Subject: Re: Q's from localtalk efforts
To: Bill Studenmund <>
From: Erik E. Fair <>
List: tech-net
Date: 02/20/1997 01:11:39
The RFC on AppleTalk Control Protocol (ATCP) for PPP is incomplete. It lays
out basic packet formats, but does not discuss related issues that must be
dealt with for a successful implementation.

Specifically, the AppleTalk Routing Table Maintenance Protocol (RTMP) is
essentially 10-second RIP with no default (i.e. a list of *all* AppleTalk
networks is blared on all networks every 10 seconds). For any sizeable
network, this would be the death knell of any low-speed link - you'd lose
it all to RTMP traffic. Thus, peers in such a low-speed link session must
do a BGP-style (or AURP-style) "exchange all routing information once, and
then exchange diffs" mechanism.

The same kind of thing goes for the Zone Information Protocol (ZIP). In
order for the Chooser to display the list of zones in bounded real time,
the zone list should be exchanged at connection time, with diffs, so that
the zone list does not come over the wire on demand; the ZIP queries must
be spoofed.

Then there is another interesting issue: are you connecting a single host
to a remote AppleTalk network (i.e. AppleTalk Remote Access), or are you
connecting two AppleTalk networks together (i.e. routing ala AURP)? The
latter case must reconcile both AppleTalk network number conflicts (either
by filtering, remapping, or simply not allowing connection until there are
no conflicts), and AppleTalk zone name conflicts (same list of alternatives

To top it all off, Apple itself is in the process of doing an AppleTalk
over PPP implementation - one that can be reasonably expected to set the
standards in this area. However, they have (to my knowledge) not released
any code or docs yet. So, any implementation that the NetBSD community does
will likely have to be changed for compatability (unless we guess right)
when Apple releases its software.

Tread carefully.