Data Center LAN Migration Guide - Juniper Networks

Data Center LAN Migration Guide
Troubleshooting
Introduction
The scope of this section is to provide an overview of common issues that might be encountered at different insertion
points when inserting Juniper platforms as a result of a trigger event (adding a new application or service to the
organization). This section won’t provide exhaustive troubleshooting details, however, we do describe the principal
recommended approaches to troubleshooting the most common issues and provide guidelines for identification,
isolation, and resolution.
Troubleshooting Overview
When investigating the root cause of a problem, it is important to determine the problem’s nature and analyze its
symptoms. When troubleshooting a problem, it is generally advisable to start at the most general level and work
progressively into the details, as needed. Using the OSI model as a reference, troubleshooting typically begins at the
lower layers (physical and data link) and works progressively up toward the application layer until the problem is found.
This approach tends to quickly identify what is working properly so that it can be eliminated from consideration, and
narrows the problem domain for quick problem identification and resolution.
The following list of questions provides a methodology on how to use clues and visible effects of a problem to reduce
the diagnostic time.
• Has the issue appeared just after a migration, a deployment of new network equipment, a new link connection, or
a configuration change? This is the context being presented in this Data Center LAN Migration Guide. The Method of
Procedure (MOP) detailing the steps of the operation in question should include the tasks to be performed to return
to the original state before the network event, should any abnormal conditions be identified. If any issue arises during
or after the operation that cannot be resolved in a timely manner, it may be necessary to roll back and disconnect
newly deployed equipment while the problem is researched and resolved. The decision to back out should be
made well in advance, prior to the expiration of the maintenance window. This type of problem is likely due to an
equipment misconfiguration or planning error.
• Does the problem have a local or a global impact on the network? The possible causes of a local problem may
likely be found at L1 or L2, or it could be related to an Ethernet switching issue at the access layer. An IP routing
problem may potentially have a global impact on networks, and the operator should focus its investigation on the
aggregation and core layer of the network.
• Is it an intermittent problem? When troubleshooting an intermittent problem, system logging and traceoptions
provide the primary debugging tools on Juniper Networks platforms, and can be focused on various protocol
mechanisms at various levels of detail. Events occurring in the network will cause the logging of state transitions
related to physical, logical, or protocols to local or remote files for analysis.
• Is it a total or partial loss of connectivity or is it a performance problem? All Juniper Networks platforms have
a common architecture in that there are separate control and forwarding planes. For connectivity issues, Juniper
recommends that you first focus on the control plane to verify routing and signaling states and then concentrate
on the forwarding or data plane, which is implemented in the forwarding hardware (Packet Forwarding Engine or
PFE). If network performance is adversely affected by packet loss, delays, and jitter impacting one or multiple traffic
types, the root cause is most likely related to network congestion, high link utilization, and packet queuing along the
traversed path.
56 Copyright © 2012, Juniper Networks, Inc.