CompTIA A+ (220-1001) Cert Prep 7: Understanding Networking

What is always the IPV6 subnet mask?

/64. No matter how many computers are in a network, all IPV6 subnet masks will give that network the ability to have 2 to the 64th power number of available IPV6 addresses.

In order, what are the 14 port numbers listed as CompTIA A+ objectives?

1) 21 is FTP 2) 22 is SSH 3) 23 is Telnet 4) 25 is SMTP 5) 53 is DNS 6) 80 is http 7) 110 is POP3 8) 143 is IMAP 9) 443 is https 10) 3389 is ROP 11) 137-139 are NETBIOS/NETBT 12) 445 is SMB/CIFS 13) 427 is SLP 14) 548 is AFP.

What are 5 ways that computers can get a wireless signal?

1) A wireless access card can be plugged into the motherboard. 2) The motherboard can come with wireless access already built into it - including an external antenna. 3) USB wireless access dongles 4) Most laptops come with a built-in wireless access card. 5) All mobile devices have built-in wireless access cards.

If you have limited or no connectivity to a wireless connection, what are 4 things that you should check?

1) Ensure that the SSID is broadcasting and that the password hasn't changed since the last time you logged into it. 2) Look at the directional antennas from the wireless access point. They might be able to be adjusted to direct the wireless signal better. 3) Ensure you are close enough to the wireless access point to get enough signal. 4) Use your wi-fi analyzer to look for other signals, such as baby monitors, microwaves, walls, etc., to see if there are other signals or blockages that are affecting your ability to connect.

Describe the 802.11n standard.

100 Mbps in the 2.4 or 5 GHz range. *

Describe the 802.11b standard.

11 Mbps in the 2.4 GHz range. *

What is the standard Loopback IP address?

127.0.0.1

How many characters are in an IPV6 address?

128 bits separated into 8 sets of 4 hexidecimal characters separated by 7 colons.

What is the default APIPA IP address that is always assigned unless the system has been manually configured to assign a specific IP address?

169.254.x.x. *

What is the range of the 2.5 GHz band?

2.412 GHz to 2.488 GHz.

What do all Class D IPv4 addresses start with?

224, and all of the values that follow.

What do all Class E IPv4 addresses start with?

240, and all of the values that follow.

How many bits are in every octet of an IPV4 IP address?

255 bits in each of the 4 octets.

What is the character limit for Fully-Qualified Domain Names?

256 characters, including the dots.

What is the range of the 5 GHz band?

5.150 GHz to 5.875 GHz.

Describe the 802.11g standard.

54 Mbps in the 2.4 GHz range. *

Describe the 802.11a standard.

54 Mbps in the 5 GHz range. *

What is an alternative DNS server that you can use if you want to statically assign a primary or secondary DNS server?

8.8.8.8 or 8.8.4.4. These are popular, high-traffic DNS servers available for public use.

What are the four 802.11 standards that have been in place over the years?

802.11a, 802.11b, 802.11g, and 802.11n.

What type of connector is on the other end of the RJ-45 connector that plugs into a router or a switch in order to configure it?

A DB-9 connector which is part of a Yost/rollover cable.

What is a downside to using NAT?

A LAN that is protected by NAT is 100% invisible to the public Internet, so you can't put any publicly needed services inside that LAN, such as a file server, web server, etc. For a normal LAN you wouldn't be providing those types of services to the outside world anyway, however.

What is a VLAN?

A Virtual Local Area Network uses one physical switch, but that switch can be segmented into 2 or more individual "LANS" on that same local area network. This segments the data flowing over the LAN and keeps the data from each VLAN separate from every other VLAN.

What is a WMN?

A Wireless Mesh Network. It is basically taking a wireless access point and then using extenders - or beacon devices- placed throughout the coverage ara to ensure that all clients receive a solid wireless signal.

What if traffic comes into a router destined for an address not in that router's routing table?

A default gateway is set up that tells the router to send all traffic out the default route unless directed otherwise.

