From: kai@pyrite.SOM.CWRU.edu (Kai Getrost)
Newsgroups: comp.protocols.appletalk
Subject: Re: Extended- vs. nonextended-net net range aging
Date: 23 Nov 92 11:16:57
Organization: WSOM CSG, CWRU, Cleve. Ohio
Distribution: comp
	<1eq6fuINNar6@roche.csl.sri.com>
NNTP-Posting-Host: felucca.som.cwru.edu
In-reply-to: dstine@cisco.com's message of 23 Nov 1992 08:58:38 GMT


In article <1eq6fuINNar6@roche.csl.sri.com> dstine@cisco.com (David Stine) writes:

> Remember that on extended cables, you can have a _range_ of network numbers.
> The router could come back on the net with a different network number in its
> address.

   Yes, I understand how and why a node's idea of who its router is
should be expired, for exactly that reason.  I was curious about the
expiration of *THIS-NET*: the network number of the link the node is
on.  For nodes on extended nets THIS-NET is a range of numbers (and
A-ROUTER is a net:node pair; I was unclear about this in my original
post, sorry).  I also understand why this value should be expired;
what I wanted to know was why THIS-NET is *not* expired on
non-extended nets (according to Inside AppleTalk) when all routers go
down.

> Example: let's say that you have an extended AppleTalk Ethernet with a
> cable-range of, oh, 10-20.[footnote 1] Let's say that the router's
> current net.node address is 10.240. Now, let's say that there is a
> hiccup in the power and when the router comes back on-line, all
> non-reserved node numbers in network 10 have been taken. The router,
> while AARP'ing for an open address, must choose a node in network
> number 11. Say 11.20.

[after a router has gone down and come back up:]
> On an extended net, the nodes' current address is still valid and the
>cable configuration hasn't changed; simply the address of the router has
>changed.

   But the data link's net range remains the same.  If *all* routers
go down on that link, and then all come up with a new net range, all
nodes (nonrouters included) must not only look for the new router
node(s), but adopt a new value of THIS-NET (the new net range) and AARP
for new node addresses themselves within this range.
   On a nonextended net, Inside AppleTalk says that nodes *don't*
expire THIS-NET (the net # for their link), though they do copy it
from every RTMP Data packet they see (so nodes' idea of THIS-NET will
also change if all routers go down and come up advertising a new net
#).

   This is what I was curious about; why nonextended nets don't revert
to net 0 the way extended nets revert to net range 0-$FFFE when all
routers go down, according to Inside AppleTalk (pp. 5-19 - 5-20).

> In addition to reading Inside AppleTalk on this issue, you should also be
> reading the document from APDA called:
>
>  "AppleTalk Phase 2 Protocol Specification, C0144LL/A"

   Ok, I'll have to get it; thanks.

-Kai





--
"`Meltdown' -- it's one of those annoying     |        Kai Getrost
 buzzwords.  We prefer to call it an          |            ---
`unrequested fission surplus.'"               | kai@pyrite.som.cwru.edu
                -- Mr. Burns, _The_Simpsons_  | kai@b62624.student.cwru.edu
Organization: Doctoral student, Physics, Carnegie Mellon, Pittsburgh, PA