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© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
ITE PC v4.0
Chapter 1 1
VLSM and CIDR
ITE PC v4.0
Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Objectives
 Compare and contrast clas...
ITE PC v4.0
Chapter 1 3© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Introduction
 Prior to 1981, IP addre...
ITE PC v4.0
Chapter 1 4© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 5© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 6© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 7© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 8© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
ITE PC v4.0
Chapter 1 9© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 11© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 12© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 13© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classful and Classless IP Addressing
...
ITE PC v4.0
Chapter 1 14© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classless Inter-Domain Routing (CIDR)...
ITE PC v4.0
Chapter 1 15© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classless Inter-Domain Routing (CIDR)...
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
ITE PC v4.0
Chapter 1 16
Distance Vector Routing
Protocols
ITE PC v4.0
Chapter 1 17© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Objectives
 Identify the characteris...
ITE PC v4.0
Chapter 1 18© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Why dynamic routing protocol
ITE PC v4.0
Chapter 1 19© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
 E...
ITE PC v4.0
Chapter 1 20© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
 D...
ITE PC v4.0
Chapter 1 21© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
Cha...
ITE PC v4.0
Chapter 1 22© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
 R...
ITE PC v4.0
Chapter 1 23© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
Rou...
ITE PC v4.0
Chapter 1 24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Distance Vector Routing Protocols
ITE PC v4.0
Chapter 1 25© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Network Discovery
 Router initial st...
ITE PC v4.0
Chapter 1 26© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Network Discovery
 Initial Exchange ...
ITE PC v4.0
Chapter 1 27© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Network Discovery
 Exchange of Routi...
ITE PC v4.0
Chapter 1 28© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Network Discovery
 Convergence must ...
ITE PC v4.0
Chapter 1 29© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Table Maintenance
 Periodic ...
ITE PC v4.0
Chapter 1 30© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Table Maintenance
 RIP uses ...
ITE PC v4.0
Chapter 1 31© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Table Maintenance
 Invalid T...
ITE PC v4.0
Chapter 1 32© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Table Maintenance
 EIGRP rou...
ITE PC v4.0
Chapter 1 33© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Table Maintenance
 Triggered...
ITE PC v4.0
Chapter 1 34© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 Routing loops are
A c...
ITE PC v4.0
Chapter 1 35© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 Routing loops may be ...
ITE PC v4.0
Chapter 1 36© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops problems
 Count to Inf...
ITE PC v4.0
Chapter 1 37© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops problems
 Distance Vec...
ITE PC v4.0
Chapter 1 38© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 Preventing loops with...
ITE PC v4.0
Chapter 1 39© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 Holddown Timer. This ...
ITE PC v4.0
Chapter 1 40© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Update, holddown & flush timers
Last ...
ITE PC v4.0
Chapter 1 41© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Update, holddown & flush timers
Last ...
ITE PC v4.0
Chapter 1 42© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 The Split Horizon Rul...
ITE PC v4.0
Chapter 1 43© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 Split horizon with po...
ITE PC v4.0
Chapter 1 44© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Route poisoning & Poison reverse
 Ro...
ITE PC v4.0
Chapter 1 45© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Loops
 IP & TTL
–Purpose of ...
ITE PC v4.0
Chapter 1 46© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Protocols Today
 Factors use...
ITE PC v4.0
Chapter 1 47© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Routing Protocols Today
 RIP
Featur...
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
ITE PC v4.0
Chapter 1 48
RIP version 1
ITE PC v4.0
Chapter 1 49© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Objectives
 Describe the functions, ...
ITE PC v4.0
Chapter 1 50© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RIPv1
 RIP Characteristics
-A classf...
ITE PC v4.0
Chapter 1 51© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RIP v1 message
ITE PC v4.0
Chapter 1 52© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RIPv1
 RIP Operation
–RIP uses 2 mes...
ITE PC v4.0
Chapter 1 53© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Basic RIPv1 Configuration
 Router RI...
ITE PC v4.0
Chapter 1 54© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Basic RIPv1 Configuration
 Specifyin...
ITE PC v4.0
Chapter 1 55© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 To...
ITE PC v4.0
Chapter 1 56© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Interpreting RIP route
ITE PC v4.0
Chapter 1 57© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 sh...
ITE PC v4.0
Chapter 1 58© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 De...
ITE PC v4.0
Chapter 1 59© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 Pa...
