On Tue, 25 Aug 2009, Nicolas Williams wrote:
> On Tue, Aug 25, 2009 at 04:50:42PM -0400, Dale Ghent wrote:
> >
> > On Aug 25, 2009, at 4:22 PM, Nicolas Williams wrote:
> >
> > >On Tue, Aug 25, 2009 at 01:34:11PM -0400, Dale Ghent wrote:
> > >>http://elektronkind.org/outbox/afs/openafs-s10u4-compat.patch
> > >
> > >What's with the use of IN_CLASS[ABC]() and IN_CLASS[ABC]_NET?
> >
> > IIRC, and it has been some years since I've had work work in this
> > code, is that it's used in part for determining if a AFS server is on
> > the local subnet and/or if a AFS server is local, on the same host.
>
> Don't you want to use the _real_ netmask? CIDR deprecated the notion of
> classes A, B and C way back in 1992! :)
Actually, CIDR didn't come out until 1994. Although RFC 1519 carries a
date of September 1993, it wasn't until early 1994 that CIDR blocks were
actually allocated, and of course, one needed BGP4 deployed to use them,
which happened in a rush during 1994.
But without looking at the code, I think that this IN_CLASS [ABC]
netmask stuff wasn't meant to be the actual netmask of the interface
(even back then we had subnetting), but a way to expand the scope to
identify "nearby" servers by trying to distinguish "nearer by" servers
from other servers by expanding the netmask and selecting the servers in
the C first, followed by the B, followed by A, followed by all others.
It was never a good way to calculate the nearness of a server, but
people did what they could. It was clever and easy. In AFS and DFS,
there is a way to (somewhat manually) select the preferred server, and a
plethora of scripts that configure systems with their preferred servers
semi-manually. Probably this code could be changed to expand the CIDR
mask a bit at a time, but one has to start with the mask of the
interface either way.
--Dean
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