Trouble-shooting 5.7 - networks (wired/wireless) Flashcards
command line: ipconfig/ifconfig
displays TCP/IP configuration of a device
command line: nbtstat
displays netBIOS info
command line: net
manages network activity & settings eg print jobs, ntwk users, etc
command line: netdom
to do with Windows domains
command line: nslookup
checks DNS record eg for domain names, IP address mapping
command line: ping
test connectivity between 2 devices
command line: tracert
traces a packet’s path through a network; incl name & IP address of each device
no connectivity
computer/network hardware - check cables, network adaptor incl its config. Check wireless card & its confg
SSID / SSID not found
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
No connectivity
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
APIPA/link-local address
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.
Limited connectivity
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.
Local connectivity only
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.
Intermittent connectivity
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).
IP conflict
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
Slow transfer speeds
- 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.
Low RF signal occurs beause
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.
Jitters
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
Poor Voice over Internet Protocol (VoIP) quality
– 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
Port flapping occurs when
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.
High latency
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).
External Interference
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.
