connectivity problem

[Richard Draves]

I'm having trouble reaching sipper.ipv6.zk3-dec.com from
ipv6.research.microsoft.com. Sometimes pings get through, and sometimes I
get Destination Unreachable (Address Unreachable) errors from
3ffe:1001:1:f004::1.

The strange thing is there seems to be a 10-second periodicity. Five pings
will succeed, then 5 pings will fail, and so on.

The good thing is that TCP has no problems coping with this and I can access
http://sipper.ipv6.zk3-dec.com just fine.

I note that the ftp server on sipper does not seem to support the EPSV
command. Does anyone have one up that I can test against?

Thanks,
Rich