North American Network Operators Group

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RE: Pitfalls of annoucing /24s

  • From: H. Michael Smith, Jr.
  • Date: Wed Oct 15 18:11:03 2003

Understood.  But... networks filtering out the /24 announcement will
always prefer the aggregate learned from the owner/issuer of the space.
They'll be completely unaware that another route exists to the (/24)
network.  If the customers link to the provider that assigned the space
goes down, those filtering /24's will still send the traffic to the
'owner' of the space (right?).

What is the issuer of the /24 is filtering incoming /24 advertisements
(Verio)?  Will they learn the route to the other ISP or blackhole
traffic destined for their own customer?

I keep hoping that I am missing something here.  If not, I sure hope
more folks don't adopt Verio's filtering techniques.  (I know that a
VERY low AS # issues /24's out of a /8)

-----Original Message-----
From: Phil Rosenthal [mailto:[email protected]] 
Sent: Wednesday, October 15, 2003 5:42 PM
To: H. Michael Smith, Jr.
Cc: [email protected]; 'John Palmer'
Subject: Re: Pitfalls of annoucing /24s

On Oct 15, 2003, at 5:24 PM, H. Michael Smith, Jr. wrote:

> What about the /24's that many ISPs (especially tier 2-3) are
> to multi-homed customers?  What about an IX or "critical
> providers" that may be issued a /24 from ARIN (Policy 2001-3)?
As long as it's provider assigned, and your provider announces the 
supernet that the /24 is from, it will still work.  If you announce PI 
space out of the old class A space in /24's, many networks wont be able 
to reach you.