Level 3 BGP Advertisements

Nick Olsen nick at flhsi.com
Wed Aug 29 19:28:04 UTC 2012

Greetings all.

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. And its never been 
a problem. Until we brought up peering with level 3..

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?
Is what I'm doing (Advertising the aggregate prefix) a good rule of thumb?

Any other thoughts?

Nick Olsen
Network Operations (855) FLSPEED  x106


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