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From: tom@wcc.oz.au (Tom Evans)
Newsgroups: comp.dcom.sys.cisco,comp.protocols.appletalk
Subject: Re: Appletalk phase 2, disappearing zones & cisco routers
Message-ID: <1796@wcc.oz.au>
Date: 6 Jun 91 06:00:04 GMT
Article-I.D.: wcc.1796
References: <ianh.675588243@morgana> <ianh.675988855@morgana>
Followup-To: comp.protocols.appletalk
Organization: Webster Computer Corp, Melbourne, Australia
Lines: 62

In article <ianh.675988855@morgana>, ianh@resmel.bhp.com.au (Ian Hoyle) writes:
> ianh@resmel.bhp.com.au (Ian Hoyle) writes:
> 
> >We are having a considerable problem here with zone information dropping out
> >of the chooser at random intervals.
> 
> [ a brief explanation ]
> 
> It was a combination of several things, one *big* blooper was our fault the 
> other ... well we could have avoided it.
> 
> Since the Cisco configuration ... we discovered much to our chagrin 
> that our Appletalk Zone  name had been misspelt. This effectively turns off 
> routing in the box and helped to explain the zone on the other side of the 
> cisco from not appearing.
> 
> However, this did not stop the zone dropouts.
> 
> After some judicious use of a packet sniffer looking at the RTMP/AARP packets
> as they hit our routers and watching what they responded with the only
> conclusion we could come to was:
> 
> "Get rid on non-seeding routers and hard wire zone names/address ranges on
> ALL routers"

That is _A_ "solution" but doesn't describe the real cause of the
problem, which was:

1. The CISCO had a mis-spelt zone name configured into it.

2. The CISCO recognised this condition and supposedly disabled its
   EtherTalk Phase 2 interface as a result. At least it said it did.

3. Disabled or not, the CISCO was still sending AppleTalk RTMP
   (Routing Table Maintenance Packets) out the "disabled" interface.

4. Other routers on the network, receiving these RTMP packets and
   learning of "new" network numbers were trying (continuously -
   every 10 seconds or so) to find out the zone names by sending ZIP
   packets to the CISCO.

5. The CISCO had disabled the AARP protocol on EtherTalk, so it
   refused to respond to any AARP requests to resolve its address.
   All the other routers were stable, but "unsatisfied".

6. Every time a Mac on EtherTalk received an RTMP packet from the
   CISCO it would switch its "A-Router" pointer to point to the
   Cisco. It would then try to send "off-net" packets there, but
   then couldn't get the AARP requests resolved, and so the packets
   got dropped.
   
7. With 6 (or so) routers on Ethernet, this means that every time
   you open the Chooser there is a 15% chance of "A-Router" pointing
   to the CISCO, which would then refuse to answer the Chooser's
   request for a Zone List. So no zones visible in Mac Choosers
   (sometimes).
   
Talk about "calling attention to a configuration problem" :-) :-).
========================
Tom Evans  tom@wcc.oz.au ** ADD ".au" MANUALLY (don't trust "reply") **
Webster Computer Corp P/L, 1270 Ferntree Gully Rd Scoresby, Melbourne 3179
Victoria, Australia 61-3-764-1100  FAX ...764-1179  A.C.N. 004 818 455