OSI Layers...

OSI models:

The standard model for networking protocols and distributed applications is the International Standard Organization’s Open System Interconnect (ISO/OSI) model released in 1984. It defines seven network layers.  Vendors design network products based on the specifications of the OSI model, it provides a description of how network hardware and software work together in a layered fashion to make communications possible It also helps with trouble shooting by providing a frame of reference that describes how components are supposed to function.

 OSI layers:

• Application
• Presentation
• Session
• Transport
• Network
• Data Link
• Physical

Application:

The Application layer provides network services directly to the user’s application such as a web browser, email software and Windows Explorer. This layer is said to be closest to the user,

Protocols that operate on this layer include: TELNET, HTTP, FTP, TFTP, SMTP, NTP, SNMP.

Presentation:

This layer represents the data in a particular format to the Application layer, this layer is responsible to code and decode data sent to the network points, and Specifications defined at this layer include: 

GIF, TIFF, JPEG, MPEG, MIME, and ASCII.

Session:

Establishes, maintains and terminates end-to-end connections between two applications on two network point, this layer helps out with the task to carry information from one node (workstation) to another node (workstation). A session layer has to be made before we can transport information to another computer. 

This layer include: RPC, SQL, and NETBIOS.

Transport:

The transport layer is the fourth layer of the OSI reference model. This layer converts the data received from the upper layers into segments. The Transport layer is responsible for end-to-end (also called source-to-destination) delivery of entire messages. It provides end-to-end connectivity, 

Protocols that operate on this layer: TCP, UDP, and NETBEUI.

• These protocols are either connectionless or connection-oriented.

Network:

This layer converts the segments from the Transport layer into packets and is responsible for path determination, routing, and the delivery of these individual packets across multiple networks without guaranteed delivery. The network layer treats these packets independently, without recognizing any relationship between those packets, it relies on upper layers for reliable delivery and sequencing and also this layer is responsible for logical addressing also known as network addressing or Layer 3 addressing for example IP addresses.

Examples of protocols defined at this layer: IP, IPX, AppleTalk, ICMP, RIP, OSPF, BGP, IGRP, and EIGRP

Devices that operate on this layer: Routers, Layer 3 Switches.

Data Link:

The Data-Link layer is the protocol layer in a program that handles the moving of data in and out across a physical link in a network. Responsible for reassembling bits taken of the wire by the Physical layer to frames, makes sure they are in the correct order and requests retransmission of frames in case an error occurs. Provides error checking by adding a CRC to the frame, and flow control.

Data Link layer has two sub layers:

• Logical Link Control(LLC)
• Media Access Control (MAC)

The Logical Link Control is the upper sub layer of the Data Link layer. LLC masks the underlying network technology by hiding their differences hence providing a single interface to the network layer. This layer is also responsible for frames sequencing and acknowledgements.

Media Access Control This refers to the procedures used by devices to control access to the network medium. Since many networks use a shared medium (such as a single network cable, or a series of cables that are electrically connected into a single virtual medium) it is necessary to have rules for managing the medium to avoid conflicts.

Physical:

Physical layer communicates directly with the physical media; it is responsible for activating, maintaining and deactivating the physical link. It supports electrical or mechanical interface to the physical medium, this layer consists of different types of metal, plastic, and glass that are assembled in a way that allows electricity, light, and other forms of energy to be transferred from one location to another. Although the Data Link Layer, Network Layer, and Transport Layer are responsible for encoding data, the Physical Layer is responsible for transferring the data to where it needs to go. Ethernet cabling, Token Ring network technology and SCSI all function at the Physical layer of the OSI model. Hubs and other repeaters are standard network devices that function at the Physical layer and WAN interfaces such as RS-232, BRI, V.24, V.35, X.25 and Frame Relay. Cables and connectors also are a part of the Physical layer. At the Physical layer, data are transmitted using the type of signaling supported by the physical medium:

• electric voltages
• radio frequencies
• pulses of infrared or ordinary light

OSI layer diagram:

Summary:

What basically happens when data passes from Host A to Host B?

• Application, Presentation and Session layer take user input and converts it  into data,
• Transport layer adds a segment header converting the data into segments,
• Network layer adds a network header and converts the segments into packets ,
• Data Link layer adds a frame header converting the packets into frames,
• MAC sub layer converts the frames into bits which the Physical layer can put on the wire.

