1. Switching Basics and Intermediate Routing CCNA 3 Chapter 3

2. EIGRP and Troubleshooting Routing Protocols - Introduction
EIGRP (Enhanced IGRP) is a proprietary Cisco routing protocol based on IGRP
Supports VLSM and CIDR
Compared to IGRP:
Faster convergence times
Improved scalability
Superior management of routing loops
EIGRP is a hybrid routing protocol
Offers the best of distance vector and link-state protocols

3. EIGRP and Troubleshooting Routing Protocols – Introduction
Features of EIGRP:
Partial updates
Neighbor discovery
Easier to configure than OSPF
Ideal choice for large, multiprotocol networks built primarily with Cisco routers

4. EIGRP and Troubleshooting Routing Protocols – Introduction
Reasons network problems occur:
Commands are entered incorrectly
Access lists are constructed or placed incorrectly
Routers, switches, or other network devices are configured incorrectly
Physical connections are bad

5. EIGRP Concepts
Balanced hybrid routing protocols like EIGRP combine aspects of distance vector and link-state protocols
Uses distance vectors with more accurate metrics to determine best paths to destination networks
Uses topology changes to trigger updates instead of using periodic updates
Converges more rapidly than distance vector
Uses less bandwidth, memory and processor overhead

6. EIGRP Concepts Comparing EIGRP and IGRP
EIGRP uses metric calculations similar to IGRP
Supports unequal-cost load balancing
EIGRP has better:
Convergence properties
Operating efficiency
Network overhead
The metric is the same (bandwidth and delay by default), but EIGRP has a weight assigned to the metric that is 256 times that for IGRP
Automatic redistribution between IGRP and EIGRP in same AS

7. EIGRP Concepts Comparing EIGRP and IGRP
EIGRP has a maximum hop count of 224
EIGRP uses convergence technology called Diffusing Update Algorithm (DUAL)
Guarantees loop-free operation at every instant throughout a route computation
Allows all devices involved in a topology change to synchronize simultaneously
Routers not affected by topology changes are not involved in recomputations
The convergence time of DUAL rivals that of any other existing routing protocol

8. EIGRP Concepts EIGRP Features
EIGRP has rapid convergence times
Almost instantaneous
Uses DUAL to achieve rapid convergence
Stores backup routes for destinations in routing table
If no backup route available, queries neighbors
Queries are propagated until an alternate route is found

9. EIGRP Concepts EIGRP Features
EIGRP has low usage of network resources during normal operation
Only hello packets are sent on a stable network
Uses EIGRP hello packets to establish relationships with neighboring EIGRP routers
Builds a neighbor table from the hello packets it receives from adjacent EIGRP routers
Does not send period routing updates

10. EIGRP Concepts EIGRP Features
EIGRP supports automatic (classful) route summarization at major network boundaries by default
Manual route summarization can be configured on arbitrary network boundaries to reduce the size of the routing table

11. EIGRP Concepts EIGRP Terminology

12. EIGRP Concepts EIGRP Terminology
Routing Protocols Supported by EIGRP

13. EIGRP Concepts EIGRP Terminology
Contents of Tables Used by EIGRP

14. EIGRP Concepts EIGRP Terminology
Reliable Transport Protocol (RTP) is a transport layer protocol that guarantees ordered delivery of EIGRP packets to all neighbors
Does not rely on TCP/IP to exchange routing information, as EIGRP is protocol-independent
RTP is a proprietary protocol
EIGRP can call on RTP to provide reliable or unreliable service as needed
Can simultaneously multicast and unicast to different peers, which allows for maximum efficiency

15. EIGRP Concepts EIGRP Packet Types
EIGRP uses hello packets
They discover, verify and rediscover neighbor routers
Hello packets are always sent unreliably
No acknowledgement is transmitted
Hello packets are sent at a fixed interval, depending on the interface’s bandwidth
Hello packets are sent to the multicast IP address
On low-speed networks (T1 or slower), hello packets are sent every 60 seconds; on faster networks they are sent every 5 seconds

16. EIGRP Concepts EIGRP Packet Types
Packets must be received within the hold time interval period to maintain a passive state, which is a reachable and operational status
If EIGRP does not receive a packet from a neighbor within the hold time, it considers that neighbor down
DUAL then reevaluates the routing table
By default, the hold time is three times the hello interval

