Request for comment -- BCP38

John Levine johnl at
Mon Sep 26 18:03:55 UTC 2016

>>> If you have links from both ISP A and ISP B and decide to send traffic
>>> out ISP A's link sourced from addresses ISP B allocated to you, ISP A
>>> *should* drop that traffic on the floor.
>> This is a legitimate and interesting use case that is broken by BCP38.
>I don't agree that this is legitimate.
>Also we're talking about typical mom & pop home users here.

There are SOHO modems that will fall back to a second connection if
the primary one fails, but that's not what we're talking about here.

The customers I'm talking about are businesses large enough to have
two dedicated upstreams, and a chunk of address spaced SWIP'ed from
each.  Some run BGP but I get the impression as likely as not they
have static routes to the two upstreams.

For people who missed it the last time, I said $50K/mo, not $50/mo.  Letters matter.


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