Basic networking for a dummy

[The Technician]

Hey guys,

As a few of you know, I am new to the technical side of computers and networking, and self-studying for the 802 A+ certification exam. Among other things that I'm struggling to understand, is the fundamentals of networking. I've gone over at least a dozen articles and videos, including Technet, and it's all really just gibberish to me. So, before I go reading yet another 'understanding basic networking' article only to come away confused, I thought I would try this...

Below is a question that I got on a practice exam...

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A critical server was replaced by the IT staff the previous night. The following morning, some users are reporting that they are unable to browse the internet upon booting their workstations. Users who did not shut down their workstations the previous day are able to connect to the internet. A technician looks at the following report from a workstation with no internet connectivity:

IP Address: 192.168.1.101
Netmask: 255.255.255.0
DHCP Server: 192.168.1.1
DNS Server: 192.168.1.2
Default Gateway: 192.168.1.1

Given the above report, which of the following is the cause of why some workstations are unable to browse the internet?
A. The DHCP server is unavailable
B. The workstation has an APIPA address
C. The DHCP server is misconfigured
D. The default gateway router is misconfigured

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Now, I know that the correct answer is C because the practice test told me so when I got it wrong. But I have no idea WHY.

I understand what everything is and what everything does. I can tell you what class an IP is, whether or not it's an APIPA. I can tell you what services like DNS and DHCP do, I can tell you what TRACERT and IPCONFIG display, etc. But when I am presented with a scenario and asked to find what's wrong with it, I do not have the understanding of how it works to solve the problem. And I need that understanding so that when I type IPCONFIG, I not only know what I'm looking at, but I understand how it works well enough to know when something is wrong by looking at the data that it shows me.

To make a long story short, I clearly don't understand the basics of networking, and I thought that the above test question was a great sandbox for you guys to show me how it works.

Thanks in advance. Any help is greatly appreciated!

 

[Spud1200]

This is from Wiki:

The Dynamic Host Configuration Protocol (DHCP) is a standardized network protocol used on Internet Protocol (IP) networks for dynamically distributing network configuration parameters, such as IP addresses for interfaces and services. With DHCP, computers request IP addresses and networking parameters automatically from a DHCP server, reducing the need for a network administrator or a user to configure these settings manually.

I understand what everything is and what everything does. I can tell you what class an IP is, whether or not it's an APIPA. I can tell you what services like DNS and DHCP do, I can tell you what TRACERT and IPCONFIG display, etc. But when I am presented with a scenario and asked to find what's wrong with it, I do not have the understanding of how it works to solve the problem. And I need that understanding so that when I type IPCONFIG, I not only know what I'm looking at, but I understand how it works well enough to know when something is wrong by looking at the data that it shows me.

I could have this totally wrong but my guess would be if you are familiar with what everything does, how it works, and it's purposes then run with it. Think of it like a Bus Network and how everything is working in tandem. If you are fault finding then think logically and look at the scenario and work threw it step by step until you have exhausted all other possibility's.

From what I can tell is that you are not looking at this as a process and thus are getting confused.
I hope I'm not insulting you but with what I have put in bold and what you have said about your understanding of Network Infrastructure it could simply be a process with you of working threw it logically.

 

[S0ULphIRE]

A technician looks at the following report from a workstation with no internet connectivity:

IP Address: 192.168.1.101
Netmask: 255.255.255.0
DHCP Server: 192.168.1.1
DNS Server: 192.168.1.2
Default Gateway: 192.168.1.1

Given the above report, which of the following is the cause of why some workstations are unable to browse the internet?
A. The DHCP server is unavailable
B. The workstation has an APIPA address
C. The DHCP server is misconfigured
D. The default gateway router is misconfigured

Um, I have to be missing something because I can't see any reason why C would be the correct answer based on the above...

It's been assigned an IP address, which means DHCP is working
The IP Address is in the same subnet as the DHCP/DNS/Gateway IPs, which means it should be able to reach the default gateway.

I don't see how any of that points to an incorrectly configured DHCP service it IS early here though

 

[The Technician]

I could have this totally wrong but my guess would be if you are familiar with what everything does, how it works, and it's purposes then run with it.

Again, that's my issue - I clearly don't understand how it works.

I know that DHCP automatically assigns IP addresses to the computer. That DNS resolves host names to IP addresses. That the Default Gateway is the node that stands between my network and the outside (my router, for example). That IPCONFIG displays the addresses of the DHCP & DNS servers, my computer, the subnet my computer resides in, and my gateway (router).

But none of that knowledge allows me to identify a problem by looking at IPCONFIG.

If I type IPCONFIG:
How do I know that the DNS server's address is wrong? And if I do, how do I know what's causing it?

I know that if IPCONFIG tells me that my computer's IP address is an APIPA, then the DHCP server is unavailable or down or can't be reached. But how can I tell that the DHCP server is misconfigured by simply viewing IPCONFIG?

