Monday, February 14, 2011

CrazyEngineers Forum - Computer Science & IT Engineering

CrazyEngineers Forum - Computer Science & IT Engineering

Subnetting Confusion

Posted: 14 Feb 2011 12:07 AM PST

I was ok with subnetting untill I read this post on internet.
VLSM- VLSM Explained
Here they have tried to subnet a IP 192.168.1.0/24
I have pasted that part below if you dont want to search for it.

"We will try and subnet 192.168.1.0 /24 to sooth this network which allows a total number of 254 hosts I recommend you get familiar with this table below. I never leave home without it!

Bit Value
128
64
32
16
8
4
2
1
Bits Borrowed
1
2
3
4
5
6
7
8
Subnet mask
128
192
224
240
248
252
254
255
Subnet Prefix /CIDR
/25
/26
/27
/28
/29
/30



Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.

HQ - 192.168.1.0 /26 Network address
HQ = 192.168.1.1 Gateway address
192.168.1.2, First usable address
192.168.1.62- Last usable address. Total address space -192.168.1.2 to 192.168.1.62
192.168.1.63 will be the broadcast address (remember to reserve the first and last address for the Network and Broadcast)
HQ Network Mask 255.255.255.192 - we got the 192 by adding the bit value from the left to the value we borrowed = 128+64=192
HQ address will look like this 192.168.1.0 /26"


Now its clear that he asked us to memorize a table. No problem with that.
Now he said "
Lets start with HQ with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the closest we can get for 50 hosts.
"
My question :-

1) We are borrowing 2 bits ? WHY ???
I know according to his table its correct. But Dont we have to use the formula 2^n -2 = No: of Hosts ? By using this we get totally different number.

I know he is trying to calculate for 50 hosts and not subnets. Is the above table hold good in case if we are calculating the no: of subnets ?

I mean to ask can we use the same table to calculate the number subnets required ?
Lets consider we want to divide 199.131.20.0/24 in to 5 subnets.

So the formula 2^3 holds good. so we need to borrow 3 bits.
How do we infer the above statement using the given table above ?

Forcing 64 bit jvm to 32 bit jvm?

Posted: 13 Feb 2011 10:42 PM PST

Hello everyone!

Would anyone please give me ideas about forcing 64 bit jvm to run as 32-bit jvm?

I need to write a jse desktop application for bluetooth connection. For that i need to implement Bluecove jar . It has 32-bit files only. So i included -D32 under VM arguments in eclipse pulsar. But still i am getting the same error that displayed before adding the argument: bluecove_x64.dll missing. I tried with -d32, and it showed me "unrecognized option: d32".

And it seems like i should install a 32-bit jvm that would run on 64-bit os. So, can anyone please tell me what exactly should i install? Java SDK in 32-bit or Eclipse software?

Thanks in advance!
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