1. RIP, IGRP, & EIGRP Characteristics and Design

2. 2 Chapter Topics  RIPv1  RIPv2  IGRP  EIGRP

3. 3 RIPv1  RFC 1058  distance-vector routing protocol  uses router hop count as the metric  classful routing protocol does not support VLSM or CIDR  no method for authenticating route updates

4. 4 RIPv1  Sends a copy of its routing table to its neighbors every 30 seconds  Uses split horizon with poison reverse  Based on the popular routed program used in UNIX systems since the 1980’s

5. 5 RIPv1  Cisco implementation of RIP adds support for load balancing will load-balance traffic if there are several paths with the same metric  Cisco RIP sends triggered updates  Administrative distance of 120

6. 6 RIPv1  Summarizes to IP network values at network boundaries Network boundary occurs at a router that has one or more interfaces that do not participate in the specified IP network

7. 7 RIPv1 Forwarding Information Base  RIPv1 protocol keeps the following information about each destination: IP address  IP address of the destination host or network Gateway  The first gateway along the path to the destination Interface  The physical network that must be used to reach the destination Metric  A number indicating the number of hops to the destination Timer  The amount of time since the entry was last updated

8. 8 RIPv1 Forwarding Information Base  Database is updated with the route updates received from neighboring routers

9. 9 RIPv1 Message Format  RIP messages are encapsulated using UDP port 520

10. 10 RIPv1 Message Format  Command Describes the purpose of the packet. The RFC describes five commands, two of which are obsolete and one of which is reserved. The two used commands are  request Requests all or part of the responding router's routing table.  response Contains all or part of the sender's routing table. This message might be a response to a request, or it might be an update message generated by the sender

11. 11 RIPv1 Message Format  Version Set to the value of 1 for RIPv1.  Address Family Identifier (AFI) Set to a value of 2 for IP.  IP address The destination route. It might be a network address, subnet, or host route. Special route 0.0.0.0 is used for the default route.

12. 12 RIPv1 Message Format  Metric A field that is 32 bits in length. It contains a value between 1 and 15 inclusive, specifying the current metric for the destination. The metric is set to 16 to indicate that a destination is not reachable. Because RIP has a maximum hop count, it implements counting to infinity

13. 13 RIPv1 Message Format  In the RIP message that there are no subnet masks accompanying each route  Five 32-bit words are repeated for each route entry Five 32-bit words equals 20 bytes for each route entry  Up to 25 routes are allowed in each RIP message  The maximum datagram size is limited to 512 bytes

14. 14 RIPv1 Timers  Cisco implementation of RIP uses four timers Update Invalid Flush Holddown  IP sends its full routing table out all configured interfaces  Table is sent periodically as a broadcast (255.255.255.255) to all hosts

15. 15 Ripv1 Timers  Update Timer frequency of the periodic broadcasts default is 30 seconds  Invalid Timer The length of time that must elapse before a router determines that a route has become invalid Default is 180 seconds

16. 16 Ripv1 Timers  Flush Timer Sets the time between a route becoming invalid and its removal from the routing table Default is 240 seconds  Holddown Timer Cisco implementation Sets the amount of time during which routing information is suppressed After the metric for a route entry changes, the router accepts no updates for the route until the holddown timer expires. Default is 180 seconds

17. 17 Ripv1 Timers

18. 18 RIPv1 Design  Things to remember does not support VLSM and CIDR RIPv1 requires the same subnet mask for the entire IP network RIPv1 is limited to 15 hops broadcasts its routing table every 30 seconds usually limited to accessing networks where it can interoperate with servers running routed or with non-Cisco routers also appears at the edge of larger networks

19. 19 RIPv2  First described in RFC 1388 and RFC 1723 (1994); the current RFC is 2453, (1998)  Need to use VLSM and other requirements prompted the definition of RIPv2

20. 20 RIPv2  RIPv2 improves upon RIPv1 with ability to use VLSM support for route authentication, multicasting of route updates  uses the IP address 224.0.0.9 Support of CIDR

