Is malicious asymmetrical routing still a thing?

Aaron1 aaron1 at
Thu Mar 9 20:27:34 UTC 2023

Sounds like something uRPF would prevent 

Does anyone do uRPF ?  lol 


> On Mar 9, 2023, at 2:03 PM, John Levine <johnl at> wrote:
> Back in the olden days, a spammer would set up a server with a fast
> broadband connection and a dialup connection, and send out lots of
> spam over the broadband connection using the dialup's IP address.  Since
> mail traffic is quite asymmetric, this got them most of the broadband
> speed, and when the dialup provider cancelled their service, they could
> just dial into someone else.  Or maybe work through that giant pile of
> AOL CD-ROMs we all had.  The broadband provider often wouldn't notice
> since it wasn't their IP and they didn't get the complaints.
> Is this still a thing? Broadband providers fixed this by some
> combination of filtering port 25 traffic both ways, and BCP38 so you
> can only send packets with your own address. Do providers do both of
> these? More of one than the other? TIA.
> R's,
> John

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