Well, not really. It doesn't mean that Comcast was re-advertising it into BGP and also advertising it to their peers. Usually you use a combination of prefix-li

Well, not really. It doesn't mean that Comcast was re-advertising it into BGP and also advertising it to their peers. Usually you use a combination of prefix-list filtering and route tagging so you don't advertise garbage to your peers. RIP and other IGP protocols do not need to have their neighbors explicitly configured, they will find neighbors automatically on enabled interfaces. On some platforms they are enabled on all interfaces by default so it will form neighbor relationships with anything connected. A sane network design would be to only enable it on interfaces connected to your own routers (or customer interface, but on a different process ID) and also use a password.