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What is Tcpdump?

Tue, 04 Jul 2006 01:00:00 +0100

Tcpdump

Tcpdump is a common computer network debugging tool that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. It was originally written by Van Jacobson, Craig Leres and Steven McCanne who were, at the time, working in the Lawrence Berkeley Laboratory Network Research Group.

Tcpdump works on most Unix-like platforms: Linux, Solaris, BSD, Mac OS X, HP-UX and AIX among others. In those systems, tcpdump is built upon the libpcap packet capture library.

On Windows, WinDump can be used; it's a version of tcpdump for Windows.

On Unix and most other operating systems, a user must have superuser privileges to use tcpdump due to its use of promiscuous mode.

The user may optionally apply any number of filters to render the output more usable on networks with a high volume of traffic.

Tcpdump prints out the headers of packets on a network interface that match the boolean expression. Under SunOS: You must be root to invoke tcpdump or it must be installed setuid to root. Under Ultrix: Any user can invoke tcpdump once the super-user has enabled promiscuous-mode operation using pfconfig(8). Under BSD: Access is controlled by the permissions on /dev/bpf0, etc.

Common uses of tcpdump
- to debug applications one is writing which utilize the network for communications
- to debug the network setup itself, by determining whether all necessary routing is or is not occurring properly, allowing the user to further isolate the source of a problem
- to intercept and display the communications of another user or computer.

Some protocols, such as telnet and HTTP, transmit information unencrypted over the network. A user with control of a router or gateway through which other computers' unencrypted traffic passes can use tcpdump to view login IDs, passwords, the URLs and content of websites being viewed, or any other information.

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Article Source What is Tcpdump?

What is SMTP?

Sat, 26 Aug 2006 01:00:00 +0100

SMTP is an acroynm for Simple Mail Transfer Protocol

SMTP is the network protocol used to send emails across the Internet

Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP.

In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.

The usual method of sending mail is your mail client will contact the given SMTP server which looks up the MX record for the destination domain then transports the mail to the destination. If the destination denies this mail it sends a bounce message to the sender, in this case the address in the 'from' field of the mail.

Article Source What is SMTP?

What is RSS?

Sat, 26 Aug 2006 01:00:00 +0100

RSS (Really Simple Syndication) is a news feed system. To view RSS news feeds, you''ll need a news reader. These can be downloaded for free from the internet, or can be part of your internet browser. When you have a news reader, all you need to do is visit the RSS feed link, and copy/type the web address into your newsreader.

In this way, you can subscribe to news feeds that are relevant to you, without needing to visit all the different websites to get the latest news.

Article Source What is RSS?

What is Active Directory?

Thu, 28 Sep 2006 01:00:00 +0100

Active Directory are registries and databases that provide directory-type facility for applications and users, but not one is interconnected, share-centric, or distributed in any way.

ActiveDirectory is a universal distributed information storehouse through which all network objects, such as application configurations, services, computers, users, and processes, can be accessed, in a consistent manner, over the full expanse of a network or inter-network.

This is made possible by the logical structure of the directory. Before you start scratching your head, you should understand that without Active Directory, you cannot log in to a Windows Server 2003 domain, period.

Article Source What is Active Directory?