CompTIA Network+
EXAM NUMBER: N10-006
Section 4.0: Troubleshooting
4.1 – Network Troubleshooting
Methodology
Network Troubleshooting Methodology
Identify the Problem
• Information gathering
• Get as much details and
information as we can
• If possible, duplicate the issue
• Identify the symptoms
• Maybe many symptoms
• Question the user
• Ask open question – to get more
details
• Ask closed questions – to get to
the point quicker
• Determine has anything changed
• Any hardware or software changes
• Does it affect anyone else
• Consider backing up the data
• Fix many issues individually
• Break problems into smaller
chunks
Establish a Theory
• Start with obvious
• Consider the not-so-obvious
• Make a list of all the possible causes
• Start with the easy theories
• And the least difficult to test
• Then progress to the hard ones
• You might want to ask fellow colleagues if
you are stuck with establishing a theory
• Top-to-bottom/
• bottom-to-top OSI model
• - Divide and conquer
Test the theory
• Confirm the theory
• Determine next steps to resolve the problem
• Test the individual theories you came up
with in your previous list
• Starting with the easiest test in your theory in
a lab environment to see if it works
• If the first theory does not work then more
onto the next possible theory on your list
• If none of them work you need to re-establish
a new theory – ask more questions
• Call an expert – may need to be escalated
Establish a plan of action / Implement the solution
• Build the plan for the fix
• How can we fix the issue with the minimum impact to
business
• Consider out of office repairs if possible
• Identify the potential side effects
• Every plan can go wrong
• Have a plan B or even C
• Implement the solution
• Fix the issue – during the change control window
• Escalate the issue – maybe a third party may need to get
involved
Verify full system functionality
• Make sure your fix did not result in something else failing
• Fixes can result in other things failing
• Testing should be part of your plan
• Get the customer to confirm everything is working
• Implement preventative measures
• Suggest security measure and user training
• Avoid the same issue in the future
Document findings
• Document how you fixed the issue
• Document all the information on the case
• Store information in a knowledge base
• This can be shared with all staff
• Searchable database
• Contain help desk notes
4.2 Given a scenario, analyze and
interpret the
output of troubleshooting tools.
Command Line Tools
• Ipconfig and ifconfig
• Ping your local router / gateway
• Determine TCP/IP and network adapter information
• Ipconfig – windows TCP/IP configuration
• Ifconfig – Linux interface configuration
• Display three key pieces of information
• Ipaddress
• Subnet mask
• Default gateway
• More information is displayed with ipconfig/all
• MAC,DNS,DHCP, Lease information etc.
Command Line Tools - Netstat
• Network statistics
• Supported in many Operating systems
• Netstat –a
• Show all active connections
• Netstat – b
• Shows binaries
• Every application which is using the internet
• Netstat – n
• it will perform that same dash A function
• Does no resolve names
Command Line Tools - Ping
• Test the connection between two devices
• Determine round-trip time
• Uses Internet Control Message Protocol (ICMP) – this displays information to
the user
• Can be used to ping any devices with a NIC card wired or wirelessly
• Made in 1983
• The sound made by a sonar
Command Line Tools - Traceroute
• Determine the route a packet take to is destination
• Map the entire path
• Windows – tracert,
• POSIX – traceroute
• Will display the ICMP – time to live exceeded error message
• The time to live TTL refers to hops (routers), not seconds or minutes
• TTL=1 is the first router.
• Not all devices will reply with ICMP time exceed messages
• Some firewalls filter ICMP
• ICMP is low priority for many devices
Command Line Tools – nslookup / DIG
• Lookup information from DNS servers
• IP address, cache timers, canonical names etc.
