You are right to assume a fragmentation problem, but it is not a simple one. One of
the first things I checked was the fragmentation bit. The weird thing is that it is
set correctly in the first frame. But the following fragments never get sent. I ran
the client and server scripts on the same vms machine, so I can eliminate a switch or
router as the problem's source.
And as I have said before: A simple C program sends fragmented UDP packets without
problems on the same machine.
So I still tend to think that there is something wrong with the combination
DECC/UCX/PERL.
Thomas
> -----Ursprungliche Nachricht-----
> Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Gesendet: Montag, 23. April 2001 22:20
> An: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Betreff: Re: AW: Problem sending UDP packets
>
>
>
> I thought I sent a reply, but looking about, I can't find it now.
> So, I'd try again, and cc the perl list, just for general interest.
>
> this problem appears to be a dead ringer for a
> don't-fragment versus a router MTU poblem.
>
> a quick web trawl turns up the following reference,
>
>
> http://www.uic.rnd.runnet.ru/doc/inet/tcp_stevens/udp_user.htm#11_1
>
> in particular:
>
> http://www.uic.rnd.runnet.ru/doc/inet/tcp_stevens/udp_user.htm#11_5
>
> I saw a similar problem long ago, and it was devilish to figure out.
>
> it was ultimately due to a change in network configuration,
> that I did not find out about, until much later.
>
> basically, a router downstream may be tossing your udp datagrams
> if longer than that router's MTU, and the don't-fragment
> flag is set.
>
>
> > Hi,
> > sorry for the delay, but I have been a bit busy.
> > I sent the test scripts to '[EMAIL PROTECTED]' (no real name
> provided), who =
> > asked for them in order to reproduce the problems.
> > To cut it short: on his/her platform everything runs fine.
> > There are some differences in the VMS/UCX versions, but
> the perl version =
> > is the same (5.6.1). At the moment I don't have a clue
> what's going =
> > wrong.
> > I am going to read about this "socket madness" :-)
> >
> > By the way: I am using the Socket module with send/recv calls.
> >
> > I'll send my two little test scripts as attachment.
> Perhaps somebody =
> > else can reproduce the errors.
> >
> > >=20
> > > Thomas,
> > >=20
> > > Your analysis and the subsequent silence indicate that
> you probably
> > > know more about this issue than anyone else does. What
> Perl module
> > > are you using to send the packets? IO::Socket? If you
> are using
> > > stdio on sockets, I'm afraid that's something that just
> doesn't work
> > > on VMS. I think you have to use sysread() and
> syswrite(). Look in
> > > the archive for a thread called "socket madness" or similar from
> > > earlier this year. Let us know if you track the problem down.
> > > --=20
> > > ____________________________________________
> > > Craig A. Berry =20
> > > mailto:[EMAIL PROTECTED]
> > >=20
> > > "Literary critics usually know what they're
> > > talking about. Even if they're wrong."
> > > -- Perl creator Larry Wall
>
>