17. EIGRP Concepts EIGRP Packet Types
EIGRP does not require that neighbors have the same hello intervals and dead intervals (OSPF does)
Neighbors learn about the times through the exchange of hello packets
They use the information to make stable relationships regardless of timer settings

18. EIGRP Concepts EIGRP Packet Types
EIGRP routers use acknowledgement packets to indicate receipt of EIGRP packets during a reliable exchange
RTP provides reliable communication
Acknowledgement packets are hello packets without data
Acknowledgement packets are unicast, hello packets are multicast
Acknowledgements can be attached to other kinds of EIGRP packets, such as reply packets

19. EIGRP Concepts EIGRP Packet Types
EIGRP uses update packets when a router discovers a new neighbor
Unicast packets are sent to the new neighbor so it can add to its topology table
More than one update packet may be needed
Update packets are also used when a router detects a topology change
The router sends a reliable multicast to all neighbors

20. EIGRP Concepts EIGRP Packet Types
EIGRP routers use query packets when they need specific information from one or all neighbors
If a router loses its successor route and cannot find a feasible successor:
DUAL places the route in active state
A query is multicast to all neighbors in an attempt to locate a successor
Neighbors send replies indicating whether or not they have a successor

21. EIGRP Configuration Basic EIGRP Configuration
The router eigrp and network commands create an EIGRP routing process:
Router(config)#router eigrp AS-number
Router(config)#network network-number
Simple EIGRP Network

22. EIGRP Configuration Basic EIGRP Configuration

23. EIGRP Configuration Basic EIGRP Configuration
Router A Command Descriptions from Previous Slide

24. EIGRP Configuration Basic EIGRP Configuration
When using serial links with EIGRP, the bandwidth setting must be configured on the interface
Otherwise EIGRP assumes the default bandwidth and not the true bandwidth
If the link is slower, the routers might not converge
To set the bandwidth use this syntax:
Router(config-if)#bandwidth kbps
Cisco also recommends adding the following command to all EIGRP configurations:
Router(conf-router)#eigrp log-neighbor-changes
Monitors stability of routing system

25. EIGRP Configuration Configuring EIGRP Summarization
Effect of Autosummarization is to Summarize at the Classful Boundary

26. EIGRP Configuration Configuring EIGRP Summarization
In many instances, autosummarization is not the preferred option
Case of discontiguous subnets
Autosummarization prevents routers from learning about discontiguous networks
With autosummarization turned off, EIGRP routers will advertise subnets
Use this command syntax to turn off autosummarization:
Router(config-router)#no auto-summary

27. EIGRP Configuration Configuring EIGRP Summarization
With EIGRP, a summary address can be manually configured on a per-interface basis (use the following syntax, all on one command line):
Router(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance

28. EIGRP Configuration Configuring EIGRP Summarization
Discontiguous Subnets With and Without Autosummarization

29. EIGRP Configuration Configuring EIGRP Summarization
By default, EIGRP summary routes have an administrative distance of 5; can be configured for any distance from 1 to 255
Granular Routing Updates with Interface Summarization

30. EIGRP Configuration Configuring EIGRP Summarization
Using Interface Summarization with EIGRP
Autosummarization is turned off with the
no auto-summary command

31. EIGRP Configuration Verifying the EIGRP Configuration
Numerous show Commands Verify EIGRP Configuration

32. Troubleshooting Routing Protocols
A foundation for building a problem-solving process:
When analyzing a network failure, make a clear problem statement
Gather the facts needed to help isolate possible causes
Consider possible problems based on gathered facts
Create an action plan based on potential problems
Implement the action plan
Analyze the results to determine if the problem has been solved
If not, create an action plan based on the next most likely problem on the list
After the actual cause of the problem is identified, solve it

33. Troubleshooting Routing Protocols
Cisco routers provide integrated commands to help in troubleshooting:
The show commands help monitor installation behavior, normal network behavior, and isolate problem areas
The debug commands assist in the isolation of protocol and configuration problems
TCP/IP tools such as ping, traceroute and Telnet help isolate the OSI layer where the problem exists

34. Troubleshooting Routing Protocols Troubleshooting RIP
The most common problem in RIP that prevents RIP routes from being advertised is VLSM
RIPv1 does not support VLSM
If RIP routes are not being advertised, check these:
Layer 1 or Layer 2 connectivity issues
VLSM subnetting is configured (can’t be used with RIPv1)
Mismatched RIPv1 and RIPv2 routing configurations exist
Network statements are missing or incorrectly assigned
Outgoing interface is down
Advertised network interface is down

