Request for comment -- BCP38

Mike Hammett nanog at
Mon Sep 26 16:29:42 UTC 2016

I would assume that on a broadband grade connection it shouldn't work unless you have a niche player and proper LOA. 

I would assume that on a BGP level circuit that it would work, again, given proper documentation (LOAs, IRRDB entry, etc.). IRRDBs make this wonderfully easier. By default, deny. Allow whatever is in the IRRDB entry. $250 for manual changes. 

Mike Hammett 
Intelligent Computing Solutions 


----- Original Message -----

From: "Hugo Slabbert" <hugo at> 
To: "Mike Hammett" <nanog at> 
Cc: "John Levine" <johnl at>, nanog at 
Sent: Monday, September 26, 2016 11:21:55 AM 
Subject: Re: Request for comment -- BCP38 

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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