On Wed, Aug 29, 2012 at 3:28 PM, Nick Olsen <nick@flhsi.com> wrote:
In practice, We've always advertised our space all the way down to /24's but also the aggregate block (the /20 or the /21). Just so there was still reachability to our network in the event that someone made the foolish mistake of filtering lets say prefixes smaller /23...
Anyways, I've always thought that was standard practice.
That's very poor practice. Each announcements costs *other people* the better part of $10k per year. Be polite with other peoples' money. If the /24 shares the exact same routing policy as the covering route, announce only the covering route. For all the good it'll do you, you can break it out to /24's when and if someone mis-announces one of your address blocks. Competing announcements of the /24 still won't leave you with correct connectivity. If anything, putting the /24 announcement in ahead of time will delay your detection of the problem by causing a partial failure instead of a total one.
I noticed that while the /24's made it out to the world. The larger counterparts (2 /21's and a /20) did not. So, I start sniffing around. Find that I do indeed see the prefixes in Level 3's looking glass but they aren't handing it off to peers. So, Naturally, I land on this being some kind of prefix filtering issue and open a ticket with Level 3. They tell me this is standard practice. And If I want to see the /20 or /21's make it out to the rest of the world, I need to stop sending the /24's.
Does this sound normal?
That's insane. Assuming you're authorized to announce that address space, Level 3 should be propagating your announcements exactly as you make them. As only one of your peers, they're in no position to understand the traffic engineering behind your announcement choices. If they are acting as you say, they are dead wrong to do so. Regards, Bill Herrin -- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004