesame status, or worse, is ignored for asame status, or worse, is ignored for apredetermined amount of time (the holddownpredetermined amount of time (the holddownperiod).period).
  • 39. Preventing routing loop withPreventing routing loop withholddown timerholddown timer (2/5)(2/5)
  • 40. Preventing routing loop withPreventing routing loop withholddown timerholddown timer (3/5)(3/5)
  • 41. Preventing routing loop withPreventing routing loop withholddown timerholddown timer (4/5)(4/5)
  • 42. Preventing routing loop withPreventing routing loop withholddown timerholddown timer (5/5)(5/5)
  • 43. Split Horizon Rules (1/5)Split Horizon Rules (1/5)• The split horizon rule says that a routerThe split horizon rule says that a routershould not advertise a network throughshould not advertise a network throughthe interface from which the update came.the interface from which the update came.
  • 44. Split Horizon Rules (2/5)Split Horizon Rules (2/5)
  • 45. Split Horizon Rules (3/5)Split Horizon Rules (3/5)
  • 46. Split Horizon Rules (4/5)Split Horizon Rules (4/5)
  • 47. Split Horizon Rules (5/5)Split Horizon Rules (5/5)
  • 48. Route Poisoning (1/4)Route Poisoning (1/4)• Route poisoning is yet another methodRoute poisoning is yet another methodemployed by distance vector routingemployed by distance vector routingprotocols to prevent routing loops.protocols to prevent routing loops.• Route poisoning is used to mark the routeRoute poisoning is used to mark the routeas unreachable in a routing update that isas unreachable in a routing update that issent to other routers.sent to other routers.• Unreachable is interpreted as a metric thatUnreachable is interpreted as a metric thatis set to the maximum.is set to the maximum.– For RIP, a poisoned route has a metric of 16.For RIP, a poisoned route has a metric of 16.
  • 49. Route Poisoning (2/4)Route Poisoning (2/4)
  • 50. Route Poisoning (3/4)Route Poisoning (3/4)
  • 51. Route Poisoning (4/4)Route Poisoning (4/4)
  • 52. Split Horizon with Poison reverseSplit Horizon with Poison reverse(1/5)(1/5)• The concept of split horizon with poisonThe concept of split horizon with poisonreverse is that explicitly telling a router toreverse is that explicitly telling a router toignore a route is better than not telling itignore a route is better than not telling itabout the route in the first place.about the route in the first place.
  • 53. Split Horizon with Poison reverseSplit Horizon with Poison reverse(2/5)(2/5)• The following process occurs:The following process occurs:• Network 10.4.0.0 becomes unavailable due to aNetwork 10.4.0.0 becomes unavailable due to alink failure.link failure.• R3 poisons the metric with a value of 16 andR3 poisons the metric with a value of 16 andthen sends out a triggered update stating thatthen sends out a triggered update stating that10.4.0.0 is unavailable.10.4.0.0 is unavailable.• R2 processes that update, invalidates theR2 processes that update, invalidates therouting entry in its routing table, and immediatelyrouting entry in its routing table, and immediatelysends a poison reverse back to R3.sends a poison reverse back to R3.
  • 54. Split Horizon with Poison reverseSplit Horizon with Poison reverse(3/5)(3/5)
  • 55. Split Horizon with Poison reverseSplit Horizon with Poison reverse(4/5)(4/5)
  • 56. Split Horizon with Poison reverseSplit Horizon with Poison reverse(5/5)(5/5)
  • 57. Time to Live (1/2)Time to Live (1/2)• Time to Live (TTL) is an 8-bit field in the IPTime to Live (TTL) is an 8-bit field in the IPheaderheader that limits the number of hops athat limits the number of hops apacket can traverse through the networkpacket can traverse through the networkbefore it is discarded.before it is discarded.• The purpose of the TTL field is to avoid aThe purpose of the TTL field is to avoid asituation in which an undeliverable packetsituation in which an undeliverable packetkeeps circulating on the network endlessly.keeps circulating on the network endlessly.
  • 58. Time to Live (2/2)Time to Live (2/2)• With TTL, the 8-bit field is set with a value by theWith TTL, the 8-bit field is set with a value by thesource device of the packet. The TTL issource device of the packet. The TTL isdecreased by one by every router on the routedecreased by one by every router on the routeto its destination.to its destination.• If the TTL field reaches zero before the packetIf the TTL field reaches zero before the packetarrives at its destination, the packet is discardedarrives at its destination, the packet is discardedand the router sends an Internet Controland the router sends an Internet ControlMessage Protocol (ICMP) error message backMessage Protocol (ICMP) error message backto the source of the IP packetto the source of the IP packet