ANS used to filter every peering session they had. Other ISPs (I won't mention any names) don't seem to filter anything, peer, customer or other. This seems to have less to do with technical or trust, than how management decides to run their business. ANS's management decided to do one thing, and paid Curtis a lot of money to do it, other ISP's management decide its too much work. See http://www.academ.com/nanog/may1996/state-of-the-internet-nsps-qna.html On Tue, 14 November 2000, "Steven M. Bellovin" wrote:

In message <20001114202940.19022.cpmta@c004.sfo.cp.net>, Sean Donelan writes:

...

On Mon, 13 November 2000, David Diaz wrote:

...

The cabal makes jokes "Officially there is no cabal." In reality the fact is that peering is a trust event. You are

Peering is a business decision. It is not an engineering decision nor a trust event.

Technically, can a peer BGP session do any more or less damage to your network than a customer BGP session? The protocol is identical.

Peer BGP is (often) worse because you can't filter it as aggressively. You *know* what prefixes your customers can advertise, and you can discard anything else. But if you have two or more peer sessions, you don't in general know which prefixes can legally come from which sessions.