BGP prefix filter list

William Herrin bill at
Fri May 24 18:22:48 UTC 2019

On Fri, May 24, 2019 at 10:29 AM Mike Hammett <nanog at> wrote:

> If networks are going to make unconventional announcements, I'm not
> concerned if they suffer because of it.

No, no no. You're not getting it.

I'm a customer of Verizon. I'm a customer of CenturyLink. I get a /24 from
CenturyLink and announce it via my two carriers: Verizon and CenturyLink.
CenturyLink also announces the aggregate, let's say /16 that the /24 is a
part of because all of the /16 containing my /24 is their allocation.

Get it? I announce the /24 via both so that you can reach me when there is
a problem with one or the other. If you drop the /24, you break the
Internet when my connection to CenturyLink is inoperable. Good job!

There is nothing unconventional about this arrangement. It was commonplace
before ARIN dropped the minimum end-user assignment to /24 and many
networks who themselves up that way have found it inconvenient to renumber.

Bill Herrin

William Herrin
bill at
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the NANOG mailing list