Difference Between Public and Private IP Addresses

A public IP address makes your equipment accessible to everyone on the internet and is needed for VoIP or if you want to give others to access to specific equipment on your network.  You must therefore be careful to protect your equipment from hackers and viruses and not to allow your equipment to be hi-jacked and used as an open email-relay, for example.  A private IP address is for private use within the network and allows many more PCs to be connected.  If a customer is using a private IP and later wants VOIP they would need to change to a public IP address. 

How many IP addresses can I use?
Link-Sat provides a set of 8 IP addresses at the time of site activation. Here is the example of how these IP addresses are used: 
1st IP is for network assignment (cannot be used)
2nd IP is for RCST IP Gateway
3rd, 4th, 5th, 6th and 7th for your router, PCs etc.
8th one is for broadcast (cannot be used)
A subnet mask and two DNS IP addresses are also provided for connected PCs.

A unique Internet Protocol (IP) address, known as a public IP address, is assigned to every computer that connects to the Internet. The IP addressing scheme makes it possible for computers to "find each other" online and exchange information. Within a private network, computers use addresses excluded by convention from use on the Internet. The difference between a private IP address and a public IP address then, is that privateIP addresses are reserved for private networks, and public IP addresses are reserved for the Internet.

The Internet Assigned Numbers Authority (IANA), a once-autonomous organization, now works within the purview of the Internet Corporation for Assigned Names and Numbers (ICANN). IANA is responsible for overseeing global allocation of IP numbers, among other related protocols. Within the range of publicly available IP addresses are specific, excluded ranges withheld for private network use. These private IP ranges are as follows:

• 10.0.0.0 … 10.255.255.255
• 172.16.0.0 … 172.31.255.255
• 192.168.0.0 … 192.168.255.255

Computers within a private network are each assigned a unique address in order to exchange files and share resources with one another. The network router, which routes information, will pass data back and forth among the connected computers, using the respective addresses. But how do computers on a private network connect to the Internet?

Assuming the network has Internet connectivity, the computer connected to the digital subscriber line (DSL) modem is assigned a public IP address by the Internet Service Provider (ISP). This single public IP address is used to identify the network on the Internet. Now the network's router acts as a gatekeeper between the private network and the public Internet. Using a built-in Network Address Translator (NAT), the router passes requests to the Internet using the assigned public IP address. Returning data is routed back to the public IP address, with the router determining which private IP address requested the information. In essence, the private IP address is daisy-chained to the public IP address through processes in the router.

A public IP address can be static or dynamic. A static public IP address does not change and is used primarily for hosting webpages or services on the Internet. Some gamers also prefer static IPs for interactive gaming. A dynamic public IP address is chosen from a pool of available addresses and changes each time one connects to the Internet. Most people have a dynamic public IP address, as it is the standard type of public IP address assigned when purchasing Internet connectivity.

Various freeware programs are available online that will display your computer's assigned public IP address for you. To see private IP addresses you can open your router's configuration dialogs, or if using Windows XP, type ipconfig at the command prompt. The command prompt is available through Start -> All Programs -> Accessories -> Command Prompt. To leave the command prompt window, type exit.

Intrusion Detection

IDS, called Intrusion Detection System (for Cisco) is an advanced form of traffic analysis for firewalls. It is also called Stateful Inspection. Depending on the amount of security needed, it may not be enough to restrict access by port, source and destination. What if I allow the WHOLE internet access to my company's public FTP server (maybe for a free download), someone might know of a FLAW for that particular FTP server that could give them some special and unwanted access. This is where Stateful Inspection comes in. Stateful Inspection is an amazing utility that knows all the valid commands to expect for your typical network services (SMTP, HTTP, FTP, DNS, etc). If you setup a Stateful Inspection firewall, it makes sure that only approved and correct commands are being used for each type of service. This is what you use to protect about know service vulnerabilities, such as buffer overruns. Stateful Inspection firewalls are CPU intensive and expensive. You can get equipment from vendors such as Cisco (PIX Firewall or IDS feature set), Symantec, and Checkpoint. Article last reviewed: 01/09/2006   del.icio.us  Created by: Digital Foundation, inc. Copyright © 2002-2005 Digital Foundation, inc.  www.networkclue.com All content of the NetworkClue website is copyrighted. Articles, notes, outlines, and all other materials may not be stored on the Internet or sold or placed by themselves or with other material in any electronic or printed format in whole or part. However materials may be referenced by links to the site.

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Symmetric vs. asymmetric algorithms

When using symmetric algorithms, both parties share the same key for en- and decryption. To provide privacy, this key needs to be kept secret. Once somebody else gets to know the key, it is not safe any more. Symmetric algorithms have the advantage of not consuming too much computing power. A few well-known examples are: DES, Triple-DES (3DES), IDEA, CAST5, BLOWFISH, TWOFISH.
Asymmetric algorithms use pairs of keys. One is used for encryption and the other one for decryption. The decryption key is typically kept secretly, therefore called ``private key'' or ``secret key'', while the encryption key is spread to all who might want to send encrypted messages, therefore called ``public key''. Everybody having the public key is able to send encrypted messages to the owner of the secret key. The secret key can't be reconstructed from the public key. The idea of asymmetric algorithms was first published 1976 by Diffie and Hellmann.
Asymmetric algorithms seem to be ideally suited for real-world use: As the secret key does not have to be shared, the risk of getting known is much smaller. Every user only needs to keep one secret key in secrecy and a collection of public keys, that only need to be protected against being changed. With symmetric keys, every pair of users would need to have an own shared secret key. Well-known asymmetric algorithms are RSA, DSA, ELGAMAL.
However, asymmetric algorithms are much slower than symmetric ones. Therefore, in many applications, a combination of both is being used. The asymmetric keys are used for authentication and after this has been successfully done, one or more symmetric keys are generated and exchanged using the asymmetric encryption. This way the advantages of both algorithms can be used. Typical examples of this procedure are the RSA/IDEA combination of PGP2 or the DSA/BLOWFISH used by GnuPG.

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Rachit Seth