North American Network Operators Group
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Re: Pitfalls of annoucing /24s

  • From: Sean Donelan
  • Date: Wed Oct 15 17:40:08 2003 
On Wed, 15 Oct 2003, Jean-Christophe Smith wrote:
> In current practice would there be serious jeopardy of portions of the
> internet not being able to reach this address space due to bgp filters or
> other restrictions? What is the smallest acceptable block of IPs that can be
> announced without adverse or unpredictable results?

The longest CIDR block that all ISPs accept is a /8.  Anything longer than
a /8 runs into some policy at some ISP.

There are many rules of thumb about what is acceptable to a wide range of
ISPs.  Generally if you follow the number registry policies, and announce
the block delegated directly from the registry most providers will accept
it.  Different address ranges have different historical CIDR lengths.