Trouble-shooting 5.7 - networks (wired/wireless)

Question 1

command line: ipconfig/ifconfig

Answer 1

displays TCP/IP configuration of a device

Question 2

command line: nbtstat

Answer 2

displays netBIOS info

Question 3

command line: net

Answer 3

manages network activity & settings eg print jobs, ntwk users, etc

Question 4

command line: netdom

Answer 4

to do with Windows domains

Question 5

command line: nslookup

Answer 5

checks DNS record eg for domain names, IP address mapping

Question 6

command line: ping

Answer 6

test connectivity between 2 devices

Question 7

command line: tracert

Answer 7

traces a packet’s path through a network; incl name & IP address of each device

Question 8

no connectivity

Answer 8

computer/network hardware - check cables, network adaptor incl its config. Check wireless card & its confg

Question 9

SSID / SSID not found

Answer 9

System Set Identifier (SSID) is the name used to identify a wireless network to which you wish to connect. SSID configuration is found in wireless settings.
*SSID not found – usually due to the wireless access point being turned off or the SSID being changed
- reboot the wireless access point
- check the wireless access point to ensure that it is using the same SSID

Question 10

No connectivity

Answer 10

either the computer’s hardware or the network hardware. Check:
- the network cabling
- network adapter
- configuration of the network adapter.
For a wireless network, check:
- the wireless card and its config

Question 11

APIPA/link-local address

Answer 11

Automatic Private IP Addressing (APIPA)
- is used when a computer cannot communicate with a DHCP server. If a computer has been issued an APIPA address, the computer will be unable to communicate with computers that have been issued addresses by the DHCP server
check:
- DHCP server is functional
- DHCP server has enough IP addresses for its clients’ needs
- all routers function as DHCP relay agents
- ensure that the computer’s hardware is functional and allows it to connect to the network.
*A link-local address is IPv6’s version of APIPA. As with APIPA, a link-local address will only allow the client computer to connect to computers and other devices on the same subnet.

Question 12

Limited connectivity

Answer 12

When a computer can connect to the network but cannot access a specific resource on the network:
- could be because the user does not have permission to access the resource
- If you can ping the resource but cannot access the resource by its host name, the DNS server could be down
- The problem could lie with the remote resource. See if other computers can connect to it.

Question 13

Local connectivity only

Answer 13

Can connect to local resources but not to resources outside the local subnet:
- incorrect subnet mask
- incorrect default gateway address, or a router problem
- Check the TCP/IP settings for the computer’s NIC
- Check the connectivity to the router.

Question 14

Intermittent connectivity

Answer 14

hardware or software related:
- Check the network cable
- check the NIC and its settings
- Ensure that the DHCP and DNS servers are fully functional
- if using wireless, check for radio frequency interference (RFI).

Question 15

IP conflict

Answer 15

IP address is duplicated on the network often where static IP addresses are used
- locate one of the computers involved in the conflict situation and change its IP address
- If the computers are both using dynamic addressing, you can use the ipconfig /release command on one of the computers

Question 16

Slow transfer speeds

Answer 16

• interference
• incorrect cabling
• malfunctioning NIC
• router or switch misconfiguration
  If only one client is experiencing the problem, check that computer’s cabling and NIC. You only need to check for interference, router misconfiguration, or switch misconfiguration if more than one client is experiencing this problem.

Question 17

Low RF signal occurs beause

Answer 17

radio transmissions have a limited maximum distance:
- moving the wireless router and wireless client so that they are closer together
- increasing the signal strength
- objects can cause obstruction or interference
- Performing a site survey can help you determine these issues.

Question 18

Jitters

Answer 18

Caused by: network over usage, poor internet connection, or insufficient routers.
- causes communications to delay, drop, or lose packets
- images and communications “stutter”
- ping spikes
- upgrade the network to a faster medium, reset or improve your Internet connection, or install new routers

Question 19

Poor Voice over Internet Protocol (VoIP) quality

Answer 19

– Poor VoIP quality is rarely the fault off the service provider
- VoIP quality can come because of insufficient network devices, poor internet connection, or latency. You may need to upgrade the network medium

Question 20

Port flapping occurs when

Answer 20

a physical interface on a switch continually cycles up and down within a second for several seconds. This causes intermittent connectivity for network devices. While common, port flapping can create latency within a network. The most common cause for port flapping is using a bad, unsupported, or non-standard cable, which causes synchronization issues.

Question 21

High latency

Answer 21

Latency is the time it takes for a data packet to be transferred from its source to its destinations
- high latency = network slowing down and reducing productivity
- different factors eg low memory space on a network device, DNS server errors, too many routers, or transmission medium issues
- can be measured and tested by: round trip time (RTT), through the ping command, or through Time to First Byte (TTFB).

Question 22

External Interference

Answer 22

Wi-Fi signal can become disrupted by outside factors that are out of the operator’s control. These interference points can be disruptive to the network, impacting both productivity and device availability. Operators can use different tools to test their network stability and see what areas may be most impacted as well as if there are open channels that can be utilized to help reduce the workload on impacted areas. For wired networks, interference is usually caused by electrical devices.