Because this is only half the answer.
I always filtered my announcements, was careful to register all the
address blocks I used, and was very responsible for my own network.
It had no effect on someone else hijacking one of my addresses and
announcing it through a large ISP's route tables.
I was effectively cut off the network not because of anything I did, or
could control. Worse there was little I could do to fix it. I had to
wait three days for the large ISP (with whom I had no direct relationship)
engineer's to decide it was worth their effort to stop the source
of the false announcement.
Unfortunately this is not a unique occurance. Cable&Wireless, Sprint,
AT&T and UUNET have all had portions of their service knocked off the
Internet for various periods of time due to bogus announcements. Until
other ISPs fix their policies, I can knock your network off most of the
Internet, and there is nothing you can do to prevent it.
