Well, this is not a promising start, to have my question title marked as 'frequently downvoted' but I can't make it more clear. So I try it anyway. Here's the problem:
ipkg update
Downloading http://ipkg.nslu2-linux.org/optware-ng/bootstrap/Packages.gz.
Segmentation fault
Some info about the architecture:
uname -a
Linux syno 3.10.105 [...] x86_64 GNU/Linux synology_braswell_216+II
First I tried the easy way with the package 'Easy Bootstrap Installer' but the command 'ipkg update' resulted in the segmentation fault error, even directly after resetting the nas to factory settings.
Then, as root and after removing all traces of previous ipkg installations (I think), I tried "wget http://ipkg.nslu2-linux.org/optware-ng/bootstrap/buildroot-i686-bootstrap.sh" and executed it. The script runs well, and then reports the same error 'segmentation fault' in line 18 that does '/opt/bin/ipkg update'.
I did not find an answer, though I searched with diligence. And that baffles me. Am I the only one with this problem? I do hope I'm not annoying this friendly community, but I've run out of options. So if anyone can help...
I've solved my problem in an unexpected way. I found entware on github for synology. I removed the /opt directory, and executed generic.sh for the x86_64 architecture. It ran without errors and the segmentation fault is gone. Now I have an up to date repository with more packages! Thank you, entware team.