DNS Message Format

Domain Name Service or Domain Name System message format.

Below screenshot is from the CN text book

Below 2 screenshots from Wireshark network capture

TCPDUMP COMMAND

TCPDUMP is a widely used tool/command that is used to capture the network packets in linux environment .

• tcpdump -h --will give the version of tcpdump that is installed

CAPTURE HOST
**********************
tcpdump -i <interface-name> host <ip-address>

it will capture each and every packet matching the ip-address whether it is a source or destination

NOTE: i means interface

NO DOMAIN LOOKUP
***************************
tcpdump -i <interface-name> -n host <ip-address>

 it will capture each and every packet matching the ip-address whether it is a source or destination
 it will not resolve the ip-address


NO DOMAIN AND PROTOCOL LOOKUP
******************************************
tcpdump -i <interface-name> -nn host <ip-address>

it will capture each and every packet matching the ip-address whether it is a source or destination
it will not resolve the ip-address
it will not resove the protocol

NOTE: n means name resolution

RESTRICT THE PACKETS BEING CAPTURED
**************************************************
tcpdump -i <interface-name> -nn host <ip-address>  -c <number of packets to be captured>

NOTE: c means count


CAPTURE HOST AND SERVICE OR PORT
**********************************************
tcpdump -i <interface-name> -nn host <ip-address> and port <port-number>-c <number of packets to be captured>

SAVE AND CAPTURE TCPDUMP DATA
*******************************************
tcpdump -i <interface-name> -nn host <ip-address> and port <port-number>-c <number of packets to be captured>   >/tmp/PacketCapture.txt

tcpdump -i <interface-name> -nn host <ip-address> and port <port-number>-c <number of packets to be captured> -w >/tmp/PacketCapture.pcap

To collect dump .pcap file,which later can be used in wireshark

CAPTURE HOST AND PROTOCOL
**************************************
tcpdump -i <interface-name> -nn host <ip-address> and <protocol> -c <number of packets to be captured>

NOTE:protocol can be replaced by udp,tcp.icmp etc

NEGATE FILTER
**********************
tcpdump -i <interface-name> -nn host <ip-address> and not <protocol> -c <number of packets to be captured>


CAPTURING PACKETS ON PARTCIULAR SOURCE/DESTINATION  ADDRESS
******************************************************************************
tcpdump -i <interface-name> -nn dst <ip-address> and not <protocol> -c <number of packets to be captured>
tcpdump -i <interface-name> -nn src <ip-address> and not <protocol> -c <number of packets to be captured>

COMBINATION
********************
tcpdump -i <interface-name> -nn dst <ip-address1> or dst <ip-addres2> and  <portnumber>

CAPTURE MAC ADDRESS
******************************
tcpdump -i <interface-name> -nn -e host <ip-address> -c <number of packets to be captured>


VERBOSE MODE
**********************
tcpdump -i <interface-name> -nn -vv host <ip-address> -c <number of packets to be captured>

more detailed information along with header


CAPTURING DUMP FOR NETWORK
***************************************
tcpdump -i <interface-name> -nn net <subnet mask> -c  <number of packets to be captured>

For ex:
tcpdump -i eth3 -nn net 10.10.11.10/16 -c     5


CAPTURING DUMP MULITCAST AND BROADCAST
*****************************************************
tcpdump -i <interface-name> -nn "broadcast or multicast" -c <number of packets to be captured>

For ex:
tcpdump -i eth3 -nn "broadcast or multicast" -c 5

CAPTURING DUMP FOR PORT RANGE
*****************************************
tcpdump -i <interface-name> -nn dst <ip-address> and portrange <port-range details>

For ex:
tcpdump -i eth3 -nn  dst 10.20.30.40 and portrange 1-100



                      

Java Keytool Commands

Keytool is very useful tool that  comes along with JRE or JDK,which is useful in creating JKS (Java Keystore files) ,helps in generating private key and CSR(Cert Signing Request) and also converting the JKS file into PKCS12 file.

Below are the steps to create a SSL cert and get it signed with CA

• Generate Key
• Generate CSR
• Validate the CSR
• Submit the CSR to Cert Signing Authority(CA),For Ex: CA-Verisign,Symatec,Godaddy etc
• Add the given public cert(.p7b format) to the JKS file.  

Below are various KEYTOOL commands which are very helpful


KEYTOOL COMMAND TO GENERATE PRIVATE KEY AND CSR
**************************************************************
cd JDK_HOME\bin

keytool -genkey -alias <ALIAS_NAME> -keyalg RSA -keysize 2048 -keystore <JKS FILE COMPLETE PATH> -dname "CN=XXXXXXXXX,OU=YYYYY, O=ZZZZZZZZZ, L=AAAAA, ST=BBBBB, C=WWWW"
KEYTOOL COMMAND TO  GENERATE CSR
******************************************
keytool -certreq -alias <ALIAS_NAME> -file <CSR FILE COMPLETE PATH> -keystore <JKS FILE ALONG WITH COMPLETE PATH>

Verify the CSR using the below link
******************************************
https://ssltools.websecurity.symantec.com/checker/views/csrCheck.jsp


KEYTOOL COMMAND TO DISPLAY or LIST OUT THE ENTRIES OF THE JKS FILE
*******************************************************************************
keytool -list -v -keystore <KEYSTORE FILE NAME WITH COMPLETE NAME> -storetype jks -storepass <PASSWORD>


KEYTOOL COMMAND TO ADD  ENTRIES OF ONE JKS FILE TO ANOTHER JKS FILE
*******************************************************************************
keytool -importkeystore -srckeystore <SOURCE KEYSTORE> -destkeystore <DESTINATION KEYSTORE> -srcalias <SRC ALIAS> -destalias <DST ALIAS> -srcstorepass **** -deststorepass ****


