Re: working group last call for PPP TRILL protocol control protocol [was Re: I-D Action:draft-ietf-pppext-trill-protocol-02.txt]

On 1/24/11 1:29 PM, William Allen Simpson wrote:
> On 1/24/11 12:05 PM, James Carlson wrote:
>> I agree that it'd be nice to fill in this hole, but I'm not so sure how
>> to accomplish that task. I don't think IETF OUI plus LCP Magic Number
>> works -- the Magic Number value is unique for a given endpoint on a
>> given link, but is not guaranteed to be unique across a network. But
>> the IS-IS System ID number does need to be unique across the network,
>> and its construction based on MAC addresses normally protects that
>> requirement.
>>
> It must be nice to live in a world with unique MAC addresses! In my
> experience, I've run into rather a lot of them that are not -- and it
> will be much worse in this cross-linked multi-media environment. Many
> vendors think that it's OK to reuse the MAC address for different link
> speeds and types.
>
I'm staring at the TRILL draft, and cannot find anything in the protocol
to detect, eliminate, or resolve duplicate System ID numbers.  Obviously,
I'm missing something.  Please advise.


> The only way that the Magic Number has any significant chance to ever be
> non-unique would be a very large number of PPP-only bridges in the network,
> on the order of 2**16. Probably best to stick an IP router in there....
>
To elaborate, I've an old story to tell.  Once upon a time, Michigan State
University supposedly had the world's largest bridged ethernet, covering
many square miles.  Performance was abysmal.  But once I stuck a 286 box
with KA9Q net (this was circa 1985) between the computing center and
engineering, performance miraculously improved!

(The problem turned out to be fragments inserted by the IBM in the
administration building next door to the computing center.)

Thus, I got the routing religion....  Never use a bridge where a router
could be used instead.

I really doubt we'll ever see more than one or two PPP-only Rbridges in a
single installation.  The point being that PPP is vastly more robust than
ethernet -- and you shouldn't let the good enough (ethernet) be the enemy
of the better (PPP).


> If the PPP-only bridges are talking to each other, there will *never* be
> any non-unique numbers. That's the more likely case of centrally
> located PPP-only bridges.
>
Of course, this assumes that the PPP Magic Number has been implemented
correctly, and it checks the number against all its interfaces to avoid
loops.  It also assumes you haven't deployed Junipers with the fairly evil
"ppp magic-number ignore-mismatch".
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