What is a Rogue DHCP server?

A device in your network - intentionally or unintentionally - is acting as a DHCP server and passing out incorrect IP addresses.

How is a LAN gateway router different than a router that connects separate LANs together?

A gateway router is just for a local area network. There is one LAN cable that goes to the switch for that LAN, and one external WAN connection from the ISP that provides Internet services to that LAN.

What do all Class A IPv4 addresses start with?

A number between 1 and 126.

What do all Class B IPv4 addresses start with?

A number between 128 and 191.

What do all Class C IPv4 addresses start with?

A number between 192 and 223.

What is another form of highly-directional antenna?

A parabolic antenna, like what is used by satellite TV or Internet providers.

When it comes to wireless, what is a "band"?

A range of radio frequencies.

How does a device's MAC address generate the last 4 sections of an IPV6 address?

A standard called EUI-64. The MAC address is split in half, and add in ff-fe.

What is Quality of Service?

A toolset that allows you to meter how much bandwidth is given to certain IP addresses, MAC addresses, etc., to ensure those devices get higher priority to consume the available bandwidth in your network.

What is Port Security?

A way to control what the LAN ports on a switch do if new or different devices plug into them. The port can shut down, send an email to an administrator, or multiple other options depending on the type of switch.

Why can't an IP address end in a zero?

A zero at the end of an IP address is the network address for that network - it does not identify a specific device.

In Windows, what do you have to do to make is so individual computers can share files with each other?

Add them all to the same Workgroup and they will be able to see each other in each computer's network.

How many IPV6 addresses will all devices have?

All devices will have both a link local IPV6 address and an IPV6 global Internet address.

What can you do with zeros to make IPV6 addresses shorter?

All leading zeros can be eliminated, i.e. - 0000 can just be displayed as 0, 0001 can just be displayed as 1, etc.

In Windows, what does Resource Monitor show you?

All of the presently open connections on your system, and all operating systems have a similar utility.

Describe a highly-directional antenna.

Also known as a Yagi antenna, highly-directional antennas propogate their signal in a straight line away from the the antenna's location. They are good for sending a wireless signal over longer distances.

What web browser works best when configuring network devices, such as switches and routers?

Although there are no industry standards on the subject, Internet Explorer often works better than other web browsers for network configuration tasks.

What is the difference between an IP address and a Port number?

An IP address will take you to a specific computer that you are trying to communicate with, while a Port number will take you to the actual application on that computer that you want to communicate with.

What 3 things are assigned to a device by a DHCP server?

An IP address, subnet mask, and default gateway.

How is Bluetooth different and RFID?

Bluetooth is used to connect 2 devices together - and ONLY 2 devices - in a Personal Area Network, or a PAN.

In the 2.4 GHz range, what are the 3 best channels to use, and why?

Channel 1, 6, or 11 are guaranteed not to overlap.

What are 2 things to check if a system is having intermitten connectivity issues.

Check for damaged cables or interference on the cable itself based on its location.

If you have limited connectivity over your network, what is one of the first things you should look at?

Check your IP address to make sure you don't have a 169.254.x.x IP address. If you do, that probably means your device is not getting an IP address from the DHCP server.

What are the 3 Classes of Bluetooth?

Class 1 has a range of 100 meters and a strength of 100 mW. Class 2 has a range of 10 meters and a strength of 2.5 mW. Class 3 has a range of 1 meter and a strength of 1 mW.

Name the 3 private IP addresses.

Class A addresses that start with 10.x.x.x. Class B addresses that range from 172.16.xx to 172.31.xx Class C addresses that start with 192.168.x.x.

Describe the octet configuration of a Class A, B, and C IP address.

Class A: 10.x.x.x Class B: 172.16.x.x Class C: 210.11.12.x

How many hosts are available for class A, B, and C IP addresses?

Class A: Million of hosts Class B: 65,534 hosts Class C: 254 hosts

How do you see the network configuration on a MAC?

