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Eigrp neighborship troubleshooting


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Eigrp neighborship troubleshooting

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Eigrp neighborship troubleshooting

  1. 1. EIGRP Neighborship TroubleshootingAs was shown in the OSPF neighborship troubleshooting article earlier, there are anumber of things that need to be configured correctly for everything to end upworking as planned. This article takes a look at these requirements from theperspective of Enhanced Interior Gateway Routing Protocol (EIGRP) and shows thedifferent commands that can be used to ensure proper EIGRP neighborshipconfiguration and communications between devices.EIGRP Neighborship RequirementsFrom the perspective of EIGRP, there are a couple of things that must match for aEIGRP neighborship to establish; keep in mind that these are different from otherrouting protocols (like OSPF), these include: 1. The devices must be in the same autonomous system (AS) 2. The devices must have the same authentication configuration 3. The devices must have the same k-valuesEIGRP Neighborship Configuration Verification and TroubleshootingStarting from the top of the list, the interfaces connecting devices must be on thesame autonomous system. To display the various commands and what to look for,Figure 1 shows a simple lab has been setup with two devices that are connectedtogether via an Ethernet connection.Figure 1 - Simple LabThe first thing that is going to be checked by the EIGRP device is whether the remotedevice is in the same autonomous system. No other processing will occur on thedevice until both devices have been configured with the same area. Thetroubleshooting for this type of problem requires someone with access to theremote device; this is because there is nodebug command that can be used that willshow an obvious AS mismatch. The only way to confirm that this is the problem is toverify the configuration of the devices and verify the AS is the same on each. Figure 2and 3 below show the EIGRP configuration on both R1 and R2; R2 has beenconfigured with the incorrect AS (AS 1).
  2. 2. Figure 2 - Mismatched Autonomous Systems (R1)Figure 3 - Mismatched Autonomous Systems (R2)The second entry on the list was that each device must have matching authenticationconfiguration; before any other information is exchanged between the devices theymust agree on an authentication type (if any is configured). EIGRP has a number ofdifferent errors messages that are given depending on the specific authenticationbased failure. The message that is shown in Figure 4 is given when a local device thatis not configured with EIGRP authentication is attempting to communicate with aremote device that has an existing authentication configuration.
  3. 3. Figure 4 - Local Missing Authentication Configuration (Complete)The message that is shown in Figure 5 is given when the local device has beenpartially configured with EIGRP authentication. In this example, EIGRPauthentication has been configured on the connecting interface but the key chainhas not yet been configured (no live authentication keys).Figure 5 - Local Missing Authentication Configuration (No key chain configured)For the next couple of authentication examples, the local device has already beenconfigured correctly for EIGRP authentication but the remote device has not. Themessage that is shown in Figure 6 is given when a remote device has not beenconfigured with any authentication configuration.
  4. 4. Figure 6 - Remote Missing Authentication Configuration (Complete)The message shown in Figure 7 is given when the remote device has EIGRPauthentication configured but does not have a configuration that matched with thelocal configuration (commonly this is a key string mismatch).Figure 7 - Remote Authentication Configuration MismatchThe final entry on the list was that the k-values must match between thecommunicating devices. Typically, the default values are not changed but if they are,each of the neighboring devices must share the same values. The message that isshown in Figure 8 is given if a mismatch is detected between EIGRP devices;no debug command is required for this message to be displayed.
  5. 5. Figure 8 - k-value MismatchSummaryA neighborship is the first thing that must be established before any communicationwill happen between devices. Each of the different routing protocols has their ownrequirements that must be met before this neighborship will establish. This articletakes a look at the elements that must match for EIGRP neighborships to establishand what commands to use to troubleshoot which misconfiguration potentially exists.Hopefully, the information in this article, when committed to memory, will help infuture EIGRP configuration endeavors.More Related Cisco Networking Tips:How to Configure EIGRP on a Cisco Router?