krb5 UDP daemons and IP pktinfo
Kenneth G Raeburn
raeburn at mit.edu
Tue Jan 12 01:58:41 EST 2016
> In 2010 I asked for help doing a platform survey, and found that while
> Linux and Solaris 11 implement an IPv4 variant of pktinfo (IP_PKTINFO),
> other platforms do not (NetBSD added it in 2013). Until yesterday, my
> operating assumption was that we were stuck with the complex code for
> the forseeable future. Yesterday, I discovered that some operating
> systems implement the same functionality in a different way
> (IP_RECVDSTADDR). If we handle both variants, then we can safely bind
> to the IPv4 wildcard address on Linux, Solaris, all of the BSDs, and OS
Have you checked that it actually works? It’s been a long time, but I remember running across IP_RECVDSTADDR, and I seem to recall that some options in this space didn’t seem to work as documented (or at all?) on some platforms, but I can’t recall for sure if IP_RECVDSTADDR was what was broken, and of course it could’ve been fixed since for the platforms you care about.
> So, I think it might be reasonable to simplify the net-server.c code at
> the expense of some degradation on the rare platforms which don't
> implement either variant of IPv4 pktinfo. My favored form of
> degradation is that we always bind to the wildcard address, and if the
> platform doesn't have IPv4 pktinfo support, we just let sendto() pick
> the source address of the reply. For those platforms, our UDP daemons
> will continue to work on single-homed machines, but might not behave
> properly on multi-homed machine depending on the routing configuration.
> Do other people agree that this is reasonable?
If RECVDSTADDR works and covers the important platforms that PKTINFO doesn’t, it sounds like quite a nice simplification. That bit with the routing socket is pretty annoying.
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