Click the "Apple" icon, then system preferences, then TCP/IP.

What is DNS?

Domain Name Service matches up fully qualified domain names with the IP address of that website.

What is DHCP?

Dynamic Host Control Protocol is a way of automatically assigning IP addresses.

What is the user account issue to remember about sharing files or folders with other computers in your network?

Every computer has its own accounts that have to be set up to be a part of the group/Workgroup that has access to those files or folders. Just because the "Aaron" account on one computer has access does not mean the the "Aaron" account on the other computer has access.

Why can't an IP address end is 255?

For any given IP address, that is the broadcast address that sends the signal to every device on that network.

How can you temporarily change the DNS server you use to look for the IP address of any given website?

From the command prompt, type in the nslookup command. After hitting return, type "server 8.8.8.8" to use 8.8.8.8 as the DNS server for every lookup that follows.

What is a good security feature - according to CompTIA - to protect a wireless network?

Hide the SSID broadcast so people do not see your network.

What are Root Servers?

High-level DNS servers that control other DNS servers that include the IP addresses for all first-level domains, such as .com, .edu., .gov, etc.

What is the baseline standard that governs all wireless networking?

IEEE 802.11.

What type of address is used to communication from one LAN to another LAN?

IP addresses.

What is a common symptom of VLAN configuration problems?

If devices plugged into the same switch can't talk to or see each other, it is likely because they are in different VLANs on that switch.

What is one reason why a wireless client might not be able to connect to a network?

If that wireless device is set up to receive an IP address via DHCP, it might pull an APIPA address in between wireless access points, so unless you manually refreshed the connection, that APIPA address will not automatically go away just because you entered a different wireless network.

What is an easier practice than setting up DHCP reservations?

If you have a series of devices that you want to have a static IP address, just take that range out of the list of IP addresses that the router or DHCP server can hand out, and you will have eliminated the step of having to reserve those IP addresses.

What is the benefit of having a secondary DNS server?

If you suspect a possible DNS server problem, you can try one of the alternate DNS server IP addresses to see if your preferred or your DHCP assigned DNS server is having problems.

What can cause intermittent connectivity?

If your connection to the wireless network is not strong, your device can go through cycles of trying to reconnect, during which time you will have no connectivity. Also, if there are too many devices in the proximity of that WAPs that are logged into that wireless network, all users on that network are subject to varying levels of intermittent connection.

Where are IP addresses stored on a router?

In the routing table for that router.

What are second level domains that are controlled by lower-level DNS servers?

Individual websites such as google.com, yahoo.com, etc. They are controlled at the "second level" of DNS, but could still have dozens or hundreds of DNS servers per second level domain, based on the traffic that goes to those websites.

What is ICMP?

Internet Control Message Protocol is a single packer of information that is sent over the Internet, such as pinging another computer. ICMP is a connectionless protocol.

Describe an omni-directional antenna.

It is a single antenna that radiates its signal in all directions equally. Its signal radiation pattern looks like a fuzzy "ball" around the antenna. The more power the antenna has, the larger the ball is.

What is the IP address of the default gateway?

It is almost always the first IP address in that network, which means that the 4th octet will most likely be the number one.

What is a good reason to not statically assign IP addresses?

It is possible that there will be IP address conflicts, especially if the DHCP server does not know to not hand out any of the statically assigned IP addresses.

What is the 802.11 wireless Infrastructure Mode?

It is the standard that is used in everyday situations where WAPs are plugged into a physical ethernet connection and then they radiate wireless signals to the area that they cover.

What does it mean if you use nslookup, temporarily change the DNS server that you are using, and the results are good, but your regular DNS server is timing out.

It means that your DNS server is down.

Describe a dipole antenna.

It radiates a signal in a circular pattern like an omni-directional antenna, but the signal primarily extends horizontally, rather than in a 360-degree pattern. That radiation pattern is useful for keeping the wireless signal roughly in a horizontal area, such as a certain floor of an office building.

