> In the long, distant past I have had a reason not to follow this
> advice. This is long enough ago that surely I can reveal my cowboy
> antics without upsetting any current operators.
> 
> The situation was related to the origination of a route from a New
> Zealand network that we definitively did not want to propagate through
> North American networks towards Telstra in Australia (we originated
> the route towards Telstra over different paths across the
> Tasman). There were covering aggregates to protect against
> reachability.
> 
> I prepended 1221 to the routes I went towards US providers for the
> purpose of poisoning those routes and making them unacceptable to 1221
> routers who might otherwise learn them.
> 
> This was effective. It served a purpose. It wasn't malicious and it
> wasn't intended to impersonate anybody or hijack anything. The 1221
> people knew I was doing it, and perhaps they had given up complaining
> about my shenanigans by that point but they didn't tell me to stop.

i think this is a great ops example of as path poisoning.  thanks for
uncloaking. i can't get into why we once did similarly for ops reasons.
but path poisoning has been used in routing research for some decades.
a very useful took.  heck, we have a paper in submission which uses it.

> I have always thought of AS_PATH as a loop avoidance mechanism

precisely!

randy

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