Net Tool Box - The Ultimate Mac Networking Utility


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IP Terminals

Background

These terminals demonstrate exactly how different protocols on the Internet work. It is important to understand the textual background that all web-based applications work upon. They are indispensable tools for developers who need help with network protocols.

How do I use it?

TCP Hook
The TCP Hook is like a simple Telnet Utility. You can connect to a port and exchange data at the ‘raw’ level. The best way to understand what it does is to try it:
Type in a web site to the "Host" field and set the port to 80. Then hit connect and paste the following text in:
GET / HTTP/1.0
Then hit return twice. It should then display the HTTP headers and HTML of the chosen web site.
That is an example of how a web browser works. You can try it with any protocol (FTP, SMTP, POP3 etc).

 

SSL Hook
SSL Hook is exactly the same as TCP hook, only it ads a standard SSL security layer. This means that you can test your SSL applications and SSL based protocols at the ‘raw’ level; something that before was almost impossible. For example, you can connect to a SSL web server (one that begins https://) on port 443 (the standard https port) and send a regular http request as in the TCP Socket example. The server will return an encrypted http response, which Net Tool Box will transparently decrypt and display. If you tried to intercept the packets using a Traffic Watcher, you would see the encrypted code – completely unreadable and therefore 100% secure.

Note: Listening on ports less than 1024 is only possible while Net Tool Box is running in the authenticated environment. See Using Net Tool Box for more information about authentication.

TCP Listener
The TCP Listener does exactly as the Hook does; only it is used for examining and interacting wityh the protocols sent by a protocol client instead of a daemon (server program). In other words, it simulates a server. For example, you make a TCP listener listen on port 80, and then type "localhost" into your web browser, and you will see exactly what your web browser sends to every web site you visit.

UDP Terminal
UDP (Or “User Datagram Protocol”) is the basis for most high-speed, highly distributed network traffic such as media streaming and video conferencing. It is a connectionless protocol that has very low overhead, but is not as secure as TCP. Since there is no connection, UDP is a much more versatile form of communication. As well as having the ability to communicate on a 1-to-1 basis (called “Unicasting”), UDP also allows you to send messages (known as “Datagrams”) to many computers as either a group of users (multicast group) or as a network (broadcasting).
The Net Tool Box implementation of the UDP protocol allows you to communicate in all three UDP states (Unicast, Multicast and Broadcast). To start, open a UDP Tool from The “Terminal” menu on the toolbar, and then choose a port to communicate on. The button next to the port field will give you access to the built in Port Database. Click “Connect” to bind your UDP Tool to that port.
Once your UDP Tool has successfully bound itself to a port, the address and data fields become enabled. By default the address field will contain your local IP address. Communicating on this address will act as a loopback (everything you send, you get back), your packets won’t go anywhere outside your computer. The “Broadcast” button, when pressed, will automatically enter your local broadcast address. Communicating to your broadcast address will send your messages to everyone listening on your specified port within your subnet.
To communicate with others in a multicast environment you must each join the same multicast group. To do this you must enter a multicast address to the address field and click the “Join Multicast Group” button. A multicast address is a special type of IP addresses in the range of 224.0.0.0 to 239.255.255.255. The “TTL” field will determine how many ‘hops’ from your computer your datagrams will go. By default the TTL is set to 1. This means that your datagrams won’t go outside your subnet.

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© Charlie Boisseau 2005
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