21. 21 RIPv2  Some features remain the same Updates every 30 seconds Retains the 15-hop limit Uses triggered updates Uses UDP port 520 Retains the loop-prevention strategies of poison reverse and counting to infinity Administrative distance of 120 Summarize IP networks at network boundaries

22. 22 RIPv2 Authentication  Prevent communication with any RIP routers that are not intended to be part of the network UNIX stations running routed  RFC 1723 defines simple plain-text authentication

23. 23 MD5 Authentication  Cisco implementation provides the ability to use Message Digest 5 (MD5) authentication RFC 1321

24. 24 RIPv2 Forwarding Information Base  Maintains the same routing table database as in Version 1 Difference is that it also keeps the subnet mask information  IP Address  Gateway  Interface  Metric  Timer

25. 25 RIPv2 Message Format

26. 26 RIPv2 Message Format  Takes advantage of the unused fields in the RIPv1 message format Adding subnet masks and other information

27. 27 RIPv2 Message Format  Description of each field Command  Indicates whether the packet is a request or a response message Version  Specifies the RIP version used AFI  Specifies the address family used  Set to a value of 2 for IP Route tag  Provides a method for distinguishing between internal routes (learned by RIP) and external routes (learned from other protocols)  Optional Tag

28. 28 RIPv2 Message Format IP address  IP address (network) of the destination Subnet mask  Subnet mask for the destination Next hop  Indicates the IP address of the next hop where packets are sent to reach the destination. Metric  Indicates how many router hops to reach the destination

29. 29 RIPv2 Timers  Same as RIPv1 Update – 30 s Invalid – 180 s Holddown – 180 s Flush – 240 s

30. 30 RIPv2 Design  Things to remember Supports VLSM within networks and CIDR for network summarization Summarization of routes in a hierarchical network Limited to 16 hops Multicasts its routing table every 30 seconds Usually limited to accessing networks where it can interoperate with servers running routed or with non-Cisco router Appears at the edge of larger internetworks

31. 31 IGRP  Developed by Cisco to overcome the limitations of RIPv1  Distance-vector routing protocol  Composite metric Uses bandwidth and delay as parameters instead of hop count Can also use reliability and load  Not limited to the 15-hop limit of RIP Default is 100 hops – configurable up to 255

32. 32 IGRP  Routers usually select paths with a larger minimum-link bandwidth over paths with a smaller hop count Links do not have a hop count They are exactly one hop  Classful protocol cannot implement VLSM or CIDR  Summarizes at network boundaries

33. 33 IGRP  Loop avoidance Split horizon with poison reverse Triggered updates Holddown timers  Can load balance over unequal-cost links  Cisco Proprietary

34. 34 IGRP Timers  Update Timer 90 seconds  Invalid Timer 270 seconds  Holddown Timer 280 seconds  Flush Timer 630 seconds

35. 35 IGRP Metrics  IGRP uses a composite metric based on bandwidth, delay, load, and reliability Default is bandwidth and delay  Formula for calculation IGRP metric = {k1 x BW + [(k2 x BW)/(256 – load)] + k3 x delay} x {k5/(reliability + k4)}

36. 36 IGRP Metrics  By default, k1 and k3 are set to 1, and k2, k4, and k5 are set to 0  Change the default metrics using the metric weight tos k1 k2 k3 k4 k5 subcommand under router igrp tos is always 0 to use all metrics: Router(config)#router igrp 10 Router(config-router)#metric weight 0 1 1 1 1 1

37. 37 IGRP Design  Things to remember does not support VLSM does not support CIDR and network summarization within the major network boundary network diameter can be larger than that of networks using RIP broadcasts its routing table every 90 seconds limited to Cisco-only networks

38. 38 IGRP Design  Starting with IOS version 12.3, IGRP is NO LONGER SUPPORTED Must migrate to EIGRP or to another protocol

39. 39 EIGRP  Released in the early 1990s as an evolution of IGRP  classless protocol Permits the use of VLSM Supports CIDR  does not send routing updates periodically  authentication with simple passwords or with MD5

