Hi,
One legitimate reason is the split of companies. In some cases, IP space needs to be divided up. For example, company A splits up in AA and AB, and has a /20. Company AA may advertise the /20, while the new AB may advertise the top or bottom /21. I know of at least one worldwide e-commerce company that is in that situation.
Thanks,
Sabri
----- On May 22, 2019, at 9:40 AM, Tom Beecher <beecher@beecher.cc> wrote:
There are sometimes legitimate reasons to have a covering aggregate with some more specific announcements. Certainly there's a lot of cleanup that many should do in this area, but it might not be the best approach to this issue.
On 5/20/19 7:26 PM, John Kristoff wrote:
> On Mon, 20 May 2019 23:09:02 +0000
> Seth Mattinen <sethm@rollernet.us> wrote:
>
>> A good start would be killing any /24 announcement where a covering
>> aggregate exists.
> I wouldn't do this as a general rule. If an attacker knows networks are
> 1) not pointing default, 2) dropping /24's, 3) not validating the
> aggregates, and 4) no actual legitimate aggregate exists, (all
> reasonable assumptions so far for many /24's), then they have a pretty
> good opportunity to capture that traffic.
+1 John
Seth approach could be an option _only_ if prefix has an aggregate
exists && as origin are the same
> John