IP/Subnet question ,PLEASE!

  • Thread starter Thread starter David H. Lipman
  • Start date Start date
D

David H. Lipman

You might want to re-post in the News Group: comp.protocols.tcp-ip

You can attention it to: Barry Margolin a TCP/IP expert!

Dave




| Hello world!
|
| Awhile ago I was asking some basic info about subnet masking.Now when I know
| more,I'd like to ask deeper.
| I understand the idea behind the subnets ,but I still don't get the
| implementation part.
| Let's say we have a Class A IP address:84.94.158.20 and we have 12,506 hosts
| on a subnet.So how would we know what subnet mask should be?
| IP in bin is:
| 01010100.01011110.10011110.00010100 (I added dots for convinience only)
| 2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
| too many and the 2nd is too few vs 12506 PC's that are given here.So I
| started playing with dec numbers and came to the closest number of 206 as a
| 3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
| times 256=12544 the highest integer that would give us more than 12506
| hosts in the subnet here.
| So the first thing is I don't know how then you define the EXACT number of
| hosts and 2nd if you translate 255.255.206.0 into bin=
| 01010100010111101001111000010100
| 11111111111111111100111000000000
| Doesn't look OK...but if I use powers example....2 in a power of 14...then
| it would be:
| 01010100010111101001111000010100
| 111111111111111111000000.00000000
| or 255.255.192.0
| I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
| would mean that we can only define a subnet much much biger than actual No.
| of hosts....ie.16,384 vs.12,506...
|
| So maybe anyone can explain it to me ?
|
|
| --
| Thanks in advance,
|
| Yours truly,
| Alon Brodski
|
|
 
www.dnsstuff.com


| Hello world!
|
| Awhile ago I was asking some basic info about subnet masking.Now when I
know
| more,I'd like to ask deeper.
| I understand the idea behind the subnets ,but I still don't get the
| implementation part.
| Let's say we have a Class A IP address:84.94.158.20 and we have 12,506
hosts
| on a subnet.So how would we know what subnet mask should be?
| IP in bin is:
| 01010100.01011110.10011110.00010100 (I added dots for convinience only)
| 2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
| too many and the 2nd is too few vs 12506 PC's that are given here.So I
| started playing with dec numbers and came to the closest number of 206 as
a
| 3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
| times 256=12544 the highest integer that would give us more than 12506
| hosts in the subnet here.
| So the first thing is I don't know how then you define the EXACT number of
| hosts and 2nd if you translate 255.255.206.0 into bin=
| 01010100010111101001111000010100
| 11111111111111111100111000000000
| Doesn't look OK...but if I use powers example....2 in a power of 14...then
| it would be:
| 01010100010111101001111000010100
| 111111111111111111000000.00000000
| or 255.255.192.0
| I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
| would mean that we can only define a subnet much much biger than actual
No.
| of hosts....ie.16,384 vs.12,506...
|
| So maybe anyone can explain it to me ?
|
|
| --
| Thanks in advance,
|
| Yours truly,
| Alon Brodski
|
|
 
Hello world!

Awhile ago I was asking some basic info about subnet masking.Now when I know
more,I'd like to ask deeper.
I understand the idea behind the subnets ,but I still don't get the
implementation part.
Let's say we have a Class A IP address:84.94.158.20 and we have 12,506 hosts
on a subnet.So how would we know what subnet mask should be?
IP in bin is:
01010100.01011110.10011110.00010100 (I added dots for convinience only)
2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
too many and the 2nd is too few vs 12506 PC's that are given here.So I
started playing with dec numbers and came to the closest number of 206 as a
3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
times 256=12544 the highest integer that would give us more than 12506
hosts in the subnet here.
So the first thing is I don't know how then you define the EXACT number of
hosts and 2nd if you translate 255.255.206.0 into bin=
01010100010111101001111000010100
11111111111111111100111000000000
Doesn't look OK...but if I use powers example....2 in a power of 14...then
it would be:
01010100010111101001111000010100
111111111111111111000000.00000000
or 255.255.192.0
I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
would mean that we can only define a subnet much much biger than actual No.
of hosts....ie.16,384 vs.12,506...