• Nslookup
• Both windows and POSIX-based
• Lookup names and IP address
• Dig or DiG (Domain Information Groper)
• More advanced domain information
• Preferred over nslookup
• Can have in windows but needs installing
• NBTStat
• Old version of DNS (Microsoft)
• NetBIOS over TCP/IP
• No longer used
Command Line Tools - ARP
• Address resolution protocol
• Determines the MAC address based on the IP
address
• Arp -a
• Display information on all the MAC address
that have communicated with your address
(NIC)
• Every switch has a list of address
• Use the list to query MAC information
• Mac address lookup table
Command Line Tools - Pathping
• Combines ping and traceroute
• Included in windows NT and later
• Traces the route for one destination to another
• Builds a map
• Second phase
• Measures round trip time and packet loss at each hop
• Pinging IPv6 address
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To ping IPv6 add a -6 at the end of the command
Ping -6 = force ping ipv6 address
Ping -4 = force ping an IPv4 address
Works with tracert -6, traceroute6, -6
Physical Testing Tools
• Cable Tester
• Used to test the wiring and connector has been crimped properly
• Can identify missing pins or crossed wires
• Does not provide any detailed information
• TDR / OTDR – Optical / Time Domain Reflector
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Give information on crosstalk, signal loss and detailed analysis – Line Tester
OTDR are quite expensive – Light Meter
You will need additional training in order to use it
Resolving issue at layer 1
Certify the cable plant – validating the installation - Certifier
Detects breaks in the cable – where is the break approx.
Physical Testing Tools
• Multi-meter
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Checks for power coming form a power source
AC voltage – checking the wall outlet voltage
DC voltage – PC Power supply output voltage
CMOS battery power etc.
Tests for Volts, Amps, Ohms
• Continuity tester
• Cable connectivity
• Test individual pins in a cable to see if a signal is
running through it
• Fuse statues
• wire mapping
Physical Testing Tools
• Toner Probe
• Also known as a fox and hound
• Used to trace one end of the cable to the other side
• Used to detect the wire ends for one side of the wall to
another if there are a lot of wires
• Tone generator
• Puts an analogue sound on the wire
• Inductive probe
• Don’t need to touch the cooper wire
• Hear a tone through a small speaker
• This will trace your cable
• Connect the tone generator to the wire
• Can combine various ports in one device
• Modular jack, Coax, Punch down connectors
https://www.youtube.com/watch?v=9gTA5kuL8YA
Web-based Troubleshooting Tools
• Speed test sites
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Websites which test your network speeds
Transferring a file and then measure the throughput
Provide a useful pre and post change analysis
Test, install firewalls / packet shaper
Measure at different time of the day
Not all site are the same – number of servers (Point of
presence – POP)
• Bandwidth at the POP
• Examples
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Speedtest.net
Speedof.me
Testmy.net
ISP sites
• www.att.com/speedtest
Looking glass sites
• Routing table configuration is challenging and complex
• ISP have massive routing tables spread over a large geographical area
• Which contain a lot of equipment and technologies
• Looking glass sites will enable a user to test connectivity from one site
to another
Protocol Analysers / Wi-Fi Analysers
• Are used to capture traffic either wired or wirelessly
• Capture and display the network traffic
• Display packet by packet
• Use a physical tap or even redirect switch traffic
• Some popular protocol analysers are
• Wireshark – popular open source option
• Wi-Fi packet analysers
• Captures wireless information in the air
• Sometimes need specialised equipment , adapters, chipsets and drivers
• Need to be quiet – can’t hear the network if you are busy transmitting
4.3 Given a scenario,
troubleshoot and resolve
common wireless issues.
Wireless signals
• Radio signal
• 2.4Ghz and 5 GHz
• Susceptible to interference
• External sources, mostly man made
• Conflicts between Wi-Fi networks – using the same frequency
• Signal strength
• Transmitting signal, transmitting antenna, receiving antenna etc.
