Network Concepts Flashcards
Compare manually assigning host configurations versus the network dynamically assigning them (DHCP)
With manual, you have to make sure that every host has the correct default gateway, subnet mask, and DNS server. Network devices, servers, and printers should have static IP addresses.
DHCP minimizes configuration mistakes, can easily add new devices, and tracks which device has which IP address
Explain the greatest number (decimal format) that can be in a IP address octet
255 because an octet of 11111111 = 255
Binary math: each bit doubles the previous, from right to left
Explain how the Subnet Mask (in decimal) determines the number of available IP addresses on a network
With 4-octet decimal IP addresses (e.g., 192.168.1.1), the first three octets are used to identify the the network, leaving the last octet to be any number between 0 and 255.
This enables 256 devices, however, certain IP addresses are reserved for certain devices:
- the first option is always reserved for the address itself (192.168.1.0)
- the last is always reserved for the network’s broadcast address (192.168.1.255)
Explain how network hosts use the subnet mask to determine if another host is on the same network
The subnet mask, in binary, can compare the IP addresses of different hosts to see if the network binary is identical.
When the network’s binary values do not match, the router comes into play to enable communication between hosts.
In subnet binary, the network bits are 1s and the host bits are 0s. These 1s and 0s must be clearly delineated to be valid, e.g., not 11111111.11111111.111110011.000000000, but rather, 11111111.11111111.11111110.00000000
What is the purpose of the Ping command?
To test the reachability of a host/between two hosts.
It is the primary TCP/IP command used to troubleshoot connectivity, reachability, and name resolution (compare pings for a device using IP Address and DNS, if DNS fails, is a naming issue)
Explain how DNS converts domain names to IP addresses
When a domain name is entered into the browser, the device sends a lookup request to its designated DNS server.
Then the server searches its database for the name you entered. If it finds a match, it sends the IP Address back to your computer; if it doesn’t find a match, it forwards the request to a higher-level DNS (the “system” in DNS).
The DNS servers are linked together so that any of them can find the IP address for any valid, registered domain name.
Compare MAC Addresses v. IP Addresses
A MAC Address is a physical address embedded into each network capable device. Uses hexadecimal notation (base-16)
An IP address is a unique identifying number assigned to every device connected to the internet. Is expressed in 8-bit binary (base-2).
When on the same network, two hosts can communicate directly through the switch via MAC Addresses.
- Host A will broadcast across the entire local network using Address Resolution Protocol (ARP).
Describe how Address Resolution Protocol (ARP) works
When a router isn’t needed to allow two hosts on a network to communicate…
- Host A broadcasts “who has X IP Address?”
- This gets sent through the switch as a broadcast transmission
- The host with the matching IP Address sends back its MAC Address
- The switch will store the MAC Addresses of devices on that network, not the IP Addresses
OSI Model Encapsulation
Occurs on the sending host side
As data flows down the stack (layers 5 –> 1), at each layer, protocols add header and trailer data blocks.
- These blocks contain addressing and error control information.
As the data moves down the stack, each layer examines the data received from the layer above, and adds its own header and if needed, a trailer.
OSI Model De-encapsulation
Occurs on the receiving host side
As data flows up the stack (layers 1 –> 5), information is examined, processed, and removed until the receiving host has just the payload of data that the sender meant to send.
Compare and contrast UDP and TCP
UDP = User Datagram Protocol
- is used to send data as quickly as possible when speed is more important than reliability.
TCP = Transport Control Protocol
- when error-free data is more important than speed.
- provides rules for a receiving host to confirm every single segment it receives, as well as having error-checking and recovery procedures.
- if any segments are lost or corrupted during transit, the sending host must re-transmit the data
- it is the protocol of choice for webpages and email, when all of the information must get to the destination
When needing to uplink/downlink two switches together - but there is no uplink-specific port - what is common practice?
Many technicians will reserve either the first or last port on the switch for uplink/downlink
What does it mean to daisy-chain switches together?
Linking switches in series.
What are the limitations with daisy-chaining switches together?
The more switches in series, the more latency as each switch has to process the frame.
Each switch (“hop”) between hosts creates more latency.
Links between switches act as bottlenecks for network traffic
- Is due to multiple devices sending data between the two+ switches simultaneously
It is best to limit the number of switches between two devices
What is switching capacity?
A rating of the switch’s maximum internal throughput between connected devices.
Sometimes referred to as “backplane”
- the data movement that happens in the background of the switches operation
- Usually measured in gigabits/second
Regarding switches, what is “non-blocking”?
When the switch has enough backplane so that all connected devices can use its full send-receive capacity to any other hosts.
What is the advantage to using fewer high-capacity switches instead of linking several smaller switches together?
Decreased latency and bottlenecks due to fewer switching hops
What can you expect to occur with a switching loop?
A broadcast has no logical place to end.
With something like Wireshark, you’ll find that there is a tsunami of packets when looking over the information.
When would fiber optic be preferred over Ethernet?
- Between buildings (is standard practice)
- Where EMI is of great concern
_________________________________________
Fiber optic is:- non-conductive (isn’t metal)
- more expensive than Ethernet
- more easily damaged than Ethernet
- EMI doesn’t impact light-signals with fiber optic like it does with Ethernet
Primary negative: the cost of cables and connectors
Explain the difference between managed and unmanaged switches
Managed Switches:
- You can select the power priority for each device/port, so that is there is excessive draw, the higher-priority devies maintain performance.