So maybe anyone can explain it to me ?
 
Hello world!

Awhile ago I was asking some basic info about subnet masking.Now when I know
more,I'd like to ask deeper.
I understand the idea behind the subnets ,but I still don't get the
implementation part.
Let's say we have a Class A IP address:84.94.158.20 and we have 12,506 hosts
on a subnet.So how would we know what subnet mask should be?
IP in bin is:
01010100.01011110.10011110.00010100 (I added dots for convinience only)
2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
too many and the 2nd is too few vs 12506 PC's that are given here.So I
started playing with dec numbers and came to the closest number of 206 as a
3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
times 256=12544 the highest integer that would give us more than 12506
hosts in the subnet here.
So the first thing is I don't know how then you define the EXACT number of
hosts and 2nd if you translate 255.255.206.0 into bin=
01010100010111101001111000010100
11111111111111111100111000000000
Doesn't look OK...but if I use powers example....2 in a power of 14...then
it would be:
01010100010111101001111000010100
111111111111111111000000.00000000
or 255.255.192.0
I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
would mean that we can only define a subnet much much biger than actual No.
of hosts....ie.16,384 vs.12,506...

So maybe anyone can explain it to me ?
Click to expand...

Sure. Hundreds of people in a more appropriate newsgroup would
probably love to help you. Libraries have many books that go over
TCP/IP protocols in all the boring, glorious detail.

Unfortunately, you asked in a group that has nothing to do with your
question. How does this relate to XP?
 
I think the 255.255.192.0 is the right answer and not 255.255.206.0 butwould mean that we can only define a subnet much bigger than actual No.
of hosts....ie.16,384 vs.12,506...

Alon:

255.255.192.0 is the right answer (correct subnet mask).

Impt concept:
The subnet mask's decimal values are limited to the equivalent decimal value
of contiguous binary 1s from the left, or all binary 0s period.

Therefore, the only possible subnet mask octect decimal values are:
0 for [0000 0000]
128 for [1000 0000]
192 for [1100 0000]
224 for [1110 0000]
240 for [1111 0000]
248 for [1111 1000]
252 for [1111 1100]
254 for [1111 1110]
255 for [1111 1111]
on a subnet.So how would we know what subnet mask should be?

Easy way:
Use a subnet calculator and select a max # of hosts per subnet that is
greater then the number you want, then use the related subnet mask that the
calculator gives you.
I use the "IP Subnet Calculator" from Net3Group

Hard way:
We want 12,506 hosts in a single subnet.
So, we want 2 to the nth power that allows more than 12,506 different
numbers.
2 to the 14th = 16384.

Host IDs are represented by contiguous binary 0s from the right in a subnet
mask:
So, we want 14 contiguous 0s from the right.
So, the subnet mask must be:
255.255.192.0 which is 8 0s in the right most octect, and 6 0s in the next
octect for a total of 14 contiguous 0s.









OP's post:
Awhile ago I was asking some basic info about subnet masking.Now when I know
more,I'd like to ask deeper.
I understand the idea behind the subnets ,but I still don't get the
implementation part.
Let's say we have a Class A IP address:84.94.158.20 and we have 12,506 hosts
on a subnet.So how would we know what subnet mask should be?
IP in bin is:
01010100.01011110.10011110.00010100 (I added dots for convenience only)
2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
too many and the 2nd is too few vs 12506 PC's that are given here.So I
started playing with dec numbers and came to the closest number of 206 as a
3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
times 256=12544 the highest integer that would give us more than 12506
hosts in the subnet here.
So the first thing is I don't know how then you define the EXACT number of
hosts and 2nd if you translate 255.255.206.0 into bin=
01010100010111101001111000010100
11111111111111111100111000000000
Doesn't look OK...but if I use powers example....2 in a power of 14...then
it would be:
01010100010111101001111000010100
111111111111111111000000.00000000
or 255.255.192.0
I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
would mean that we can only define a subnet much bigger than actual No.
of hosts....ie.16,384 vs.12,506...

