Request for comment -- BCP38

Hugo Slabbert hugo at
Mon Sep 26 16:21:55 UTC 2016

On Mon 2016-Sep-26 11:15:11 -0500, Mike Hammett <nanog at> wrote:

>>----- Original Message -----
>>From: "John Levine" <johnl at>
>>To: nanog at
>>Sent: Monday, September 26, 2016 11:04:33 AM
>>Subject: Re: Request for comment -- BCP38
>>>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. There is no automated or scalable way for
>>>ISP A to distinguish this "legitimate" use from spoofing; unless you
>>>consider it scalable for ISP A to maintain thousands if not more
>>>"exception" ACLs to uRPF and BCP38 egress filters to cover all of the cases
>>>of customers X, Y, and Z sourcing traffic into ISP A's network using IPs
>>>allocated to them by other ISPs?
>>I gather the usual customer response to this is "if you don't want our
>>$50K/mo, I'm sure we can find another ISP who does."
>>From the conversations I've had with ISPs, the inability to manage
>>legitimate traffic from dual homed customer networks is the most
>>significant bar to widespread BCP38. I realize there's no way to do
>>it automatically now, but it doesn't seem like total rocket science to
>>come up with some way for providers to pass down a signed object to
>>the customer routers that the routers can then pass back up to the
>>customer's other providers.
>>PS: "Illegitimate" is not a synonym for inconvenient, or hard to handle.

>Are you talking BGP level customers or individual small businesses' 
>broadband service?

I myself am talking about the latter and included the option of PI space to 
cover that (although I guess at some point this can be made fly with PA 
space from another provider if both providers are willing enough to play 
ball), though from the $50/mo figure John listed, I'm assuming he's talking 
about the latter.

Do people really expect to be able to do this on residential or small 
business broadband networks?  I can't remember any time in recent memory 
where I assumed I could set a source address to any IP I fancy and have 
that packet successfully make its way through the SP's network.

>Mike Hammett
>Intelligent Computing Solutions

Hugo Slabbert       | email, xmpp/jabber: hugo at
pgp key: B178313E   | also on Signal
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