ITE PC v4.0
Chapter 1 60© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 Pa...
ITE PC v4.0
Chapter 1 61© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Boundary Ro...
ITE PC v4.0
Chapter 1 62© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
Processing RI...
ITE PC v4.0
Chapter 1 63© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Sending RIP...
ITE PC v4.0
Chapter 1 64© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Advantages ...
ITE PC v4.0
Chapter 1 65© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Disadvantag...
ITE PC v4.0
Chapter 1 66© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Discontiguo...
ITE PC v4.0
Chapter 1 67© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Default Route and RIPv1
 Default rou...
ITE PC v4.0
Chapter 1 68© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Default Route and RIPv1
 Propagating...
ITE PC v4.0
Chapter 1 69© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Summary: Commands used by RIP
Command...
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
ITE PC v4.0
Chapter 1 70
RIPv2
ITE PC v4.0
Chapter 1 71© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Introduction
 Chapter focus
-Differe...
ITE PC v4.0
Chapter 1 72© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Introduction
 Similarities between R...
ITE PC v4.0
Chapter 1 73© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
RIPv1 Limitations
Examining the rout...
ITE PC v4.0
Chapter 1 74© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Configuring RIPv2
 Enabling and Veri...
ITE PC v4.0
Chapter 1 75© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Configuring RIPv2
 Configuring RIPv2...
ITE PC v4.0
Chapter 1 76© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Configuring RIPv2
 Auto-Summary & RI...
ITE PC v4.0
Chapter 1 77© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
 Disabling Auto-
Summary in RIPv2
 ...
ITE PC v4.0
Chapter 1 78© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
VLSM & CIDR
 Networks using a VLSM I...
ITE PC v4.0
Chapter 1 79© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verifying & Troubleshooting RIPv2
 B...
ITE PC v4.0
Chapter 1 80© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verifying & Troubleshooting RIPv2
 C...
ITE PC v4.0
Chapter 1 81© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verifying & Troubleshooting RIPv2
 R...
ITE PC v4.0
Chapter 1 82© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Summary
Routing
Protocol
Distance
Vec...
ITE PC v4.0
Chapter 1 83© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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  1. 1. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 VLSM and CIDR
  2. 2. ITE PC v4.0 Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Objectives  Compare and contrast classful and classless IP addressing.  Review VLSM and explain the benefits of classless IP addressing.  Describe the role of the Classless Inter-Domain Routing (CIDR) standard in making efficient use of scarce IPv4 addresses
  3. 3. ITE PC v4.0 Chapter 1 3© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction  Prior to 1981, IP addresses used only the first 8 bits to specify the network portion of the address  In 1981, RFC 791 modified the IPv4 32-bit address to allow for three different classes  IP address space was depleting rapidly the Internet Engineering Task Force (IETF) introduced Classless Inter-Domain Routing (CIDR) –CIDR uses Variable Length Subnet Masking (VLSM) to help conserve address space. -VLSM is simply subnetting a subnet
  4. 4. ITE PC v4.0 Chapter 1 4© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Classful IP addressing  As of January 2007, there are over 433 million hosts on internet  Initiatives to conserve IPv4 address space include: -VLSM & CIDR notation (1993, RFC 1519) -Network Address Translation (1994, RFC 1631) -Private Addressing (1996, RFC 1918)
  5. 5. ITE PC v4.0 Chapter 1 5© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  The High Order Bits These are the leftmost bits in a 32 bit address
  6. 6. ITE PC v4.0 Chapter 1 6© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Classes of IP addresses are identified by the decimal number of the 1st octet Class A address begin with a 0 bit Range of class A addresses = 0.0.0.0 to 127.255.255.255 Class B address begin with a 1 bit and a 0 bit Range of class B addresses = 128.0.0.0 to 191.255.255.255 Class C addresses begin with two 1 bits & a 0 bit Range of class C addresses = 192.0.0.0 to 223.255.255.255.
