Wired Network Troubleshooting Flashcards

Question

Reflection

Answer 1

• Wireless signals can bounce off some surfaces • Depends on the frequencies and the surfaces • Too much reflection can weaken the signal • A little multipath interference actually helps with MIMO • Position antennas to avoid excessive reflection • May not be a problem for MIMO in 802.11n and 802.11ac

Answer 2

• Signal passes through an object and exits at a different angle • Similar to light through water • Data rates are affected - Signal is less directional • Outdoor long-distance wireless links • Changes in air temperature and water vapor

Answer 3

* Signal passes through an object and loses signal strength * Especially through walls and windows * Different objects absorb differently as frequencies change * 2.4 GHz may have less absorption than 5 GHz * Put the antennas on the ceiling * And avoid going through walls

Answer 4

* Latency - Delays between transmission and reception * Jitter - Deviation from a predictable data stream * Wireless interference and signal issues * Slower data rates * Increase in retransmissions * Capacity issues * Many people using the same wireless frequencies

Answer 5

• Wireless signals get weaker as you move farther from the antenna • The attenuation can be measured with a Wi-Fi analyzer • Control the power output on the access point • Not always an option • Use a receive antenna with a higher gain • Capture more of the signal • Move closer to the antenna - May not be possible

Answer 6

``` • Interference • Something else is using our frequency • Predictable • Florescent lights, microwave ovens, cordless telephones, high-power sources • Unpredictable - Multi-tenant building • Measurements • netstat –e • Performance Monitor ```

Answer 7

* The antenna must fit the room * Or the distance between sender and receiver * Omnidirectional * Useful on the ceiling * Not very useful between buildings * Directional * Used often between two points * Or on a wall-mounted access point * The access point may provide options * Connect different antennas

Answer 8

* Interference * Overlapping channels * Slow throughput * Data fighting to be heard through the interference * Check access point locations and channel settings * A challenge for 2.4 GHz * Much easier for 5 GHz

Answer 9

* Device saturation * Too many devices on one wireless network * There are only so many frequencies * The 5 GHz can really help with this * Bandwidth saturation * Large data transfers * Common in large meeting places * Conferences * Airports * Hotels

Answer 10

• Devices have to match the access point • 2.4 GHz, 5 GHz • Verify the client is communicating over the correct channel • This is normally done automatically • May not operate correctly if manually configured • Older standards may slow down the newer network • 802.11b compatibility mode on 802.11n networks • Every access point has an SSID • But did you connect to the right one? • This can be more confusing than you might think • Public Wi-Fi Internet • Guest Internet • Internet • Confirm the correct SSID settings • Should be listed in the current connection status

Answer 11

* Wireless authentication * Many different methods * Required to connect to the wireless network * If not connected, check the authentication * Shared passphrase * Common in a SOHO, not in the enterprise * 802.1X * Used for the enterprise * Make sure the client is configured to use 802.1X

Answer 12

• Encryption on wireless is important • Make sure the client matches the access point • This is much easier these days • Almost everything is at the level of WPA2 • Some legacy equipment may not be able to keep up • If you change the access point, you may not be able to support it • Migrate all of your WEP to WPA2 • And any WPA

Answer 13

* Signal * What you want * Noise * What you don’t want * Interference from other networks and devices * You want a very large ratio * The same amount of signal to noise (1:1) would be bad

Answer 14

* Web browsing doesn’t work * The Internet is broken! * Pinging the IP address works * There isn’t a communication problem * Applications aren’t communicating * They often use names and not IP addresses

Answer 15

* Check your IP configuration * Is the DNS IP address correct? * Use nslookup or dig to test - Does resolution work? * Try a different DNS server - Google is 8.8.8.8 & 8.8.4.4

Answer 16

* Communicate to local IP addresses * But not outside subnets * No IP communication - Local or remote * Communicate to some IP addresses - But not others

Answer 17

* Check your documentation * IP address, subnet mask, gateway * Monitor the traffic * Examine local broadcasts * Difficult to determine subnet mask * Check devices around you * Confirm your subnet mask and gateway * Traceroute and ping * The issue might be your infrastructure * Ping local IP, default gateway, and outside address

Answer 18

* Static address assignments - Must be very organized * DHCP isn’t a panacea * Static IP addressing * Multiple DHCP servers overlap * Rogue DHCP servers * Intermittent connectivity * Two addresses “fight” with each other * Blocked by the OS - Checks when it starts

Answer 19

* Check your IP addressing - Did you misconfigure? * Ping an IP address before static addressing * Does it respond? * Determine the IP addresses * Ping the IP address, check your ARP table * Find the MAC address in your switch MAC table * Capture the DHCP process * What DHCP servers are responding?

Answer 20

``` • Not a common occurrence • MAC addresses are designed to be unique • May be a man-in-the-middle attempt • Mistakes can happen • Locally administered MAC addresses • Manufacturing error • Intermittent connectivity • Confirm with a packet capture, should see ARP contention • Use the ARP command from another computer • Confirm the MAC matches the IP ```

Answer 21

* A DHCP address should renew well before the lease expires * The DHCP server(s) could be down * Client gives up the IP address at the end of the lease * APIPA address is assigned * Checks in occasionally for a DHCP server * Look for an APIPA assigned address * 169.254.*.* * Check the status of your DHCP server

Answer 22

* IP addresses assigned by a non-authorized server * There’s no inherent security in DHCP * Client is assigned an invalid or duplicate address * Intermittent connectivity, no connectivity * Disable rogue DHCP communication * Enable DHCP snooping on your switch * Authorized DHCP servers in Active Directory * Disable the rogue * Renew the IP leases

Answer 23

* Browsers trust signatures from certain CAs * A certificate was signed by a CA that’s not in our list * Error message on the browser * Certificate Authority Invalid * Check the certificate details * Look for the issuing CA * Compare to the CA list on your computer * If it’s an internal server, it may be internally signed * Add your internal CA certificate to the list

Answer 24

• Some cryptography is very time sensitive • Active Directory requires clocks set within five minutes of each other • Kerberos communication uses a time stamp • If the ticket shown during authentication is too old, it’s invalid • Client can’t login • Check the timestamp of the client and the server • Configure NTP on all devices • Automate the clock setting

Answer 25

* Client received an APIPA address * Local subnet communication only * Check the DHCP server * Add more IP addresses if possible * IP address management (IPAM) may help * Monitor and report on IP address shortages * Lower the lease time * Especially if there are a lot of transient users

Answer 26

* Applications not working * Slowdowns with other applications * Firewall or ACL configuration * Security choke points * Confirm with a packet capture * No response to requests * Run a TCP- or UDP-based traceroute tool * See how far your packet can go

Answer 27

``` • Applications not working • Based on the application in use and not necessarily the protocol and port • Check the host-based firewall settings • Accessibility may be limited to an administrator • Managed from a central console • Take a packet capture • The traffic may never make it to the network • Dropped by the operating system ```

Answer 28

``` • Only certain IP addresses accessible • Or none • Access Control Lists • IP address, port numbers, and other parameters • Can allow or deny traffic by filtering packets • Confirm with packet captures and TCP/UDP traceroutes • Identify the point of no return ```

Answer 29

* No response to an application request * No answer * Do you have the right port number? * And protocol (TCP/UDP)? * Confirm connectivity * Ping, traceroute * Is the application still working? * Telnet to the port number and see if it responds

Answer 30

* No response * Application doesn’t respond * Confirm connectivity * Without a ping, you’re not going to connect * Run a traceroute * See if you’re being filtered * Should make it to the other side * Check the server * Lights? Fire?

Wired Network Troubleshooting Flashcards

(54 cards)