- You can optimize network traffic
- Two reasons to have a managed switch:
1) Management
2) Monitoring and optimization
Unmanaged switches:
- You can’t monitor/manage an unmanaged switch
How can IGMP optimize network traffic?
IGMP = Internet Group Management Protocol
Is a way for a host to tell the network that they want to “join” or listen to a multicast group address, so that a switch can direct that group’s multicast traffic to only those devices that have joined.
Is a Layer 3 protocol. With IGMP enabled, a switch listens for multicast traffic which has its own group of MAC addresses (akin to Multicast Group IP addresses) - this listening is called “IGMP snooping”
*must have a managed switch, otherwise, will pass through an unmanaged switch like a broadcast transmission
When should IGMP Snooping be enabled on a managed switch?
When you want to catch IGMP-join messages that were originally designed to go between hosts and their router.
To have a direct switch multicast in this way, you need to have a managed switch. Otherwise, it will pass through an unmanaged switch like a broadcast transmission.
Managed switches, however, direct multicast traffic only to those ports that requested it.
Explain the impact that Routing Hops have on a network.
Routing hops create more latency than switching hops.
Routers have to read the data within a packet and determine the appropriate hosts
Switches only have to read the headers in a frame and ignore the rest of the data.
How do you know if there is a Routing Hop on your network?
Using Traceroute in the Command Prompt:
- if the next routing hops after your router’s 192.168.1.1 begins with 10.x.x.x., 172.16.x.x, or 192.168.x.x, then you probably have an extra, unnecessary router on your network.
Why should you put an ISP’s combo unit into bridge mode?
It removes an unnecessary routing hop and allows the setup of external access to the internal network, like VPN.
How are unicast and multicast traffic routed between VLANs?
Broadcast traffic never leaves its broadcast domain.
Unicast is most of the traffic on a network (email, Control4 commands, etc.)
VLAN, at its core, is its own broadcast domain.
What devices need to be configured for VLANs to work?
Router, managed switch, and sometimes the APs.
Only managed switches have the capability to configure VLANs
How are APs and network switches similar?
Both operate at OSI Layers 1 and 2…
…Therefore, both use MAC Addresses to communicate with devices on the same network (OSI Layer 2 = MAC Addresses)
How are APs and network switches different?
Switches use ports and wires to connect host devices.
APs use radio waves. These radio waves are the “physical layer” that replaces Ethernet cables.
What risks are associated with leaving a wireless network “open” (without a password or encryption method)?
Anyone can join the network and could theoretically have access to all of the devices currently connected to the whole LAN.
What is best practice for SSIDs while the wireless network is being setup and configured, versus when it’s ready to be handed off to the customer?
During setup:
- separate 2.4 and 5 GHz (e.g., “HomeWiFi2.4” and “HomeWiFi5”
- Assess RSSI for each SSID at multiple locations in the facility
After the network has been configured and optimized, combine them into a single recognizable and user-friendly SSID: “HomeWifi”
Why should you not hide the customer’s SSID?
It just makes things more difficult for the customer to use while providing zero security benefit.
What is currently the strongest method for wireless encryption?
WPA3 = Wireless Protected Access 3
Is the strongest and most current encryption method in wide-use.
What factors should be considered when selecting a switch?
- Number of ports (known devices plus extra)
- POE: number and power budget (plus extra for expansion)
- SFP uplink
- Management features (e.g., VLANs, link aggregation, STP, remote monitoring and management)
Within the OSI Model, frames move ______ ___ network
Frames move WITHIN a network
OSI Layer 2, the switch
Within the OSI Model, packets move ______ network
Packets move between networks
OSI Layer 3, the router
Why reserve DHCP IP Addresses?
It tells the router to assign only that IP Address to a host with that particular MAC Address
It allows for the predictability of a static IP Address, but without the error-prone nature of manually configuring each device
When you need a host to have a consistent IP Address on a network, use a DHCP reservation.
When would you use static assignments for network configuration?
The router’s LAN port must be assigned statically - it’s the default gateway for all other hosts, so it has to be a predictable address
Sometimes (rarely) a device is not DHCP capable
What is the benefit of IP Address ranges?
Address ranges help you set aside blocks of IP Addresses for specific uses.
Static: for devices that can only be configured manually
Reserved: want to assign a specific address using DHCP reservations
Dynamic: provides addresses for the rest of the network using DHCP
How is the passphrase for an SSID used?
It enables encryption and decryption of data for the SSID
Compare the 5 GHz and 2.4 GHz bands
5 GHz:
- 5 GHz bands designed to not overlap
- fewer sources of interference
- higher data rate potential
2.4 GHz:
- attenuates less over distance
- less susceptible to obstructions
When troubleshooting a wireless network and the wired infrastructure is sound, what should you do?
For each AP on the network, look into the channel selection, AP placement, and transmit power.
This includes creating separate SSIDs for each band on each AP (Office-5, Office-2.4, RecRoom-5, RecRoom-2.4, etc.)
When troubleshooting a wireless network, what types of devices should you first check?
Provide examples.
The wired infrastructure:
- router
- each switch
- Ethernet cables
- and power supply (POE and plugs)