  7. 7. ITE PC v4.0 Chapter 1 7© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  The IPv4 Classful Addressing Structure (RFC 790) An IP address has 2 parts: -The network portion Found on the left side of an IP address -The host portion Found on the right side of an IP address
  8. 8. ITE PC v4.0 Chapter 1 8© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing
  9. 9. ITE PC v4.0 Chapter 1 9© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Purpose of a subnet mask It is used to determine the network portion of an IP address
  10. 10. ITE PC v4.0 Chapter 1 10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Classful Routing Updates -Recall that classful routing protocols (i.e. RIPv1) do not send subnet masks in their routing updates The reason is that the Subnet mask is directly related to the network address
  11. 11. ITE PC v4.0 Chapter 1 11© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Classless Inter-domain Routing (CIDR – RFC 1517) Advantage of CIDR : -More efficient use of IPv4 address space -Route summarization Requires subnet mask to be included in routing update because address class is meaningless Recall purpose of a subnet mask: -To determine the network and host portion of an IP address
  12. 12. ITE PC v4.0 Chapter 1 12© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing  Classless Routing Protocol  Characteristics of classless routing protocols: -Routing updates include the subnet mask -Supports VLSM Supports Route Summarization
  13. 13. ITE PC v4.0 Chapter 1 13© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classful and Classless IP Addressing Routing Protocol Routing updates Include subnet Mask Supports VLSM Ability to send Supernet routes Classful No No No Classless Yes Yes Yes  Classless Routing Protocol
  14. 14. ITE PC v4.0 Chapter 1 14© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classless Inter-Domain Routing (CIDR)  Route summarization done by CIDR -Routes are summarized with masks that are less than that of the default classful mask -Example: 172.16.0.0 / 13 is the summarized route for the 172.16.0.0 / 16 to 172.23.0.0 / 16 classful networks
  15. 15. ITE PC v4.0 Chapter 1 15© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Classless Inter-Domain Routing (CIDR)  Steps to calculate a route summary -List networks in binary format -Count number of left most matching bits to determine summary route’s mask -Copy the matching bits and add zero bits to determine the summarized network address
  16. 16. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 16 Distance Vector Routing Protocols
  17. 17. ITE PC v4.0 Chapter 1 17© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Objectives  Identify the characteristics of distance vector routing protocols.  Describe the network discovery process of distance vector routing protocols using Routing Information Protocol (RIP).  Describe the processes to maintain accurate routing tables used by distance vector routing protocols.  Identify the conditions leading to a routing loop and explain the implications for router performance.
  18. 18. ITE PC v4.0 Chapter 1 18© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Why dynamic routing protocol
  19. 19. ITE PC v4.0 Chapter 1 19© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols  Examples of Distance Vector routing protocols: Routing Information Protocol (RIP) v1,2 Interior Gateway Routing Protocol (IGRP) Enhanced Interior Gateway Routing Protocol (EIGRP)
  20. 20. ITE PC v4.0 Chapter 1 20© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols  Distance Vector Technology –The Meaning of Distance Vector: •A router using distance vector routing protocols knows 2 things: Distance to final destination Vector, or direction, traffic should be directed
  21. 21. ITE PC v4.0 Chapter 1 21© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols Characteristics of Distance Vector routing protocols:  Periodic updates  Broadcast updates  Entire routing table is included into routing update
  22. 22. ITE PC v4.0 Chapter 1 22© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols  Routing Protocol Algorithm: -Defined as a procedure for accomplishing a certain task
  23. 23. ITE PC v4.0 Chapter 1 23© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols Routing Protocol Characteristics –Criteria used to compare routing protocols includes Time to convergence Scalability Resource usage Implementation & maintenance
  24. 24. ITE PC v4.0 Chapter 1 24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Distance Vector Routing Protocols
  25. 25. ITE PC v4.0 Chapter 1 25© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery  Router initial start up -Initial network discovery Directly connected networks are initially placed in routing table
  26. 26. ITE PC v4.0 Chapter 1 26© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery  Initial Exchange of Routing Information –If a routing protocol is configured then -Routers will exchange routing information  Routing updates received from other routers -Router checks update for new information If there is new information: -Metric is updated -New information is stored in routing table
  27. 27. ITE PC v4.0 Chapter 1 27© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery  Exchange of Routing Information –Router convergence is reached when -All routing tables in the network contain the same network information –Routers continue to exchange routing information -If no new information is found then Convergence is reached
  28. 28. ITE PC v4.0 Chapter 1 28© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Network Discovery  Convergence must be reached before a network is considered completely operable  Speed of achieving convergence consists of 2 independent categories -Speed of broadcasting routing information -Speed of calculating routes
  29. 29. ITE PC v4.0 Chapter 1 29© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Table Maintenance  Periodic Updates: RIPv1 & RIPv2 These are time intervals in which a router sends out its entire routing table.