35. Troubleshooting Routing Protocols Troubleshooting RIP
Use these commands to help with RIP troubleshooting:
The debug ip rip command displays information on RIP routing transactions
Use the no debug ip rip, undebug all, or u all commands to turn off debugging
Sample RIP Network for Troubleshooting

36. Troubleshooting Routing Protocols Troubleshooting RIP
Troubleshooting with debug ip rip
Might see entries such as:
RIP: broadcasting general request on Ethernet0

37. Troubleshooting Routing Protocols Troubleshooting EIGRP
Reasons why EIGRP might not work properly:
Layer 1 or Layer 2 connectivity issues
AS numbers on EIGRP routers are mismatched
Link might be congested or down
Outgoing interface is down
Advertised network interface is down
Autosummarization is enabled on routers with discontiguous subnets
Use the no auto-summary command to disable automatic network summarization
One of the most common reasons for a missing EIGRP neighbor is a failure on the actual link

38. Troubleshooting Routing Protocols Troubleshooting EIGRP
Using debug ip eigrp to Troubleshoot

39. Troubleshooting Routing Protocols Troubleshooting EIGRP
The debug ip eigrp Output Fields

40. Troubleshooting Routing Protocols Troubleshooting EIGRP
The debug ip eigrp command generates a lot of output, use it only when network traffic is light
The debug eigrp fsm command is also used for EIGRP debugging
Displays information on DUAL feasible successor maps
Helps engineers analyze packets that are sent and received on an interface

41. Troubleshooting Routing Protocols Troubleshooting OSPF
The majority of problems with OSPF relate to formation of adjacencies and synchronization of link-state databases
Output from the debug ip ospf events Command

42. Troubleshooting Routing Protocols Troubleshooting OSPF
The debug ip ospf events output seen in the previous slide might appear if:
The subnet masks for routers on the same network do not match
The OSPF hello interval for the router does not match that configured for a neighbor
The OSPF dead interval does not match that configured for a neighbor
If a router configured for OSPF routing does not see an OSPF neighbor on an attached network, perform these tasks:
Make sure both routers have been configured with the same IP mask, OSPF hello interval, and OSPF dead interval
Make sure that both neighbors are part of the same area type

43. Troubleshooting Routing Protocols Troubleshooting OSPF
To Provide Detailed Output Relating to OSPF, Use the
debug ip ospf packet command

44. Troubleshooting Routing Protocols Troubleshooting OSPF
Output Fields for the debug ip ospf packet Command

45. Summary EIGRP characteristics
Interior Gateway Protocol
Quick convergence times with minimum traffic
Enhanced version of IGRP; Cisco proprietary protocol
EIGRP and IGRP are compatible, with some differences
EIGRP offers multiprotocol support
EIGRP uses same metric as IGRP
EIGRP uses a multiplier of 256 which makes the EIGRP metrics larger that IGRP metrics

46. Summary EIGRP routers keep route and topology information in RAM
Information is saved in three tables
Neighbor table lists adjacent routers
Topology table has all the routes in the AS
The routing table holds the best routes to a destination
DUAL takes the information in the neighbor and topology tables and calculates the lowest cost to each destination
This is called the successor route
The backup route is called the feasible successor

47. Summary EIGRP is a balanced hybrid routing protocol
Acts as a link-state protocol when updating neighbors and maintaining routing information
Advantages include:
Rapid convergence
Efficient use of bandwidth
Support for VLSM and CIDR
Support for multiple network layers
Independence from routed protocols

48. Summary DUAL results in the fast convergence of EIGRP
Each router constructs a topology table
The topology table identifies the routing protocol (EIGRP), the lowest cost of the route (the feasible distance)
The cost of the route as reported by the neighbor (the reported distance)
EIGRP commands vary depending on which routed protocol is used
The network command configures connected networks
EIGRP automatically summarizes routes at classful boundaries prior to IOS Release 12.2(8)T
If discontiguous subnets exist, autosummarization must be turned off

49. Summary
Manual summarization is done at the interface level with the ip summary-address eigrp
The show ip eigrp command can verify the EIGRP configuration
The debug ip eigrp command can display information on eigrp packets and troubleshoot EIGRP
Troubleshooting can be approached with an eight-step troubleshooting methodology
Network engineers rely on show and debug commands to troubleshoot routing protocols
RIP, IGRP, EIGRP, and OSPF have their own set of debug commands tailored for troubleshooting