Sorry Florian, I accidentally sent this directly to just you and not to the ML. ---- Thanks for the quick response. > Compare straces of both ping runs? The slow `ping6 -c1 icadpytes.eleuther.net` strace dump: http://go-beyond.org/sega01/misc/slowping6.txt The working `ping6 -c1 icadpytes.go-beyond.org` strace dump: http://go-beyond.org/sega01/misc/workingping6.txt Things start to differ around line 150. I thought that this was an interesting line: connect(5, {sa_family=AF_INET6, sin6_port=htons(53), inet_pton(AF_INET6, "::ffff:0.0.0.0", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0 There are 4 instances of "::ffff:0.0.0.0" in the icadyptes.eleuther.net dump and none from one that works fine. I am suprised that it works when using Zoneedit's servers directly but not when through Unbound. > It looks like the problem is with the reverse lookup for > 2001:470:3:e::1123:5813, which is broken. Apparently, Unbound tries > harder to get a resolution, which takes more time and slows ping6 down. After investigating what you said a bit more, it is definitely the reverse lookup. OpenDNS resolves the ip6.arpa record fine while Unbound either takes 5 seconds or fails. Unbound works fine when there is a PTR record in place however. Should I file a bug report? Thanks, Teran (sega01)