Basically, if this exam shows me a screenshot of a hypothetical IPCONFIG, and asks me to "identify the problem shown in the screenshot", knowing what DHCP and DNS are isn't going to help me.

 

[Spud1200]

Again, that's my issue - I clearly don't understand how it works.

I know that DHCP automatically assigns IP addresses to the computer. That DNS resolves host names to IP addresses. That the Default Gateway is the node that stands between my network and the outside (my router, for example). That IPCONFIG displays the addresses of the DHCP & DNS servers, my computer, the subnet my computer resides in, and my gateway (router).

But none of that knowledge allows me to identify a problem by looking at IPCONFIG.

If I type IPCONFIG:
How do I know that the DNS server's address is wrong? And if I do, how do I know what's causing it?

I know that if IPCONFIG tells me that my computer's IP address is an APIPA, then the DHCP server is unavailable or down or can't be reached. But how can I tell that the DHCP server is misconfigured by simply viewing IPCONFIG?

Basically, if this exam shows me a screenshot of a hypothetical IPCONFIG, and asks me to "identify the problem shown in the screenshot", knowing what DHCP and DNS are isn't going to help me.

Dude now I get you. Ahh I say.

When typing IPCONFIG check you have even basic connectivity by pinging the IP Address.

I know that DHCP automatically assigns IP addresses to the computer. That DNS resolves host names to IP addresses. That the Default Gateway is the node that stands between my network and the outside (my router, for example).

As you have said as I think you have answered you own question the DHCP assigns IP Addresses . The reason I think the answers C is because the Scope and Range of the IP Addresses available is given by that server and thus its miss configured because the DNS is like a Hierarchical distribution system.

I'm not an expert so you'll have to check.

Ask Carnage, that gyes a pure brain box with Windows ECT:

 

[cyclones]

I would think the DHCP IP address would need to be different than the Default gateway;s IPM address, wouldn't it?

 

[S0ULphIRE]

Nope! If you check your average home network the IP is usually the same for all three - i.e. you use your router's IP address for all three fields.

There is seriously no reason I can see that C is the correct answer there...all the values are 100% potentially acceptable.

If I type IPCONFIG:
How do I know that the DNS server's address is wrong? And if I do, how do I know what's causing it?

IPConfig won't always tell you what's wrong - but there are certain situations where you can spot something wrong

For example, if you did an IPCONFIG on a home network and it told you the following:

IP Address: 192.168.1.55
Subnet: 255.255.255.0
DNS Server: 192.168.2.1
DHCP Server: 192.168.1.1
Default Gateway: 192.168.1.1

We can see straight away that there's a potential problem with our DNS server config - we specified a subnet that ranges from 192.168.1.x, but the DNS server is in a different network 192.168.2.x

Or if you did an IPCONFIG and it told you your address was 169.254.253.116, we could straight away know that our DHCP server isn't contactable. Stuff like that is what you can glean

As for knowing what's causing it, I guess that's where experience can come in. How about you tell me, what likely causes could there be for a PC to not get a DHCP address?

 

[1etherer]

Strange question...

If the DHCP was a server then it would have a different IP to the Default gateway... which it doesn't, so the router is running the DHCP.

The DNS is on a different IP, so its on a server (of course the DC).

So the new DC server would be put in and the PC turning back on will pick up the new info needed. and the PC's left on over night would need to reconnect or flush DNS.

So the answer should be along the lines of the DC server (DNS)...

But, what happens when a DHCP server is replaced while PCs are on is, the PCs will keep the IP e.g 192.168.0.10 and when the other PCs turn back on DHCP will give out 192.168.0.10.. so there will be conflict... and if its misconfig then "all" PCs will get an APIPA IP...

This question is either typed wrong or the person has tried to make it confusing but in doing so he/she has messed up the possible answers..
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What is the exam software your using? I think some answers and questions may be wrong...

I know with examcollection software they have wrong answers..

 

[MidnightShadow]

A critical server was replaced by the IT staff the previous night. The following morning, some users are reporting that they are unable to browse the internet upon booting their workstations. Users who did not shut down their workstations the previous day are able to connect to the internet. A technician looks at the following report from a workstation with no internet connectivity:

IP Address: 192.168.1.101
[/SIZE][/FONT]Netmask: 255.255.255.0
DHCP Server: 192.168.1.1
DNS Server: 192.168.1.2
Default Gateway: 192.168.1.1

Given the above report, which of the following is the cause of why some workstations are unable to browse the internet?
A. The DHCP server is unavailable
B. The workstation has an APIPA address
C. The DHCP server is misconfigured
D. The default gateway router is misconfigured

Nope! If you check your average home network the IP is usually the same for all three - i.e. you use your router's IP address for all three fields.

There is seriously no reason I can see that C is the correct answer there...all the values are 100% potentially acceptable.

