NETWORK TROUBLESHOOTING
ACCESSING THE WAN – CHAPTER 8
SANDRA COLEMAN, CCNA, CCAI
Version 4.0
OBJECTIVES
•
Establish a network baseline
•
Describe troubleshooting methodologies and troubleshooting tools
•
Describe the common issues that occur during WAN implementation
•
Troubleshoot enterprise network implementation issues
ESTABLISH A NETWORK BASELINE
• When establishing a baseline, consider how a network has been designed and what
the expected performance for this network should be under normal operating
conditions.
DOCUMENTING YOUR NETWORK
Network topology diagram – should include symbols for
all devices and how they are connected.
DOCUMENTING YOUR NETWORK
End system documentation - hardware and software used in
end-system devices such as servers, network management
consoles, and desktop workstations. An incorrectly configured
end system can have a negative impact on the overall
performance of a network.
ESTABLISH A NETWORK BASELINE
stages of the network documentation process
DOCUMENTING YOUR NETWORK
• You don’t always have immediate access to every
device. Some devices you only have remote access
to.
• So, how do you discover information about them?
• Use these commands:
•Ping and/or telnet
•Show ip int brief
•Show ip route
•Show cdp neighbor detail (this will get you IP addresses..
From layer 1 to layer 3… YEAH!)
DOCUMENTING YOUR NETWORK
• Once you know everything, record the information about what you discovered
in the ENTIRE network into the appropriate place… even the remote locations
• Transfer that information from the network config tables to the topology
diagram.
• I had to so something similar to this on my CCNA exam. I was given access to
only 1 switch in an entire topology and had to find out IP and MAC addresses of
almost every other device. These are the commands I used!
ESTABLISH A NETWORK BASELINE
• Measuring the initial performance and availability of critical network devices
and links allows a network administrator to determine the difference between
abnormal behavior and proper network performance as the network grows or
traffic patterns change.
STEP 1. DETERMINE WHAT TYPES OF DATA TO COLLECT
• CPU utilization, and interface utilization is a good place to start.
STEP 2: IDENTIFY DEVICES AND PORTS OF INTEREST
Network device ports that connect to other network devices,
servers, key users, anything else considered critical to
operations.
STEP 3. DETERMINE THE BASELINE DURATION
This period should be at least seven days to capture any daily
or weekly trends. Weekly trends are just as important as daily
or hourly trends.
PERFORMANCE
A combination of manual data collection and simple
network protocol inspectors would do great. Use these
commands on mission critical devices.
TROUBLESHOOTING METHODOLOGIES AND TROUBLESHOOTING
TOOLS
• troubleshooting is a process that takes the greatest percentage their time. Using
efficient troubleshooting techniques shortens overall troubleshooting time
when working in a production environment.
DESCRIBE TROUBLESHOOTING METHODOLOGIES AND
TROUBLESHOOTING TOOLS
layered models, such as the OSI reference model or TCP/IP model, are used for
troubleshooting. Know how these layered models correspond to one another!
DESCRIBE TROUBLESHOOTING METHODOLOGIES AND
TROUBLESHOOTING TOOLS
BOTTOM-UP
• you start with the physical components of the network and move up through
the layers of the OSI model until the cause of the problem is identified. Most
problems are physical ones, so this works well.
TOP-DOWN
•Start with the end-user applications and move down through the
layers of the OSI model until the cause of the problem has been
identified.
•The disadvantage with the top-down approach is it requires
checking every network application until the possible cause of the
problem is found. Each conclusion and possibility must be
documented. and the challenge is to determine which application to
start examining first.
DIVIDE AND CONQUER
When you apply the divide-and-conquer approach toward
troubleshooting a networking problem, you select a layer
and test in both directions from the starting layer.
DESCRIBE TROUBLESHOOTING METHODOLOGIES AND
TROUBLESHOOTING TOOLS
• If the problem is outside the boundary of your control, for example, lost Internet
connectivity outside of the autonomous system, you need to contact an administrator
for the external system before gathering additional network symptoms.
QUESTIONS TO ASK USERS
Use effective questioning techniques. This way you will
get the information you need to effectively document the
symptoms of a problem.
SOFTWARE TROUBLESHOOTING TOOLS
• NMS tools – device-level monitoring, configuration, and fault
management tools. These tools can be used to investigate and correct
network problems. Examples: CiscoView, HP Openview, Solar Winds, and
What's Up Gold.
