[HECnet] Intermittent Connection with PyDECnet?

[David Moylan]

And I agree with that logic as well. I did the same for the same reasons.

 

 

From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Keith Halewood
Sent: Wednesday, 11 March 2020 8:46 AM
To: hecnet at Update.UU.SE
Subject: RE: [HECnet] Intermittent Connection with PyDECnet?

 

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] On Behalf Of Thomas DeBellis
Sent: Wednesday, 11 March 2020 2:08 AM
To: 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] On Behalf Of David Moylan
		Sent: 10 March 2020 07:46
		To: 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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