In preparation to write my CompTIA A+ Certification....

[Drone4four]

I intend to write my CompTIA A+ Certification in the next few weeks. In preparation, I have come across some questions I can’t answer by my self. A few of the questions are Windows specific, so I will spare asking you folks these questions. I was hoping that you Ubuntu people could field some of my questions that are platform agnostic. Here they are:

1. My textbook claims, in the context of wireless device standards:

Another issue is the standard supported by each device. If possible, for each wireless network installation, select NICs and WAPs that comply with the exact same Wi-Fi standard. Even though 802.11g, which is faster than 802.11b, is downward compatible with the slower standard, even a singly 802.11b device on the wireless network will slow down the entire WLAN.

(Holcombe, 2012: 803)

If I connect my slow Kyocera RISE smartphone to my home WLAN, would that bring down/drag down all the download speeds of all the laptops? I’m not sure exactly what the Wi-Fi standard is of my smart phone device and I don’t know how fast my wireless router is, neither do I know what standard the laptops are on my WLAN. What I know for sure is that my cell is really slow (1Mbps down) and my laptops consistently download at 12Mbps. Accessing the WLAN with my cell doesn't slow down my laptops. What is my textbook referring to when it claims that 802.11b devices will slow down all the 802.11n devices connected to a network?

2. Let’s say I have 3 laptops on my home network with these IP addresses:

192.168.1.0
192.168.2.0
192.168.3.0

Are these addresses unique compared to all the other 4.2+ Billion devices on the global IPv4 internet? That can’t be true because 192.168.1.0 is a common ip address I have seen on many computers. How can every ip address assigned using a dhcpd service on the global internet be unique and yet devices on home networks be duplicated hundreds of thousands of times over and over, as in my example?

3. Are FTP/HTTP/IRC/BitTorrent protocols built on top of more basic protocols such as TCP/IP and UDP?

4. Practice review question # 3 for chapter # 1 says: “I plan to replace the power supply in a computer. What is the most important safety measure I should take to protect myself? The incorrect answer is to ground yourself by wearing an anti-static wrist band.” The correct answer is to NOT ground yourself. Why is that? Holcombe’s text on page 14 seems to contradict itself. The text book claims, “Touching a grounded portion of your computer’s chassis will work to some extent, but for complete safety, us an ESD wrist strap with a ground wire attached to the computer frame.” WTF? Is wearing an anti-static wrist strap a good idea or not?

5.Can you use a loopback plug to test whether or not a switch port is functioning? (Ch16Q#1)
Do you use nslookup as an alternative or substitute for a DHCP daemon to obtain an ip address for the localhost so it can access the internet? Could you furthermore use, ipconfig /renew as an alternative?

6. If a default gateway is down, I would think that I wouldn’t be able to communicate on LAN and access the internet, rather than only be able to access the global internet. (Ch15Q#13)

[misterbiskits]

I'm not an expert but:
#2: 192.168.x.0 are unique on the LAN side of the internet. The WAN side knows nothing about these adresses. The router has its own unique WAN IP address. The LAN IP requests things from the router, and the router then requests from the internet. The router receives the data and relays it to the requesting LAN address. As I said not an expert but does that sound correct?

[coldraven]

4. The power supply has two sides. On the input side there are high, possibly lethal, voltages. On the output side you have low (12volt, 5volt) voltages.
Also, inside the power supply there are large capacitors that could retain a high voltage even when turned off.



If you were, say, adding memory to the motherboard you would wear a wrist-strap to eliminate static electricity from your body by shorting it to ground.
(The static could be caused by your synthetic clothing)
Static voltages can be high but the total amount of electrical charge is very low so it is dissipated in a microsecond.
But you would have disconnected the mains supply so that there was no chance of electrocution.

However, if you were wearing a grounded wrist-strap and touched a high voltage item with the other hand you would get a shock right across your heart.
Even as little as 100volts will stop your heart in this situation. (Much higher charge - see http://en.wikipedia.org/wiki/Coulomb)

An old electricians tip was to keep one hand in your pocket when fiddling with live equipment. If you get a shock it will go down your legs to ground and miss your heart. OK you will still jump, but your chances of living are higher.

