Data Center LAN Migration Guide - Juniper Networks

Hardware
Data Center LAN Migration Guide
The first action to take when troubleshooting a problem and also before making any change in the network is to ensure
proper functionality and integrity of the network equipment and systems. A series of validation checks and inspection
tests should be completed to verify that the hardware and the software operate properly and there are not any fault
conditions. The following presents a list of “show commands” from the Junos OS CLI relative to this, as well as a brief
description of expected outcomes.
• show system boot-messages
Review the output and verify that no abnormal conditions or errors occurred during the booting process. POST (poweron
self-test) results are captured in the bootup message log and stored on the hard drive.
• show chassis hardware detail
Verify that all hardware appears in the output (i.e., routing engines, control boards, switch fabric boards, power
supplies, line cards, and physical ports). Verify that no hardware indicates a failure condition.
• show chassis alarms
Verify that there are no active alarms.
• show log messages
Search log for errors and failures and review the log for any abnormal conditions. The search can be narrowed to
specific keywords using the “grep” function.
• show system core-dumps
Verify any transient software failures. Junos OS under fatal fault condition will create a core file of the kernel and
processes in question for diagnostic analysis.
For more details on platform specifics, please refer to the Juniper technical documentation that can be found at:
www.juniper.net/techpubs.
OSI Layer 1: Physical Troubleshooting
An OSI Layer 1 problem or physical link failure can occur in any part of the network. Each media type has different
physical and logical properties and provides different diagnostic capabilities. Focus here will be on Ethernet, as it is
universally deployed in data centers at all tiers and in multiple flavors: GbE, 10GbE, copper, fiber, etc.
• show interface extensive command produces the most detailed and complete information about all interfaces. It
displays input and output errors for the interface displayed in multiple categories such as carrier transition, cyclic
redundancy check (CRC) errors, L3 incomplete errors, policed discard, L2 channel errors, static RAM (SRAM) errors,
packet drops, etc. It also contains interface status and setup information at both physical and logical layers. Ethernet
networks can present many symptoms, but troubleshooting can be helped by applying common principles: verify
media type, speed, fiber mode and length, interface and protocol maximum transmission unit (MTU), flow control
and link mode. The physical interface may have a link status of “up” because the physical link is operational with no
active alarm, but the logical interface has a link status of “down” because the data link layer cannot be established
end to end. If this occurs, refer to the next command.
• monitor interface provides real-time packets and byte counters as well as displaying error and alarm conditions.
After an equipment migration or a new link activation, the network operator should ping a locally connected host to
verify that the link and interface are operating correctly and monitor if there are any incrementing error counters. The
do-not-fragment flag in a ping test is a good tool to detect MTU problems which can adversely affect end-to-end
communication.
For 802.3ad aggregated Ethernet interfaces, we recommend enabling Link Aggregation Control Protocol (LACP) as a
dynamic bundling protocol to form one logical interface with multiple physical interfaces. LACP is designed to provide
link monitoring capabilities and fast failure detection over an Ethernet bundle connection.
Copyright © 2012, Juniper Networks, Inc. 57