The steps are known as the 5 steps of data encapsulation. When the bits stream arrives at the destination, the Physical layer takes it of the wire and converts it into frames, each layer will remove their corresponding header while the dataflow up the OSI model until it is converted back to data and presented to the user, this is known as de-capsulation.

OSI layers reference table:          

Share and Enjoy..

Protocols Port numbers

What is Port number ?

Port number is part of the addressing information used to identify the senders and receivers of messages. Port numbers are most commonly used with TCP/IP connections. Home network routers and computer software work with ports and sometimes allow you to configure port number settings. These port numbers allow different applications on the same computer to share network resources simultaneously. Port number is a 16 bit binary number in the TCP. Therefore the port number is in the range of 0-65535.The port numbers are divided into three ranges.

1.Well Known ports

2.Registered Ports

3.Dynamic Ports/Ephemeral ports

How Port Numbers Work ?

Port numbers are associated with network addresses. For example, in TCP/IP networking, both TCP and UDP utilize their own set of ports that work together with IP addresses.

Port numbers work like telephone extensions. Just as a business telephone switchboard can use a main phone number and assign each employee and extension number (like x100, x101, etc.), so a computer has a main address and a set of port numbers to handle incoming and outgoing connections.

In both TCP and UDP, port numbers start at 0 and go up to 65535. Numbers in the lower ranges are dedicated to common Internet protocols.

When You May Need to Take Action with Port Numbers:

Port numbers are typically processed by network hardware and software automatically. Normally you will not see them while casually using a network nor need to take any action involving them. However, in these special cases you can work with network port numbers:

* Network administrators may need to set up port forwarding to allow the port numbers of specific applications to pass through a firewall. On home networks, broadband routers support port forwarding on their configuration screens.

* Network programmers sometimes need to specify port numbers in their code, such as in socket programming.

* Sometimes, a Web site URL will require a specific TCP port number be included. For example, http://localhost:8080/ uses TCP port 8080. Again, this is more usually seen in software development environments than on the Internet.

How to clear short cut virus in pen drive and external hard disk using command prompt

Sometimes it’s very irritating when you insert any USB and it shows many shortcuts folders and some files become invisible. Many of them facing the problems with this virus, Most of the anti-virus can’t  remove this virus. But it is possible to remove the virus using command prompt.

 

Now follow these steps and clear the virus:

1. Click on “Start” –>Run –> type cmd and click on OK.

For example E: drive is removable drive.

2. Enter this command.
attrib -h -r -s /s /d e:\*.*

Note : Replace the letter E: with your removable drive letter.

Now check for your files and folder in Pen Drive or external hard disk, you have successfully removed the shortcut virus from your pen drive all your invisible files are back now.

Top 120 Commands for Linux Administrators

In this post i have described about the most used top 120 linux commands. It is more recommended for linux administrators.

1. Command to Open pdf file from Command Mode

#acroread Bash-Beginners-Guide.pdf

2. Command to Open pdf file from Command Mode

#evince Bash-Beginners-Guide.pdf

3.Command used to open Web Page from Command mode

#links

4.Command used to get in to tutorial in VIM editor

#vimtutor

5.Command used to find Spelling mistake in a file linux admin commands, unix admin commands, linux administrator commands, unix administrator

#aspell list < newfile

6.Command used to change between  Virtual terminal

chvt 1
chvt 1 2 3 .. 7

7.Command used to view a file content in reverse order

#tac

8.Command used to display an image from command mode

#display test.png

9.Command to convert pdf to any format

#convert bash.pdf pash.jpg

10.Redirecting Output to another pesto terminal

#cal > /dev/tty3

11.Delete the first line from the file file.txt

#sed -i 1d file.txt
 

12.Delete the fifth ,Sixth and seventh line of file file.txt

# sed -i 5,7d file.txt

13.Way to empty a file

#cat /dev/null > test.txt
#echo  > test.txt

14.Command to show the number of lines, words and letters in a file

#.wc if.sh
23  449 3535 if.sh

15.command to change man page to txt file.

