Module 20: Troubleshoot Common Network Problems Flashcards
here we may see
- Cables which are not connected
- Cables connected to the wrong port
- Loose cable connections
- Damaged cables and connectors
- Use of the wrong type of cable
using
sight
name 5 types of layer 1 (physical) problems might we encounter
when troubleshooting a wired or wireless issue
what 3 steps can we take using ping to verify proper communication
here we can:
- Ping from a wireless client to the default gateway. This verifies if the wireless client is connecting as expected.
- Ping from a wired client to the default gateway. This verifies if the wired client is connecting as expected.
- Ping from the wireless client to a wired client. This verifies if the wireless router is functioning as expected.
using
smeel and taste, touch and sound
how might we discover
layer 1 (physical)
problems
- smell and taste
- can you smell or taste any burning or overheating components
- touch
- is there a lack of vibration or too much vibration this could indicate a cooling fan is not running or running to fast perhaps something else is causing excessive vibration
- sound
- can you hear any clicking or whirling from the device or unfamiliar sounds this may signal a component is damaged or working incorectly
when documenting
previous troubleshooting
what information could we include
here we can include information about if the problem occured before. is there any documentation
specifically we may include
- Steps taken
- Results achieved
what is
ipconfig
used for
this command is used to view current IP configurations. this is a handy tool for knowing if a host has an ip address or other IP configurations
describe the command
nslookup host name | IP address
will make a query to the DNS server about the host name or IP address
the information we would include here is found by questioning end users about any symptoms or error messages seen
when including the
nature of the problem
in the documentation what information might we include
describe the
top-down troubleshooting method
this approach is best employed when it is suspected that an application is causing the issue and so determining the problem in the application would be the first step
when including the
nature of the problem
in the documentation what information might we include
the information we would include here is found by questioning end users about any symptoms or error messages seen
display detailed IP configuration. including DHCP, DNS server and MAC address
describe the command
ipconfig /all
this involves comparing a non working device with a working one and assesssing differences such as configurations, software version, installed hardware. the non working system can then be configured identically to the working one. this approach may work in solving the problem but may not reveal the root cause
describe the
comparison / spot the difference troubleshooting method
displays all connections and listening ports
describe the command
netstat -a
when a
networking problem arises
what are the first 3 steps to take
the steps include:
- confirm if there is really a problem
- asses what areas of the network have been affected
- start taking documentation
name 4 technical cable problems that could arise
these include:
- straight through vs crossover
- correct termination T568A vs T568B
- cable length
- is the correct port being used
describe the
substitution / swap-the-component troubleshooting method
this simply involves swapping out a device with a working device if the problem persists then it can be assumed that the problem lies elsewhere
this command can be used to trace the path that a packet takes from the source to a destination. this command can be usefull when ping has failed since it can be seen exactly where the packet failed to be routed and in turn did not acheive communication
what is
tracert
useful for
when making
the initial documentation
what 4 peices of information might we include
this may include:
- nature of the problem
- equipment
- configuration and topology
- previous troubleshooting
describe the
bottom-up troubleshooting method
this involves working from the bottom of the OSI model and working your way up. this approach typically works best when it is suspected that physical equipment has failed (EXAMPLE: if the NIC lights are flashing then it can be assumed that layer 1 (physical) layer is not where the problem lies and so we can move up to layer 2)
describe the command
ipconfig /all
display detailed IP configuration. including DHCP, DNS server and MAC address
if pinging a remote server or local host appears to be working then it can be assumed that there are no problems on the layer 3 (network) and it is time to move up.
