Level 3 BGP Advertisements

Jon Lewis jlewis at lewis.org
Wed Aug 29 15:03:11 CDT 2012


My more specifics are advertise to customers only (not supposed to be 
visible to peers), which was how I found that TWT had transitioned from 
Level3 peer to customer...and I'm only going 1 bit more specific (not down 
to the /24s) for TE purposes.

On Wed, 29 Aug 2012, Nick Olsen wrote:

> Thanks for the input Jon.
> I should note that is exactly what we are doing. The /24's are actually
> tagged with the advertise to customers, prepend to peers community.
>
> Nick Olsen
> Network Operations (855) FLSPEED  x106
>
> ----------------------------------------
> From: "Jon Lewis" <jlewis at lewis.org>
> Sent: Wednesday, August 29, 2012 3:48 PM
> To: "Nick Olsen" <nick at flhsi.com>
> Subject: Re: Level 3 BGP Advertisements
>
> On Wed, 29 Aug 2012, Nick Olsen wrote:
>
>> Anyways, I've always thought that was standard practice. And its never
> been
>> a problem. Until we brought up peering with level 3..
>
> No...I'd call that global table pollution.  In general, there's no reason
> you should announce your CIDRs and all their /24 subnets.
>
>> 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?
>
> No.  I announce to Level3 our IP space and 2 subnets of each CIDR (i.e.
> /17 + 2 /18 subnets of that /17, etc.), but I use community tags (and
> other tricks) to mark the more specifics as advertise to [certain] L3
> customers only, and let the less specifics out to the world.  The only
> problems I've had with this have been when L3 peers have become customers,
>
> and one L3 customer doing something odd (never did find out what) that
> caused them to effectively null route our space until I kept them from
> seeing the more specifics (creative abuse of loop detection).
>
> Level3's prefix filter for your session should be built based on IRR data.
>
> If it's not doing what you want, you probably haven't setup the IRR data
> properly.
>
> ----------------------------------------------------------------------
> Jon Lewis, MCP :)           |  I route
> Senior Network Engineer     |  therefore you are
> Atlantic Net                |
> _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
>
>

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________



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