SOUL, you are correct by saying that they are potentially right, BUT you're thinking consumer grade routers such as Netgear, Linksys, etc. This is clearly an enterprise environment which makes a huge difference. Routers typically just route and don't provide DHCP or DNS in this environment, and the question actually tells you that a critical server was replaced and since then there has been a problem.

C would make the most sense here and I'll explain why. The KEY to this whole question is:

"A critical server was replaced by the IT staff the previous night. The following morning, some users are reporting that they are unable to browse the internet upon booting their workstations. Users who did not shut down their workstations the previous day are able to connect to the internet."

The users who didn't shut down have workstations that retained the previous settings, so they're not reaching out to the DHCP server for new settings like the folks who are booting up and are able to connect with no issue. The folks booting up are getting their settings from the DHCP server, which isn't providing them properly.

In a consumer environment (we'll use Linksys here as the example) the router handles DHCP settings and usually provides DNS settings as well. Think of it as the teacher of the classroom, and the teacher gives assigned seats as the students come into the class (printers, iPads, etc). The router can choose from the range, which is 192.168.1.1 (typically on consumer) through 192.168.1.254. So, that's 254 seats, but the first one belongs to the teacher. So, there's 253 left from .2 - .254.

In these cases, the router also provides DNS, which is usually provided by the ISP. If not, it can also use it's own IP address as a DNS server. DNS, simply put, translates Best Buy: Expert Service. Unbeatable Price. (which is easy to remember) into 23.212.109.99 (which isn't as easy to remember. You can type either of those into a web browser and still end up at Best Buy's web site, but the purpose of DNS is to make addresses easy to get to without remembering a bunch of numbers (which is going to be much more difficult/impossible with IPv6).

Now then, in an enterprise environment such as this, a DHCP server is typically NOT the router. Even the DNS server could be completely different. Some places will use an external DNS server such as Google's DNS, one of which is 8.8.8.8, for example. All of those can be different and, at the end of the day, don't relate back to the original problem.

Focus only on the facts you're given in the question. A critical server was changed, newly booted workstations (trying to get their settings) cannot connect, workstations that were already booted from yesterday are still connecting (they already had their settings and aren't trying to reach the server for them).

Hope that rambling helps. If I can clarify anything, I'm happy to try.

 

[1etherer]

SOUL, you are correct by saying that they are potentially right, BUT you're thinking consumer grade routers such as Netgear, Linksys, etc. This is clearly an enterprise environment which makes a huge difference. Routers typically just route and don't provide DHCP or DNS in this environment, and the question actually tells you that a critical server was replaced and since then there has been a problem.

C would make the most sense here and I'll explain why. The KEY to this whole question is:

"A critical server was replaced by the IT staff the previous night. The following morning, some users are reporting that they are unable to browse the internet upon booting their workstations. Users who did not shut down their workstations the previous day are able to connect to the internet."

The users who didn't shut down have workstations that retained the previous settings, so they're not reaching out to the DHCP server for new settings like the folks who are booting up and are able to connect with no issue. The folks booting up are getting their settings from the DHCP server, which isn't providing them properly.

In a consumer environment (we'll use Linksys here as the example) the router handles DHCP settings and usually provides DNS settings as well. Think of it as the teacher of the classroom, and the teacher gives assigned seats as the students come into the class (printers, iPads, etc). The router can choose from the range, which is 192.168.1.1 (typically on consumer) through 192.168.1.254. So, that's 254 seats, but the first one belongs to the teacher. So, there's 253 left from .2 - .254.

In these cases, the router also provides DNS, which is usually provided by the ISP. If not, it can also use it's own IP address as a DNS server. DNS, simply put, translates Best Buy: Expert Service. Unbeatable Price. (which is easy to remember) into 23.212.109.99 (which isn't as easy to remember. You can type either of those into a web browser and still end up at Best Buy's web site, but the purpose of DNS is to make addresses easy to get to without remembering a bunch of numbers (which is going to be much more difficult/impossible with IPv6).

Now then, in an enterprise environment such as this, a DHCP server is typically NOT the router. Even the DNS server could be completely different. Some places will use an external DNS server such as Google's DNS, one of which is 8.8.8.8, for example. All of those can be different and, at the end of the day, don't relate back to the original problem.

Focus only on the facts you're given in the question. A critical server was changed, newly booted workstations (trying to get their settings) cannot connect, workstations that were already booted from yesterday are still connecting (they already had their settings and aren't trying to reach the server for them).

Hope that rambling helps. If I can clarify anything, I'm happy to try.

But the DHCP and router are the same (same IP so on the same hardware/ NIC).. The DNS is on a different IP (so its on a server, I guess DC)...

So the only server here is the DNS server.. The router is using the DHCP service and they didnt say the router was replaced... so it doesn't make sense to me...