Thanks for the offer. I think there may be a simpler answer, worth
trying first.

Looking back through the git history, this looks like a bug introduced
into 2.78 by the patches for security problems found by Google, in 2017.

It was fixed for 2.79, by  patch


http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=499d8dde2b1a216eab9252ee500cc31b8c2b2974

So, first either move to 2.79 (or preferably 2.80) or apply that patch.

If that doesn't fix it, we'll go for debugging.


Cheers,

Simon.



On 10/01/2019 12:18, Sandeep K M wrote:
> Hi Simon,
> 
> Thanks again for the response.
> 
> I will be happy to be your tester :)
> 
> Its fairly a simple setup with two hosts and a switch. I can create this
> any time you want.
> 
> Please provide me the instructions. I am using dnsmasq version 2.78.
> 
> Thanks
> -Sandeep
> 
> On Wed, Jan 9, 2019 at 10:33 PM Simon Kelley <si...@thekelleys.org.uk
> <mailto:si...@thekelleys.org.uk>> wrote:
> 
>     On 04/01/2019 06:25, Sandeep K M wrote:
>     > Hi Simon,
>     >
>     > Thanks a lot for your prompt reply.
>     >
>     > Attached are the packet captures:
>     >
>     > 1. Packets exchanged between client and relay (client-relay.pcap)
>     > 2.  Packets exchanged between relay and server (relay-server.pcap)
>     > 3. strace of dnsmasq (dnsmasq.trace)
>     >
>     > Please let me know if any other information is required.  
>     >
>     > I am not an expert in reading pcap's or strace but I do see in the
>     > attached strace i.e. dnsmasq.trace file that ""DHCPADVERTISE"
>     message is
>     > being written to the same interface from which it received the
>     > "DHCPSOLICIT" packet. But still it is fails to go out of that
>     interface.
>     >
>     > 06:04:09.371741 write(2, "DHCPADVERTISE(m1s1p7) 2020::14
>     > 00:01:00:01:23:c1:b0:e2:00:50:56:bd:09:fb ", 73) = 73
>     >
>     > Any help on this would be greatly appreciated. Also is there any
>     example
>     > configuration of dnsmasq dhcpv6 working with relay ? Any reference
>     would
>     > be of great help.
>     >
> 
>     I'm sure this was tested with a relay, but the current test harnesses
>     here would take some work to get into a position to test this code, so
>     I'm going to try and use you as a tester, if that's OK?
> 
> 
>     Looking at the strace output, dnsmasq logs that it's sending a
>     DHCPADVERTISE reply, but it never calls sendto() to actually send the
>     packet. This is definitely a dnsmasq bug, and not something in your
>     network that's causing the packet to get lost: it never gets sent.
> 
> 
>     What's confusing me is that manually tracing the code paths from what's
>     known to be working (log the DHCPADVERTISE) to the sendto() call that
>     should send that packet, I can't see any reason why the code should
>     fail.
> 
>     Are you in a position to run dnsmasq under gdb and step through the
>     relevant code? I can give you detailed instructions on where to set
>     breakpoints and where the reply packet could be getting lost. The path
>     is maybe 50 lines.
> 
>     Staring at the code has found me one bug, but it's not relevant in this
>     case. (The code to avoid copying an RFC6939 link address option in a
>     relay request to the reply to the relay actually sends a zero-length
>     option, instead of eliding it entirely.)
> 
>     Cheers,
> 
>     Simon.
> 
> 
> 
> 

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