  30. 30. ITE PC v4.0 Chapter 1 30© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Table Maintenance  RIP uses 4 timers -Update timer -Invalid timer -Hold-down timer -Flush timer
  31. 31. ITE PC v4.0 Chapter 1 31© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Table Maintenance  Invalid Timer:- If an update has not been received to refresh an existing route after 180 seconds (the default), the route is marked as invalid by setting the metric to 16. The route is retained in the routing table until the flush timer expires.  Flush Timer:- By default, the flush timer is set for 240 seconds, which is 60 seconds longer than the invalid timer. When the flush timer expires, the route is removed from the routing table.
  32. 32. ITE PC v4.0 Chapter 1 32© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Table Maintenance  EIGRP routing updates are -Partial updates (The Update Contain only the changed Routes) -Triggered by topology changes (Once a change happen, Update is sent) -Bounded (Update sent only to Routers who need it ) -Non periodic
  33. 33. ITE PC v4.0 Chapter 1 33© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Table Maintenance  Triggered Updates –Conditions in which triggered updates are sent -Interface changes state -Route becomes unreachable -Route is placed in routing table
  34. 34. ITE PC v4.0 Chapter 1 34© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  Routing loops are A condition in which a packet is continuously transmitted within a series of routers without ever reaching its destination.
  35. 35. ITE PC v4.0 Chapter 1 35© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  Routing loops may be caused by: -Incorrectly configured static routes -Incorrectly configured route redistribution -Slow convergence -Incorrectly configured discard routes  Routing loops can create the following issues -Excess use of bandwidth -CPU resources may be strained -Network convergence is degraded -Routing updates may be lost or not processed in a timely manner
  36. 36. ITE PC v4.0 Chapter 1 36© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops problems  Count to Infinity This is a routing loop whereby packets bounce infinitely around a network.
  37. 37. ITE PC v4.0 Chapter 1 37© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops problems  Distance Vector routing protocols set a specified metric value to indicate infinity Once a router “counts to infinity” it marks the route as unreachable
  38. 38. ITE PC v4.0 Chapter 1 38© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  Preventing loops with holddown timers -Holddown timers allow a router to not accept any changes to a route for a specified period of time. -Point of using holddown timers Allows routing updates to propagate through network with the most current information. Holddown timers are used to prevent regular update messages from inappropriately reinstaling a route that may have gone bad.
  39. 39. ITE PC v4.0 Chapter 1 39© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  Holddown Timer. This timer stabilizes routing information and helps prevent routing loops during periods when the topology is converging on new information. Once a route is marked as unreachable (Invalid), it must stay in holddown long enough for all routers in the topology to learn about the unreachable network. By default, the holddown timer is set for 180 seconds.
  40. 40. ITE PC v4.0 Chapter 1 40© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Update, holddown & flush timers Last update about certain network Invalid timer Flush timerHolddown timer 180 sec 180 sec 240 sec
  41. 41. ITE PC v4.0 Chapter 1 41© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Update, holddown & flush timers Last update about certain network Update about the same network with metric=16 Invalid timer Flush timerHolddown timer 180 sec 180 sec 240 sec
  42. 42. ITE PC v4.0 Chapter 1 42© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  The Split Horizon Rule is used to prevent routing loops  Split Horizon rule: A router should not advertise a network through the interface from which the update came.
  43. 43. ITE PC v4.0 Chapter 1 43© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  Split horizon with poison reverse The rule states that once a router learns of an unreachable route through an interface, advertise it as unreachable back through the same interface
  44. 44. ITE PC v4.0 Chapter 1 44© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Route poisoning & Poison reverse  Route poisoning: sending update about the unreachable network with setting the metric (hop count) to 16  Poison reverse: after receiving the poisoned update the router will suspend the split horizon rule and send the same poisoned update again across the same interface then resume split horizon rule again
  45. 45. ITE PC v4.0 Chapter 1 45© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Loops  IP & TTL –Purpose of the TTL field The TTL field is found in an IP header and is used to prevent packets from endlessly traveling on a network  How the TTL field works -TTL field contains a numeric value The numeric value is decreased by one by every router on the route to the destination. If numeric value reaches 0 then Packet is discarded.