What does the command nslookup do?

It shows you your local DNS server, and from there you can type in a website address to find out its IP address.

Describe the 802.11ac standard.

It uses Multi-user MIMO, which is the same as standard MIMO, only multiple different devices can be sought after to connect to.

On a Windows machine, what does adding the "-t" switch to the ping command do?

It will make the ping continue past the standard 4 pings, as opposed to using a Linux or MAC machine, which ping non-stop by default.

What will a router do if it is given a private IP address?

It will not route that packet because private IP addresses are not routable on the Internet.

If you are having a problem with any given wireless profile, what is the easiest way to fix it?

Just forget the network and then start all over again.

If a critical device is experiencing slow network speeds, what can you do?

Log into the router or switch to enable QoS and configure it to give your critical devices a higher priority.

What is important to remember about the application of Bluetooth classes.

Make sure you choose a class that is appropriate for the application. For example, you don't need a Class 1 Bluetooth keyboard, because you won't be using your keyboard 100 meters away from your computer.

What is VLAN 1?

Many managed switches will have a VLAN 1 by default which includes every port on that switch unless they are assigned to a different VLAN.

What are Class D IP addresses usually used for?

Multicasting.

What is MIMO?

Multiple-input Multiple Output is an 802.11 ONLY standard that allows the wireless signals that are propogated to actively seek out one device to connect to.

What is NFC?

Near Field Communication is an RFID technology where a device - such as a smart phone - taps an RFID sticker on something such as a printer, and the very low power signal tells the printer what to do. Another example is Tap to Pay.

What replaced NetBIOS/NetBEUI?

NetBT, which just meant NetBIOS over TCP/IP. Unlike the original NetBIOS/NetBEUI, it used IP addresses instead of MAC addresses.

What is NAT?

Network Address Translation. It allows a LAN to have only IP address that faces the outside world that has to be routable on the Internet. Every other device in that LAN can have as many private IP addresses as they need, because those IP addresses do not have to be routable on the public Internet.

If a DHCP server goes down, do all devices automatically lose their IP addresses?

No, it is only when a computer restarts that it goes looking for a new IP address via DHCP. If a DHCP server goes down, the best thing to do is not restart any of the devices in your network until it comes back up.

Do you have to configure encryption on the extenders that are used in a wireless mesh network?

No, most of them use their own, internal encryption.

Are wireless access points (WAPs) actually wireless?

No, not at all. Wireless access points are plugged into a physical LAN connection, and then they radiate that network wirelessly to the area that they cover.

Do switches use IP addresses?

No, switches operate on MAC addresses. However, you can assign a switch an IP address in order to configure it, thus making it a Managed Switch.

If a DHCP server can't be contacted, and all of the computers in that LAN can no longer get IP addresses, is that LAN dead until the DHCP server comes back up?

No, those devices just won't be able to get out to the public Internet. Since every device in that network will have a Class B APIPA IP address that starts with 169.254, they will all still be on the same network. The devices will still be able to communicate with each other and with other devices such as printers and file shares that are inside that network.

Do routers have to have an Ethernet connection to the outside world in order to work?

No. Ethernet is just common. A router can gets its connection from a cable modem, satellite, etc.

If you are connected to a wireless network, does that mean that you automatically have full access to that wireless network?

No. Sometimes a connection to a wireless network is just enough to connect to it, but not enough to actually transmit and receive data.

Do people set up their wireless devices to use a specific frequency range in the 2.4 GHz band?

No. There are 14 channels that the 2.4 GHz range is broken up into that can be chosen from in order to determine where the most effective wireless signals are. This keeps everyone who is using the 2.4 GHz range from constantly interferring with each other.

What are the 3 types of antennas that are used to direct wireless signals?

Omnidirectional, patch, and highly directional.

What can you do to eliminate multiple consecutive sets of zeros in an IPV6 address?

One time - and only one time - per IPV6 address, you can eliminate consecutive sets of zeros by typing 2 sets of colons next to each other.

