Author Topic: Networking gurus of GATT, I seek your assistance. (Read 6303 times)

Spazosaurus · « **on:** July 27, 2009, 03:35:43 PM »

Im not really a networking expert, trying to be. A little assistance please. No need to laugh at the noob.

The following question is posed to me...

Now I understand the /28 after the IP address is the extended address, aka the subnet, which in this case is 255.255.255.240 after you convert from binary. Other than that, i've got no idea how you determine what IP address you should use.

Help me please.

Carigamers · « **on:** July 27, 2009, 03:35:43 PM »

SPK · « **Reply #1 on:** July 27, 2009, 04:00:19 PM »

Answer is B.

Spazosaurus · « **Reply #2 on:** July 27, 2009, 04:01:27 PM »

That it is, but HOW? Explain.

SPK · « **Reply #3 on:** July 27, 2009, 04:10:10 PM »

Oh...

Well, for the server has to reside in the specific subnet as the local router (I'm going to leave out the first 3 octets, and refer to the final octet in the IP address, since that's where the subnet will differentiate in this case), which is 62.

Using the subnet mask of 255.255.255.240, that leaves 16 addresses in total per subnet (256-240 in this example.)

In any subnet, typically 2 addresses are reserved - the subnet address (first address in the subnet), and the broadcast address (last address in the subnet).

The address of the router is your hint, being 62. Since there are 16 addresses per subnet, you can count each subnet in groups of 16 -> so first subnet is from 0-15, second one is 16-31, third one is 32-47, forth subnet is 48-63. In the 4th subnet, we can see that the router address falls in that range, so that will be the subnet to focus upon.

Now, given the reserved address issues, we will know that 48 is the subnet address, 63 is the broadcast address, so only addresses 49-62 are valid addresses. From your given options, only B falls in that range, hence being your final answer.

Hope that sheds some light.

...anyone hiring for IT lecturers btw? I could use the work (and pay) right now

...

W1nTry · « **Reply #4 on:** July 27, 2009, 04:15:09 PM »

This should help:
http://www.mindflip.com/inet/tcpip/subnets.html
Also check out Solarwinds Subnet Calculator.

So you're doing variable length subnetting. Doing CCNA by chance?

As quickly as I can, basically you have a /28 subnet or 255.255.255.240 subnet mask. Inherently this means you have roughly 14 addresses or a 16 address space (e.g. 192.168.0.0-192.168.0.15). You can't use the first and last IP addresses as these are the Subnet and Broadcast addresses thus 192.168.0.0 is the subnet address and 192.168.0.15 is the broadcast address. Thus 1-14 are the USEABLE IP addresses. Now if you break a Class C address space usign a /28 address mask then every 16 addresses is a different subnet. Thus:
Subnet Useable IPs Broadcast IPs
192.168.0.0/28 1-14 15
192.168.0.16/28 17-30 31
192.168.0.32/28 33-46 47
192.168.0.48/28 49-62 63
192.168.0.64/28 etc

If you follow what i've been doing you'll get it.

Carigamers · « **Reply #4 on:** July 27, 2009, 04:15:09 PM »

Spazosaurus · « **Reply #5 on:** July 27, 2009, 04:25:05 PM »

Thanks a mill SPK and W1ntry, I think I have the basic idea now. I am sitting here now trying to make it stick.

Muchas gracias gentlemen

+1 SPK today, +1 W1n tomorrow.

Btw, its Implementing, Managing, and Maintaining a Windows Server 2003 Network Infrastructure, MCSA cert.

One other question...

2^4 - 2= Number of hosts per subnet. How do we figure out number of possible subnets again?

W1nTry · « **Reply #6 on:** July 27, 2009, 04:28:00 PM »

Quote from: Captain Awesome on July 27, 2009, 04:25:05 PM

Thanks a mill SPK and W1ntry, I think I have the basic idea now. I am sitting here now trying to make it stick.

Muchas gracias gentlemen

+1 SPK today, +1 W1n tomorrow.

Btw, its Implementing, Managing, and Maintaining a Windows Server 2003 Network Infrastructure, MCSA cert.

Funny I just sold the whole set of MCSE books XD in fact just today I emailed the quote for that same book... PS why I get +1 tomorrow?

Arcmanov · « **Reply #7 on:** July 27, 2009, 04:32:34 PM »

Lawd...killer explanation. I feel I could take some official Network+ lessons from allyuh yes.

Spazosaurus · « **Reply #8 on:** July 27, 2009, 04:32:39 PM »

Ayeee I thought it was only 1 karma action per day. Didnt realise it was one per user. +1 today.

The books aint no scene as they are easily available in e-book form, much easier to handle and search.

What is the formula for determining the number of subnets again?

SPK · « **Reply #9 on:** July 27, 2009, 04:42:24 PM »

I assume the answer you are looking for, unless if I have misunderstood the question, would be:

Number of subnets = 2ⁿ - 2 (where n = number of bits set aside for subnetting)

Assuming that you are using Zero Subnet Rule, of course. If not, then forget the * -2 * part of the equation...