  46. 46. ITE PC v4.0 Chapter 1 46© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Protocols Today  Factors used to determine whether to use RIP or EIGRP include -Network size -Compatibility between models of routers -Administrative knowledge
  47. 47. ITE PC v4.0 Chapter 1 47© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Routing Protocols Today  RIP Features of RIP: -Supports split horizon & split horizon with poison reverse -Capable of load balancing -Easy to configure -Works in a multi vendor router environment
  48. 48. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 48 RIP version 1
  49. 49. ITE PC v4.0 Chapter 1 49© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Objectives  Describe the functions, characteristics, and operation of the RIPv1 protocol.  Configure a device for using RIPv1.  Verify proper RIPv1 operation.  Describe how RIPv1 performs automatic summarization.  Configure, verify, and troubleshoot default routes propagated in a routed network implementing RIPv1.  Use recommended techniques to solve problems related to RIPv1
  50. 50. ITE PC v4.0 Chapter 1 50© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public RIPv1  RIP Characteristics -A classful, Distance Vector (DV) routing protocol -Metric = hop count -Routes with a hop count > 15 are unreachable -Updates are broadcast every 30 seconds
  51. 51. ITE PC v4.0 Chapter 1 51© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public RIP v1 message
  52. 52. ITE PC v4.0 Chapter 1 52© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public RIPv1  RIP Operation –RIP uses 2 message types: Request message -This is sent out on startup by each RIP enabled interface -Requests all RIP enabled neighbors to send routing table Response message -Message sent to requesting router containing routing table
  53. 53. ITE PC v4.0 Chapter 1 53© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Basic RIPv1 Configuration  Router RIP Command –To enable RIP enter: -Router rip at the global configuration prompt -Prompt will look like R1(config-router)#
  54. 54. ITE PC v4.0 Chapter 1 54© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Basic RIPv1 Configuration  Specifying Networks –Use the network command to: -Enable RIP on all interfaces that belong to this network -Advertise this network in RIP updates sent to other routers every 30 seconds
  55. 55. ITE PC v4.0 Chapter 1 55© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verification and Troubleshooting  To verify and troubleshoot routing -Use the following commands: -show ip route -show ip protocols -debug ip rip
  56. 56. ITE PC v4.0 Chapter 1 56© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Interpreting RIP route
  57. 57. ITE PC v4.0 Chapter 1 57© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verification and Troubleshooting  show ip protocols command -Displays routing protocol configured on router
  58. 58. ITE PC v4.0 Chapter 1 58© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verification and Troubleshooting  Debug ip rip command -Used to display RIP routing updates as they are happening
  59. 59. ITE PC v4.0 Chapter 1 59© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verification and Troubleshooting  Passive interface command -Used to prevent a router from sending updates through an interface -Example: Router(config-router)#passive-interface interface-type interface-number
  60. 60. ITE PC v4.0 Chapter 1 60© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verification and Troubleshooting  Passive interfaces
  61. 61. ITE PC v4.0 Chapter 1 61© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization  Boundary Routers –RIP automatically summarizes classful networks –Boundary routers summarize RIP subnets from one major network to another.
  62. 62. ITE PC v4.0 Chapter 1 62© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization Processing RIP Updates  2 rules govern RIPv1 updates: -If a routing update and the interface it’s received on belong to the same network then The subnet mask of the interface is applied to the network in the routing update -If a routing update and the interface it’s received on belong to a different network then The classful subnet mask of the network is applied to the network in the routing update.
  63. 63. ITE PC v4.0 Chapter 1 63© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization  Sending RIP Updates –RIP uses automatic summarization to reduce the size of a routing table.
  64. 64. ITE PC v4.0 Chapter 1 64© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization  Advantages of automatic summarization: –The size of routing updates is reduced –Single routes are used to represent multiple routes which results in faster lookup in the routing table. –Stability in routing table
  65. 65. ITE PC v4.0 Chapter 1 65© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization  Disadvantage of Automatic Summarization: -Does not support discontiguous networks
  66. 66. ITE PC v4.0 Chapter 1 66© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Automatic Summarization  Discontiguous Topologies do not converge with RIPv1  A router will only advertise major network addresses out interfaces that do not belong to the advertised route.
  67. 67. ITE PC v4.0 Chapter 1 67© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Default Route and RIPv1  Default routes Packets that are not defined specifically in a routing table will go to the specified interface for the default route Example: Customer routers use default routes to connect to an ISP router. Command used to configure a default route is ip route 0.0.0.0 0.0.0.0 s0/0/1
  68. 68. ITE PC v4.0 Chapter 1 68© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Default Route and RIPv1  Propagating the Default Route in RIPv1  Default-information originate command -This command is used to specify that the router is to originate default information, by propagating the static default route in RIP update.
