BGP behavior / default route

[mwilson]

Hello all.  I have a few questions that came up during a design session.  

BGP default rout behavior?  In my lab I setup 4 ISP routers running BGP.   They peer to customer routers that advertise their subnets back to the ISP routers.  All seems to be dine.  Until a default-originate statement is added to an ISP router.   That default route propagated through all routers.  Is that normal?  I thought the statement neighbor x.x.x.x default-originate would tell that specific neighbor the default.  My lab proved otherwise.   

In real world I assume all ISPS have filters to block this?

Thanks for any clarification!

[Julio E. Moisa]

Hi

It should advertise a default route to the peer only. Could you provide your topology and configuration?

Thank you 

[Jon Marshall]

The default route will only be advertised to the specific neighbor but that neighbor will then advertise it to any of it's BGP neighbors.

Jon

[mwilson]

That makes sense then.  In a topology where all the ISP routers peer with an Internet backbone router then the route would just run wild until it hit them all?  Thanks!

[paul driver]

Hello

If applicable controlling on what prefixes you wish to be propergated in/out of your environment is preferable without relying on the isp to do so 

res

paul

[Pawan Raut]

default-originate command user router bgp xxx will advertised default route to all BGP peer. And neighbor x.x.x.x default-originate advertised the default route to that selected BGP neighbor.

[claurie]

Hi,

I have read and tried to digest the implications of the subject of this thread to my own situation and I would ask if someone could confirm my understanding. Firstly, my situation is - I currently receive a Default Route from my IP Transit Provider (in preference to the entire Global Routing Table, which will completely use the available router memory I have available for the present). Out of necessity, I am considering using this same router to connect to a local Peering Exchange and understand that I must not advertise my Default Route to my eBGP peers on the exchange. Is there a way to utilise the neighbor X.X.X.X default-originate  command to allow the advertising of the default route to a defined network thus ensuring I comply with proper peering behavior of not advertising to other BGP neighbors on the Peering Exchange? Appreciate any guidance!

Thanks

Craig