5 – Network Troubleshooting Flashcards
What is a TDR?
Time Domain Reflectometer A tool that provides advanced analysis of network cables. For copper, it’s a TDR. For fiber, it’s an OTDR.
What is an OTDR?
Optical Time Domain Reflectometer Same thing as a TDR, but for fiber optic cable.
What types of things can a TDR be used to identify?
• Frequency testing • Crosstalk • Signal loss • Cable impedance information • Estimated cable length • Cut or break locations (estimates how far down the cable that break is located)
How does a TDR work?
It sends an electrical pulse down the cable (or, for an OTDR, it sends a light). Impedance discontinuities cause a reflect, and the TDR calculates time and distance based on that reflection.
What is a light meter used for?
It sends a light (either laser or LED) from one side of a fiber optic cable, and measures the light power on the other side, to determine the strength of the signal getting through the cable.
What is a Multimeter?
A tool to check either AC or DC voltage. AC voltage to checke the wall outlet output; DC voltage to check the PC power supply output or CMOS battery power.
What is a Spectrum Analyzer?
Measures and displays signals from the full wireless frequency spectrum. Useful to visually see signal strength, conflicts, and interference.
What is DIG?
Domain Information Groper • Looks up info from DNS servers. • Replaces nslookup, which is now deprecated. • More advanced than nslookup. • Not native to any Windows version, but it can be downloaded and added.
What is iptables?
A stateful firewall available for Linux • One of the more popular of the many firewall options for Linux’ • Provides stateful filtering of traffic in the kernel of the Linux OS • Usually placed on a device or server to filter traffic to and from the device • Can also serve as a firewall at the edge of a network to filter the entire network
What is netstat?
A command line tool for Network Statistics, available on many different OSs, including Windows, Linux, and Unix.
What is tcpdump?
A command line tool to capture packets • Available in most Unix/Linux OSs • included in MacOs, can be downloaded for Windows (it’s called WinDump) You can: • apply filters • view in real-time • save the data and use in another application
What is a pcap file?
A file format that is easily readable by many protocol analyzer applications. It contains tcpdump data, or similar.
What is pathping?
It combines ping and traceroute and adds some additional functions. This command provides details of the path between two hosts, and Ping-like statistics for each node in the path based on samples taken over a time period. It is included in Windows NT and later.
What is nmap?
Network Mapper A Linux CLI tool
What is arp?
CLI windows more info…
In Networking, what does “attenuation” refer to?
Attenuation is the lose of intensity as a signal moves through a medium. Signal strength diminishes / degrades over distance. This degradation is called attenuation.
What is jitter?
Jitter is a delays between frames. Data should arrive at regular intervals. This is most problematic for real-time applications, because if you miss a packet, there’s no retransmission.
What is an open circuit?
A break in a connection. Often, a broken cable.
ping
the packet internet groper comand is utilized in Windows through th ecommand processing window. The ping comand uses IMCP packets to attempt to communicate with with hter other connected deveces via internet protocol
ipconfig
the ipconfig is the command that provides the local host’s ip configuration information on all adapters, such as ethernet and wireless, as well as being capable of providing the NIC physical address, the DHCP server and lease information and mre
SSID
the AP and the client has to have same SSID, SSID is case sensitive and should be same in both devices
ipconfig /all release and renew
the “release” and “renew” commands relate to DHCP integration
netstat
netstat command can be used to display a variety of information about ip-based connections on a PC. For example, you can view information about current sessions, including source and destination, Ip address and port numbers, you can also display protocol statistics
nslookup
nslookup command can e used to provide DNS information such as hostname-to-IP address mappings, as well as other DNS record types. It is a very useful tool for troubleshooting DNS problems, such as host name resolution
traceroute
niux version of tracert, pings every router hop from a source IP address to a specified destination Ip address, and reports the round-trip time for each router hop. If a router is not reachable, you might want to investigate the router hop that timed out or the router hop just before the one that timed out. Therefore, the primary uses of the traceroute command are to determine the path a packet takes to a specific destination and to determine where along that path an issue might exist
command to add 200.200.10,10 to mac address 08-00-8b-9a-ff-20
arp -s 200.200.10,10 08-00-8b-9a-ff-20
nbtstat
the command is used to examine the NetBIOS name information
command generate NetBiOS cache on a windows system
nbtstat -c
what command do yo use to check route table
route print, netstat -r
dB loss
the signal power of a data transmission might be degraded to the point where the transmission is not correctly interpreted by a receiving device. This loss of signal power, called a decivel loss, could result from exceeding the distance limitation of a copper or fiber cable
dance
a combination of resistance ,inductance, and capacitance in an electrical circuit that can impact the current flowing through the circuit
AM
Amplitude modulation is a method carrying information by varying the amplitude of carrier frequency
ping and ICMP operates on which layer
layer 3 , if a successful replay is returned it is safe to assume that the alyers lower than and including 3 are functional
RFI
radio frequency interference. Common RFI sources that affect wireles snetworks include 2.4GHz cordless phones, mocrowave ovens, baby monitors, and game consoles.