So maybe anyone can explain it to me ?
 
OK,let me try the last time the hard way :-)
4,449 hosts in Class B IP address:166.233.212.5
So instead of over 65,000 possible hosts I would have "ONLY" :-)===8,192 2
in power of 13
10100110111010011101010000000101
1111111111111111.11100000.00000000
so in dec my subnet mask would be here=255.255.224.0



CZ said:
would mean that we can only define a subnet much bigger than actual No.
of hosts....ie.16,384 vs.12,506...

Alon:

255.255.192.0 is the right answer (correct subnet mask).

Impt concept:
The subnet mask's decimal values are limited to the equivalent decimal value
of contiguous binary 1s from the left, or all binary 0s period.

Therefore, the only possible subnet mask octect decimal values are:
0 for [0000 0000]
128 for [1000 0000]
192 for [1100 0000]
224 for [1110 0000]
240 for [1111 0000]
248 for [1111 1000]
252 for [1111 1100]
254 for [1111 1110]
255 for [1111 1111]
on a subnet.So how would we know what subnet mask should be?

Easy way:
Use a subnet calculator and select a max # of hosts per subnet that is
greater then the number you want, then use the related subnet mask that the
calculator gives you.
I use the "IP Subnet Calculator" from Net3Group

Hard way:
We want 12,506 hosts in a single subnet.
So, we want 2 to the nth power that allows more than 12,506 different
numbers.
2 to the 14th = 16384.

Host IDs are represented by contiguous binary 0s from the right in a subnet
mask:
So, we want 14 contiguous 0s from the right.
So, the subnet mask must be:
255.255.192.0 which is 8 0s in the right most octect, and 6 0s in the next
octect for a total of 14 contiguous 0s.









OP's post:
Awhile ago I was asking some basic info about subnet masking.Now when I know
more,I'd like to ask deeper.
I understand the idea behind the subnets ,but I still don't get the
implementation part.
Let's say we have a Class A IP address:84.94.158.20 and we have 12,506 hosts
on a subnet.So how would we know what subnet mask should be?
IP in bin is:
01010100.01011110.10011110.00010100 (I added dots for convenience only)
2 in a power of 14 is 16,384 and in a power of 13 is 8,192.But the 1st is
too many and the 2nd is too few vs 12506 PC's that are given here.So I
started playing with dec numbers and came to the closest number of 206 as a
3rd dec octet of a subnet mask,ie 255.255.206.0 'cos 255-206=49 and 49
times 256=12544 the highest integer that would give us more than 12506
hosts in the subnet here.
So the first thing is I don't know how then you define the EXACT number of
hosts and 2nd if you translate 255.255.206.0 into bin=
01010100010111101001111000010100
11111111111111111100111000000000
Doesn't look OK...but if I use powers example....2 in a power of 14...then
it would be:
01010100010111101001111000010100
111111111111111111000000.00000000
or 255.255.192.0
I think the 255.255.192.0 is the right answer and not 255.255.206.0 but it
would mean that we can only define a subnet much bigger than actual No.
of hosts....ie.16,384 vs.12,506...

So maybe anyone can explain it to me ?
Click to expand...
 
OK,let me try the last time the hard way :-)
4,449 hosts in Class B IP address:166.233.212.5
So instead of over 65,000 possible hosts I would have "ONLY" :-)===8,192 2
in power of 13
10100110111010011101010000000101
1111111111111111.11100000.00000000
so in dec my subnet mask would be here=255.255.224.0

Alon:

Correct
 

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