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:pr@isprime.com] Sent: Wednesday, October 15, 2003 5:42 PM To: H. Michael Smith, Jr. Cc: nanog@merit.edu; '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

assigning

to multi-homed customers? What about an IX or "critical infrastructure 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.