a device which deals with and might cause problems at the layer 4 (transport) is a firewall. it may be configured to block specific TCP or UDP packets such as TCP 80 which is HTTP traffic if this were being inspected and blocked by source then you would not receive any HTTP traffic
describe a scnenario where you might encounter a
layer 4 (transport)
problem while troubleshooting
will make a query to the DNS server about the host name or IP address
describe the command
nslookup host name | IP address
describe the
comparison / spot the difference troubleshooting method
this involves comparing a non working device with a working one and assesssing differences such as configurations, software version, installed hardware. the non working system can then be configured identically to the working one. this approach may work in solving the problem but may not reveal the root cause
describe the command
ipconfig /release
this will release all current IP configurations if they were configured dynamically
when documenting the
equipment
involved in the problem where might we look for information and what information might we include
when documenting this we can look at log files and documentation. documentation may reveal recent changes
the information we can include in the documentation are
- Manufacturer
- Make / model
- Firmware version
- Operating system version
- Ownership / warranty information
describe the command
nslookup
will show the DNS configuration for the host. and enter the nslookup programme
the default maximum hops that tracert will use is 30. this command can be used to increase the number of hops it seraches for
describe the command
tracert ip address | host name -h maximum_hops
this involves working from the bottom of the OSI model and working your way up. this approach typically works best when it is suspected that physical equipment has failed (EXAMPLE: if the NIC lights are flashing then it can be assumed that layer 1 (physical) layer is not where the problem lies and so we can move up to layer 2)
describe the
bottom-up troubleshooting method
display basic IP configuration information
describe the command
ipconfig
describe a scnenario where you might encounter a
layer 4 (transport)
problem while troubleshooting
if pinging a remote server or local host appears to be working then it can be assumed that there are no problems on the layer 3 (network) and it is time to move up.
a device which deals with and might cause problems at the layer 4 (transport) is a firewall. it may be configured to block specific TCP or UDP packets such as TCP 80 which is HTTP traffic if this were being inspected and blocked by source then you would not receive any HTTP traffic
describe the
educated guess / shoot from the hip troubleshooting method
this is an approach for more experienced technicians and relies on past kowledge to take a guess at where the problem lies
what is
tracert
useful for
this command can be used to trace the path that a packet takes from the source to a destination. this command can be usefull when ping has failed since it can be seen exactly where the packet failed to be routed and in turn did not acheive communication
describe the command
tracert ip address | host name
this will send 3 packets with a time to live set for each router. when a router receives a packet that has a time to live of 0 then it will drop the packet and return information about itself to the source
describe the command
ipconfig /renew
this will ask the DHCP server for new IP configurations. if a new IP address is not given this could point to problems at a lower level or a problem with the DHCP server
this command is used to view current IP configurations. this is a handy tool for knowing if a host has an ip address or other IP configurations
what is
ipconfig
used for
what is a consideration to take into account when pinging a domain name
when pinging a domain name and there is no reply it is wise to ping the IP address if known. this is because when pinging a domain name a DNS lookup must occur if this method fails it could point to a DNS problem
these include:
- straight through vs crossover
- correct termination T568A vs T568B
- cable length
- is the correct port being used
name 4 technical cable problems that could arise
this approach takes the documentation into account and from there making an educated choice as to where to start troubleshooting in the OSI model
EXAMPLE:
if you started troubleshooting at layer 3 (transport layer) and found that you cannot get an ip address then you would move down the OSI model however if this layer works correctly it can beassumed lower levels do aswell and so you move up
describe the
divide and conqeur troubleshooting method
this command is used to view current network statistics such as current connections with other hosts. this command could reveal connections to your host which should not be there this may indicate that someone is connected to your host when they shouldnt be
what is
netstat
usefull for
once initial documentation has been taken what is the next step
starting the process of troubleshooting would be the next step after this
starting the process of troubleshooting would be the next step after this
once initial documentation has been taken what is the next step
this command is used to directly make a query to a dns server
what is
nslookup
useful for
this will release all current IP configurations if they were configured dynamically
describe the command
ipconfig /release
this will send an echo request packet to the ip address or domain name
describe the command
ping ip-address | domain name
describe the
divide and conqeur troubleshooting method
this approach takes the documentation into account and from there making an educated choice as to where to start troubleshooting in the OSI model
EXAMPLE:
if you started troubleshooting at layer 3 (transport layer) and found that you cannot get an ip address then you would move down the OSI model however if this layer works correctly it can beassumed lower levels do aswell and so you move up
the steps include:
- confirm if there is really a problem
- asses what areas of the network have been affected
- start taking documentation
when a
networking problem arises
what are the first 3 steps to take
when documenting this we can look at log files and documentation. documentation may reveal recent changes
the information we can include in the documentation are
- Manufacturer
- Make / model
- Firmware version
- Operating system version
