ax25 filter

[Pete Carah <ames!elroy.Jpl.Nasa.Gov!grian!puffin!pete>]

> I have been getting garbage calls in my NOS ax heard lists, at my
> switch, since changing from NRS to KISS interface on two of my ports.
I get them in unix too.

> I looked at the code and I believe that it does not really filter but
> rather allows listing of source/destination data based on a switch.
> It this correct?
AX25 doesn't filter at all, so far as I can see.

> What I did not understand is why no bad data ever appears in the Netrom
> node listings. In looking at the code it appears that there is some
> small amount of checking - like if the alias is ASCII and within a
> certain length but I did not see more than that.
Maybe there is a packet checksum in NRS; there isn't in SLIP/KISS.

> Since I do not see any RX HW data overruns on this system then can I
> assume that the TNC is decoding garbage and sending it to NOS. Why
> would'nt NOS reject based on a packet checksum?
KISS has no packet checksum.  That is a rather fundamental problem.

> The real netrom code uses an algorithum to look at the call and determine
> if it is valid. Although not 100% efficient it does work. Could this be
> applied to NOS.
Causes some interesting problems if you have an alias that looks like a
callsign based on that algorithm (like you can't connect to that node using
the alias).  Packet checksums would be a better fix (and handle, e.g.
commercial users).

-- Pete (pete@puffin.uucp; elroy.jpl.nasa.gov!grian!puffin!pete)
   K6JRR