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Groups > comp.os.linux.networking > #3064

Re: Totally stuck --> UDP packets refused

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Palmisano a écrit :
> On Fri, 29 Aug 2014 01:05:23 +0200, Pascal Hambourg wrote:
> 
>> Jorgen Grahn a écrit :
>>>> # tcpdump host 192.168.1.246
>>>> 23:01:02.112832 IP zon.57758 > ics1000.9760: UDP, length 11
>>>> 23:01:02.221171 IP ics1000.9760 > zon.9761: UDP, length 8
>>>> 23:01:02.221196 IP zon > ics1000: ICMP zon udp port 9761 unreachable, 
>>>>
>>>> aha, unreachable...
>>>>
>>>> So my thought was: FIREWALL.  So I added 9761 UDP to iptables
>>> The more likely explanation is that noone is listening on zon.9761
>>> (or *.9761).
>> I agree. "Port unreachable" is the ICMP type/code generated by the UDP
>> stack when nothing listens on the destination port. The REJECT rule at
>> the end of the INPUT chain in the iptables ruleset would have generated
>> a "host prohibited" ICMP type/code.
> Great advice guys. I am blushing with shame.
> The bind() failed and due to a typo that I overlooked <n> times, the
> exit value test didn't notic ethe failure.
> 
> Fixed now.
> 
> BTW: I agree that replying on another port is weird. But I didn't
> build the device that accepts the commands :-).

It may make things a bit easier to use 9761 as the source port for the
outgoing packet instead of an ephemeral port. I see two advantages :
- it requires only one single UDP socket for sending and receiving ;
- a stateful iptables ruleset can handle the reply packet automatically
(as ESTABLISHED) without requiring an explicit rule in the INPUT chain.

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Thread

Totally stuck --> UDP packets refused Palmisano <xspalm1@hotmail.com> - 2014-08-28 23:18 +0200
  Re: Totally stuck --> UDP packets refused Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-08-28 22:41 +0000
    Re: Totally stuck --> UDP packets refused Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-08-29 01:05 +0200
      Re: Totally stuck --> UDP packets refused Palmisano <xspalm1@hotmail.com> - 2014-08-29 21:20 +0200
        Re: Totally stuck --> UDP packets refused Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-08-30 05:14 +0000
          Re: Totally stuck --> UDP packets refused Palmisano <xspalm1@hotmail.com> - 2014-08-30 14:14 +0200
            Re: Totally stuck --> UDP packets refused Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-08-30 14:15 +0000
              Re: Totally stuck --> UDP packets refused Palmisano <xspalm1@hotmail.com> - 2014-08-31 14:52 +0200
        Re: Totally stuck --> UDP packets refused Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-08-30 14:52 +0200
          Re: Totally stuck --> UDP packets refused Jorgen Grahn <grahn+nntp@snipabacken.se> - 2014-08-30 14:09 +0000

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