[HECnet] DECnet for Linux

[Erik Olofsen]

Some more notes on this:

The problem of accessing a Linux machine seems to be related to
the standard mtu of 1500 of a network interface.

Reducing the maximum packet size to 576 helps;

https://sourceforge.net/p/linux-decnet/mailman/message/2395733/

This can be done using ifconfig or using 576 instead of dst_mtu()
in dn_current_mss() af_decnet.c of the kernel module source.

tcpdump shows that a large data packet is one byte too long.
Perhaps this occurs because the pad byte in the header is not counted
in dn_mss_from_pmtu() in af_decnet.c; with an additional mtu--
this seems to be fixed.

Kernel warnings related to dst.h;

https://www.spinics.net/lists/netdev/msg225996.html

indeed disappear by using dst_metric_raw at two places.

The above was tested with kernel 3.10.17, and can be tested
with http://mim.update.uu.se/hecnet and nodename RULLFL.

dntype mim::nodenames.dat works very well on a real machine; why
it doesn't work very well with the virtual machine is not really
solved yet...


On Wed, Jan 03, 2018 at 04:44:54PM +0100, Johnny Billquist wrote:
> On 2018-01-03 16:02, Erik Olofsen wrote:
> >On a virtual machine with lubuntu 12.04, kernel 3.2.0, I have
> >DECnet for Linux V.2.5.68s working, with dnprogs version 2.65.
> >It is node RULLFL.
> >
> >The daemons and utilities use decnet.conf with node information,
> >so something useful would be to create it from mim::nodenames.dat.
> >
> >On a VAX, TYPEing it works well, but on the Linux machine, dntype
> >hangs after giving parts of the file; dndir mim:: works well.
> >
> >Does anyone have dntype mim::nodenames.dat working properly (with
> >perhaps different versions of the above)?
> 
> I can't help, but I can report that trying to read a file from a Linux
> machine on MIM also hangs after a while.
> A big problem with the DECnet/Linux implementation is that the developers
> only ever tested against VMS, and nothing else.
> 
> I've known for ages that it does not play well with RSX. But I do not want
> to dig into the Linux implementation.
> 
> (The Linux DAP claims to be a VMS system, by the way, which is probably also
> not a good idea. Better if it had claimed to be some Unix derivative.)
> 
>   Johnny
> 
> -- 
> Johnny Billquist                  || "I'm on a bus
>                                   ||  on a psychedelic trip
> email: bqt at softjar.se             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol