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Re: InetAddress.isReachable() ?

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Sorry to be slow responding Martin.  It's been one of those weeks.

The basic setup is this;  we have a server sending Multicast data 
packets through a VPN over the internet.  The end points have user 
programs that use this data for some presentations.  We are tasked with 
supporting the system but large parts of it are beyond our control.  The 
main issue for us is the remote locations ISP reliability.  I wanted a 
simple way to tell on the first phone call whether there was a network 
path to the server without having to log into the VPN network.  The 
software running on the remote locations has indications that data has 
not arrived recently but it has no indication of quality.  When they 
call and tell me the system is showing old data I can ask if the box is 
red or green and start trouble shooting from there.  These folks are not 
up to running nmap or wireshark or anything for that matter.  Using a 
Process to run ping seems to work fine, just more code that I wanted to 
write.  Since Windows and Linux use a different set of options for ping 
I had to detect the OS and change the accordingly.

I'm not sure why Java has the privilege issue with 
InetAddress.isReachable() but it does.

knute...


On 10/24/2020 06:45, Martin Gregorie wrote:
> 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.
> 
> 

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Thread

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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