40. 40 EIGRP  Autosummarizes networks at network borders  Can load-balance over unequal–cost paths  Uses IP protocol 88  Cisco Proprietary

41. 41 EIGRP  An “advanced distance-vector” protocol Advertises its routing table to its neighbors Uses hellos and forms neighbor relationships Sends partial updates when a metric or the topology changes  does not send full routing-table updates in periodic fashion Uses DUAL to determine loop-free paths

42. 42 EIGRP  Administrative Distances Internal routes have an AD of 90 Summary routes have an AD of 5 External routes (from redistribution) have an AD of 170

43. 43 EIGRP Components  EIGRP has four components that characterize it: Protocol-dependent modules Neighbor discovery and recovery Reliable Transport Protocol (RTP) DUAL

44. 44 Protocol-Dependent Modules  Different modules that independently support IP, Internetwork Packet Exchange (IPX), and AppleTalk  The logical interface between DUAL and routing protocols  Module sends and receives packets but passes received information to DUAL, which makes routing decisions.

45. 45 Neighbor Discovery and Recovery  multicasts hello packets (224.0.0.10) every 5 seconds for most networks  router builds a table with EIGRP neighbor information  holdtime to maintain a neighbor is three times the hello time: 15 seconds  multicasts hellos every 60 seconds on multipoint WAN interfaces (X.25, Frame Relay, ATM) with speeds less than 1544 Mbps Holdtime is now 180 seconds

46. 46 RTP  ensures the reliable delivery of route updates  uses sequence numbers to ensure ordered delivery  sends update packets using multicast address 224.0.0.10  acknowledges updates using unicast hello packets with no data

47. 47 DUAL  Implemented to select paths and guarantee freedom from routing loops Mathematically proven to result in a loop-free topology No need for periodic updates or route- holddown mechanisms

48. 48 DUAL  Selects a best path and a second best path to reach a destination Best path is the successor Second best path (if available) is the feasible successor  Feasible distance is the lowest calculated metric of a path to reach the destination

49. 49 DUAL  Passive state when the router is not performing any recomputations for an entry

50. 50 DUAL  Active State successor goes down and there are no feasible successors routers send query packets to neighboring routers  Neighbor can send a reply packet It has a feasible successor  Neighbor can send a query packet Does not have a feasible successor Route does not return to passive state until it has received a reply packet from each neighboring router

51. 51 EIGRP Timers  Sends updates only when necessary Sends them only to neighboring routers  There is no periodic update timer  On high-speed networks, the default hello packet interval is 5 seconds multipoint networks with link speeds of T1 and slower, hello packets are unicast every 60 seconds  Holdtime to maintain a neighbor adjacency is three times the hello time 15 seconds or 180 seconds  Updates are sent to the multicast address 224.0.0.10 (all EIGRP routers)

52. 52 EIGRP Metrics  Uses the same composite metric as IGRP BW term is multiplied by 256 for finer granularity  Metric is based on bandwidth, delay, load, and reliability MTU is not an attribute

53. 53 EIGRP Packet Types  EIGRP uses five packet types: Hello  Discovery of neighbors. They are multicast to 224.0.0.10 Acknowledgment  Acknowledges the reception of an update packet  It is a hello packet with no data.  Sent to the unicast address of the sender of the update packet Update  Update packets contain routing information for destinations.  Unicasts update packets to newly discovered neighbors  Multicasts update packets to 224.0.0.10 when a link or metric changes. Update packets are acknowledged to ensure reliable transmission.

54. 54 EIGRP Packet Types Query  sent to find feasible successors to a destination  Always multicast. Reply  Sent to respond to query packets.  Provide a feasible successor to the sender of the query  Packets are unicast to the sender of the query packet.

55. 55 EIGRP Design  Things to remember Supports VLSM, CIDR, and network summarization Not limited to 16 hops as RIP is Does not broadcasts its routing table periodically  No large network overhead Use EIGRP for large networks Potential routing protocol for the core of a large network Provides for route authentication

56. 56 Summary