• Incorrect channel
• Might need to change from automatic to manual
• Bounce and latency
• Multi-path interference, flat surfaces
• Incorrect access point placement
• Locate closer to the user
• Avoid placing in areas of high interference
Wireless signals
• Equipment causing interference
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Microwaves
Baby monitors
Cordless phones, high power sources
Florescent lights, Bluetooth
• Problems in multi-tenant building
• Measurement
• Netstat –e
• displays interface statistics
• Sent, received etc
• Performance monitor
• Saturation
• Device saturation - Too many devices on
one wireless network
• Bandwidth saturation – large data transfers
hogging the network
• Common in conferences, airports, hotels
• Untested Updates
• When wireless firmware updates
• Can have a dramatic effect on performance
• Issue with compatibility with chipsets from
other devices
Troubleshooting Wireless Configurations
• SSID mismatch
• Need to connect to the correct AP
• Avoid open networks – security risk
• Incompatibilities
• 802.11b vs 802.11g vs 802.11n
• Encryption type
• WPA, WPA2, WPA enterprise etc.
• Encryption keys
• Rogue Access point
• Third party gaining access to your network using another AP with the same
settings configured
Troubleshooting Wireless Configurations
• Power Levels
• Want to limit the power level of you access point only cover the area you
need
• Reduce war driving attacks
• Wrong antenna type
• Is it omnidirectional (Dipole) or directional
• MIMO
• Multiple-in multiple-out
• The quality of the signal is important – enable or disable the antennas
• Help to refine the signal
Troubleshooting Wireless Configurations
• LWAPP
• Lightweight Access Point Protocol
• Cisco proprietary – CAPWAP is an RFC standard, based on LWAPP
• Manage multiple access points simultaneously
• Thick Access point
• The access point handles most of the wireless tasks
• All of configuration settings.
• Connected to a switch which is not wireless-aware
• Thin Access Point
• Basic 802.11 wireless
• The intelligence is in the switch
• Less expensive
Troubleshooting Wireless Configurations
• Environmental factors
• Concrete walls
• 2.4GHz goes through concrete better then 5GHz
• Windows / Mirrors
• Specialised film can cause signal loss
• Metal Studs
• Reflect the signal, reduce wireless range
Troubleshooting Wireless Configurations
• Wireless standard issues
• Throughput
• Maximum theoretical throughput will vary widely
• Frequency
• Sometimes 2.4GHz will be faster then 5GHz and vice versa
• Distance
• Range can be affected or improved with a combination of antennas
• Channels
• Different countries use different channels
• Non-overlapping channel from your neighbour
4.4 – Given a scenario,
troubleshoot and resolve
common copper cable issues.
Troubleshooting Copper Cables - Open and shorts
• A Short Circuit
• Break in the cable and two connection are touching
• Wires inside of a cable or connection
• An open circuit
• A Break in the connection
• Will result in interruption of the signal
• Cutting a cord
• You may need to have a look inside the cable
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Short or closed?
The wire has to be moved just the right way
Wiggle it here and there
Replace the cable with the short or open – difficult to repair
• Advanced troubleshooting
• Time domain reflector (TDR)
Wiring standards
• There are two standards for Ethernet
• EIA/TIA -568-B standard
• Eight conductors 100-ohm balanced twisted pair
• T568A and T568B are different pin assignment for 8P8C
• Straight-through cable - T568A- T568A or T568B- T568B
• Crossover cable - T568A - T568B
Crosstalk (XT)
• Signal on one circuit affects another circuit in a bad way
• Leaking of signals
• Data from one cable has jumped onto another cable causing
gobbledegook
• Measure XT with advanced cable testers
• Near End Crosstalk (NEXT)
• Interference measured at the transmitting end – the near end
• Far end crosstalk (FEXT)
• Interference measured away from the transmitter
Troubleshooting crosstalk
• To stop crosstalk
• Incorrect termination
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Always check your crimping of the connector to the wire
Maintain the twists in your Ethernet cable – this help against crosstalk
Category 6A recommended against crosstalk – increase the cable diameter
Test and certify your installation
Solve issues before they become big
Troubleshooting Signal Loss
• Attenuation
• Loss of signal as it moves down the wire over a long distance
