[j-nsp] MX480 - 10.4R4.5 BGP

[David Miller]

On 1/16/2013 10:11 PM, Brandon Ross wrote:
> On Wed, 16 Jan 2013, Keith wrote:
> 
>> Peer #1 - all 4 networks are prepended with our AS 5 times:
> 
> Okay so far...
> 
>> This way I have two networks coming in on one gig link and the other two
>> networks are coming in over the other gig link.
> 
> No, you don't.  You have all 4 networks coming in on all 4 links.
> 
>> There should be no traffic incoming in on Peer #1 from the internet.
>> But there is.
> 
> Not quite.  You have advertised a route to another AS.  Each AS will use
> it's own criteria to decide how to route traffic.  For example, most
> service providers will prefer to send traffic to their customers' direct
> connections instead of sending that traffic to an intermediate AS.  That
> preference is usually implemented using localpref which is a decision
> made by routers before AS path length, just like you are doing to choose
> how to send traffic out of your network.
> 
> The only way to ensure that NO traffic comes in on that link is to
> advertise NO routes at all.
> 
> You can, however, influence traffic in a stronger way by advertising
> more specific routes (since more specific routes are always preferred)
> on links that you want to carry traffic.

You may also be able to set BGP communities on your announcements to
Peer1 to control their handling of your prefixes.

http://bgp.he.net/AS13768#_irr

-DMM