Request for comment -- BCP38

Hugo Slabbert hugo at
Mon Sep 26 16:24:34 UTC 2016

On Mon 2016-Sep-26 09:21:55 -0700, Hugo Slabbert <hugo at> wrote:

>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... 

...dammit...obviously "former" here, not "latter".  Caffeine injection 

>...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 
>>Mike Hammett
>>Intelligent Computing Solutions

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: Digital signature
URL: <>

More information about the NANOG mailing list