Windows 8 and Windows 7 will be different in a lot of ways Windows 8 will be a lot more secure than Seven
and will be less prone to attacks from viruses etc it accepts more usb based peripheals than Windows7
its going to be a great shot in the Arm that Windows needs
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Dive Deep into PING Command
We all are aware of PING command, hardly any person has not used this command using computer in day to day life but there are lot of this you may not be aware of . So, I’ll be going to take you deep into the "PING" command .
Before getting into deep, lets get into the basics first some of the things you may not be knowing.
What Does PING means ?
PING stands for Packet Internet Gropher.
Why we use it ?
It is a network utility in computer which sends the ICMP or ECHO packets to test the reachability of host on an Internet Protocol (IP) network .
What is ICMP packet ?
ICMP is internet control message protocol having port number 7 . Every protocol having a port number .You can check list of protocos with their port numbers here:
http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml
We can use several options with PING to enchance it’s capability .
- -t : Specifies that ping continue sending Echo Request messages to the destination until interrupted. To interrupt and display statistics, press CTRL-BREAK. To interrupt and quit ping, press CTRL-C.
- -a : Specifies that reverse name resolution is performed on the destination IP address. If this is successful, ping displays the corresponding host name.
- -n Count : Specifies the number of Echo Request messages sent. The default is 4.
- -l Size : Specifies the length, in bytes, of the Data field in the Echo Request messages sent. The default is 32. The maximum size is 65,527.
- -f : Specifies that Echo Request messages are sent with the Don't Fragment flag in the IP header set to 1. The Echo Request message cannot be fragmented by routers in the path to the destination. This parameter is useful for troubleshooting path Maximum Transmission Unit (PMTU) problems.
- -i TTL : Specifies the value of the TTL field in the IP header for Echo Request messages sent. The default is the default TTL value for the host. For Windows XP hosts, this is typically 128. The maximum TTL is 255.
- -v TOS : Specifies the value of the Type of Service (TOS) field in the IP header for Echo Request messages sent. The default is 0. TOS is specified as a decimal value from 0 to 255.
- -r Count : Specifies that the Record Route option in the IP header is used to record the path taken by the Echo Request message and corresponding Echo Reply message. Each hop in the path uses an entry in the Record Route option. If possible, specify a Count that is equal to or greater than the number of hops between the source and destination. The Count must be a minimum of 1 and a maximum of 9.
- -s Count : Specifies that the Internet Timestamp option in the IP header is used to record the time of arrival for the Echo Request message and corresponding Echo Reply message for each hop. The Count must be a minimum of 1 and a maximum of 4.
- -j HostList : Specifies that the Echo Request messages use the Loose Source Route option in the IP header with the set of intermediate destinations specified in HostList. With loose source routing, successive intermediate destinations can be separated by one or multiple routers. The maximum number of addresses or names in the host list is 9. The host list is a series of IP addresses (in dotted decimal notation) separated by spaces.
- -k HostList : Specifies that the Echo Request messages use the Strict Source Route option in the IP header with the set of intermediate destinations specified in HostList. With strict source routing, the next intermediate destination must be directly reachable (it must be a neighbor on an interface of the router). The maximum number of addresses or names in the host list is 9. The host list is a series of IP addresses (in dotted decimal notation) separated by spaces.
- -w Timeout : Specifies the amount of time, in milliseconds, to wait for the Echo Reply message that corresponds to a given Echo Request message to be received. The default time-out is 4000 (4 seconds).
- TargetName : Specifies the destination, which is identified either by IP address or host name.
- /? : Displays help at the command prompt.
Coming to the point :
How does it work ?
When we execute PING command For Example: >ping www.google.com
Basically the process of ping takes place in two steps :
a) [REQUEST ICMP PACKET]: ICMP packets will be send to Google Server to check if we have reachability to google server or not ? This step will complete process from only one side.
b) [REPLY ICMP PACKET]: Google Server will reply and let our system to know reachability is compete and thus complete 2 way process.
Now, a single ICMP packet contains a lot of information that we will going to study now .
I did ping www.google.com and captured icmp packets to understand it better:
What we can observe from here ?
Google Server IP is 74.125.236.51
You can even put this ip or whatever will come in your case ( google search engine has many servers) on browser instead of this.
I captured those ICMP packets on wireshark to look what's inside it ?
We can see, in info- two types of echo packets: request and reply.
Now, Understanding what’s behind those echo packets ?
- Version – This should always be set to 4.
- Internet Header Length – The length of the header in 32 bit words.
- Type of Service – This should be set to 0, as this is the only legit setting according to
- Total Length – Total length of the header and data portion of the packet, counted in octets.
- Identification , Flags and Fragment offsets – Ripped from the IP protocol.
- Time To Live – How many hops this packet will survive.
- Protocol – which version of ICMP is being used (should always be 1).
- Header Checksum – .This field is recomputed at every host that changes the header, which means pretty much every host that the packet traverses over, since they most often change the packets TTL field or some other.
