Request for comment -- BCP38

Mike Hammett nanog at
Mon Sep 26 16:15:11 UTC 2016

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

Mike Hammett 
Intelligent Computing Solutions 


----- 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. 

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