#man set | col -b > set.txt

16.Command to change man page to doc file.
#man set | col -b > set.doc

17.Command to change man page to pdf file.
#man -t pwd | ps2pdf – pwd.pdf

18.Command to take screen shot from terminal

#import a.png

19.Commands used to show routing table in linux system

#netstat -r
 

20.Commands used to show routing table in linux system

#route

#route -n

21.Commands used to show routing table in linux system

#ip route list

22.Command used to create shortcuts for commands

#alias
#alias lll=’ls -1tr | tail -1′
 

22.Command used to remove all alias commands.

#unalias

23.Command will remove only alias of lll.
#unalias lll

24.Command will remove all alias
#unalias -a

25.Same as like of history command

#fc -l -5

26.Command will display in what all the groups the user is present

#groups
 

27.Command used to save every printed in the screen.

#script  aa.txt

28. Command used to add append and display content of a file

#cat hello.txt

29. Command used to add append and display content of a file

#ul  hello.txt

30.Command used to add append and display content of a file

#colcrt hello.txt
 

31. Command used to add append and display content of a file

#nroff hello.txt

32.Command used to display uid,gid of the user

#id

33.Command used to display only group name the user belongs to.

#id -ng rajm

34.Command used to display group ID of the user belongs to.

#id -g rajm

35.Command used to change tab to space.

#expand

36. Command used to convert all tab in file a to one space

#expand -1 a
 

37. Command used to change space to tab

#unexpand

38. History entry is temporally stopped

#set +o history

39. To start again after temporally stopped.

#set -o history

40. Command to display the boot up message of the machine.

#dmesg

41. Command used to remove all the empty directory recursively in the present working directory.

#cleanlinks

42. Command to view permission of the file or folder in order

#namei

43. Command to view permission of /etc , squid and squid.conf individually

#namei -m /etc/squid/squid.conf
 

44. Command to view whether it is a file or folder in order.

#namei -x /etc/squid/squid.conf

45. Command to export a variable in a Shell

#export raj=rajkumar
#env | grep raj
raj=rajkumar

46. Command to print the list of names exported
#export -p

47. Command used to display where the executable file is stored. basically its in /bin or /sbin

#which
#which iptables
/sbin/iptables

48. Command to open an doc file from command prompt

#gnome-open raj.doc

49. Command to view content of an tar ball

#zcat pkg-config-0.20.tar.gz

50. Command used to clear the terminal Screen.

#clear

51. Command read and execute command from file and execute it in the prompt.

#source

#cat >> ~/.bashrc
hi(){ ls -l }
#source ~/.bashrc

52.Command to change the time stamp of a file. It’s in the format of (YYMMDDhhmm[.ss])

#touch -t 201107132224.30 *.sql

53. Command used to print sequence of number from 1 – 25.

#seq 1 25

54. Command displays user’s Login, Home directory, IP,shell and logged in pts & idle time

#finger rajm
 

55. Command to displays all  Logged in users with their logged in terminals, from IP and idle time.

#finger

56. Command used to tell what type of file is it.

#file a.txt

57. Command used to list all UUID(Universally Unique Identifier library).

#blkid

58. Inform the OS of partition table changes

#partprobe

59. Find file by name

#locate

60. Displays IP address of the system from /etc/hosts file.

#hostname -i

61. Displays domain name of the system from /etc/hosts file.

#hostname -d

62. Mount all file systems (of the given types) mentioned in fstab.

#mount -a

63. Adjust tunable file system parameters on ext2/ext3 filesystems

#tune2fs

64. Add  an  ext3  journal  to the filesystem.

#tuen2fs -j

65. Build a Linux file system in ext3 format

#mkfs -t ext3 /dev/hda1
 

66. Build a Linux file system in ext2 format

#mkfs -t ext2 /dev/hda2

67. Creating a ext3 file system

#mkfs.ext /dev/sdb1

68. Creating a ext2 file system

#mkfs.ext2 /dev/sdb2

69. Command to find folder size

#du -sh

70. Command to find mounted partition with file system type.

#mount

71. To find whether a port is opened or not

#nc -z google.com 80

72. Command to find swap partition

swapon -s

73. Print the word rajkumar until its been killed

#yes rajkumar

74.list contents of directories in a tree-like format and it also displays number of files and directories in the folder.

