BGP prefix filter list

Wed May 22 17:08:29 UTC 2019

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 at 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 Tue, May 21, 2019 at 5:30 AM Alejandro Acosta < [
> mailto:alejandroacostaalamo at gmail.com | alejandroacostaalamo at gmail.com ] >
> wrote:

>> On 5/20/19 7:26 PM, John Kristoff wrote:
>> > On Mon, 20 May 2019 23:09:02 +0000
>> > Seth Mattinen < [ mailto:sethm at rollernet.us | sethm at 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
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