how to calculate subnet mask?
e.g - 200.10.10.0 --> usable host 16
what is 6th usable subnet range?
: from here we know every subnet must have 16 hosts..
so 6th usable subnet range is from 6th to 7th subnet
6th subnet address = 16 x 6 = 96
7th subnet address = 16 x 7 = 112
the answer is : 200.10.10.96 to 200.10.10.111
what is subnet number for 4th usable subnet?
: 16 x 4 = 64
the answer is : 200.10.10.64
what is subnet broadcast address for the 3rd usable subnet?
: take 4th subnet becoz the broadcast address of 3rd subnet is before 4th subnet address.
16 x 4 =64
the answer is : 200.10.10.63
what are the assignable address for the 5th usable subnet?
: 16 x 5 = 80 ; 16 x 6 = 96
range 200.10.10.80 to 200.10.10.95 ... then exclude address and broadcast
the answer is : 200.10.10.81 to 200.10.10.94
Friday, November 11, 2005
Thursday, November 10, 2005
Data Can Be Corrupted During Transmission
Data can be corrupted during transmission. For reliable communication, errors must be detected and corrected.
Single-Bit err vs Burs err --> only 1 err vs more than 1
Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination.
CRC is one of Detection Method (lain²: parity check [vrc + lrc], checksum)
crc use polynomial as divisor. e.g. x7 + x5 + x² + x + 1 --> 10100111
b4 sent, generate remainder as redundant bit.
e.g data=100100 divisor=1101
then sent data+remainder
receive.. (data+remainder) divide 1101 must get remainder '0'. else --> error.
in data correction, can use Hamming Code.
place a redundant bit to take care of every single bit of data..
then put the redundant bit.. r8, r4, r2, r1
do check.. if error, calculate which bit is error...
Error detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination.
CRC is one of Detection Method (lain²: parity check [vrc + lrc], checksum)
crc use polynomial as divisor. e.g. x7 + x5 + x² + x + 1 --> 10100111
b4 sent, generate remainder as redundant bit.
e.g data=100100 divisor=1101
then sent data+remainder
receive.. (data+remainder) divide 1101 must get remainder '0'. else --> error.
in data correction, can use Hamming Code.place a redundant bit to take care of every single bit of data..
then put the redundant bit.. r8, r4, r2, r1do check.. if error, calculate which bit is error...Tuesday, October 18, 2005
Idea - Study nmap Source code
mission: source code nmap
objective: to know how scanner created
vision: we can create our own scanner
how to do:
- download nmap with source code
- use nmap with option provided
- compile nmap
- read source code
when:
-during UiTM semester holiday...
team:
-SIGs "Security & Network Admin" members... ;)
objective: to know how scanner created
vision: we can create our own scanner
how to do:
- download nmap with source code
- use nmap with option provided
- compile nmap
- read source code
when:
-during UiTM semester holiday...
team:
-SIGs "Security & Network Admin" members... ;)
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