I was doing some timing tests, transferring random data between different hosts on the same gigabit LAN, using different protocols (TCP vs SCTP) and address families (IPv4 vs IPv6). The IPv6 tests included both a "private IP" space address in fcc0::/64 and link-local space address in fe80::/64.

I did see variations in performance, which is what I wanted to discover. But I also encountered the case where tests were consistently failing if IPv6 link-local was used. The transfers were 1GB per measured test (repeated many times), in all combinations. Only the SCTP + IPv6 + link-local combination had problems in all its runs. After somewhere between 195MB and 480MB transferred, the association would shut down. The message from "socat" on the sending end was "2012/03/04 20:56:58 socat[3031] E write(4, 0x80ceec8, 8192): Connection reset by peer". The receiving end produced no error message. "socat" was used on both ends for all tests.

Any idea what to look at next? Any other tests to try? I'm going to be setting up some tcpdump observations to see what more I can gather about the failures.