get IP addresses of computer available on a network? -java

Question

I am making a file sharing application which would look for computers which are running the application on the same network. So I would like my application to discover compu

Answer 1

This is one of the basic problems in distributed computing, and there are two approaches that work, to a degree:

Registry Service

• Somewhere on the network, you run a Registry Service with a well-known host and port number. This service has to be reachable / addressable from every place you want to run the application.

• On startup each instance of the application on the network registers itself with the registry.

• When some machine / program needs to locate an instance of the application, it asks the registry.

Problems:

• You have to deal with application instances that "go away" without telling the registry.

• You have to have a way to restore state if the registry restarts.

• The applications have to know the name (or address) and port of the registry instance.

Broadcast / Multicast

• Every instance of the application listens on a well-known "broadcast" or "multicast" address / port.

• When a program wants to locate instances of the application, it sends a broadcast / multicast request.

• Each instance responds to the request giving its details.

• The program accumulates the responses to build a list of all "live" instances.

Problems:

• This doesn't scale. Each and every request from M programs goes to N machines and generates N responses. As M and N grow, the network traffic grows quadratically.

• Broadcast and Multicast are lossy, especially on busy networks.

• Broadcast typically doesn't cross network boundaries. Multicast requires special configuration.

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Either approach should work on a small network with a limited number of instances.

The simple approach is to identify an existing distributed computing technology that does most of the work for you. For example, RMI and a RMI registry, dynamic DNS, CORBA, JINI.