Re: SUN and Subnets

Steve D. Miller (
Mon, 11 Aug 86 09:49:57 EDT

   I've heard a lot of things from a lot of people, and have some things
to say on my own. Let's see if I can't make a stab at answering some
of the questions here...

   In the first article in this discussion, Milo Medin (In the first article in this discussion, Milo Medin (medin@ames) says:

        When I asked my SUN rep. about subnetting, he said that SUN OS 4.0
        might have it, and that would be released in the Jan./Feb. '87
        timeframe, but would make no committments. Other people I know who
        have asked got no commitment from SUN at all. Further, my SUN rep.
        mentioned that subnetting requires some non-trivial changes in NFS.
        I can't understand why this would be the case.

   OK. From what I have heard, Sun is trying to move to a 4.3BSD networking
base with the 4.0 release. I have talked to (a) some people at a Sun/LMI
NFS conference held in Boston in April and (b) one of the people supposedly
working on it, and unless I have grossly misunderstood something I believe
that this is indeed the case. The timeframe for the release sounds right
to me; the 3.0 release is slated for October. Again, no commitments...but
I did it myself and didn't think it was too hard. I didn't even have a real
understanding of the networking code at the time I did it and I'm sure that
the Sun people do, so they should have even less of a problem.

   Sun said at the NFS workshop that they were trying to get rid of ND,
and that NFS was going to undergo a protocol rollover with the 4.0 release.
I'm sure that NFS will need a lot of work to allow things like swapping,
but I *know* that NFS version 2 (the one running in 2.0 and 3.0) works
with little or no changes on top of a subnet-based kernel. I *ran* it
on top of one (see below). If there's a problem, I'd love to hear what
it is so I can fix it...but I think the rep is wrong on this one. The
only thing that comes to mind at all is that the kudp_fastsend() routine
used to get kernel RPC/UDP packets onto the wire as fast as possible
takes a number of liberties (like no checksums) with the UDP/IP output
routines and might well need a rewrite for subnets. Commenting it out
works just as well, though...and I confess that's what I did.

   In another article on the subject, Mike Karels (

        I have been tempted to figure out how to package and distribute
        subnet support for Suns, but haven't taken the time to do so.
        Perhaps I could convince someone else working with Suns at Berkeley
        to package things up if a few sites could test it.

   You've got yourself a volunteer. I don't know how useful I'd be, but I
can try to make sure that the stuff works for gatewaying. There's a room
here that could stand to be its own network; now if I can just convince my

   In yet another article, Chris Torek ( says:

        Steve Miller dropped the 4.3 TCP into our 3.0 kernels. Aside from
        one locally-introduced bug, it has been working well for some time.
        (The local bug was fixed a few days ago.) Once the file servers are
        stable---we have been suffering with disk problems (another local
        hack, this time in hardware)---we might consider distributing the
        code; but we will likely have to require both 4.3 and 3.0 source
        licenses (alas!).

   Well, I haven't really done all that yet. I had all of the 4.3BSD (beta!)
networking code, including XNS and a protocol-independent version of NFS, in
a local kernel based on Sun 2.0. It ran subnets to the same extent as the
4.3BSD beta release, and NFS didn't hiccup at all. As I said though, I did
comment out the one (relatively small) piece of code that did the fastsend
stuff. I will probably start work on the 3.0-based version in the next
week or two, and we will probably let it out (with licensing restrictions
like I stated above) once it seems stable. I don't know if "distribute"
is the right word...


Spoken: Steve Miller ARPA: Phone: +1-301-454-1516
CSNet: CSNet: steve@umcp-cs UUCP: {seismo,allegra}!umcp-cs!steve
USPS: Computer Science Dept., University of Maryland, College Park, MD 20742

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