Todd Underwood was a little late

William Herrin bill at herrin.us
Thu Jun 17 16:10:15 CDT 2010


On Thu, Jun 17, 2010 at 12:38 AM, Roy <r.engehausen at gmail.com> wrote:
> On 6/16/2010 7:43 PM, Jon Lewis wrote:
>> With a larger
>> network, multiple IP blocks, ***numerous multihomed customers***, some of which
>> use IP's we've assigned them, it gets a little more complicated to do.
>> I could reject at our border, packets sourced from our IP ranges with
>> exceptions for any of the IP blocks we've assigned to multihomed customers.
>
> Sounds like a good use of URPF.

Reverse path filtering + asymmetric routing = epic fail. Jon did say
Multihomed customer.

Refer to RFC 3704 (BCP84). Note section 2.2 (Strict Reverse Path
Forwarding) last part of the final sentence: "in particular, when
applied to multihoming to different ISPs, this assumption may fail."

Regards,
Bill Herrin


-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
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