Traffic Engineering

Jay R. Ashworth jra at
Thu Sep 18 17:20:10 UTC 1997

On Thu, Sep 18, 1997 at 12:55:37PM -0400, Sean M. Doran wrote:
> "Jay R. Ashworth" <jra at> writes:
> > Are there any major potholes in this theory that I'm missing?
> Well, you have two technical problems to solve: firstly,
> the same numbering problem that anyone else has,
> viz. addresses will change.

[ Looks at From: address ]  Oh.  Hi, Sean.  :-)

>                             Secondly, you have a traffic
> attraction/traffic dispersion problem for non-local
> connectivity.  You also have to provide better
> value-for-money than the classical hierarchy-of-providers
> model your competitors will be using.

Probably.  But, given the relative pricing of T-3s and T-1s, I don't
think this will be that hard to do, especially if wireless last mile
picks up as fast I I expect it will...

> The "classical" approach is to renumber to solve the first
> case and do the oh-so-fun BGP tricks Dennis Ferguson
> described here a couple of incarnations ago.
> A better approach to both problems is to use NAT to deal
> with the renumbering issue, and large-scale NAT to deal
> with your border problem (you not only want to reduce the
> number of prefixes you advertise outbound, and use the DNS
> to offer back different topolical locators (i.e., IP
> addresses) for the things connected to you, but you also
> want to reduce the amount of information you take in from
> the outside world).

Well, yeah, but the delights of NAT in a two or three customer-level
deep commercial environment are an administrative problem I don't think
I even want to go near...

> To deal with connectivity failures outside the NATs
> themselves you build tunnels through working inside or
> outside infrastructure between your NATs.   This is
> straightforward and is what is done now.
> Dealing with the failures of the NATs themselves requires
> synchronized or deterministic address mappings,
> NAT-friendly higher-layer protocols, and a simple IGP.

Um... I haven't gotten quite this far down the pike, yet, Sean.  :-)

> With some performance-affecting trade-offs you can deal
> with many NAT-unfriendly higher-layer protocols in various
> ways too, mostly by sharing state information among your 
> border NATs.

Sometimes I feel like I'm at a multi-level marketing seminar... :-)

-- jra
Jay R. Ashworth                                                jra at
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