  69. 69. ITE PC v4.0 Chapter 1 69© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Summary: Commands used by RIP Command Command’s purpose Rtr(config)#router rip Enables RIP routing process Rtr(config-router)#network Associates a network with a RIP routing process Rtr#debug ip rip used to view real time RIP routing updates Rtr(config-router)#passive-interface fa0/0 Prevent RIP updates from going out an interface Rtr(config-router)#default-information originate Used by RIP to propagate default routes Rtr#show ip protocols Used to display timers used by RIP
  70. 70. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 70 RIPv2
  71. 71. ITE PC v4.0 Chapter 1 71© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction  Chapter focus -Difference between RIPv1 & RIPv2 RIPv1 -A classful distance vector routing protocol -Does not support discontiguous subnets -Does not support VLSM -Does not send subnet mask in routing update -Routing updates are broadcast RIPv2 -A classless distance vector routing protocol that is an enhancement of RIPv1’s features. -Next hop address is included in updates -Routing updates are multicast -The use of authentication is an option
  72. 72. ITE PC v4.0 Chapter 1 72© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction  Similarities between RIPv1 & RIPv2 -Use of timers to prevent routing loops -Use of split horizon or split horizon with poison reverse -Use of triggered updates -Maximum hop count of 15
  73. 73. ITE PC v4.0 Chapter 1 73© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public RIPv1 Limitations Examining the routing tables -To examine the contents of routing updates use the debug ip rip command -If RIPv1 is configured then Subnet masks will not be included with the network address
  74. 74. ITE PC v4.0 Chapter 1 74© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Configuring RIPv2  Enabling and Verifying RIPv2  Configuring RIP on a Cisco router By default it is running RIPv1
  75. 75. ITE PC v4.0 Chapter 1 75© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Configuring RIPv2  Configuring RIPv2 on a Cisco router -Requires using the version 2 command -RIPv2 ignores RIPv1 updates  To verify RIPv2 is configured use the show ip protocols command
  76. 76. ITE PC v4.0 Chapter 1 76© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Configuring RIPv2  Auto-Summary & RIPv2  RIPv2 will automatically summarize routes at major network boundaries and can also summarize routes with a subnet mask that is smaller than the classful subnet mask
  77. 77. ITE PC v4.0 Chapter 1 77© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public  Disabling Auto- Summary in RIPv2  To disable automatic summarization issue the no auto-summary command Configuring RIPv2
  78. 78. ITE PC v4.0 Chapter 1 78© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public VLSM & CIDR  Networks using a VLSM IP addressing scheme Use classless routing protocols (i.e. RIPv2) to disseminate network addresses and their subnet masks
  79. 79. ITE PC v4.0 Chapter 1 79© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verifying & Troubleshooting RIPv2  Basic Troubleshooting steps -Check the status of all links -Check cabling -Check IP address & subnet mask configuration -Remove any unneeded configuration commands  Commands used to verify proper operation of RIPv2 –Show ip interfaces brief –Show ip protocols –Debug ip rip –Show ip route
  80. 80. ITE PC v4.0 Chapter 1 80© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verifying & Troubleshooting RIPv2  Common RIPv2 Issues  When trouble shooting RIPv2 examine the following issues: Version Check to make sure you are using version 2 Network statements Network statements may be incorrectly typed or missing Automatic summarization If summarized routes are not needed then disable automatic summarization
  81. 81. ITE PC v4.0 Chapter 1 81© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Verifying & Troubleshooting RIPv2  Reasons why it’s good to authenticate routing information -Prevent the possibility of accepting invalid routing updates -Contents of routing updates are encrypted  Types of routing protocols that can use authentication -RIPv2 -EIGRP -OSPF -IS-IS -BGP
  82. 82. ITE PC v4.0 Chapter 1 82© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Summary Routing Protocol Distance Vector Classless Routing Protocol Uses Hold- Down Timers Use of Split Horizon or Split Horizon w/ Poison Reverse Max Hop count = 15 Auto Summary Support CIDR Supports VLSM Uses Authen- tication RIPv1 Yes No Yes Yes Yes Yes No No No RIPv2 Yes Yes Yes Yes Yes Yes Yes Yes Yes
  83. 83. ITE PC v4.0 Chapter 1 83© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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