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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
Newsgroups: comp.lang.java.programmer
Subject: Re: How to give ip address as a input on java...if I give ip addrees as a input need to display ip adress present in the server or not???
Date: Thu, 14 Jun 2018 14:09:18 -0400
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On 6/14/2018 2:02 PM, Knute Johnson wrote:
> On 6/14/2018 01:14, siddareddy.moolam@gmail.com wrote:
>> i need to also check whether the ip is up or down ???
> 
> InetAddress::isReachable is just a ping and only tells you the machine 
> is there and responding to pings.  Connecting to the server tells you 
> the machine is there and the server is running.

isReachable is one of those methods that one should be very careful
relying too much on.

It can give both false negatives and false positives.

The documentation sort of hint at it:

<quote>
Test whether that address is reachable. Best effort is made by the 
implementation to try to reach the host, but firewalls and server 
configuration may block requests resulting in a unreachable status while 
some specific ports may be accessible. A typical implementation will use 
ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will 
try to establish a TCP connection on port 7 (Echo) of the destination host.
</quote>

It will do a "best effort".

:-)

Arne