As was shown in the OSPF
neighborship troubleshooting article earlier, there are a number of
things that need to be configured correctly for everything to end up working as
planned. This article takes a look at these requirements from the perspective
of Enhanced Interior Gateway Routing Protocol (EIGRP) and
shows the different commands that can be used to ensure proper EIGRP
neighborship configuration and communications between devices.
EIGRP Neighborship Requirements
From the perspective of EIGRP, there are a
couple of things that must match for a EIGRP neighborship to establish; keep in
mind that these are different from other routing protocols (like OSPF ), these
include:
- The devices must be in the same autonomous system (AS)
- The devices must have the same authentication configuration
- The devices must have the same k-values
EIGRP Neighborship Configuration
Verification and Troubleshooting
Starting from the top of the list, the
interfaces connecting devices must be on the same 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 connected together via an Ethernet connection.
Figure 1 - Simple Lab
The first thing that is going to be checked
by the EIGRP device is whether the remote device is in the same autonomous
system. No other processing will occur on the device until both devices have
been configured with the same area. The troubleshooting for this type of
problem requires someone with access to the remote device; this is because
there is nodebug command that can be used that will show an obvious
AS mismatch. The only way to confirm that this is the problem is to verify the
configuration of the devices and verify the AS is the same on each. Figure 2
and 3 below show the EIGRP configuration on both R1 and R2; R2 has been
configured with the incorrect AS (AS 1).
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 authentication configuration; before any other
information is exchanged between the devices they must agree on an
authentication type (if any is configured). EIGRP has a number of different
errors messages that are given depending on the specific authentication based
failure. The message that is shown in Figure 4 is given when a local device
that is not configured with EIGRP authentication is attempting to communicate
with a remote device that has an existing authentication configuration.
Figure 4 - Local Missing Authentication
Configuration (Complete)
The message that is shown in Figure 5 is
given when the local device has been partially configured with EIGRP
authentication. In this example, EIGRP authentication has been configured
on the connecting interface but the key chain has 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 been configured correctly for EIGRP
authentication but the remote device has not. The message that is shown in
Figure 6 is given when a remote device has not been configured with any
authentication configuration.
Figure 6 - Remote Missing Authentication
Configuration (Complete)
The message shown in Figure 7 is given when
the remote device has EIGRP authentication configured but does not have a
configuration that matched with the local configuration (commonly this is a key
string mismatch).
Figure 7 - Remote Authentication
Configuration Mismatch
The final entry on the list was that
the k-values must match between the communicating 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 is shown in
Figure 8 is given if a mismatch is detected between EIGRP devices; no debug command
is required for this message to be displayed.
Figure 8 - k-value Mismatch
Summary
A neighborship is the first thing that must
be established before any communication will happen between devices. Each of
the different routing protocols has their own requirements that must be met
before this neighborship will establish. This article takes a look at the
elements that must match for EIGRP neighborships to establish and what commands
to use to troubleshoot which misconfiguration potentially exists. Hopefully,
the information in this article, when committed to memory, will help in future
EIGRP configuration endeavors.
---http://www.petri.co.il/eigrp-neighborship-troubleshooting.htm
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