• Electrical signals through copper, light through fibre, radio waves in the air
• Signal strength is measure in decibels (dB)
• Signal strength ratio measurement – one-tenth of a bel
• Logarithmic scale
• Add and subtract losses and gain
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3 dB = 2x the signal
10 dB = 10x the signal
20 dB = 100x the signal
30 dB = 1000x the signal
Calculate the dB loss . Symptoms
• Signal loss calculation: Total loss through 1km fibre
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Add the loss through each section
1 km fibre =3.5dB (Patch panel at each end = 0.5dB)
X2 patch panel = 1dB
Total link loss = 4.5dB
• Symptoms of dB loss
• No connectivity or signal
• Intermittent connectivity
• Just enough signal to sync the link
• Poor performance – signal too weak, data corruption
• Test each connection – test distance and signal loss
• TDR and OTDR
Cable placement
• Separate you fibre and copper cables
• Cooper bundles can crush the fibre
• Install the highest category possible
• Future proofing
• Place data centre in the middle of the building
• Centralise your wiring plant
• Reduces cable lengths
• Keep cabling neat and tidy
• Cable ties
• trunking
Avoiding EMI and interference
• Cabling handing
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Do not twist the cables
Don’t pull and stretch
Watch your bend radius
Don’t use staples, don’t over tighten your cable ties
• EMI and inference with copper cables
• Avoid power cords, fluorescent lights, electrical cables, and fire prevention
components
Troubleshooting Network Cabling
• Cabling issues
• No connection – no transfer happening
• Is there any link lights
• Is the cable crimped or punched in properly
• Swap the cable with a well known one – connectors as well
• Slow throughput – does not work very well
• Check the link light
• Cable crimped might be damaged
• Swap the cable
• Intermittent connectivity
• Check for link light flickering
• Swap the cable
Troubleshooting Network Cabling
• Split pair
• A wiring mistake
• You may have create a wire map pass which states everything is ok
• Performance will be impacted
• Suffers from near-end crosstalk (NEXT)
• The twist in the cable has cross over onto another wire
TX/RX reversal troubleshooting
• An Ethernet crossover cable will swap the transmission end to the
receiving in
• You can not connect a crossover cable from a PC to a switch
• If a switch supports the Auto-MIDX this will correct the issue automatically
• Locate reversal location
• Often at a punch down patch panel
• Easy to find with a wire map
• SFPs or GBIC
• Fibre optic connectors which swap over the transmit and receiver – crossover
convertors
• Small form-factor pluggable (SFP) / Gigabit interface converter
4.5 Given a scenario,
troubleshoot and resolve
common fiber cable issues.
Troubleshooting Fiber Issues
• Attenuation and dB loss
• Splices and terminations – cutting the cable and placing in the connector
• Every time you splice and terminate – dB loss occurs
• The connector should be clear
• No scratches, no dirt
• Needs to be clean or otherwise re-terminate
• Fibre may be broken at the connector or along the fibre
• Test with an OTDR
• Check your SFP+ or GBIC – not all modules work exactly the same
• Certain manufacturers recommend a certain type of brand or module
Troubleshooting Fiber Issues
• Check you fibre types
• Equipment expect a certain type of fibre cable, don’t mix and match fibre
types
• Don’t mix single –mode and multimode cables together
• Monitor the Statistics
• Check for CRC errors on the connection (cyclic redundancy check)
• Connector mismatch
• When connecting two fibre cables together using a fibre coupler
• Make sure it is of good quality
Troubleshooting Fibre Issues
• Bend Radius
• Fibre is glass
• You can break it, if the cable has been bent too much
• The bend radius will vary between cable designs
• Will have a minimum bend radius
• Microbending
• Something sitting on the fibre cable placing pressure on it.
• Macrobending
• The actual bending of the cable to go round corners etc.
• Light leaks through the cladding if bent too much
Fibre distance limitations
• Signal decrease over time
• Must have enough light left at the end other of the cable
• The amount needed is determined by the equipment
• Multimode fibre
• Short distances, used in buildings
• Maximum distance is 600 metres (2000 feet)
• Single mode cable
• Long distance
• Distance of 100 kilometres (100, 000 metres)
4.6 Given a scenario,
troubleshoot and resolve
common network issues.
