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Re: InetAddress.isReachable() ?

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On Fri, 23 Oct 2020 19:38:34 -0500, Knute Johnson wrote:

> On 10/23/2020 19:30, Arne Vajhøj wrote:
>> On 10/23/2020 7:10 PM, Knute Johnson wrote:
>>> On 10/23/20 12:14 PM, Arne Vajhøj wrote:
>>>> On 10/23/2020 12:50 PM, Knute Johnson wrote:
>>>>> InetAddress.isReachable() only works if I run Java as root.  Any
>>>>> idea how to make it work with a regular user?  The docs say "A
>>>>> typical implementation will use ICMP ECHO REQUESTs if the privilege
>>>>> can be obtained".  I'm assuming that's why it won't work as a
>>>>> regular user.
>>>>
>>>> Is it worth it?
>>>
>>> Yes
>> 
>> OK.
>> 
>>>> The method can return false and the service you want to use can be
>>>> available (firewall blocking ICMP and Echo but not application
>>>> protocol).
>>>
>>> No firewalls there.
>>>
>>>> The method can return true and the service you want to use can be
>>>> unavailable (OS running but server application down).
>>>
>>> No service to connect to.  Just want to see if there is a path to the
>>> router.
>>>
>>>> I think you would be better of connecting to the service you want to
>>>> use and handle errors there.
>>>
>>> Again no service to connect to.
>>>
>>> It's an internal network and I'm fielding calls all the time that 'we
>>> aren't getting updates to our data'.  If I can ask is the little box
>>> green or red I'll know with some certainty the status of their network
>>> connection.  I'm 1600 km from the site so I can't just pop over for a
>>> look see.  I can't ask them to ping the router, that's a step too far.
>>> The network service at the remote sites is interrupted on a fairly
>>> regular basis.
>>>
>>> So yes I would really like to figure out how to make this work is it
>>> is possible.
>> 
>> I cannot believe there are any ways to get around the privilege issue.
>> 
>> If there were then it would be a bug that would be fixed.
>> 
>> That leaves you with the awful hack of running the external ping
>> command and read output.
>> 
>> Arne
>> 
>> 
> That's what I was afraid of Arne.  Oh well, I didn't have anything else
> to do this week :-).

Apologies if this is stuff you already know, but I tend to use 
traceroute, wireshark and nmap to sort out network problems and this 
sounds as if it might be some sort of network problem.

Could it be a physical problem, e.g. rodent or physical cable damage 
causing an intermittent connection?

traceroute can show which switch or device is the last device accessible 
along the message route.

Wireshark can be used to show what is being transferred and what 
responses are returned when a problem occurs.

nmap would seem less useful in this case, though at least it shows what 
ports are open at the destination IP address, so can spot firewall 
problems and dodgy interface cards.


-- 
--  
Martin    | martin at
Gregorie  | gregorie dot org

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InetAddress.isReachable() ? Knute Johnson <knute2020@585ranch.com> - 2020-10-23 11:50 -0500
  Re: InetAddress.isReachable() ? Arne Vajhøj <arne@vajhoej.dk> - 2020-10-23 13:14 -0400
    Re: InetAddress.isReachable() ? Knute Johnson <knute2020@585ranch.com> - 2020-10-23 18:10 -0500
      Re: InetAddress.isReachable() ? Arne Vajhøj <arne@vajhoej.dk> - 2020-10-23 20:30 -0400
        Re: InetAddress.isReachable() ? Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2020-10-23 19:38 -0500
          Re: InetAddress.isReachable() ? Martin Gregorie <martin@mydomain.invalid> - 2020-10-24 11:45 +0000
            Re: InetAddress.isReachable() ? Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2020-10-29 15:23 -0500
              Re: InetAddress.isReachable() ? Martin Gregorie <martin@mydomain.invalid> - 2020-10-29 21:36 +0000
              Re: InetAddress.isReachable() ? Arne Vajhøj <arne@vajhoej.dk> - 2020-10-29 21:47 -0400
                Re: InetAddress.isReachable() ? Knute Johnson <knute2020@585ranch.com> - 2020-11-01 10:30 -0600

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