- Source Address – The source address from whom the packet was sent. This is not entirely true, since the packet can have another source address, than that which is located on the machine in question. The ICMP types that can have this effect will be noted if so.
- Destination Address – The destination address of the packet.
There are also a couple of new headers that are used by all of the ICMP types. The new headers are as follows, this time with a few more notes about them:
- Type – The type field contains the ICMP type of the packet. This is always different from ICMP type to type. For example ICMP Destination Unreachable packets will have a type 3 set to it. For a complete listing of the different ICMP types. This field contains 8 bits total.
- ·Code – All ICMP types can contain different codes as well. Some types only have a single code, while others have several codes that they can use. For example, the ICMP Destination Unreachable (type 3) can have at least code 0, 1, 2, 3, 4 or 5 set. Each code has a different meaning in that context then. For a complete listing of the different codes, see the ICMP types. This field is 8 bits in length, total. We will discuss the different codes a little bit more in detail for each type later on in this section.
- Checksum – The Checksum is a 16 bit field containing a one's complement of the ones complement of the headers starting with the ICMP type and down. While calculating the checksum, the checksum field should be set to zero.
Hope this is informative for you.
Thank you !
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5 Key Benefits of VoIP Phone Systems
Telecommunication systems around the world have experienced immense changes in the recent past. The complex old PBX systems are being replaced with the latest digital phones that both improve the office ergonomics and offer advanced telephony features. Businesses around the world are migrating to the latest telephony system like VoIP and IP. The advantages and the features being offered by VoIP make it one of the most sought after telephone technology in the world. Low cost of operations and user-friendly interface of VoIP has made it a champion among business owners who want to whittle down their calling expenses.
How to find the list of installed modules in Perl
This is one of the questions asked in many Perl related job interviews. See the question here: http://www.aliencoders.org/content/interview-questions-perl-freshers-and-experienced
There will be some situations when you will need to know about installed modules, its version or you may need to check if required module is installed or not with mentioned version or higher than that.
Here are few ways through which you can achieve the result that I found over the internet from different websites.
1. To list all installed Perl modules using perl script
[perl]
#!/usr/bin/perl #change the path with your perl location
use strict;
use warnings;
use ExtUtils::Installed; # By default this module will be available in Perl
my $instmod = ExtUtils::Installed->new();
foreach my $module ($instmod->modules()) {
my $version = $instmod->version($module) || “Version Not Found.”;
print “$module version=$version \n”;
}
[/perl]
2. To list installed Perl modules using command line in Linux box
Try instmodsh command in linux box
and then type l to list modules or m to give particular module name or q to quit
[code] $ instmodsh[/code]
Output:
[code]Available commands are:
l – List all installed modules
m – Select a module
q – Quit the program
cmd?[/code]
At cmd? prompt type l to list all installed modules:
[code]cmd? l[/code]
Output:
[code]Installed modules are:
Archive::Tar
CPAN
Compress::Zlib
MIME::Lite
Module::Build
Net::Telnet
PAR::Dist
Perl
Spiffy
Test::Base
Test::Simple
XML::Simple
cmd?
[/code]
This command itself is a perl script that use ExtUtils::Installed module. Try following command to see its source code:
[code]$ vi $(which instmodsh)[/code]
For more details, visit this link: http://perldoc.perl.org/instmodsh.html
3. To compare and check installed Perl modules with respect to given modules with its version
[perl]
#!/usr/bin/perl
use strict;
use warnings;
my @modules = ([‘SOAP::Lite’, 0.50],
[‘IO::Socket’, 0],
[‘HTML::Parser’, 3.26],
[‘LWP’, 5.65],
);
print “\n”,
“==========================\n”,
“Testing for the given Perl modules\n”,
“===========================\n”;
for my $arr_ref (@modules) {
my($mod, $ver) = @$arr_ref;
print “$mod” . ($ver ? ” (version >= $ver)” : “”) . “\n”;
eval(“use $mod” . ($ver ? ” $ver;” : “;”));
if ($@) {
my $msg = $ver ?
“\tEither it doesn’t have $mod installed,\n” .
“\tor the version that is installed is too old.\n” :
“\tIt does NOT have $mod installed.\n”;
print “$msg\n”;
}
else {
print “\tYour system has $mod installed ” .
“with version @{[ $mod->VERSION ]}\n\n”;
}
}
print “Module Testing Done!\n”;
[/perl]
Note: If you are putting module name dynamically, then use @{[ $mod->VERSION ]} for version number
else $Module-Name::VERSION ex: $SOAP::Lite::VERSION
[perl]
print “SOAP::Lite Version is “. $SOAP::Lite::VERSION.”\n”;
#or
print “$mod version is @{[ $mod->VERSION ]} \n”;
[/perl]
4. To list Perl modules that comes preinstalled with the standard Perl package and installed from outside
[perl]
perldoc perlmodlib #lists all the modules that come with standard Perl package already
perldoc perllocal #lists all modules that is installed from outside
[/perl]
Both modules reveal lots of information about each installed modules like installation date, directory, module version etc.
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