Re: Autoconfig & dead horses

schulter@zk3.dec.com Fri, 10 May 1996 17:26 UTC

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From: schulter@zk3.dec.com
Message-Id: <9605101656.AA01641@dogfish.zk3.dec.com>
To: Albert Manfredi <manfredi@engr05.comsys.rockwell.com>
Cc: mohta@necom830.hpcl.titech.ac.jp, IP-ATM Working Group <ip-atm@nexen.com>
Subject: Re: Autoconfig & dead horses
In-Reply-To: Your message of "Fri, 10 May 96 10:37:00 PDT." <31937EBC.122@engr05.comsys.rockwell.com>
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Date: Fri, 10 May 1996 12:56:06 -0400
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On Fri, 10 May 96 10:37:00 PDT Albert Manfredi wrote:

> We have 16 bytes of IPv6 address and 20 bytes of ATM NSAPA. Both are
> global addresses.

No.  Not all IPv6 addresses are global.  IPv6 addresses have a concept of
scope.  So, for example, two nodes on different links can have the exact
same link-local addresses.  Two nodes on different sites can have the
exact same site-local addresses.  Only global IPv6 addresses have global
scope and are routed globally.  Not all nodes on a link necessarily need,
or will get, a global address.

>  Therefore, right up front, we know that there are not
> just 256 wasted associations if we don't make use of SEL, but rather
> 4 billion wasted associations no matter what we do.

Again, this is not the case because of the way IPv6 addresses are formated.
Some number of the upper bits determine address type, scope, etc.  Many 
combinations are undefined.

I still don't see what the problem is with using a SEL value for each
IPv6 link.   Since the SEL is used to identify a specific service at
an address (and I would think each IPv6 virtual link would represent
a service) the SEL is the cheapest thing to use.  This is using
only 8 bits to select a service (rather than 48 if you use ESIs).  And
if there are more than 256 services at the endpoint you register another
ESI to get an additional 256 services.

> Why don't we define a fourth AFI
> value to denote "IPv6 address," and simply incorporate IP routing within
> ATM switches?? 

This would be nice for global address, but I'm not sure how link-local
and site-local addresses would work in this case.

 --- pete

------------------
Peter Schulter					schulter@zk3.dec.com
Digital UNIX Networking				voice (603) 881-2920
Digital Equipment Corp				voice (DTN) 381-2920
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Autoconfig & dead horses Albert Manfredi
Re: Autoconfig & dead horses schulter