Network Troubleshooting Flashcards
phenomenon where an electrical signal from one wire bleeds into another wire, creating interference
crosstalk
spurious signals caused by faulty hardware or badly crimped jacks
noise
cable problem caused by the connection of two cables with difference impedances (natural resistance), resulting in echo
impedance mismatch
tool used to see if a cable can handle the rated amount of capacity; checks for crosstalk, attenuation, interference, and even impedance mismatch; used when there is a slowdown, not disconnects; needs some kind of loopback adapter installed at the other end of the cable
certifier
tool used to measure the amount of light loss in an fiber cable; a calibrated detector is installed at the other end of the cable
light/optical power meter
tool used to tell if there is a power/electrical problem with a cable/device?’ used to check intermittent problems
voltage quality recorder
tool used to measure the temperature in a room, like a server room; used to check intermittent problems
temperature monitor
utility used to inform one of the IP information/settings for a computer; for Windows, Macos/UNIX, and Linux respectively
ipconfig/ifconfig/ip
utility that resolves an IP address to a MAC address; stored on computers and Level 3 devices (routers)
Address Resolution Protocol (arp)
utility that uses ARP frames instead of ICMP packets to query a device; can only be used within a broadcast domain - can’t cross routers since it doesn’t use IP packets, only frames; supported by UNIX and UNIX-like systems
arping
Microsoft utility that combines the functionality of ping and tracert
pathping
utilities used to troubleshoot DNS issues; supported by all OS’s and MacOS/UNIX/Linux respectively
nslookup/dig
dynamic equivalent to tracert, not supported by Windows
My Traceroute (mtr)
utility used to display a device’s routing table
route
utility used to display the state of all running processes; shows which sessions are active and provide statistics based on ports and protocols; without switches, this command only shows current sessions
netstat
Linux utility that enables control over IPv4 tables - rules that determine what happens to IPv4 packets on a firewall; replaced by nftables
iptables
Linux/UNIX command line tool that monitors and filters network packets and it can create files for later viewing in Wireshark
tcpdump
tool used to measure the flow of data through a network
throughput/bandwidth speed tester
remote servers accessed via a web browser that provides diagnostic tools like ping and tracert from outside the local network; also provides some BGP query tools
looking glass site
technology that combines multiple NICs together in order to increase bandwidth in smaller increments (and cheaper) than upgrading NICs to the next standard; can also create redundancy by setting one NIC to primary (live) and the other to hot spare (standby)
link aggregation/NIC teaming
IEEE 802.3ad protocol for enabling two or more network connections to work together simultaneously; ports can be in active or passive mode and must communicate at the same speeds
Ling Aggregation Control Protocol (LACP)
Cisco proprietary protocol for combining multiple network connection into one logical connection
Port Aggregation Protocol (PAgP)
issue where one’s IP packets are so large that they must be fragmented to fit into an ISP’s packets
MTU mismatch
method for automatically determining the right MTU size; this-aware OS can send ICMP packets with a “Don’t Fragment” flag (DF) to another device until the ping is successful; worthless if firewall is set to block ICMP requests
Path MTU Discovery (PMTU)
Cisco network appliance, which possibly contains routing, NAT, switching, and IDS features, plus firewall
Cisco Adaptive Security Appliance (ASA)
problem where the NAT rule order on a “router”/network appliance is incorrect, causing traffic to go out an incorrect interface
NAT interference misconfiguration
process of making remote computers act as though they are on a local network, such as VPN; almost all such problems occur on the VPN concentrator, which can cause what appears to be a DoS attack
proxy ARP
principle stating that work should happen only on the endpoints of a network
end-to-end principle