- Ownership / warranty information
when documenting the
equipment
involved in the problem where might we look for information and what information might we include
this may include:
- The problem encountered
- all attempts and steps taken to determine the cause of the problem
- all attempts and steps taken to correct the problem and ensure that it will not reoccur
whilst we are resolving an issue
what 3 types of notes might we make in the documentation
whilst we are resolving an issue
what 3 types of notes might we make in the documentation
this may include:
- The problem encountered
- all attempts and steps taken to determine the cause of the problem
- all attempts and steps taken to correct the problem and ensure that it will not reoccur
when documenting the
configuration and topology
what information can we include
here we can include information about where are we in the network, who are we connected to is there any network monitoring logs that we can gather
specifically we may include
- Physical and logical topology
- Configuration files
- Log files
this may include:
- nature of the problem
- equipment
- configuration and topology
- previous troubleshooting
when making
the initial documentation
what 4 peices of information might we include
this will send 3 packets with a time to live set for each router. when a router receives a packet that has a time to live of 0 then it will drop the packet and return information about itself to the source
describe the command
tracert ip address | host name
- smell and taste
- can you smell or taste any burning or overheating components
- touch
- is there a lack of vibration or too much vibration this could indicate a cooling fan is not running or running to fast perhaps something else is causing excessive vibration
- sound
- can you hear any clicking or whirling from the device or unfamiliar sounds this may signal a component is damaged or working incorectly
using
smeel and taste, touch and sound
how might we discover
layer 1 (physical)
problems
will show the DNS configuration for the host. and enter the nslookup programme
describe the command
nslookup
what is
ping
usefull for
this command can verify communication between two IP hosts
using
sight
name 5 types of layer 1 (physical) problems might we encounter
here we may see
- Cables which are not connected
- Cables connected to the wrong port
- Loose cable connections
- Damaged cables and connectors
- Use of the wrong type of cable
describe the command
ping ip-address | domain name
this will send an echo request packet to the ip address or domain name
describe the
follow-the-path troubleshooting method
this troubleshooting methods requires knowing the source and destination of the problem from here you assess each of the links disregarding any devices that are not in the path
this will ask the DHCP server for new IP configurations. if a new IP address is not given this could point to problems at a lower level or a problem with the DHCP server
describe the command
ipconfig /renew
describe the command
tracert ip address | host name -h maximum_hops
the default maximum hops that tracert will use is 30. this command can be used to increase the number of hops it seraches for
here we can:
- Ping from a wireless client to the default gateway. This verifies if the wireless client is connecting as expected.
- Ping from a wired client to the default gateway. This verifies if the wired client is connecting as expected.
- Ping from the wireless client to a wired client. This verifies if the wireless router is functioning as expected.
when troubleshooting a wired or wireless issue
what 3 steps can we take using ping to verify proper communication
this approach is best employed when it is suspected that an application is causing the issue and so determining the problem in the application would be the first step
describe the
top-down troubleshooting method
when pinging a domain name and there is no reply it is wise to ping the IP address if known. this is because when pinging a domain name a DNS lookup must occur if this method fails it could point to a DNS problem
what is a consideration to take into account when pinging a domain name
describe the command
ipconfig
display basic IP configuration information
what is
netstat
usefull for
this command is used to view current network statistics such as current connections with other hosts. this command could reveal connections to your host which should not be there this may indicate that someone is connected to your host when they shouldnt be
these include:
- bottom-up
- top-down
- divide and conquer
- follow the path
- substitution / swap the component
- comparison / spot the difference
- educated guess / shoot from the hip
what are 7
troubleshooting methods
that can be used to isolate and find a problem
here we can include information about where are we in the network, who are we connected to is there any network monitoring logs that we can gather
specifically we may include
- Physical and logical topology
- Configuration files
- Log files
when documenting the
configuration and topology
what information can we include
what are 7
troubleshooting methods
that can be used to isolate and find a problem
these include:
- bottom-up
- top-down
- divide and conquer
- follow the path
- substitution / swap the component
- comparison / spot the difference
- educated guess / shoot from the hip
what is
nslookup
useful for
this command is used to directly make a query to a dns server
this is an approach for more experienced technicians and relies on past kowledge to take a guess at where the problem lies
describe the
educated guess / shoot from the hip troubleshooting method
this simply involves swapping out a device with a working device if the problem persists then it can be assumed that the problem lies elsewhere
describe the
substitution / swap-the-component troubleshooting method
describe the command
netstat -a
displays all connections and listening ports
this command can verify communication between two IP hosts
what is
ping
usefull for
here we can include information about if the problem occured before. is there any documentation
specifically we may include
- Steps taken
- Results achieved
when documenting
previous troubleshooting
what information could we include
this troubleshooting methods requires knowing the source and destination of the problem from here you assess each of the links disregarding any devices that are not in the path
describe the
follow-the-path troubleshooting method