[HECnet] Intermittent Connection with PyDECnet?

[Keith Halewood]

I chose the code change I made simply because I don’t use pcap. I also don’t like layers for layers sake.

From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of David Moylan
Sent: 10 March 2020 21:19
To: hecnet at Update.UU.SE
Subject: RE: [HECnet] Intermittent Connection with PyDECnet?

I’m all for backwards compatibility, however the /dev/net/tun interface has been in linux since the 2.6 days. A quick google shows that people back in 2010 have been using it, and browsing on kernel.org for the oldest archived kernel entry of 2.6.11 shows code examples for /dev/net/tun dated 2005.

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/networking/tuntap.txt?h=linux-2.6.11.y

I think the starting date for support of /dev/net/tun is earlier than that of the discontinuation of support for /dev/tapx.

Given that the whole goal of pyDECnet is to permit usage of decnet on more modern environments, I think having code that supports back to 2005 is a pretty solid move.

Cheers, Wiz!!

From: owner-hecnet at Update.UU.SE<mailto:owner-hecnet at Update.UU.SE> [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Thomas DeBellis
Sent: Wednesday, 11 March 2020 2:08 AM
To: hecnet at Update.UU.SE<mailto:hecnet at Update.UU.SE>
Subject: Re: [HECnet] Intermittent Connection with PyDECnet?


Since you may be running both on newer and older kernels, does it make sense to test for which tunnel type interface exists and simply use that?

You don't even need to test versions, but rather try /dev/net/tun and if it works, use that or if it fails, use /dev/tapx.

I'm a big fan of dynamic configuration, also known in the trade as 'auto magic' or 'automatic nice things'.

________________________________

On 3/10/20 9:40 AM, Paul Koning wrote:



Thanks, sorry for leaving that dangling.  I'll test that and merge it into my code.



 paul



________________________________

On Mar 10, 2020, at 4:28 AM, Keith Halewood <Keith.Halewood at pitbulluk.org><mailto:Keith.Halewood at pitbulluk.org> wrote:



Hi,



These are the changes:



In  Ethernet.py:



   class _TapEth (_Ethernet):

       def open (self):

           fd = os.open('/dev/net/tun', os.O_RDWR | os.O_NONBLOCK)

           ifr = struct.pack('16sH', self.dev.encode('utf-8'), IFF_TAP | IFF_NO_PI)

           ioctl(fd, TUNSETIFF, ifr)

           self.tap = fd

           self.sellist = ( fd, )

           # Turn the interface on -- needed only on Mac OS



With the definitions of those constants up near the top:



TUNSETIFF = 0x400454ca

TUNSETOWNER = TUNSETIFF + 2

IFF_TUN = 0x0001

IFF_TAP = 0x0002

IFF_NO_PI = 0x1000









Keith



________________________________



From: owner-hecnet at Update.UU.SE<mailto:owner-hecnet at Update.UU.SE> [mailto:owner-hecnet at Update.UU.SE] On Behalf Of David Moylan

Sent: 10 March 2020 07:46

To: hecnet at Update.UU.SE<mailto:hecnet at Update.UU.SE>

Subject: RE: [HECnet] Intermittent Connection with PyDECnet?



Robert Armstrong said on Tuesday, 10 March 2020 4:17 AM



 FWIW, the "tap:" option in pyDECnet never worked for me.  I use pcap

to

access tap devices -



    circuit TAP-0 Ethernet pcap:tap0 --single-address --cost=2



works for me with Ubuntu 18.04...



When I first went to play with pyDECnet under Ubuntu 18, I also discovered issues with the tap adapter. Fundamentally the issue comes down to newer kernels (such as in Ubuntu 18) that use a /dev/net/tun interface to communicate instead of /dev/tapx



I heard on the list that Keith Halewood had modified Paul's code to work with the newer interface standard, so I reached out to him and he provided me with the changes. It's only a few lines of code that need modification.



I believe Keith has provided Paul with the changes. I'd love to see them become mainstream in pyDECnet, as at the moment if I pull down a new build, I have to make the modifications by hand again.



With the code changes, tap works a dream for me.



circuit tap-1022 Ethernet tap:tap1022 --random-address



cheers, Wiz!!




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