Bob, thanks a lot for your help.

Is a -0 SSID valid for a hardware address?

That's what was given in an example I followed, but I changed VA2JF-0
to VA2JF-2 just to be sure. It's also easier to match each host to it's
IP address: VA2JF-1 has 172.25.25.1 and VA2JF-2 has 172.25.25.2.

Is gfk@ali a root user? I had lots of trouble running TCP/IP AX25 apps
as a non priv user on my old SuSE system. Something about denying port
access. Didn't actually try "call" in user mode though.

gfk@ali is not a root user, but I'm using sudo, so it shouldn't be a
problem. This is a good advice, however. I'll use root whenever I
playing with this.

There has to be an ARP system somewhere.

Indeed I think that the problem might be related to ARP. I used to
think that ARP was just used on Ethernet, but I learn something new
every day.

Here's what I got on ali:
ali:~# arp -an
[...]
? (172.25.25.2) at incomplete on eth0
ali:~# arp -H ax25 -i ax0 -s 172.25.25.2 VA2JF-2
ali:~# arp -an
[...]
? (172.25.25.2) at VA2JF-2 [ax25] PERM on ax0

Unfortunately, the slug is running busybox which is a very slimed down
Unix. It looks like busybox's ifconfig is not compatible with ax25,
hence the "Link encap:UNSPEC". I would like to try to compile a "real"
ifconfig but unfortunately the slug is running with 288KB of free disk
space. I'll need to transfer the system to a bigger flash drive when I
get some free time.

Also busybox doesn't have /usr/sbin/arp on the system, and
/proc/net/arp doesn't list any ax25 address...

OBTW I remember too that tcpdump doesnt work on an ax25 interface. You
might try that to see if you get any valid data. This will show the
arp conversation as well as IP

You're right:
ali:~# tcpdump -eni ax0
tcpdump: unknown data link type 3

I found a patch for tcpdump to work with ax25, but didn't tried it yet.
http://he.fi/archive/linux-hams/200509/0060.html

PPP may be much more desirable because you can get huge compression
gains (ie using BSD or deflate compression) I use to use it over an
old 28K8 modem connection and got data rates in the order of 20-30x
when moving logfiles around. As its compressed before it gets to the
modem you aren't limited by the 115K2 DTE rate either..

PPP requires full duplex and any radio link is inherently half-duplex.
I had to use "full duplex simulation" in the radio firmware which is
documented like this in the manual:
=====
Full Duplex: This mode restricts Client radios to transmitting on odd
numbered frequency hop bins and the Server to even numbered frequency
hop bins. Though the RF hardware is still technically half duplex, it
makes the transceiver seem full duplex. This can cause overall
throughputs to be cut in half. Note: All transceivers on the same
network must have the same setting for Full Duplex.
=== Ref: http://www.aerocomm.com/Docs/User_Manual_CL4490.pdf (p.16)

Also, the RF baud rate is fixed at 76.8 Kbps, so in "full duplex
simulation" it is effectively 33.6 Kbps. Even with compression, I
speculated that half duplex AX.25 would perform better for activities
such as web browsing where most of the heavy content (jpg images) is
already compressed.

I'll keep playing with this, thanks a lot for your help,
GFK's
--
Guillaume Filion, ing. jr
Logidac Tech., Beaumont, Québec, Canada - http://logidac.com/
PGP Key and mo http://guillaume.filion.org/