[Drone4four]

4. The power supply has two sides. On the input side there are high, possibly lethal, voltages. On the output side you have low (12volt, 5volt) voltages.
Also, inside the power supply there are large capacitors that could retain a high voltage even when turned off.



If you were, say, adding memory to the motherboard you would wear a wrist-strap to eliminate static electricity from your body by shorting it to ground.
(The static could be caused by your synthetic clothing)
Static voltages can be high but the total amount of electrical charge is very low so it is dissipated in a microsecond.
But you would have disconnected the mains supply so that there was no chance of electrocution.

However, if you were wearing a grounded wrist-strap and touched a high voltage item with the other hand you would get a shock right across your heart.
Even as little as 100volts will stop your heart in this situation. (Much higher charge - see http://en.wikipedia.org/wiki/Coulomb)

An old electricians tip was to keep one hand in your pocket when fiddling with live equipment. If you get a shock it will go down your legs to ground and miss your heart. OK you will still jump, but your chances of living are higher.

I am still wrestling with the analysis for my question #4. But thanks to coldraven, I think I am beginning to understand. Can someone please verify that I understand this correctly? From what I gather from coldraven’s post, it is a good idea to wear an anti static wrist strap when handling smaller hardware in a PC, like RAM, because it's conceivable that electrostatic build up could transfer from my clothes to the RAM, rendering the RAM permanently damage. By wearing a strap, I am proactively avoiding damage to said computer components. But when handling more sensitive higher voltage electrical components, like a power supply, wearing an anti static wrist strap could be lethal -- if 100 volts are discharge from the PSU, it could potentially stop the heart of a given technician. The difference between the first instance of ESD is a minor transfer of electricity from my clothes to the RAM, meanwhile the other instance of ESD is a huge transfer of 100+ volts from the PSU to the heart. This is why it's a good idea to wear a an anti static strap when replacing RAM, but a bad idea to wear such a strap when replacing a PSU. Is this accurate?

[Drone4four]

I'm not an expert but:
#2: 192.168.x.0 are unique on the LAN side of the internet. The WAN side knows nothing about these adresses. The router has its own unique WAN IP address. The LAN IP requests things from the router, and the router then requests from the internet. The router receives the data and relays it to the requesting LAN address. As I said not an expert but does that sound correct?

So misterbiskits, are you basically saying that the address assigned to devices on a SOHO are unique only to that LAN? So can I infer that a DHCP service hosted by my ISP will assign a unique address to the chief router of my LAN, enabling that router to serve as the gateway to the global WAN for all the devices under it on my SOHO LAN? ...and therefore each default gateway should be among the unique ~4.2 billion IPv4 addresses? I suppose that these 4.2+ Billion address are either (1) other default gateways, (2) devices which directly access the internet (like smartphones) or (2) servers resolved by a DNS?

I think this explanation is relevant to one of my other question (#6). My textbook says that if my default gateway is down, I should only be able to communicate with the global internet and unable to communicate with the other devices on my LAN. I’m all like, wtf? I would think that if my default gateway was down, I wouldn’t be able to communicate with the other devices on my LAN and I also wouldn’t have access to the global WAN. Can someone please clarify?

[lykwydchykyn]

So misterbiskits, are you basically saying that the address assigned to devices on a SOHO are unique only to that LAN? So can I infer that a DHCP service hosted by my ISP will assign a unique address to the chief router of my LAN, enabling that router to serve as the gateway to the global WAN for all the devices under it on my SOHO LAN? ...and therefore each default gateway should be among the unique ~4.2 billion IPv4 addresses? I suppose that these 4.2+ Billion address are either (1) other default gateways, (2) devices which directly access the internet (like smartphones) or (2) servers resolved by a DNS?

You want to read up on NAT and private IP ranges. There are several IP ranges designated as private ranges, and they will not route across the internet. 192.168.x.x is the most commonly used in consumer equipment, but there are a couple others. What you're saying is basically correct, though.