Spazosaurus · « **Reply #10 on:** July 27, 2009, 05:15:13 PM »

Man, do I love this site or what. Cant find a decent explanation for this ish for nun online dread (at least one I can understand)

SPK, I see u used 256-240 to determine the number of subnets. Is that a rule? 256 - (number of used bits converted to decimal form)? Just like you can calculate it using 2^number of used bits?

Arcmanov · « **Reply #11 on:** July 27, 2009, 05:20:37 PM »

Quote from: SPK on July 27, 2009, 04:42:24 PM

I assume the answer you are looking for, unless if I have misunderstood the question would be:

Number of subnets = 2ⁿ - 2 (where n = number of bits set aside for subnetting)

Assuming that you are using Zero Subnet Rule, of course. If not, then forget the * -2 * part of the equation...

My hero.

I aint fooling nobody...I'm not a networking super-pimp either, so the 'lessons' here are welcome.

Spazosaurus · « **Reply #12 on:** July 27, 2009, 05:33:48 PM »

Yea boy, rem SPK IS a lecturer eh, so is like a classroom experience he giving yuh. w1n eh too backward heself.

SPK · « **Reply #13 on:** July 27, 2009, 06:45:13 PM »

Quote from: Captain Awesome on July 27, 2009, 05:15:13 PM

SPK, I see u used 256-240 to determine the number of subnets. Is that a rule? 256 - (number of used bits converted to decimal form)? Just like you can calculate it using 2^number of used bits?

Well, (256-240) was used to determine the number of addresses per subnet. It's a little CCNA-derived trick I learned some time back, since each octet has 256 values: 0-255. It's a shorthand route to allow quick calculations. Another method would be to use the number of host bits, and determine the number of addresses available, but it can lead to issues when it comes to dealing with larger subnets.

Officially, you'd break down the subnet mask into binary, determine the number of subnet bits being used, and use Boolean calculations from there.

However, you have to make sure you double-check your calculations, especially when it comes to dealing with Class B-type IP addresses.

Spazosaurus · « **Reply #14 on:** July 27, 2009, 08:18:09 PM »

And you're out of a job...why?

What is special about the class B addresses though?

SPK · « **Reply #15 on:** July 27, 2009, 08:56:37 PM »

It's not a case of being special per se, it's just that values can be a little less straightforward...

Eg: State the subnet and broadcast addresses of the following IP address:

145.12.63.13 /22

Also, state the number of usable IP addresses in the above subnet.

I'm out of a job because....I suppose my skills are not required in the market at this time...and that a person with a BSc behind their name means that they can do a better job... *shrugs*

W1nTry · « **Reply #16 on:** July 28, 2009, 10:33:11 AM »

If you want to understand VLSM better, I suggest reading the first few chapters of any CCNA texts. The Sybex is particularly good and once you've run it through you'll have a very thorough understanding of subnetting. Also shame I couldn't add meh 2c too, iman was working till 1am this morning and didn't get back to the interweb till now XD. Perhaps this is the start of an IT tutoring thread.

SPK · « **Reply #17 on:** July 28, 2009, 01:25:33 PM »

Quote from: W1nTry on July 28, 2009, 10:33:11 AM

If you want to understand VLSM better, I suggest reading the first few chapters of any CCNA texts.

Agreed. Personally, I prefer the Cisco Press books to the Sybex, but that's just me.

Spazosaurus · « **Reply #18 on:** July 29, 2009, 12:17:04 PM »

People, I have another question...

Again, I know the answer, but im trying to figure out how they arrived at it.

Your assistance is much appreciated as usual.

W1nTry · « **Reply #19 on:** July 29, 2009, 12:34:17 PM »

Based on the ideology behind the last one, I am at a glance thinking the answer is A. Simple reason being that the Main office has an IP address 10.10.11.x - It's important to know that the 3rd octet is 11 not 10 as is in the Server 1 address space. Remember how subnets work 255==11111111 it also means that all parts of that octet MUST match.

If I have an address 172.16.1.x 255.255.255.0 - It means the first 3 octet MUST match i.e. 172, 16, 1
If the subnet mask was 255.255.0.0 - This means the first 2 octets MUST match i.e. 172, 16

Since the 3rd Octet in the example you gave does NOT match this suggest that the 3 octet in the MASK could be a 0 meaning 255.255.0.0
Likewise we can go to even a class A 255.0.0.0 meaning ONLY the FIRST octect MUST match.
10.1.1.0/8 (10.1.1.0 255.0.0.0) can communicate with EVERYTHING below it, meaning once the FIRST octet is 10, that's all that matters.
10.1.1.0/8 can directly communicate with ANY IP between 10.0.0.1-10.255.255.255

Now strictly speaking from a NETWORKING perpective, this is USUALLY NOT the practive. The answer could then be C - 129 is the 1st IP address in the 255.255.255.128 subnet. Thus 10.10.10.222 can speak to 10.10.10.129. Normally ROUTERS segment networks and ROUTE data between subnets, thereby elliminating the need to have LARGE subnet masks like class B and Class A.

Hope this helps

Carigamers · « **Reply #19 on:** July 29, 2009, 12:34:17 PM »

Author Topic: Networking gurus of GATT, I seek your assistance. (Read 6303 times)

Carigamers

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