Request for comment -- BCP38

Stephen Satchell list at
Tue Sep 27 11:34:15 UTC 2016

I'm trying to come up with a simple picture that embraces all the 
comments I've seen thus far on the definition of BCP38.  The example 
scenario I'm about to paint may be over-simplified -- but I like to 
start simple.

Given a single local inside network with:
   * multiple uplink providers (typical multi-home situation)
   * multiple edge routers, each connected to an upstream via a public 
routeable /30, and each further connected to the downstream inside network
   * 50 subnets (to pick a number) of routeable IP address space 
downstream from the edge routers, with routing announcements to the 
world that direct packets back to the edge routers

BCP38 demands that ANY packet leaving ANY edge router to the upstream 
MUST have a source address:
   * within the 50 inside public route-able subnets, or
   * within a list of "my" addresses in the public /30 subnets.

True statement?

What am I missing here?

(In this simplified view, I'm divorcing the BCP38 aspects from the 
practical effects of any policy or input filtering done by the 
upstreams, as I think that's a separate discussion -- important but 
off-topic right now for my understanding of BCP38 at its core.  Those 
practical aspects can be added later, AFTER describing the basics.)

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