id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
8627	JOSM never falls back to IPv4 if IPv6 stack available	osm@…	team	"If there is a IPv6 stack available: Since r5892/josm does not fall back to a IPv4 connection on IPv6 connection failure.

On a connections with faulty IPv6 connectivity (very common) JOSM will always timeout without fallback.

Test Case on Linux:
 sudo ip6tables -I OUTPUT -d spike-01.osm.org -p tcp --dport 80 -j DROP
 sudo ip6tables -I OUTPUT -d spike-02.osm.org -p tcp --dport 80 -j DROP
 sudo ip6tables -I OUTPUT -d spike-03.osm.org -p tcp --dport 80 -j DROP
 JOSM pref prefer.ipv6=true  : JOSM fails
 JOSM pref prefer.ipv6=false : JOSM OK

To clear ip6tables:
 sudo ip6tables -D OUTPUT -d spike-01.osm.org -p tcp --dport 80 -j DROP
 ...

PS: java.net.preferIPv6Addresses=true likely better than java.net.preferIPv6Stack=true
PPS: As a sysadmin, I would really prefer that JOSM didn't override java's IP stack preference.

/ Grant aka Firefishy"	defect	closed	blocker		Core	latest	fixed	IPv6 fallback IPv4 Connectivity Timeout