• Knowledge Bases - On-line network device vendor knowledge bases have
become indispensable sources of information
• Baselining tools – tools are available for Windows, Linux, AUX operating
systems. Help you with common baseling documentation tasks. For
example they can help you draw network diagrams, help you to keep
network software and hardware documentation up-to-date and help you
to cost-effectively measure baseline network bandwidth use.
• Protocol Analyzers - decodes the various protocol layers in a recorded
frame and presents this information in a relatively easy to use format.
Wireshark is a protocol analyzer.
HARDWARE TROUBLESHOOTING TOOLS
• Network Analysis Module - can be installed in Cisco Catalyst 6500 series
switches and Cisco 7600 series routers to provide a graphical
representation of traffic from local and remote switches and routers.
• Digital Multimeter – used to directly measure electrical values of voltage,
current, and resistance.
• Cable Tester –used to detect broken wires, crossed-over wiring, shorted
connections, and improperly paired connections.
• Cable Analyzer – est and certify copper and fiber cables for different
services and standards.
• Network Analyzer - By plugging the network analyzer in anywhere on the
network, a network engineer can see the switch port to which the device
is connected and the average and peak utilization. The analyzer can also
be used to discover VLAN configuration, identify top network talkers,
analyze network traffic, and view interface details.
DESCRIBE THE COMMON ISSUES THAT OCCUR DURING WAN
IMPLEMENTATION
• Steps for designing or
modifying a WAN
DESCRIBE THE COMMON ISSUES THAT OCCUR DURING WAN
IMPLEMENTATION
• Considerations for analyzing WAN traffic
DESCRIBE THE COMMON ISSUES THAT OCCUR DURING WAN
IMPLEMENTATION
• Common WAN connections
DESCRIBE THE COMMON ISSUES THAT OCCUR DURING WAN
IMPLEMENTATION
• Describe common WAN implementation issues
PHYSICAL NETWORK DIAGRAM
• depicts IP addresses, IP routes, devices such as firewalls and switches, device type,
model and manufacturer, OS version, cable type and identifier, cable specification,
connector type, cabling endpoints etc. to adequately troubleshoot.
LOGICAL NETWORK DIAGRAM
Includes Device identifiers, IP address and subnet,
Interface identifiers, Connection type, DLCI for virtual
circuits, Site-to-site VPNs, Routing protocols, Static routes,
Data-link protocols, WAN technologies used
PHYSICAL LAYER PROBLEMS
• Serial links reconfigured as
asynchronous instead of
synchronous, Incorrect clock
rate, Incorrect clock source,
Interface not turned on,
noise, attenuation, cable
faults, power-related
problems, CPU overload, etc.
DATA LINK LAYER PROBLEMS
• Encapsulation errors, address mapping errors, framing errors, STP errors or
loops. Go to online curriculum 8.4.3, page 3 and finish out this section.
NETWORK LAYER PROBLEMS
• Consider these things – has anything changed
recently? Is anyone currently working on the
network infrastructure?
• Connectivity issues – includes checking for layer 1
problems
• Neighbor Issues – have protocols that require an
adjacency formed one?
• Topology database – are there missing or
unexpected entries?
• Routing table – are there missing or unexpected
routes?
TRANSPORT LAYER PROBLEMS
NAT issues
DHCP
DNS
WINS
Inbound/outbound traffic
Incorrect NAT timers
TRANSPORT LAYER PROBLEMS
Be sure to check the order of the ACL statements.
This DOES matter!
APPLICATION LAYER PROBLEMS
Layer 7 protocols
Telnet, HTTP, FTP, TFTP,
SMTP, POP, DNS, NFS,
SNMP
APPLICATION LAYER ISSUES
• If ping works, layer 1 & 2 are functioning.
• Use extended ping – if it works, layer 3 is functioning.
• Continue until you solve the problem.
CCNA 4 IS OVER… YEAH! YOU SURVIVED!
• Study Guide – None
• Labs – Activity 8-1, pg. 284-285
• Online Test – Take by midnight, Sunday, April 21, 2013
• Test on this chapter will be the PT Skills Integration
Challenge. You have until April 23, 2013 to complete it and
send it to me. It is LONG, don’t wait until last minute. It
incorporates Semester 2,3,and 4.
• Hands-on Final – May 1-2, 2013
• We will practice hands on for the remainder of our days in
class.