I think this explanation is relevant to one of my other question (#6). My textbook says that if my default gateway is down, I should only be able to communicate with the global internet and unable to communicate with the other devices on my LAN. I’m all like, wtf? I would think that if my default gateway was down, I wouldn’t be able to communicate with the other devices on my LAN and I also wouldn’t have access to the global WAN. Can someone please clarify?

Your textbook is wrong. If your gateway (and ONLY the gateway) is down, you can still communicate with devices on the same subnet (LAN, basically, though it's possible to set up a LAN with multiple subnets). You won't be able to communicate outside the subnet.

3. Are FTP/HTTP/IRC/BitTorrent protocols built on top of more basic protocols such as TCP/IP and UDP?

This gets into different layers of the OSI stack. I think this is more Network+ stuff rather than A+, but basically IP is one layer (logical addressing), TCP/UDP are another layer up (transport layer), and those other protocols are on top of that (application layer).

[CharlesA]

You might see some basic stuff on the OSI model on the A+, but it's unlikely. When I took the A+, it was super easy to figure out which answer was the right one and the version I took was probably 75% customer service questions.

[coldraven]

Re:4
I think you have understood it correctly.
I did not make clear the danger of AC electricity. Rather simplified, think of your heart as a fuse. Which do you think would blow first, your heart or the fuse in the circuit?
Good luck with your exams.

[Drone4four]

Thank you, lykwydchykyn , for replying to my questions for clarification.

And thanks, coldraven, for your follow up post.

I have come across a practice question in the Network Basics chapter. I read the in depth answer key and looked up the corresponding material in the companion textbook but I still can't figure out why the correct answer is correct. Here is the question transcribed from the textbook, along with my analysis of the answer choices.

#4
For a client’s SOHO, all the devices need to have their network addressing information configured using static, rather than dynamic, addressing. Of the following, what addressing information can you configure for the computer? (Choose three.)
A. The computer’s IP address and subnet mask
B. The address of the default gateway
C. The address of the preferred DHCP server
D. The address of the preferred DNS server

I am inclined to cross off D, because my understanding of the Domain Name Service is that it’s basically a centralized database of IP addresses of web servers resolved to human readable words or phrases. The IP, ‘173.194.64.99’, is resolved to Google.com by America’s centralized Domain Name Service servers that are hosted at FCC headquarters in Washington DC. Right now every country has a DNS like this one. The wingnuts on Slashdot chime in whenever authoritarian governments like Russia, China or Iran push to have a global centralized location so they can control by rendering inaccessible certain websites that offend the morals of the state. Is this all a fair assessment of how DNS’es work? Getting back to answer choice D in the question, small home office networks don’t have to use a DNS because DNS is only used by servers in the cloud. A sysadmin for a SOHO can manually set the computers’ IP addresses and subnet masks, along with default gateways, if s/he were so inclined to do so. So I circled A and B. I have to circle one more. As I have discussed, DNS is a centralized FCC thing, so a sysadmin for a SOHO isn’t going to specify a DNS server. By process of elimination, C should be the other correct answer choice, even though DHCP is a program you use to request IP addresses from your ISP -- again, something a sysadmin has no control over. I looked up the in depth answer key at the end of this chapter and from what I can tell, it says mostly the same things I have talked about except for some reason it says that a SOHO sysadmin can specify the preferred DNS server. How and why is that possible?

Can someone clarify how and why a sysadmin can specify a preferred DNS server?

[CharlesA]

DNS is used for name resolution. That doesn't mean it is limited to strictly web servers or web traffic. Depending on how your network is set up, you can either use broadcast for name resolution (messy on large networks) or have a server holding a catalog of all the hosts on the network and forwarding requests to external DNS servers if they do not have a record othe host being accessed.

If you have a static IP, you would need to configure the DNS servers, otherwise the machine won't know who to talk to to resolve host/domain names.

In Linux, it depends on your flavor. I use the interfaces file, but I think Ubuntu defaults to network manager.

In Windows, network connections.

No idea where it is in OSX, but it's probably similar to Linux.

The answer is A,B, D. You cannot use DHCP on a static address.