Troubleshooting IP Configurations
• IP configuration issues
• Ping to local IP address
• Ping outside IP address
• Viewing you ipconfig – Check against your documentation
• Ipaddress
• Subnet mask
• Default gateway
• Check IP configuration of the devices around you
• Use traceroute and ping commands – Ping local host, default gateway and external ip
address
• Duplicate IP address
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Static IP address has been set and conflict with the DHCP
Multiple DHCP servers will cause overlapping
Rogue DHCP server
Same IP address will cause intermittent issues
• Troubleshoot Duplicate IP address
• Ping your IP address, check your ARP table
• Find the MAC address in your switch MAC table
Troubleshooting IP Configurations
• DNS issues
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Check if you can ping the IP address and name of a web service
None work – internet is down
Ping works but browser doesn’t – problem with browser
Applications aren’t communicating – DNS resolution on the application has
failed
• Troubleshooting DNS
• Check your IP configuration to see if the DNS IP address is correct
• CMD > nslookup or dig to test
• Try using a different DNS server
Troubleshooting IP Configurations
• DHCP issues
• You can tell if the DHCP is offline if your computer has an APIPA address
• 169.254.x.x
• Automatic Private IP address
• DHCP troubleshooting
• Check the network connection with the DHCP server
• DHCP server may have issues – address pool has run out
• DHCP server may be down – or disabled (Static IP address will be self
assigned)
Troubleshooting Broadcast Storms
• Broadcasting is one device communicating with all devices
of the subnet
• Broadcasting is general does not go through a router
• VLANs configured, a broadcast will not pass through onto
another VLAN
• Large amount of broadcasts impacting all of the devices
• Slow down your network
• Troubleshooting Broadcast storms
• Packet capture – identify the source
• Use a protocol analyser – see how many broadcasts are going
though the network
• Separate the network into smaller broadcast domains
• Change one large subnet into many smaller routed subnets
Troubleshooting Switching Loops
• Spanning tree is used to cure switching loops
• Switches communicate by MAC address
• Every device has its own address
• Every packet is directed
• Broadcast and Multicast are sent to all
• Broadcast repeated to all switch ports
• Switch does not know that a loop has occurred
• IP has TTL (time to live)
Resolving Switching loops
17.23.15.89
Switch 2
Switch 1
Router
192.168.0.1
Switch 3
Troubleshooting Interface Configurations
• Poor throughput
• Very inconsistent, easily reproducible
• Slow transfer speeds
• No connectivity
• No link lights, no activity lights
• Automatic or Manual Configuration (NIC)
• Manually set speed on the NIC or have it automatically – duplex or half duplex
• Speed must be sync and running the same on both sides
• Duplex mismatched – if speeds differ on both ends – check lights on NIC
• VLAN Configuration
• Link light will be working but can not communicate outside of the subnet
• Verify two-way traffic
• End to end communication is occurring
Incorrect VLAN assignment
• Sometime hard to troubleshoot
• Virtual network configured by the switch
• A device might be incorrectly configured
• Given wrong IP address in the wrong Subnet
• The device will not be able to communicate with anyone
• This can be resolved by the DCHP server giving you the right information
• Troubleshooting VLAN assignments
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Check documentation – compared with switch configuration
Verify IP addressing – is the correct IP address in the correct subnet
Confirm trunk configuration – Is the VLAN part of the trunk
Is the switch port configured for a trunk on both sides
• Change the VLAN configuration and update client IP address
Troubleshooting Network Connectivity
• Many devices have both wired and wireless connectivity options
• Operating systems can choose whether to use wired or wireless
• Internal determination to see what is best
• Might use routing table and determine what route will be best to use for that
particular interface to send traffic
• Disable one interface, modify the routing table
• Missing IP routes
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Seen when network link is lost
WAN outage or internet outage – “No route to host”
Packets are dropped at the router
Check the router table for more details
Discovering neighbour devices
• Process of connecting to your neighbours devices
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Useful for troubleshooting
Connect to local devices on your subnet
Check if you can ping your local default gateway
Ping other devices on your network
Use third party tool
• Nmap, IP scanners, wireless scanners
• Windows network
Troubleshooting Mismatched MTUs
• Maximum transmission unit. – largest amount of IP packet
information that could be sent without fragmentation
• Fragmentation can slow down the network
• Lose a fragment and entire packet needs to be resent
• Requires overhead along the path
• Troubleshooting
• MTU sizes are normally configured once – administrator
• If you set packets with don’t fragment (DF) set – router will respond back and
tell you to fragment
• Ping with DF and force a maximum size of 1472 bytes
Troubleshooting NIC Teaming
• Uses multiple network interface cards in a single device
• Provides load balancing / Fail over (LBFO)
• Aggregate bandwidth, redundant paths
• Multiple network adaptors
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Look like a single adaptor
Integrate with switches
NICs will talk to each other using multicast not broadcast
Fails over when NIC doesn’t respond
• Active-active vs. active-passive
• Active-active – Two servers sharing the load – if one fails the other takes on both
loads
• Active-passive – a backup server which kicks if the main servers fails to continue the
work
4.7 Given a scenario,
troubleshoot and resolve
common security issues.
