[Dnsmasq-discuss] IP6 DNS UDP strange behaviour

[Roger James]

Hi Simon,

Sending ICMP unreachable is not very friendly with my ISP. They treat the 
host as offline. The host is my VoIP PBX so I don't get any incoming calls 
for a while. Would it not be better to hold the port open until all 
requests have been received. I have turned on the strict-order option to 
try and circumvent this.

Roger


On 27 June 2017 10:31:59 am Simon Kelley <simon at thekelleys.org.uk> wrote:

> What's probably happening is this.
>
> 1) query arrives from client,
> 2) UDP socket opened, and query send from socket to more than one
> upstream server.
> 3) Reply arrives from fastest upstream server, reply returned to client.
> 4) upstream socket closed.
> 5) reply arrives from slower upstream server -> destination unreachable.
>
> dnsmasq does the "send the query to all available servers" trick every
> once in a while to find the fastest one.
>
> If this is what you're seeing, it's a feature, not a bug.
>
> Cheers,
>
> Simon.
>
>
>
>
> On 27/06/17 06:56, Roger James wrote:
>> I am seeing some rather perplexing behaviour regarding the reception of
>> upstream IPV6 UDP DNS query responses on a Debian (raspian) system
>> running on a Raspberry Pi. It appears that dnsmasq is not holding open
>> an IPV6 UDP port to handle a response to an upstream query. What my
>> network monitor shows is the upstream request going out and a reply
>> coming back in. However the Pi rejects the incoming UDP packet with a
>> ICMPV6 Destination unreachable (port unreachable).
>>
>> I may be missing something obvious here, but it looks like dnsmasq is
>> not holding open a listening port for the response.
>>
>> Has anyone got any ideas on what is going, or can point me at some ways
>> of tracking this down.
>>
>> The configuration of dnsmasq is out of the box Debian.
>>
>> Thanks,
>>
>> Roger
>>
>>
>>
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>>
>
>
>
>
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