Date:	Wed, 18 Nov 2009 13:14:32 +1100
From:	andrew hendry <andrew.hendry@...il.com>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Documentation, clarify tuntap IPX example.

Hi Max,

I started looking through the documentation because im looking to use
tun for X.25 over TCP. The IPX example sounded similar but i couldn't
get it to work as I was expecting. Looking for a hint in the right
direction.
There is an old non-mainline patch called x25tap (clone of obsolete
ethertap). I'm hoping to replace x25tap with tun.

The old x25tap creates a device like:
x25tap0   Link encap:generic X.25  HWaddr
          UP BROADCAST RUNNING NOARP MULTICAST  MTU:1024  Metric:1
          RX packets:3040785 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2895530 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:10
          RX bytes:138787339 (132.3 Mb)  TX bytes:91395983 (87.1 Mb)
When the x25tap is loaded it has dev->type = ARPHRD_X25, after which
x.25 routing and AF_X25 sockets can be created.  Along with an XoT
userspace program which handles some basic headers and TCP port 1998
it works well.

If using tun, how does something get registered to handle protocol AF_X25?

Regards,
Andrew.

On Wed, Nov 18, 2009 at 12:40 PM, Max Krasnyansky <maxk@...lcomm.com> wrote:
> On 11/17/2009 05:30 PM, andrew hendry wrote:
>>
>> Can the TUNSETIFF ioctl change a tap's protocol to IPX as the
>> documentation suggests?
>> I think tun.c would need IFF_IPX_TAP added for it to work as described?
>> Otherwise tap can only be ptp or ethernet, and there is no way to
>> route or use AF_IPX.
>
> TAP is an Ethernet device. No special handling is required for IPX or for
> that matter any other protocol. Example seems fine too.
>
> Max
>
>> Signed-off-by: Andrew Hendry<andrew.hendry@...il.com>
>>
>> --- a/Documentation/networking/tuntap.txt       2009-11-11
>> 14:03:22.676167648 +1100
>> +++ b/Documentation/networking/tuntap.txt       2009-11-18
>> 11:34:18.106647029 +1100
>> @@ -127,12 +127,14 @@ Ethernet device, which instead of receiv
>>  media, receives them from user space program and instead of sending
>>  packets via physical media sends them to the user space program.
>>
>> -Let's say that you configured IPX on the tap0, then whenever
>> -the kernel sends an IPX packet to tap0, it is passed to the application
>> -(VTun for example). The application encrypts, compresses and sends it to
>> -the other side over TCP or UDP. The application on the other side
>> decompresses
>> -and decrypts the data received and writes the packet to the TAP device,
>> -the kernel handles the packet like it came from real physical device.
>> +Let's say for the purpose of example, IPX support was added to tuntap.
>> +Then whenever the kernel routes an IPX packet to tap0, it is passed to
>> the
>> +application reading the file descriptor from /dev/net/tun (VTun for
>> example).
>> +The application encrypts, compresses and sends it to the other side over
>> TCP
>> +or UDP. The application on the other side decompresses and decrypts the
>> data
>> +received and writes the packet to the TAP device, the remote kernel
>> handles
>> +the packet like it came from real physical device. The IPX applications
>> are
>> +able to communicate as if there was a real IPX network.
>>
>>  4. What is the difference between TUN driver and TAP driver?
>>  TUN works with IP frames. TAP works with Ethernet frames.
>
>
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