Finding asymmetric path

Stefan Fouant sfouant at
Sat Nov 28 04:16:29 UTC 2009

> -----Original Message-----
> From: ML [mailto:ml at]
> Sent: Friday, November 27, 2009 10:44 PM
> I'm reasonable certain a customer of ours who is using one of our
> netblocks is using a different reverse path to reach us.  How might I
> figure out who is allowing them to source traffic from IPs that belong
> to us?

It's been my experience that many providers do not care what address is used
for sourcing traffic.  This is why it is not uncommon to see traffic sourced
from RFC1918 space coming across various providers networks.  If more
providers adopted BCP 38 this wouldn't be a problem, but that doesn't seem
to be happening anytime soon...

I'd try to identify which providers the customer is connected to and take it
from there...

Stefan Fouant
GPG Key ID: 0xB5E3803D

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