Troubleshooting guide

8-3
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 8 Troubleshooting the Cisco Catalyst 6509
Redundancy
• Redundant Switch Fabrics (Catalyst 6500 Series only)
• Redundant power supply and cooling
• Redundant System Clocks
• Redundant Supervisors
• Redundant Uplinks
Troubleshooting the Switch
There are many ways to troubleshoot a switch. As the features of switches grow, the possible things that
can break also increase. If you develop an approach or test plan for troubleshooting, you will be better
off in the long run than if you just try a hit-and-miss approach. Here are some general suggestions for
making your troubleshooting more effective:
• Take the time to become familiar with normal switch operation. Cisco's web site has a tremendous
amount of technical information describing how their switches work, as mentioned in the previous
section. The configuration guides in particular are very helpful. Many cases are opened with Cisco's
TAC (Technical Assistance Center) that are solved with information from the product configuration
guides.
• For the more complex situations, have an accurate physical and logical map of your network. A
physical map shows how the devices and cables are connected. A logical map shows what segments
(VLANs) exist in your network, and which routers provide routing services to these segments. A
spanning tree map is highly useful for troubleshooting complex issues. Because of a switch's ability
to create different segments by implementing VLANs, the physical connections alone do not tell the
whole story; one has to know how the switches are configured to determine which segments
(VLANs) exist, and to know how they are logically connected.
• Have a plan. Some problems and solutions are obvious, some are not. The symptoms that you see in
your network may be the result of problems in another area or layer. Before jumping to conclusions,
try to verify in a structured way what is working and what is not. Since networks can be complex, it
is helpful to isolate possible problem domains. One way of doing this is by using the OSI seven-layer
model. For example: check the physical connections involved (layer 1), check connectivity issues
within the VLAN (layer 2), check connectivity issues across different VLANs (layer 3), etc.
Assuming a correct configuration on the switch, many of the problems you encounter will be related
to physical layer issues (physical ports and cabling). Today, switches are involved in layer 3 and 4
issues, incorporating intelligence to switch packets based on information derived from routers, or
by actually having routers living inside the switch (layer three or layer four switching).
• Do not assume a component is working without checking it first. This can save you a lot of wasted
time. For example, if a PC is not able to log in to a server across your network, there are many things
that could be wrong. Don't skip the basic things and assume something works - someone might have
changed something without telling you. It only takes a minute to check some of the basic things (for
example, that the ports involved are connected to the right place and active), which could save you
many wasted hours.
Troubleshooting Port Connectivity
If the port doesn't work, nothing works! Ports are the foundation of your switching network. Some ports have
special significance because of their location in the network, and the amount of traffic they carry. These
ports would include connections to other switches, routers, and servers. These ports can be more