#tree /home/rajm

75. Prints name of current/working directory.

#pwd
 

76.Report current working directory of a process

#pwdx pids

77. Used to determine wireless is enabled or not&configure a wireless network interface.

#iwconfig

78. Command used to bring up the eth0 interface down

#ifconfig eth0 down

79. Command used to bring up the eth0 interface up

#ifconfig eth0 up

80.Command used to query and set the hardware clock (RTC)

#hwclock
#hwclock –set –date “27 Sep 2011 23:01″

81. Command used to print or set the system date and time

#date
#date -s ” 24 JUL 2011 00:33:09″

82. Command used to change the time zone(“Asia/Calcutta”) information.If applied it also do changes in the configuration file(/etc/sysconfig/clock).

#timeconfig

83. Uptime command gives output of current time, how long the system has been running,how many users are currently logged on, and the system load averages for the past 1,5,15 min.

#uptime

84.Displays the exact last reboot Date & Time.

#who -b

85. Display current username(effective id – euid)

#whoami

85. Display parent username

#who am i

86. To view the time stamp of current time

#date +%s

87. To check the time stamp with current date & time

#date –d @1321266648 ; date

88. To close a terminal

skill -KILL /pts/20

89.It will tell how long the time taken to run the command.It can also be used in script

#time ls

90.It will display only hosts.deny. Used to display only last path filename.

#basename /etc/hosts.deny

91. Used to show the number of available semaphores in the system.

#ipcs -s

92.Show’s all the environment variable present in the system

#env

93. Show’s all the environment variable present in the system

#printenv

94. Print all the declared variables present in the system

#set

95. Print all the declared variables present in the system

#declare
 

96. Print all the declared variables present in the system

#typeset

97. Command to install a package in Ubuntu

#dpkg -i <package-name>

98. Command to install a package in Ubuntu

#apt-get install <package-name> 

#apt-get install php-mysql

99.Command to remove a package in Ubuntu

#apt-get remove <package-name>

100.  Command to display the label of the partition /dev/sda1.

#e2label /dev/sda1

boot
 

101. Command to assign label for the partition /dev/sda2

#e2label /dev/sda2 /home

102. List permission, accessed, modified, changed, inode, size, UID, GID, Owner, full path and even type of a FILE.

#stat /etc/passwd

103. Command to open “Menu Layout” (or)Right Click Application “Edit Menu”

#alacarte

104. Command to shutdown the system

#poweroff

105.Command to shutdown the system
#init 0

106. Command to shutdown the system
#shutdown -h now

107. Visual shell for Unix-like systems.Make Commander

#mc

108. Displays all the command available in the Linux Box

#compgen -c

109.Register Redhat updates via Command line.

#rhn_register

110. Command to assign password like “passwd command”

#chpasswd

111. Used to create /etc/shadow file when it is deleted. pwconv uses /etc/passwd file to create /etc/shadow file

#pwconv

112. Reports the most recent Login of all users or of a given user

#lastlog

113. Command to create panel if the panel is not present

#gnome-panel

114. To kill gnome-panel if present

#killall gnome-panel

115. Command to find all opened ports in running linux machine

#netstat -ntpl

116. Command to find all opened ports in running linux machine

#lsof -i

117. TO list all chkconfig list

#chkconfig –list
 

118.find file based on size greater than 1kb

#find . -size +1k

119.find file based on size lesser than 1kb
#find . -size -1k

120. To change the history size

#HISTSIZE=450

Every Windows User Needs to Know About Using the Windows Task Manager

The Windows Task Manager is an important tool for every Windows user. It can show you why your computer is slow and help you deal with misbehaving and resource-hungry programs, whether they’re draining CPU, RAM, disk, or network resources.
Windows 8 has the best built-in Task Manager yet, but even Windows 7′s Task Manager is a powerful tool that every Windows user should familiarize themselves with. Many of these tasks are easier on Windows 8.

Opening the Task Manager

Windows lets you get to the Task Manger in a variety of ways:

• Keyboard Shortcut: Press Ctrl+Shift+Escape anywhere in Windows.
• Mouse Shortcut: Right-click the Windows taskbar and select Start Task Manager.
• Traditional Method: Press Ctrl+Alt+Delete and select Start Task Manager.

View CPU and RAM Hogs

On Windows 7, the Task Manger opens to the Applications tab, which lists open applications and allows you to quickly close them with the End Task button. This works even if they have frozen and aren’t responding.
This tab doesn’t allow you to view resource usage. It also doesn’t show every program running on your computer — programs running in the background without visible windows aren’t listed here.

