5.7 - Troubleshooting Networks Flashcards
No network connectivity
Do you have a link light?
– Is it plugged in?
Ping loopback (127.0.0.1)
– Is the protocol stack working?
– Availability and intermittent connectivity
Ping local IP address
– Checks local configuration, adapter, and link signal
Ping default gateway
– Connectivity on the local network
Ping devices on router’s other side
– 8.8.8.8 or 9.9.9.9
Intermittent wireless connectivity
Interference
– Something else is using our frequency
Signal strength
– Transmitting signal, transmitting antenna,
receiving antenna, etc.
Incorrect channel
– Usually automatic; look for manual tuning
Bounce and latency
– Multipath interference; flat surfaces
Incorrect access point placement
– Locate close to the users
Wireless interference
Predictable
– Fluorescent lights
– Microwave ovens
– Cordless telephones
– High-power sources
Unpredictable
– Multi-tenant building
Measurements
– Signal to noise ratio (SNR)
– Performance Monitor
Signal to noise ratio (SNR)
Signal
– What you want
Noise
– What you don’t want
– Interference from other networks and devices
You want a very large ratio
– The same amount of signal to noise (1:1)
would be bad
Limited/no connectivity
Windows alert in the system tray
– “Limited or No connectivity”
– “No Internet Access”
Check the local IP address
– An APIPA address will only have local connectivity
If DHCP address is obtained,perform the ping tests
– Local gateway, remote IP address
Jitter
Most real-time media is sensitive to delay
– Data should arrive at regular intervals
– Voice communication, live video
If you miss a packet, there’s no retransmission
– There’s no time to “rewind” your phone call
Jitter is the time between frames
– Excessive jitter can cause you to miss information,
“choppy” voice calls
Poor VoIP quality
High speed and low latency
– Real-time applications are demanding
Check the Internet connection
– A speed test can identify slow links
Verify the local networking equipment
– An old router can cause significant problems
View the network performance
– A packet capture would be useful
Latency
A delay between the request and the response
– Waiting time
Some latency is expected and normal
– Laws of physics apply
Examine the response times at every step along the way
– This may require multiple measurement tools
Packet captures can provide detailed analysis
– Microsecond granularity
– Get captures from both sides
Port flapping
Network interface goes up and down
– Over and over again
Verify the cable
– Check the wiring
Move between switch interfaces
– Is the flapping associated with the switch
interface or the device?
Replace bad hardware or cables
– May require additional purchases