Troubleshooting Firewall Security Issues
• If you have issue with your configured firewall
• Check the management interface
• Check the IP address, sub mask and default gateway
• Network configuration
• Virtual wire, L2, L3, confirm physical wiring
• Check your router tables
• Check logging options – local and syslog
• Check your security polices
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How are you protecting your data
Firewall security rules – top-down
Check the logs – denies are usually logged, check you rules
Go though your security polices
• Misconfigured ACL list
• Wrong setup, applications security has been misconfigured
Troubleshooting Operating System Security
Issues
• Make sure all patches and updates are applied
• Apply a service pack update – contains all updates
• Monthly updates – incrementally
• Use windows updates – Use the WSUS in an organisation
• Windows server updates services – centralised control over your updates
• Plan when you will deploy your updates to your clients – out of office
• MAC OS X – software updates – available on the Apple menu or app
store
• Linux – yum, apt-get, rpm, various GUI options
Malware / Denial of service
• Malicious software
• Can be dangerous on the network
• Include virus and worms
• Can be infected through a Trojan horse, emails, drive by download – visit a
web site and it automatically downloads
• Keep operating system up to date
• Denial of service will overload the servers
• Keep your systems patched
• Other attack will be DDOS, Zombie attack, botnets, Asymmetric threat
Wireless DOS attack
• Frequency Jamming
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Disrupt the spectrum
2,4GHz and 5GHz
The microwave oven effect – power overloads the signal
Caused by Rogue devices
• Protocol Vulnerabilities
• Disrupt the 802.11 protocol
• Flood the network with packets
• Send 802.11 disassociation frames to everyone on the network
• Troubleshooting
• Add encryption onto your access point
• Reputation-based filtering – filters bad traffic from bad places
Troubleshooting ICMP
• Ping of death
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Ping are normal 64 bytes
Send a ping greater than 65,536 bytes, crash a computer
Exploit a fragment reassembly bug
Mainly affects vulnerable legacy operating systems
Windows 95, MAC Os 7, Linux, Unix
• Unreachable Default gateway
• Always on your subnet
• Ping the default gateway, if it does not work verify the IP address
• Ping the outside interface of the gateway
ARP issues
• ARP will display the devices that you are communicating with
• Can use this method if ping is blocked, and you want to see if your device can
connect to another device
• Local subnet devices only – ARP does not go through a router
• Display the windows ARP cache – CMD > arp –a
• Compare the ARP cache with the physical MAC address
• If they don’t match there might be an issue.
