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| cnet_designer 2002-09-19, 4:05 am |
| If we have a class C address: 192.168.24.0/22 which means that the subnet mask is 255.255.252.0 , so we are not using the default class c subnet mask. and we need different networks for 50 hosts, 400 hosts, 200 hosts , and another seperate network for other 50 hosts. What i am confused about is how can i create VLSM over an already subnetted address. I can easily do it with an address that uses default subnet mask, but in this case i tried but always end up confused... | |
| marathoner 2002-09-19, 8:33 am |
| OK you have been given
192.168.24.0/22 and you need to have four networks with a max of 400 hosts on the biggest network and you have ten bits to work with.
If you use the zero subnet you can cram your four networks into two bits which leaves 8 for hosts which is not enough to accommodate 400.
So you will need to get creative. Perhaps you could supernet what you have been given and get one more bit, suppose you had 192.168.24.0/21 (this is still doable since 24 = 00011000). Now you could use the the 4 and the 2 bits for your subnets and use the LSB plus the 8 bits of your 4th octet for up to 510 hosts. | |
| cnet_designer 2002-09-20, 2:49 pm |
| Thanks for your help  but do u mean this:
192.168.24.0/21
24= 00011000
/22= 11111100
/21= 11111000
so do you mean i can easily change the subnet mask by subtracting a bit, cause i thought that all what i can do is to add 1s bits in the subnet mask but not to eliminate the already network bits used... so is that what u meant? | |
| Yankee 2002-09-21, 5:11 am |
| His suggestion made you use a 255.255.248.0 mask which was not your question. The answer to the question you gave is it can't be done with your /22 block. You are attempting to address 700 hosts with only 500+ IPs.
Yankee | |
| dmaftei 2002-09-21, 4:16 pm |
| quote:
Originally posted by Yankee
...
it can't be done with your /22 block. You are attempting to address 700 hosts with only 500+ IPs.
/22 (255.255.255.252) holds 1024 addresses. | |
| Yankee 2002-09-22, 5:07 am |
| man do I feel stupid....
Thanks dmaftei
Yankee | |
| marathoner 2002-09-22, 7:49 am |
| you can of course address 1022 hosts with ten bits but you can't have any subnetting that way. I believe the question specified 4 subnets of the given /22
Maybe if some of the hosts on the large proposed subnet wouldn't mind moving to one of the smaller ones you could accommodate them.  | |
| marathoner 2002-09-22, 8:06 am |
| Oh, BTW....
/22 was 255.255.252.0 last time I checked.
255.255.255.252 is /30
Proves a point:
We need visual tools to do subnetting. Doing it with these confounded DECIMAL numbers makes EVERYONE make silly mistakes and is needlessly confusing.
Decimal numbers are a poor choice
of representation IMHO. Hex would be better, colored bars would be even better.
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BTW, CNET designer, yes I did mean negotiate another network bit to use for your subnets. Obviously you can't just TAKE it, the higher levels would need to adjust their addressing as well. In an academic situation such as this, such givens are not negotiable, but u have to think outside the box. In real life if there is some intermediate authority who has allocated those bits you might be able to negotiate another bit for your own administrative control if you can prove that you need it. | |
| dmaftei 2002-09-22, 8:31 am |
| quote:
Originally posted by marathoner
/22 was 255.255.252.0 last time I checked.
255.255.255.252 is /30
I stand corrected...
quote:
Proves a point:
We need visual tools to do subnetting.
...but I doubt the point is "we need visual tools"; we need to be careful and double check. | |
| Yankee 2002-09-23, 3:07 am |
| or be wide awake when we type
Yankee | |
| dmaftei 2002-09-23, 6:58 am |
| quote:
Originally posted by Yankee
or be wide awake when we type
Got that right! Lots of coffe might help too... |
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