Network + Part 10

Signal strength diminishes over distance either through a physical or wireless connection.

Signal strength ratio measurements. One tenth of a bel.

Electromagnetic interference. Can come from any electrical device.

When the port itself is bad.

When 2 wires that are not supposed to touch connect. Can happen inside of a cable.

Open Circuit

Transceiver types need to match. Single to single. Multi to Multi. The wavelength also needs to match 850nm and can’t be used with 1100mn.

Duplex must match. Either side much have half or full duplex

Pinch the connector into the wire.

For punching a wire into a 66 or 110 block.

Put a tone on the wire. A probe is used to identify where the other end of the wire is located.

Useful for testing physical ports. You can transmit and receive a data stream and check if there are errors on that device.

Time Domain Reflector. Estimate cable lengths. Identify splice locations. Signal loss. Certify cable installations. Locate breaks. Used for copper. Sends an electrical pulse similar to a radar ping.

Optical Time Domain Reflector. Estimate cable lengths. Identify splice locations. Signal loss. Certify cable installations. Locate breaks. Used for fiber. Sends a light pulse similar to a radar ping.

Checks AC voltage. Checks DC voltage inside computers.

Checks if your copper wire is fully functional. Check each individual pins.

Intercept network traffic either with a physical device or setting up a port on a switch.

Joins the ends of fiber together. Uses Heat.

Measures how much light is going through the fiber optic cable. Sends a laser or LED on one end and another device on the other end picks it up.

Check the frequencies in the area. Useful for changing wifi channels.

Available for free on wireshark.

Gathers frames on the network and view traffic patterns.

Test the bandwidth.

Scan for IP addresses and open ports. Can help you pick an available IP address. Visually maps the network. Useful for rouge system detection.

Gathers traffic statistics from all traffic flows. Sends a probe to watch communication.

Trivial File Transfer Protocol server. For initial file transfers and firmware upgrades.

Received Signal Strength Indication. The strength of the received radio signal. dBm decibal milliwatts. The closer to zero is better. 50 dBm is excellent. 70 is ok. 80 is low.

Effective isotropic radiated power. The radiated signal strength from the transceiver.

Bunny ears. Signals are evenly distributed on all sides.

Focus the signal for increased distance. Sends and receives in a single direction.

Directional antenna that looks like a tree triangle.

Directional antenna that looks like a C with a stick in the middle.

The orientation of the antenna is relative to the surface of the earth. When setting up 2 directional antennas they must face each other.

Devices must associate with an access point. This can occur multiple times as a device roams. Determined by signal strength.

Too many people using 1 access point.

Determine the existing wireless landscape and identify existing access points. Helps work around existing frequencies. Similar to heat maps.

When 2 or more access points use the same channel. Recommend we use channels 1 , 6 , 11.

Digital phonebook. Shows how to get from point A to point B.

Collisions may occur if 1 device is set for half duplex and another for full duplex.

Some processes use broadcasts to communicate. A device will send a signal to every other device on the VLAN. Each device will process that broadcast and it will impact performance. You can use packet capture to check how many broadcasts are in the network.

May be an attack or a manufacturing error. Virtual machines also create MAC addresses. 2 MAC addresses will interfere with ARP.

Static IP address assigned to more than one machine. OS checks if this happens.

Used for one-to-many traffic flows such as video feeds. Switches may forward this unnecessary traffic to every computer on the network.

Internet Group Management Protocol. Hosts and routers use IGMP to direct multicast transmissions. Switches can also watch for these messages and direct them to the correct device.

Ingress flows on one path and egress flows on another path.

Happens when Spanning Tree Protocol is not configured. Switches communicate by MAC address, and they can end up sending traffic to each other, back and forth.

• Router A thinks the next best hop is router B.
• Router B thinks the next best hop is router A.
• This repeats until the TTL expires. Using a traceroute can find out if this is happening. Solved my modifying the routing tables.

A route to the destination network does not exist and the packet is dropped. ICMP host unreachable message will be sent to the source device.

IP address assigned by a non-authorized server. Client is designed a duplicate or invalid IP address. Prevented by DHCP snooping. Active Directory can identify legit servers. Renewing IP leases also works.

Client receives an APIPA since the number of IP addresses has been depleted. They will only be able to communicate with the local subnet. Lowering the lease time can help.

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