ISP port blocking practice

William Herrin bill at
Fri Sep 3 15:23:00 UTC 2010

On Thu, Sep 2, 2010 at 11:04 PM, Daniel Senie <dts at> wrote:
> Ingress filtering is the correct tool for the job.

Not really. Ingress filtering only ever protected you from being the
source of spooding attacks, not the destination. The point of Zhiyun's
results is that it doesn't fully protect you from being the source

Frankly, Zhiyun offers the first truly rational case I've personally
seen for packet filtering based on the TCP source port. You should
give his work more careful scrutiny.

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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