[Linux-ham] wrong packet size

[folkert]

> As far as I know, AX.25 MTU is only take care of on transmitting.
> There are no trunked buffer sizes on the rx-routines in the kernel.
> => larger packets, even beyond the ax25 protocol spec (>256 bytes)
> could be handled.
> 
> On transmission, the MTU is respected.
> But if you read my last posts on this list, that's not always true (IP):
> I proposed a fix for packets leaving the interface that are much
> larger than the configured MTU or / and the max-mtu of 256.
> For normal PID=text packets, data sent with write() is adjusted to the
> MTU, and data tried to send with syscall sendto() and a size > MTU are
> rejected.

check
In which kernel is this implemented?

> Btw, in your line:
> > 23    11.084320000    FH4GOU-01       TRDS01-01       AX.25-NoL3 271 Text
>
> => 271 is beyond the standard. You'll might find many old software, 
> TNCs, etc. that would even not be capable to decode such a packet.

Yes, that's how I found it out :-)

> On the other hand I wonder what packet that was.
> "NoL3" => I assume PID=text (not IP, ARP, etc.).

It was a conversation between "axcall" and "ax25-node" (or "node"). In
that packet was the result of "M ax0" (or "mheard ax0"). 

> Sender is FH4GOU-1 (but that's not a call of one of the two sides in
> your test setup). How does that callsign comes to the line and what
> computer / os / pr-program / userspacesprogram sends this data?

It should be correct, I checked it moments ago.

Ok setup:

- laptop with a tnc and a radio running linux kernel 4.2.1-2 from debian
- raspberry pi with a tnc and a radio running kernel 4.1.18+ (raspbian)

Both are connected to the TNCs via USB to serial converters. Both TNCs
run the same software.

The TNCs are arduinos and the radios are LoRa modules connected to them.
https://www.vanheusden.com/radio/arduino-tnc.php


Folkert van Heusden