Click over to the Processes tab to view the processes running on your computer, both processes with open windows and background processes that may be invisible or hidden in your system tray.
Click the CPU or Memory heading to sort the processes by their CPU or memory usage. This will show you which programs are using the most CPU time and amount of RAM.

To view all the processes running on your computer, click the Show processes from all users button. By default, the list just displays processes running as your user account. The button shows system processes and processes running under other user accounts.

You may also want to click the View menu, click Select Columns, and enable the CPU Time column. Click the CPU Time column to sort the list by CPU Time. This will show you how much CPU resources each process has used, so you can identify programs that may currently be using a low amount of CPU but have used a higher amount of CPU when you weren’t looking.

On Windows 8, the main Processes tab shows processes’ CPU, memory, disk, and network usage all in one place. You can find this information on Windows 7, too, but it’s scattered in several places.

Kill Background Programs

If an process is misbehaving — for example, you may have closed a PC game and it continued running in the background, possibly using 99% of your CPU — sorting by CPU and memory usage will show you the misbehaving process consuming too many resources at the top of the list. Right-click the process and select End Process to close it if you can’t close it normally.

Check Total CPU and RAM Usage

Click over to the Performance tab to view your computer’s total CPU and physical memory (RAM) usage. The CPU usage history graph shows total CPU usage as well as separate graphs for each CPU’s usage over time, while the Memory graph shows you total memory usage and how your memory usage has changed over time.

If the CPU usage or Memory bars are completely full and your computer is running slowly, you should close some CPU or memory-hungry programs — check the processes list to see which those are — and free up resources. If your Memory and CPU usage are always high, you may want to upgrade your RAM or get a computer with a faster CPU to speed things up.

View System Network Activity

If you’re having problems with your Internet connection — maybe web pages are loading slowly or your voice is dropping out while you’re talking to someone on Skype or a similar VoIP program — you may want to check your computer’s total network usage. You can do this from the Networking tab in the Task Manager.
You’ll see a separate graph for each of your computer’s network adapters, which will inform you how much of your network’s resources the programs on your computer are consuming. This allows you to see whether there are any programs running in the background and saturating your network connection.

On Windows 8, you’ll find this information on the Performance tab, too.

Check Per-Process Network Activity

If you can see that your network connection is being used, you may want to know which applications are using the network. To see a list of processes accessing the network and how much network resources they’re each using, click over to the Performance tab and click the Resource Monitor button.

On the Resource Monitor’s network tab, you can view the list of processes with network activity and see what’s sucking up resources. Note that this counts all network activity — even processes just communicating with other devices on the local network and not connecting to the Internet.

On Windows 8, you can view per-process network activity on the Processes tab.

Check Per-Process Disk Activity

With the Resource Monitor opened from the Performance tab in the Task Manager, you can also click the Disk tab and see which programs are reading and writing to your disk the most. If your hard drive is grinding away, this tool will show you which programs are taking up all your disk resources.

On Windows 8, this information is available on the Task Manager’s Processes tab.

Manage Startup Programs

On Windows 8, you can use the Startup tab in the Task Manager to control which programs automatically start with your computer.

On Windows 7, you’ll need to use another tool, like the startup manager built into CCleaner.

---

If you want a more advanced Task Manager replacement, download the free Process Explorer utility. This tool is developed by Microsoft and offers a variety of features you won’t find in the standard task manager, even on Windows 8, including the ability to view which files and folders a program has “locked” and unlock them so they can be modified.

How Can I Find Out Where an Email Really Came From?

Just because an email shows up in your inbox labeled Bill.Smith@somehost.com, doesn’t mean that Bill actually had anything to do with it. Read on as we explore how to dig in and see where a suspicious email actually came from.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-drive grouping of Q&A web sites.

The Question

SuperUser reader Sirwan wants to know how to figure out where emails actually originate from:

How can I know where an Email really came from?
Is there any way to find it out?
I have heard about email headers, but I don’t know where can I see email headers for example in Gmail.

Let’s take a look at these email headers.

