What is Tunneling ?

What is Tunneling ?

Tunneling is the most significant component of VPN technology.  Tunneling is the technique of encapsulating an entire data packet in the packet of another protocol format. When a tunneled packet is routed to the destination node, it travels across the internet work through a logical path. This logical path is referred to as a tunnel.  Tunneling is analogous to sending a letter. After you write a letter, you place it in an envelope. This envelope displays the address of the recipient. When you post this letter, it is delivered to the recipient according to the address on the envelope. The recipient then needs to open the envelope to read the letter.

What are VLANs ?

What are VLANs ?

VLANs are broadcast domains in a Layer 2 network. Each broadcast domain is like a distinct virutal bridge within the switch. Each virtual bridge you create in a switch defines a broadcast domain. By default, traffic from one VLAN cannot pass to another VLAN. Each of the users in a VLAN would also be in the same IP Subnet. Each switch port can belong to only one VLAN.

What are the advantages & disadvantages of VPN ?

What are the advantages & disadvantages of VPN ?
Advantages

    * Reduce cost implementation (We don’t need to use lease line/ ISDN/ FR, mobile only need to dial local ISP to connect to branch office)
    * Security (VPN provide strong security mechanism through encryption, authentication etc)
    * Lower cost (Bring down cost of Wan equipment)
    * More Flexible
    * Simple Management
    * Interoperability of devices from multiple vendors
    * Centralized VPN management
    * Easy implementation
    * Easy usability
    * Scalability
    * Performance
    * Bandwidth management
    * Service provider’s infrastructure
    * High availability

Disadvantages

    * Highly dependent on Internet
    * Lack of support to legacy protocol

What is a loopback address?

This IP address corresponds to the software loopback interface of the network card, which does not have hardware associated with it, and does not require a physical connection to a network.

The loopback address allows for a reliable method of testing the functionality of an Ethernet card and its drivers and software without a physical network. It also allows information technology professionals to test IP software without worrying about broken or corrupted drivers or hardware.
To test a network card using the loopback address, you can use the TCP/IP utility Ping. The best way to do this is with the Ping utility that comes with most operating systems. This is a simple command-line utility that will try to communicate to an IP address.

Once you are at a command prompt, enter the following:
        ping 127.0.0.1
If the command is successful, the Ping utility will return results similar to the following. The exact information returned will vary depending on your operating system:

Pinging 127.0.0.1 with 32 bytes of data:
Reply from 127.0.0.1: bytes=32 time<10ms TTL=128
Ping statistics for 127.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum =  0ms, Average =  0ms
This indicates that the network card and drivers are functioning properly. If the Ping utility is not able to get a return on the network card, this may indicate either a driver problem, or a physical problem with the card.

What is NAT (Network Address Translation)?

Network Address Translation (NAT) is an IETF standard that enables a local area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic.

All necessary IP address translations occur where the LAN interfaces with the broader Internet. NAT converts the packet headers (and in some cases the port numbers in the headers) for incoming and outgoing traffic and keeps track of each session.
This does mean, however, that NAT overrides "Internet transparency", a practice in which packets remain intact throughout their transmission. NAT is also provided with Windows Internet Connection Sharing.

NAT accomplishes these key purposes:

•It acts as a firewall by hiding internal IP addresses.
•It enables an enterprise to use more internal IP addresses, since there is no possibility of conflict between its internal-only IP addresses and those used by other organizations. Essentially, an organization can present itself to the Internet with fewer IP addresses than used on its internal network, which conserves public IP addresses.
•It allows an enterprise to bundle multiple ISDN connections into one Internet connection.

Private Address Space

Private Address Space

   The Internet Assigned Numbers Authority (IANA) has reserved the
   following three blocks of the IP address space for private internets:

     10.0.0.0        -   10.255.255.255  (10/8 prefix)
     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

Difference between Socket and Port

Imagine you computer as a House with many doors. The address of your house would be equal to the the IP address of a computer. Each door would be equal to a computer's port. A socket would sit at a door and listen and talk. A socket is an a a connection to another computer. It would sit at one of your doors and yell across the street to your neighbour's house. In order to do this, you need to know what door your neighbour is listening at otherwise he can't answer. You call up your neighbour and he tells you that he is listening on port 150. You pick a random door at your house with a number above 1024 and make sure it's empty. If it isn't, you find another one and repeat.(This is usually handled by the socket and you don't need to specify this.) Then you open this door and throw a rock to your neighbour's house across the street and hit the door numbered 150. Your neighbour opens his door(#150) and you now can talk to him and send him data.

http://www.coderanch.com/t/206360/sockets/java/port-vs-socket