Troubleshooting Malicious User Activities
• Don’t trust everyone
• If you detect malicious activity use a packet analyser to see what is
coming into your network
• Banner Grabbing
• What service is running on a devices
• Banner will provide you with more details – Service name, version,
manufacturer – you can then research yourself
Troubleshooting Authentication Issues
• Authentication points
• Domain login, VPN login, application logging
• Single database authentication server
• RADIUS or TACACS
• If it works or not – check security logs
• Common misconfigurations
• Incorrect authentication database address
• Incorrect, expired or lock credentials
• Firewall restrictions or packet filtering
Troubleshooting Authentication Issues
• User groups
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Users placed in the wrong user groups
Some groups will have more access then others
Easy to add or remove users
Formal tracking or change control process
Audit constantly – check who is on what group
• Default passwords and settings
• Change these immediately
• Backdoors
• Can be a way into your network which your didn't think about
• Placed by malware
• Some OS and apps had inbuilt backdoors – bad software
4.8 Given a scenario,
troubleshoot and resolve
common WAN issues.
Troubleshooting WAN Issues
• Physical problems
• WANs are out side of your immediate control
• Your ISP will provide the hardware and cabling for you
• WAN issues include, hardware failure, fibre cuts etc.
• If you experience any issue with you interface
• ISP can run a loopback test from their location to your home
• They will send a test packet to you, can see if they receive the same information back
• Interference
• Copper cables can be in an environment with lots of RF – heavy machine causes a lot
of interference
• Latency
• Non-terrestrial networks i.e. satellite suffers from high latency
Troubleshooting WAN Issues – Configuration
issues
• Split Horizon
• WAN protocol configuration issues
• Designed to prevent routing loops on the network
• Dynamic routers are used to advertise all the routes they know about to all
other routers they can connect to.
• This is constantly being advertised – causing duplication of information to the
same device
• Split horizon – the router determines what routes have been learned
over a particular interface and does not advertise back to the
originally location again.
Troubleshooting WAN Issues – Configuration
issues
• DNS issue
• DNS stops responding, the entire network will no longer be able to resolve
names into their IP addresses
• Slow DNS resolution will cause delays
• Always have multiple DNS options – load balancing
• Router Configurations
• You can configure routers speeds and routing tables to make sure they are
correct from one side of the connection to the other side
Troubleshooting Customer Premise
Equipment
• Demarc point
• The box outside your home whereby the ISP equipment goes into
• The point where the ISP responsibility ends and yours begins
• WAN provider, ISP provider
• Used at home, offices etc.
• In a building its usually in a central point.
• All the demarcations may be coming into a single room – off to the LANs
• Can simple be a RJ-45 jack on the wall
• You will connect this to you CPE (Customer premise equipment)
• Customers routers, CSU/DSU and anything else you have
• “Customer prem”
Smartjack
• More then just a simple interface
• Can be a circuit card in a chassis
• Built in diagnostics – loopback test
• Alarm indicators – configuration and status
• Network interface unit (NIU)
• The device that determines the demarc
• Network connection that creates that demarcation between the inside and
outside
CSU / DSU
• Channel Service Unit / Data Service Unit
• Sits between the router and the circuit
• CSU – connects to the network provider
• Connect the router to a digital circuit – such as a digital signal ISDN line
• DSU – connects to the data terminal equipment (DTE)
• Responsible for managing the interface with the DTE
• Some will have a jack on it to connect to a protocol analyser to see network statistics
• Physical device – or built into the router
• From the demarc
• RJ-48c wiring
• To the router
• Serial connector
• V.35
• RS-232
Copper line drivers and extenders
• Extend the range of copper wire
• Over the maximum range recommended
• Serial link, copper Ethernet
• Used by the ISP inside and outside of data centres
• Powered devices
• regenerates the signal
• Troubleshooting
• Perform extensive testing after the installation
• No power, no signal
• Bad power supply, noisy signal
Company Security Policies
• A security policy
• Every organisation has a different philosophy
• Block policies
• URL, applications, username /passwords
• Block everything
• Only allow certain traffic types – required administration
• Allow everything
• Then block only certain traffic
• More common
Fair access policy/utilization limits
• Throttling traffic
• Allow traffic, but limit the speed
• Controlled with firewalls, routers, QoS devices etc.
• Allow YouTube, but prioritise important apps
• Mission-critical applications will continue to work
• Fair Access Policy
• Service providers will provide a fair access to everyone
• Stop small percentages who use large amount of bandwidth
• QoS technology provides control down to the individual users.
Any Questions