[josm-dev] IPv6 problems

[Dirk Stöcker]

On Wed, 30 Dec 2015, Greg Troxel wrote:

> I have been running JOSM for a long time, on a Mac, currently at OSX
> 10.7.  I have functional IPv6, but my tunnel is from OCCAID, and
> occasionally some places are unreachable - currently
> api.openstreetmap.org is one of them.
>
> josm starts up and proclaims:
>
>  INFO: Detected useable IPv6 network, prefering IPv6 over IPv4.

If you have a version older than 8706 you should update. If you have a 
newer one read the description below.

> which is fine, but then when downloading data (simple pushing of
> download icon, letting area be, and then pushing the download button in
> the popup) normally, I get an API error.  I can ping
> api.openstreetmap.org on v4, but not v6, where I get a network
> unreachable in New York.  If I had a 2-minute delay and then a download,
> there would be a more subtle happy eyeballs issue, but I totally failed
> to download data a few hours ago.
>
> Just now, I was able to download data.
>
> So it seems that there is some notion of only trying one address family,
> vs. trying all addresses in all familes in some sort order, and only
> failing if all fail.
>
> OSX itself has some version of Happy Eyeballs which uses RTT on v4 and
> v6 to the address (prefix?) to decide which to try first, I think via
> sorting getaddrinfo results.  I am totally unclear on how this interacts
> with Java.

JOSM and Java do not try different protocols. If you (and the remote 
server) have IPv6 it uses IPv6, if not IPv4.

It seems you have a broken IPv6 connection which sometimes works and 
sometimes not. You should fix it.

Trying multiple connections can hide such broken connections, but most 
applications don't do this. Web browsers are the main exception. JOSM not.

> This can likely be reproduced by configuring nonworking IPv6.

No. JOSM verifies if IPv6 works by testing one IPv6 connection (to JOSM 
server). Thus it can detect whether IPv6 works or not.

But it cannot detect a partially broken connection and I also don't plan 
to do something about this. This must be fixed on user side.

To get JOSM working with your setup set expert option "prefer.ipv6" to 
"false". That simply disables IPv6.

Ciao
-- 
http://www.dstoecker.eu/ (PGP key available)