From: jra@law7.DaytonOH.NCR.COM (John Ackermann)
Subject: Re: TCP/IP Routing Help 
Organization: NCR Corporation -- Law Department
Date: Fri, 20 Nov 1992 14:55:36 GMT

Steve_Wright@kcbbs.gen.nz (Steve Wright) writes:

>>  
>>It's great to use rough geographical bounds to define address groupings,  
>>but remember that radio waves don't obey borders.  By definition, a  
>>network consists of stations that can reach each other (and therefore in  
>>most places 44.xx <ain't> a network!).  Subnets should be assigned based  
>>on connectivity, not geography.  
>  
>Yes, but you assign IP addresses according to what RF domain (repeater) they  
>belong to, not which geographical area.  A (bit-regen 9k6) repeater  may  
>provide coverage to nodes that overlap geographical boundaries, but to  
>allocate different subnet addresses to nodes sharing one repeater seems silly.
>And what if a user has ports on two repeaters/subnets?  

I <thought> that's what I was saying -- assuming a repeater, all the
stations using it would be on the same subnet.  As mentioned later in my
posting, geography enters into the address assignment only to the extent
that the location of the <switch or server> determines the actual subnet
number.  All users of that switch or server are in that subnet.

>>Subnets would be normally be assigned around switches or servers, and  
>>the subnet address would be based on the geographical location OF THE  
>>SWITCH/SERVER ONLY.  All users "homing" to that switch or server would  
>>have an address in that subnet, regardless of their geographical  
>>location.  
>  
>This all assumes that your users are not using RSPF or any other routing  
>protocol and have only ONE port on their system. If a user has more than one  
>port, the routing then gets impossibly complex if you are going to start  
>typing 'route add ' anything...  

We treat different frequencies as different subnets, so if (as in my
area) you have a 2M freq and a UHF one, each is a distinct subnet and
multi-port users have a different address on each port.  It works quite
well, though it means that such users also have multiple hostnames.


>aren't all all NOS nodes switches and servers ??  

Not unless the owner offers services to the user community.  I'm 
talking primarily about switches that offer 24 hour routing to other
areas, but also about dedicated systems such as full-time routers, mail 
servers, ftp sites, etc.  In a connected network, the subnets would 
be built around switches (and other servers would be part of the subnet
defined by the switch); in an unconnected one, using servers simply 
provides a convenient geographical "center" for determining what subnet 
number is assigned according to the geographical plan.

> How do you fix the 'hidden transmitter' problem  ?   Users 'homing' to a  
>central switch sounds like (the bygone) days of digipeaters and CSMA on a  
>simplex channel.. ;-)  but seriously ;-) how  is the hidden transmitter  
>problem being solved  ?  I like the idea of two (one) 9K6 modem back to  
>digital back replacing the audio stages of a UHF repeater (standard  
>bandpass notch-reject type) triggered by a STATE-DCD in the modem.  

I'm assuming that we take our networks as we find them.  Hidden
transmitters are a problem no matter what address assignment scheme you
use.  But FWIW, here in Dayton we <are> using a full-duplex repeater on
our 19.2kB UHF network to avoid this problem.  It works very well.

I was not implying that local traffic on the subnet would be routed
through the switch (which would be less efficient than a digipeater), 
but rather that the switch would offer a natural central point around 
which the subnet would revolve.  Users who can reach each other directly 
would certainly do so.  Ideally, the subnet would be small enough, or
would use a repeater, to ensure that everyone could hear everyone else.

That's the whole point -- SUBNETS SHOULD BE BASED ON CONNECTIVITY!!!  
(sorry for shouting).

John

-- 
John R. Ackermann, Jr.        Law Department, NCR Corporation, Dayton, Ohio
(513) 445-2966		      John.Ackermann@daytonoh.ncr.com
Packet Radio: ag9v@n8acv      tcp/ip: ag9v@ag9v.ampr [44.70.12.34]
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