Need some help with subnets

R

Rusky

Limp Gawd
Joined
Jan 4, 2005
Messages
380
I'm doing a homework assignment and this was the problem:


Given the network 11.0.0.0 and netmask 255.0.0.0, subnet the network into 4 subnets each capable of incorporating 4000 hosts. Determine subnet mask, subnet IP address, first and last usable host address, and broadcast address of each network. Show your work.
Click to expand...

I've come up with this:

subnetvd1.jpg



Is this correct or did I do it totally wrong?
 
well class A give to many host over 4000, and you don't want to use that.
ok i get it they give you 11.0.0.0
ic your block size is 32 since is a 255.255.224.0 mask thats is right.
now the subnetting is wrong should be, 0,32,64,96...
your first subnet is wring or network 1
here is how it should be;
network 1; 1st host 11.0.0.1, last host 11.255.30.254
network 2; 1st host 11.0.33.1 last host 11.255.62.254
network 3 1st host 11.0.64.1 last host 11.255.94.254
and so on, and you broadcast addy will be always after the last valid host
is this some type of Cisco class?
 
Ya fubar'd it. All of your "networks" are actually just hosts in the 11.0.0.0/8 network.

*IF* my math is right, you should be looking at a subnet of 20. But don't quote me.

edit: I see what you were trying to do, but I don't think that'd work ( someone correct me if I'm wrong ). You want all the active bits in a subnet to the "left", which would then move the network address to the left of the address ( 11.16.0.0 for example ).

For the record, you can get a metric shit-load of addresses out of that range. I just did the math. :)
 
XOR != OR said:
*IF* my math is right, you should be looking at a subnet of 20. But don't quote me.
Click to expand...

12 bits is 4096 possible hosts (minus two... yeah yeah yeah)
11111111.11111111.11110000.00000000

So yes, /20 is what he is looking for.

****
Edit [because I need to practice as well]
2^12 = 4096 - 2 = 4094 possible hosts.

Network bits = N
Subnet bits = S
Host bits = H
NNNNNNNN.SSSSSSSS.SSSSHHHH.HHHHHHHH

00001011.00000000.00000000.00000000 = 11.0.0.0
11111111.11111111.11110000.00000000 = 255.255.240

00001011.00000000.00000000.00000000 - subnet zero 11.0.0.0
00001011.00000000.00010000.00000000 - first network 11.0.16.0 <- verification anyone?
 
This is just a general class and we are doing subnets right now.

So I found a few errors myself and with the help of the posts here.

The subnet mask is in fact 255.255.240.0

The IP is 11.0.0.0/20

Now I'm not sure if this is correct, but shouldn't the last host be 11.255.14.254 or 11.255.15.254?
I'm not sure how it would work since I've never done a problem like this.
 
Malk-a-mite said:
12 bits is 4096 possible hosts (minus two... yeah yeah yeah)
11111111.11111111.11110000.00000000

So yes, /20 is what he is looking for.

****
Edit [because I need to practice as well]
2^12 = 4096 - 2 = 4094 possible hosts.

Network bits = N
Subnet bits = S
Host bits = H
NNNNNNNN.SSSSSSSS.SSSSHHHH.HHHHHHHH

00001011.00000000.00000000.00000000 = 11.0.0.0
11111111.11111111.11110000.00000000 = 255.255.240

00001011.00000000.00000000.00000000 - subnet zero 11.0.0.0
00001011.00000000.00010000.00000000 - first network 11.0.16.0 <- verification anyone?
Click to expand...
Verified.

Rusky;
Last host would be 11.255.255.254. Last network would be 11.255.240.0/20.
 
Rusky said:
This is just a general class and we are doing subnets right now.
So I found a few errors myself and with the help of the posts here.
The subnet mask is in fact 255.255.240.0
The IP is 11.0.0.0/20
Now I'm not sure if this is correct, but shouldn't the last host be 11.255.14.254 or 11.255.15.254?
I'm not sure how it would work since I've never done a problem like this.
Click to expand...
I don’t think that’s correct.
You were given 11.0.0.0 and a subnet of 255.0.0.0, which looks like the (old-skool) class-A with a default subnet mask.

The question asks you to make 4 subnets. Isn’t a subnet just the amount of 1 bits borrowed from the HOST bits of a particular class? If so, your subnet mask should be either 255.192.0.0. (using the ip subnet-zero command) or it could also be 255.224.0.0. (using the 2^N-2 procedure).

