A virtual IP address (VIP or VIPA) is an IP address that is not connected to a specific computer or network interface card (NIC) on a computer. Incoming packets are sent to the VIP address, but all packets travel through real network interfaces.
VIPs are mostly used for connection redundancy; a VIP address may still be available if a computer or NIC fails because an alternative computer or NIC replies to connections
We can also use VIP for load balancing and Automatic Failover
Definition: A port number represents an endpoint or “channel” for network communications. Port numbers allow different applications on the same computer to utilize network resources without interfering with each other.
Port numbers most commonly appear in network programming, particularly socket programming. Sometimes, though, port numbers are made visible to the casual user. For example, some Web sites a person visits on the Internet use a URL like the following:
In this example, the number 8080 refers to the port number used by the Web browser to connect to the Web server. Normally, a Web site uses port number 80 and this number need not be included with the URL (although it can be).
In IP networking, port numbers can theoretically range from 0 to 65535. Most popular network applications, though, use port numbers at the low end of the range (such as 80 for HTTP). The port number is included as a field within the header of each IP packet.
Note: The term port also refers to several other aspects of network technology. A port can refer to a physical connection point for peripheral devices such as serial, parallel, and USB ports. The term port also refers to certain Ethernet connection points, such as those on a hub, switch, or router.
You can find the list of port number at below URL
UDP (User Datagram Protocol)
Definition: UDP is a lightweight transport built on top of IP. UDP squeezes extra performance from IP by not implementing some of the features a more heavyweight protocol like TCP offers. Specifically, UDP allows individual packets to be dropped (with no retries) and UDP packets to be received in a different order than they were sent.
UDP is often used in videoconferencing applications or games where optimal performance is preferred over guaranteed message delivery. UDP is one of the oldest network protocols, introduced in 1980 in RFC document 768.
DNS Server (Domain Name System)
Definition: The DNS translates Internet domain and host names to IP Addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites.
DNS implements a distributed database to store this name and address information for all public hosts on the Internet. DNS assumes IP addresses do not change (are statically assigned rather than dynamically assigned).
The DNS database resides on a hierarchy of special database servers. When clients like Web browsers issue requests involving Internet host names, a piece of software called the DNS resolver (usually built into the network operating system) first contacts a DNS server to determine the server’s IP address. If the DNS server does not contain the needed mapping, it will in turn forward the request to a different DNS server at the next higher level in the hierarchy. After potentially several forwarding and delegation messages are sent within the DNS hierarchy, the IP address for the given host eventually arrives at the resolver, that in turn completes the request over Internet Protocol.
DNS additionally includes support for caching requests and for redundancy. Most network operating systems support configuration of primary, secondary, and tertiary DNS servers, each of which can service initial requests from clients. ISPs maintain their own DNS servers and use DHCP to automatically configure clients, relieving most home users of the burden of DNS configuration.
Also Known As: Domain Name System, Domain Name Service, Domain Name Server
Dynamic Host Configuration Protocol Definition: DHCP allows a computer to join an IP-based network without having a pre-configured IP address. DHCP is a protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network.
Internet Service Providers (ISPs) usually use DHCP to allow customers to join the Internet with minimum effort. Likewise, home network equipment like broadband routers offers DHCP support for added convenience in joining home computers to the LAN.
DHCP environments require a DHCP server set up with the appropriate configuration parameters for the given network. Key DHCP parameters include the range or “pool” of available IP addresses, the correct subnet masks, plus gateway and name server addresses.
Devices running DHCP client software can then automatically retrieve these settings from DHCP servers as needed. Using DHCP on a network means system administrators do not need to configure these parameters individually for each client device.
NetBIOS Definition: NetBIOS is a software protocol for providing computer communication services on local networks. Microsoft Windows uses NetBIOS on Ethernet or Token Ring networks.
Software applications on a NetBIOS network locate each other via their NetBIOS names. A NetBIOS name is up to 16 characters long and in Windows, separate from the computer name. Applications on other computers access NetBIOS names over UDP port 137. It provides name resolution services for NetBIOS.
Two applications start a NetBIOS session when one (the client) sends a command to “Call” another (the server) over TCP port 139 on a remote computer. Both sides issue “Send” and “Receive” commands to deliver messages in both directions. The “Hang-Up” command terminates a NetBIOS session.
NetBIOS also supports connectionless communications via UDP datagrams. Applications listen on UDP port 138 to receive NetBIOS datagrams.
NetBIOS and NetBEUI are separate but related technologies. NetBEUI extends NetBIOS with additional networking capabilities.
Also Known As: Network Basic Input/Output System
WINS Definition: The Windows Internet Naming Service (WINS) supports name resolution, the automated conversion of computer names to network addresses, for Windows networks. Specifically, WINS converts NETBIOS names to IP addresses on a LAN or WAN.
Like DNS, the Windows Internet Naming Service employs a distributed client/server system to maintain the mapping of computer names to addresses. Windows clients can be configured to use primary and secondary WINS servers that dynamically update name/address pairings as computers join and leave the network. The dynamic behavior of WINS means that it also supports networks using