Cogent BCP-38

William Herrin bill at
Thu Aug 17 13:11:05 UTC 2017

On Thu, Aug 17, 2017 at 7:35 AM, Mike Hammett <nanog at> wrote:

> Strict vs. loose.

Hi Mike,

Doesn't loose mode URPF allow packets from anything that exists in the
routing table regardless of source? Seems just about worthless. You're
allowing the site to spoof anything in the routing table which is NOT

Strict mode URPF down paths guaranteed to be single-homed. Manually
configure allowed sources and announcements for BGP-talking customers.

Bill Herrin

William Herrin ................ herrin at  bill at
Dirtside Systems ......... Web: <>

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