Describe a patch antenna.

Patch antenna are flat in appearance and radiate in only half of a circular area - the area in front of the patch antenna. They are idial if you only want your wireless signal to go in front of your antenna, rather than all around it.

When you get a new SOHO router, how can you configure it if you don't know its IP address?

Plug it into your computer that is set up via DHCP and then run IP or IFCONFIG. The default gateway that is listed will be the router's IP address, and then you can navigate to that IP address to configure that router.

What does RFID stand for?

Radio Frequency Identification.

What is SNMP?

Simple Network Management Protocol is a tool that allows you to not only view or query all network devices such as routers, switches, etc., but to also see specific details about what and how those devices are acting on the network.

What is SMB?

Symmetric Message Block also sometimes known as Server Message Block. It is a more modern Microsoft file-sharing system that some operating systems call Samba.

What does a computer receive if it got a communication over TCP vs. UDP?

TCP would deliver a TCP packer while UDP would deliver a UDP datagram.

What does the term Dual Stack mean?

That device is running both IPV4 and IPV6.

What are the 2 ISM bands that are used by the 802.11 standards?

The 2.4 GHz band or the 5 GHz band.

When setting up a wireless access point, should you let the WAP choose its channels automatically, or manually set them?

The 2.4 GHz range tends to be more crowded, so it is often best to manually set the channels, whereas the 5 GHz band has enough room that letting the WAP automatically choose channels usually works. However, as the network administrator, you should still use a wi-fi analyzer regularly around your WAPs to determine if their signal needs to be manually configured for a less crowded area of the band.

What is APIPA.

The Automatically Programmable IP Addressing. It is the method that all computers use to assign themselves an IP address if they can't connect to their DHCP server.

What is an IPV6 Internet address?

The IPV6 address that is assigned to you by your gateway router.

What is an IPV6 link local address?

The IPV6 address that is automatically generated by a device using IPV6 whenever the device starts up.

What is ISM?

The Industrial, Scientific, and Medical radio bands.

What is an SSID?

The Service Set Identifier is the actual name of any given wireless network. It can be broadcast, which is normally the default setting, or it can be hidden.

On a laptop computer, what serves as the antenna for the the built-in wireless access card?

The antenna is physically built into the monitor.

What does the link local IPV6 address end with?

The last 4 sections of the address are generated using the 48-bit MAC address of the device.

What is the purpose behind specifying specific DNS servers for the computers in your LAN to use?

The number of DNS servers between your LAN and the "all-knowing" root servers could be dozens or hundreds of computers. It is faster and more efficient to just query a closer second level DNS server.

What was NetBIOS/NetBEUI?

The original, MAC-address based system of sharing files and folders between computers that were running Microsoft Windows.

In most SOHO - small office/home office - LANS, what serves as the DHCP server?

The router normally doubles as the DHCP server for SOHO LANs.

What if the second level DNS server that a LAN queries doesn't recognize the DNS request from your LAN?

The second level DNS server knows to then go to the geographically closest DNS root server to find that information.

In addition to the source and destination IP address, what other source and destination information is added to a packet that is routed across the Internet?

The source and destination Port number, so the packet knows what application to send the data to, and what application on the originating computer to send the data back to.

What is the security concern with sharing files/folders with computers that have similar login accounts?

The temptation will be to use the same password for the "Aaron" account on every computer in that workgroup, but that creates a single point of failure if that same password is used for every "Aaron" account in that workgroup

How does RFID work?

There are stickers that have a specific radio frequency, and those stickers are placed on objects, such as boxes in a warehouse. Then, when a portable RFID reader points it's beam at the sticker, the sticker is actually momentarily energized with RF energy, and the information contained on that sticker is then sent to the reader.

Are all switches managed or unmanaged switches?

There are switches that do not have the option of being managed in any way - they just move network traffic according to default settings. A managed switch gives the option of configuring that switch in many way, and managed switches are more expensive as a result.

What are Class E IP addresses usually used for?