The Answers

SuperUser contributor Tomas offers a very detailed and insightful response:

See an example of scam that has been sent to me, pretending it is from my friend, claiming she has been robbed and asking me for financial aid. I have changed the names — suppose that I am Bill, the scammer has send an email to bill@domain.com, pretending he is alice@yahoo.com. Note that Bill has forward to bill@gmail.com.
First, in Gmail, use show original:

Then, the full email and its headers will open:

Delivered-To: bill@gmail.com
Received: by 10.64.21.33 with SMTP id s1csp177937iee;
        Mon, 8 Jul 2013 04:11:00 -0700 (PDT)
X-Received: by 10.14.47.73 with SMTP id s49mr24756966eeb.71.1373281860071;
        Mon, 08 Jul 2013 04:11:00 -0700 (PDT)
Return-Path: <SRS0=Znlt=QW=yahoo.com=alice@domain.com>
Received: from maxipes.logix.cz (maxipes.logix.cz. [2a01:348:0:6:5d59:50c3:0:b0b1])
        by mx.google.com with ESMTPS id j47si6975462eeg.108.2013.07.08.04.10.59
        for <bill@gmail.com>
        (version=TLSv1 cipher=RC4-SHA bits=128/128);
        Mon, 08 Jul 2013 04:11:00 -0700 (PDT)
Received-SPF: neutral (google.com: 2a01:348:0:6:5d59:50c3:0:b0b1 is neither permitted nor denied by best guess record for domain of SRS0=Znlt=QW=yahoo.com=alice@domain.com) client-ip=2a01:348:0:6:5d59:50c3:0:b0b1;
Authentication-Results: mx.google.com;
       spf=neutral (google.com: 2a01:348:0:6:5d59:50c3:0:b0b1 is neither permitted nor denied by best guess record for domain of SRS0=Znlt=QW=yahoo.com=alice@domain.com) smtp.mail=SRS0=Znlt=QW=yahoo.com=alice@domain.com
Received: by maxipes.logix.cz (Postfix, from userid 604)
    id C923E5D3A45; Mon,  8 Jul 2013 23:10:50 +1200 (NZST)
X-Original-To: bill@domain.com
X-Greylist: delayed 00:06:34 by SQLgrey-1.8.0-rc1
Received: from elasmtp-curtail.atl.sa.earthlink.net (elasmtp-curtail.atl.sa.earthlink.net [209.86.89.64])
    by maxipes.logix.cz (Postfix) with ESMTP id B43175D3A44
    for <bill@domain.com>; Mon,  8 Jul 2013 23:10:48 +1200 (NZST)
Received: from [168.62.170.129] (helo=laurence39)
    by elasmtp-curtail.atl.sa.earthlink.net with esmtpa (Exim 4.67)
    (envelope-from <alice@yahoo.com>)
    id 1Uw98w-0006KI-6y
    for bill@domain.com; Mon, 08 Jul 2013 06:58:06 -0400
From: "Alice" <alice@yahoo.com>
Subject: Terrible Travel Issue.....Kindly reply ASAP
To: bill@domain.com
Content-Type: multipart/alternative; boundary="jtkoS2PA6LIOS7nZ3bDeIHwhuXF=_9jxn70"
MIME-Version: 1.0
Reply-To: alice@yahoo.com
Date: Mon, 8 Jul 2013 10:58:06 +0000
Message-ID: <E1Uw98w-0006KI-6y@elasmtp-curtail.atl.sa.earthlink.net>
X-ELNK-Trace: 52111ec6c5e88d9189cb21dbd10cbf767e972de0d01da940e632614284761929eac30959a519613a350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c
X-Originating-IP: 168.62.170.129

[... I have cut the email body ...]

The headers are to be read chronologically from bottom to top — oldest are at the bottom. Every new server on the way will add its own message — starting with Received. For example:

Received: from maxipes.logix.cz (maxipes.logix.cz. [2a01:348:0:6:5d59:50c3:0:b0b1])
        by mx.google.com with ESMTPS id j47si6975462eeg.108.2013.07.08.04.10.59
        for <bill@gmail.com>
        (version=TLSv1 cipher=RC4-SHA bits=128/128);
        Mon, 08 Jul 2013 04:11:00 -0700 (PDT)

This says that mx.google.com has received the mail from maxipes.logix.cz at Mon, 08 Jul 2013 04:11:00 -0700 (PDT).