If you use 2 bits (and the ip subnet-zero command), you get 2^2 = 4 subnets and the subnets are:
11.0.0.0 -- 11.0.0.1(1st usable host addr) 11.63.255.254 (last usable host addr) etc.
11.64.0.0
11.128.0.0
11.192.0.0

On the other hand, if you use 3 bits (using the 2^N-2 procedure) you get 2^3-2=6 usable subnets.
The subnets are:
11.0.0.0 (not used, the all-zeros subnet)
11.32.0.0 -- 11.32.0.1(1st usable host addr) 11.32.255.254(last usable host addr) etc.
11.64.0.0
11.96.0.0
11.128.0.0
11.160.0.0 (extra)
11.192.0.0 (extra)
11.224.0.0 (not used, the all-ones subnet)
The broadcast for the 1st subnet (11.0.0.0) is just the last ip addr before the next subnet, that is 11.63.255.255.
==
Malk-a-mike, your answer is correct but only if the question was: please create 4000 hosts and we don’t care how many subnets, otherwise you have the correct hosts, but you created too many subnets (12): 8+4 subnets (255.255.240.0).
 
warbird said:
I don’t think that’s correct.
You were given 11.0.0.0 and a subnet of 255.0.0.0, which looks like the (old-skool) class-A with a default subnet mask.

The question asks you to make 4 subnets. Isn’t a subnet just the amount of 1 bits borrowed from the HOST bits of a particular class? If so, your subnet mask should be either 255.192.0.0. (using the ip subnet-zero command) or it could also be 255.224.0.0. (using the 2^N-2 procedure).

If you use 2 bits (and the ip subnet-zero command), you get 2^2 = 4 subnets and the subnets are:
11.0.0.0 -- 11.0.0.1(1st usable host addr) 11.63.255.254 (last usable host addr) etc.
11.64.0.0
11.128.0.0
11.192.0.0

On the other hand, if you use 3 bits (using the 2^N-2 procedure) you get 2^3-2=6 usable subnets.
The subnets are:
11.0.0.0 (not used, the all-zeros subnet)
11.32.0.0 -- 11.32.0.1(1st usable host addr) 11.32.255.254(last usable host addr) etc.
11.64.0.0
11.96.0.0
11.128.0.0
11.160.0.0 (extra)
11.192.0.0 (extra)
11.224.0.0 (not used, the all-ones subnet)
The broadcast for the 1st subnet (11.0.0.0) is just the last ip addr before the next subnet, that is 11.63.255.255.
==
Click to expand...
Ya, cause that's easier to understand. :D

Malk-a-mike, your answer is correct but only if the question was: please create 4000 hosts and we don’t care how many subnets, otherwise you have the correct hosts, but you created too many subnets (12): 8+4 subnets (255.255.240.0).
Click to expand...
The question was a bit ambiguous. 4 subnets, with 4000 hosts each. There is no way to follow those instructions exactly, given the parameters of the question, therefore a little license is given to come up with something. The easiest, and probably the right, course is to come up with 4 subnets with around 4000 hosts each.

Maybe I'm just reading the question goofy.
 
warbird said:
It sure does!
But the question tells him to show his work. Is he going to hand in an online subnet calculator in class? :D
Click to expand...
Bet it'd at least be original.
 
warbird said:
Malk-a-mike, your answer is correct but only if the question was: please create 4000 hosts and we don’t care how many subnets, otherwise you have the correct hosts, but you created too many subnets (12): 8+4 subnets .255.255.240.0).
Click to expand...

I went with the silly idea that you subnet to preserve available host space. The requirement is 4000 hosts per each subnet. With that in mind, why would you be wasting whole Class Bs?

You only need to create 4 subnets, you can stop after you have 4. If you subnet the way you have suggested how many IPs are wasted?
 
Malk-a-mite said:
I went with the silly idea that you subnet to preserve available host space. The requirement is 4000 hosts per each subnet. With that in mind, why would you be wasting whole Class Bs?
You only need to create 4 subnets, you can stop after you have 4. If you subnet the way you have suggested how many IPs are wasted?
Click to expand...
You're right of course, but I guess the key is that he said he was in a general class. I noticed &#8734;Velocitymaster&#8734; ask what kind of class he was in.

I figured posters would be thinking about advanced stuff, but I think it is just generic subnetting. Any way you slice it, you will be wasting hosts or subnets. In a beginning class normally no one cares. Only the OP would know for sure. :)
 
Hey thanks so much for all the info.
I'll be reading it over and over until my brain gets it.

I think I got class B and C subnetting down, but we never did an example like this in class.

According to the calculator:

Network: 11.0.0.0
First IP: 11.0.0.1
Last IP: 11.0.15.254
Broadcast: 11.0.15.255

The reason I was confused in the beginning was because I wasn't sure what to do with the 2nd octet.

Anyway I'll post back here when I talk to my professor and get the answer.

Thanks again
 
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