CompTIA A+ 220-1201 (5.5 - Troubleshooting Networks)

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

Slow network speeds

• The network is slow!

- It's probably not the network

• Confirm end-to-end connectivity

- Ping or application login

- Validate with a speed test

• Evaluate connectivity on each network hop

- Utilization, errors, total throughput, filtering/ACLs,

etc.

• May require a packet capture

- The ultimate verification

Limited or 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

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

High 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

External 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

Authentication issues

• Access a resource

- Requires the proper credentials

- Username, password, other factors

• Verify an active session

- May need to be refreshed

- Logout and back in

• May be difficult to see

- Part of a service or background process

• Perform a packet capture

- Verify connectivity and look for errors

Intermittent Internet connectivity

• Determine the scope of the outage

- Ongoing pings

- Traceroute to a known location

- Speed tests

• External issues require external support

- Work directly with the Internet service provider (ISP)

- Have your contact and account information available

• Check your SLA

- Service level agreement