KEYTOOL COMMAND TO CHANGE THE ALIAS OF THE GIVEN THE JKS FILE
**********************************************************************
keytool -changealias -alias <CURRENT ALIAS> -destalias <DEST ALIAS> -keypass *********  -keystore <JKS FILE ALONG WITH COMPLETE PATH> -storepass *******


KEYTOOL COMMAND TO Import the signed (public) certificate to the keystore:
******************************************************************
keytool -import -trustcacerts -alias <ALIAS_NAME> -file <.P7B FILE COMPLETE PATH> -keystore <JKS FILE ALONG WITH COMPLETE PATH>


KEYTOOL COMMAND TO EXPORT  CER file from JKS file
**********************************************************
keytool -export -keystore <JKS FILE ALONG WITH COMPLETE PATH> -alias <ALIAS-NAME> -file <CER FILE NAME>


KEYTOOL COMMAND TO CHANGE PASSWORD OF A JKS FILE
*********************************************************
keytool -keypasswd -keystore <JKS FILE ALONG WITH COMPLETE PATH> -alias <ALIAS-NAME>


KEYTOOL COMMAND TO CONVERT JKS to PKCS12
*************************************************
keytool -importkeystore -srckeystore <JKS FILE ALONG WITH COMPLETE PATH> -srcstoretype JKS -deststoretype PKCS12 -destkeystore <PKCS12 FILE ALONG WITH COMPLETE PATH>


NOTE:<>-this are parameters and we need to substitute with the appropriate values.

Sed-Stream Editor tutorial

Sed is one of the  interesting command in Unix
Sed - Stream Editor

******************************************************************************
sed 's/t/T/' test.txt

substitute the first occurrence of 't' with 'T' in the file test.txt and display on screen,orginal files remains unchanged

--------------------------------------------------------------------------------------------------------------------------
sed 's/t/T/g' test.txt

substitute all/globally the occurrences of 't' with 'T' in the file test.txt and display on screen,orginal files remains unchanged.

--------------------------------------------------------------------------------------------------------------------------
sed -i 's/t/T/g' test.txt

substitute  inline/in the file all/globally the occurrences of 't' with 'T' in the file test.txt,orginal file gets modified.

--------------------------------------------------------------------------------------------------------------------------

sed 's/^t/T/g' test.txt

substitute only  the begining of the line with 't' with the 'T'

^--indicates the begining of the file

--------------------------------------------------------------------------------------------------------------------------

sed 's/t$/T/g' test.txt

substitute only  the ending of the line with 't' with the 'T'

$--indicates the ending of the file

--------------------------------------------------------------------------------------------------------------------------

sed 's/[0-9]/*/g' test.txt

substitute all the numbers in the file with *

--------------------------------------------------------------------------------------------------------------------------
sed 's/[a-z]/*/g' test.txt


substitute all the lowercase letters in the file with *
--------------------------------------------------------------------------------------------------------------------------
sed 's/[A-Z]/*/g' test.txt


substitute all the capital letters in the file with *
--------------------------------------------------------------------------------------------------------------------------

SED Whole Word Match with Boundaries

sed 's/\bnew\b\old/I/g' test.txt

replaces only the word new with old in the test file

\b -means boundary

--------------------------------------------------------------------------------------------------------------------------

SED Remove Lines When Match is Found

sed '/new/d' test.txt

--------------------------------------------------------------------------------------------------------------------------

SED Like Head to Display Top of File

sed '5,$ d' test.txt

Deletes the lines starting from 5 to end of the file ,i.e displays only first 4 lines of the file


sed '4 q' test.txt

Display first 4 lines in the file and then quit

--------------------------------------------------------------------------------------------------------------------------
SED Remove Comments From a file

sed '/^#/d' test.txt

Delete all the lines starting with #

sed '1!{/^#/d;}' test.txt

Skip line 1 and Delete all the lines starting with #

--------------------------------------------------------------------------------------------------------------------------
SED print every other line

sed -n 'p;n' test.txt

print every other line(1,3,5,7),skip one line

sed -n 'p;n;n' test.txt
print every other 2 lines(1,4,7,10),skip 2 lines

--------------------------------------------------------------------------------------------------------------------------

sed '=' test.txt
print line number and print the line after that

sed -n '$=' test.txt
print last line number alone ,which is nothing but the count of number of lines in a file
--------------------------------------------------------------------------------------------------------------------------

Step By Step process to download the You Tube videos using the VLC Player

• Open VLC Player
• Ctrl +N
• Give the url the below highlighted part

• And then click on Play
• Press Ctrl+J
• Take the url from the below location

• Copy paste the url in browser

• Right Click on the video and then Save Video as,this will save the You tube video in  the given location

How To Determine whether installed java is 32 bit or 64 bit?

Run the java -version command in Windows command prompt .Below is how 32 bit java appears and 64 bit java appears respectively

32 bit Java 

64 bit Java

Singleton Factory  Pattern is a design solution where an application wants one and only instance of an class,in all possible scenarios


Steps to create a Singleton Object
-----------------------------------

• create a default private constructor.
• create a method which returns an object.
• make the method accessible by only one thread at a time by adding synchronized keyword.
• override the clone method i.e throw Clone not support Exception.

Creating an object from a connection pool is a best example for Singleton

Links
------
http://www.javabeginner.com/learn-java/java-singleton-design-pattern
http://howtodoinjava.com/2012/10/22/singleton-design-pattern-in-java/