Now, to find the real sender of your email, your goal is to find the last trusted gateway — last when reading the headers from top, i.e. first in the chronological order. Let’s start by finding the Bill’s mail server. For this, you query MX record for the domain. You can use some online tools, or on Linux you can query it on command line (note the real domain name was changed to domain.com):

~$ host -t MX domain.com
domain.com               MX      10 broucek.logix.cz
domain.com               MX      5 maxipes.logix.cz

So you see the mail server for domain.com is maxipes.logix.cz or broucek.logix.cz. Hence, the last (first chronologically) trusted “hop” — or last trusted “Received record” or whatever you call it — is this one:

Received: from elasmtp-curtail.atl.sa.earthlink.net (elasmtp-curtail.atl.sa.earthlink.net [209.86.89.64])
    by maxipes.logix.cz (Postfix) with ESMTP id B43175D3A44
    for <bill@domain.com>; Mon,  8 Jul 2013 23:10:48 +1200 (NZST)

You can trust this because this was recorded by Bill’s mail server for domain.com. This server got it from 209.86.89.64. This could be, and very often is, the real sender of the email — in this case the scammer! You can check this IP on a blacklist. — See, he is listed in 3 blacklists! There is yet another record below it:

Received: from [168.62.170.129] (helo=laurence39)
    by elasmtp-curtail.atl.sa.earthlink.net with esmtpa (Exim 4.67)
    (envelope-from <alice@yahoo.com>)
    id 1Uw98w-0006KI-6y
    for bill@domain.com; Mon, 08 Jul 2013 06:58:06 -0400

but you cannot actually trust this, because that could just be added by the scammer to wipe out his traces and/or lay a false trail. Of course there is still the possibility that the server 209.86.89.64 is innocent and only acted as a relay for the real attacker at 168.62.170.129, but then the relay is often considered to be guilty and is very often blacklisted. In this case, 168.62.170.129 is clean so we can be almost sure the attack was done from 209.86.89.64.
And of course, as we know that Alice uses Yahoo! and elasmtp-curtail.atl.sa.earthlink.netisn’t on the Yahoo! network (you may want to re-check its IP Whois information), we may safely conclude that this email was not from Alice, and that we should not send her any money to her claimed vacation in the Philippines.

Two other contributors, Ex Umbris and Vijay, recommended, respectively, the following services for assisting in decoding of email headers: SpamCop and Google’s Header Analysis tool.

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Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

How To Download Torrent Files with IDM-New Trick

We all use Torrent to download various kinds of files like songs,movies,books,software's and much more. The download speed of torrent depends on many factors like seeders,leeches,peers, Internet connection and much more.Sometimes you may face difficulty in downloading torrent files with less seeds which results in slow download.So here I got a trick to Download Torrent Files With IDM keep reading.

Advantages of downloading torrent files with IDM:

1. Internet Download Manager(IDM) is the best download manager and speeds up your overall download speed by 5 times.
2. Internet download manager speed doesn't depend on seeders,leeches etc,it only depends on your Internet connection. So, you can download torrent files with IDM without any difficulty if you have good net connection.
3. If Torrent is blocked in your offices,schools,colleges etc then you can download torrent files with Internet download Manager(IDM) easily.
4. Downloading Torrent Files With IDM is really useful when you are downloading files with less seeds.

What is the alternate website or website like Torrific.com?

1. The website similar to Torrific.com is zbigz.com.Keep Reading on how to download torrent files with zbigz.com.

Steps To Download Torrent Files With IDM:

1. First go to Zbigz.com[Click Here].
2. Signup for a free account there.Get Premium account from here.
3. After the signup process is finished go to your torrent search engine and search for the file which you want to download with idm.

4.Then download the torrent file from your desired torrent.

5.Now go to Zbigz.com[Click Here].

6.There hit on upload and choose the torrent file which you have downloaded previously then hit Go.

 7.Then a window will pop up asking for premium or free download.Choose Free Download.

 8.After choosing free your torrent file will be downloaded by high speed servers and your file will be ready to download(If its a large file then wait for few minutes).

9.When you hit download button then a box will pop up asking the type of download which you want either free or premium.Go for free download.

10.That's it your download will be ready and you can download torrent files with idm.

Update 1:If you feel that your file is not caching properly by zbigz,then first get cached link using torcache.net then paste that link in zbigz  and hit go.

Video Tutorial on How To Download torrent files with IDM:

So now you can comfortably download torrent files with IDM without any difficulty.If you have any problem then please leave a comment I will definitely help you.Those who have already downloaded torrent files with IDM share your experience.