[arch-general] ipv6 only half working

[David Rosenstrauch]

On 2018-07-23 12:42 pm, Giancarlo Razzolini via arch-general wrote:
> Em julho 23, 2018 12:46 David Rosenstrauch escreveu:
>> 
>> 
>> I'm really stumped as to how ipv6 could partially fail like this only 
>> on specific apps.  Seems like it should either completely work or 
>> completely fail.
>> 
>> Anyone have any idea what might be happening here and/or how to fix?
>> 
> 
> Hi David,
> 
> If ping works, but bigger packet things don't, then you might have some 
> PMTU
> issue that is only affecting IPv6. You can confirm this with a tcpdump 
> trace
> quite easily. Look at the packet sizes. Both things you've mentioned 
> (opening a
> web page and updating antivirus) are http, and it does usually use the 
> maximum
> transmission unit.
> 
> Regards,
> Giancarlo Razzolini


I finally had some time to dig into this issue, and ran wireshark on a 
"freshclam" download, although I'm not sure it's helped me get any 
closer to figuring out what's going on.  To the best of my knowledge 
(I'm definitely not an expert in networking) it looks like I'm having 
some packets dropped - but again I have no idea why (or where)?  I put 
up a wireshark screenshot at http://darose.net/packets-dropped.png which 
shows the download humming along nicely, when all of a sudden it looks 
like the other server seems to jump way ahead in the sequence numbering, 
and my server keeps re-sending duplicate acks based on where it thinks 
the correct sequence number is.  In addition, "ifconfig" shows 17 Rx 
dropped packets on eth0.  (Possibly coincidental, possibly not.)

Any idea what I might look for / where I might look from here to figure 
out what's causing the issue?  My server is running (an up to date) Arch 
installation, and is behind a Netgear WNDR3700 router.  Any suggestions 
appreciated!

Thanks,

DR