rfc 1812 third party address on traceroute

Wed Jun 1 21:45:41 UTC 2016

On Wed, Jun 1, 2016 at 3:16 PM, Marc Storck <mstorck at voipgate.com> wrote:
>>               .-----------------.
>>               |                 |
>>               |               B |--------- D
>>    S ---------| A      R        |
>>               |               C |--------- (toward S)
>>               |                 |
>>               `-----------------'
>>
> With BCP38 in mind, could there be situations
> where Router R is not allowed to source packets
> with address A out of interface C?

Hi Marc,

I think you're right. Address A in a /30 from ISP A. ISP C accepts
source addresses from your /24 but not the A /30.  So if the router
does not follow the RFC (sends an ICMP packet out C with a source
address from A), typical asynchronous routing can result in
black-holding the ICMP error message.

You've hit on a good reason to follow the RFC by default instead of
doing what Randy wants. ;)

-Bill

-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>