They are reserved and not used on the public Internet.

What is unique about the channels in the 5 GHz band?

They are seemingly random, and most of the channel numbers are even.

What does TCP/IP stand for?

Transmission Control Protocal/Internet Protocol. The TCP portion is a connection-oriented protocol.

What can you do if you don't want to be connected to the local DHCP server anymore?

Type ipconfig /release to be released from automatically getting IP addresses from that DHCP server.

How do you manually reach out to a DHCP server to request a new IP address?

Type ipconfig /renew.

How do you find out more detailed network information about a system?

Type ipconfig or ifconfig /all.

What is UPnP?

Universal Plug and Play is an option that can be enabled on routers, switches, and other devices in order to make themselves more "noisy" so they will be discovered by other computers or network devices. It is similar to LLDP, or Link Layer Discovery Protocol.

How do you see the IP configuration for your own system?

Use the ipconfig command or if config command.

What is UDP?

User Datagram Protocol is a connectionless protocol where there is no confirmation between the communicating computers that there messages are being received by each other.

What does VLSM stand for?

Variable Length Subnet Mask.

What are the 3 different types of Port numbers?

Well-known port numbers from 0 to 1,023, registered port numbers from 1,024 to 49,151, and Dynamic/Ephemeral ports from 49,152 to 65,535.

What is Ad-Hoc mode?

When one computer on any given network acts as the wireless access point and all of the computers in the area can log into that Ad-Hoc network. This is useful for local gaming or file sharing.

When looking at a subnet mask, what do the number 255 mean?

When trying to communicate with another device, any octet that has a 255 in the subnet mask must match with the device that also has 255 in those octets. Those devices are in the same network because the octets that have 255 are always going to be exactly the same.

What is the purpose of setting up DHCP reservations?

When you set up a range of IP addresses for your router or DHCP server to give out, you can manually reserve IP addresses so they will never be given out. You would do this if you had any individual device(s) that you statically assigned an IP address to that you wanted that device to always keep.

What are Wi-Fi 4 and Wi-Fi 5?

Wi-Fi 4 is another way to describe 802.11n, and Wi-Fi 5 describes 802.11ac.

What is the purpose behind wireless profiles and how can they work against you?

Wireless profles on any given device remember your settings so the next time you are in range of that wireless network, you automatically connect to it. However, if you change your settings and/or if the adminstrator for the WAP changes the network settings, you will no longer be able to connect until you update your profile.

Are SOHO routers that generate wireless signals considered WAPs?

Yes, but remember that the wireless portion of what they are doing is just that one task. They are also still a router, and - depending on the model - often times they are a switch as well.

Is it possible for a router to also be a Wireless Access Point (WAP).

Yes, depending on the manufacturer and how it is configured.

Can you assign IP addresses and other network information to a computer that it can use if the DHCP server goes down?

Yes, in the alternate settings of the network configuration on your device, you can manually type in an IP address, subnet mask, default gateway, etc.

What is the purpose of using a Loopback address?

You can ping your loopback IP address to make sure your network card is working properly.

What is the important thing to remember about connectivity between WAPs that produce a particular 802.11 standard signal vs the device they are connecting to?

You will only get the full benefits of any given 802.11 standard if both the WAP and the device it is connected to support the same standards.

What is important to remember about the firmware for a SOHO router?

Your ISP will not tell you when a firmware update is available, so unless your SOHO router has an auto-upgrade feature, you will need to periodically go to the router manufacturer's website to search for an update.

If you request a web page over the regular, unencrypted Internet over Port 80, the http port, what Port on your computer does the information come back?

Your operating system assigns your request a generic port number, rather than Port 80, because Port 80 is for all requests for http services. If you have multiple tabs open, your computer randomly assigns a port number to each of those tabs so the computer you are trying to talk to over Port 80 knows which tab to respond to.

What does the link local IPV6 address always start with?

fe80:0000:0000:0000, which is concatenated down to fe80::.