RSSI
the Received Signal Strength Indicator value measure the power of a wireless signal. An RSSI value varies based on distance from a wireless antena and physical objects interfering with line-f-sight communication with a wireless antenna.
AP
a wireless LAN device that interconnects wireless clients with a wired network
Latency
delay, in wireless network can increase due to a WLAN’s use of Carrier Sense Multiple Access with Collision Avoidance, which introduces a random delay before transmitting data, in an attempt to avoid collisions.
crosstalk
crosstalk refers to the interference of a signal from a neighboring signal
jitter
the variation in delay in the network
attenuation
the weakiening of a signal over distance
a strucured troubleshooting methodology includes the following steps
- define the problem
- hypothesize a probable cause
- test the hypothesis
- implement the action plan
- verify problem resolution
- create a post mortem report
channel overlap
while overlapping WLAN channels can cause interference and degrade performance, that issue is unrelated to a WLAN use of CSMA/CA
MDIX
medium dependent interface crossover is a technology supported by many modern Ethernet switches that automatically selects appropriate transmit and receive wires in an Ethernet cable. This allows you to connect an Ethernet switch port to another Ethernet device without being concerned about whether you should use a straight-through cable or a crossover cable.
RR
route reflector is a network routing component in BGP that offers an alternative to the logical full-mesh requirement of internal border gateway protocol, An RR acts as a central point for IBGP sessions. The purpose of the RR is concentration
a next-hop router
a parameter appearing in a routing table, indicating the IP address of the next router to which a packet should be forwarded to reach specific destination network
black-hole router
a router attempts to fragment packets exceedign an itnerface’s MTU. However, if a packet does exceed an interface’s MTU and has its DF bit set, the router drops the packet. Normally the router responds to the sender with an ICMP emssage indicating why the packet was dropped however, if a router is configured to not respond to such a condition by sending an ICMP message, the packet is dropped without the sender being notified. SUch a router is called a black-ole router. You can use the trace route utility to help locate a black hole router
ABR
an area border router is the designation given to a router running the Open Shortest Path First routing protocol that has one interface participating in one OSPF area and one or more other interfaces participating in a different OSPF area
cable placement
since copper cables are subject to electromagnetic interference, you should arrange cables to minimize interference. Ideally, Ethernet cables should not be placed in close proximity to high voltage cables, generators, motors, or radio transmitters.
final step in a structured troubleshoot methodology
creation of a post mortem report. A post mortem report is a document describing the reported issue, its underlying causes, and what was done to resolve the issue. This report might be useful when troubleshooting similar issues in the future
a diagnostic report
a collection of information gathered from systems on a network, nothing any anomalous behavior. Therefore, a diagnostic report might be generated during the define the problem step of a structured troubleshooting methodology
a trouble ticked
generated when an issue is first identified
a change notification report
a notification sent out by one network administrator to notify other network administrators about upcoming network maintenance
