07-07-2017 02:08 PM - edited 03-05-2019 08:49 AM
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!
07-07-2017 02:31 PM
Hi
It should advertise a default route to the peer only. Could you provide your topology and configuration?
Thank you
07-07-2017 02:47 PM
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
07-07-2017 02:51 PM
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!
07-08-2017 04:11 AM
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
07-13-2017 11:30 PM
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.
12-27-2017 02:35 PM
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
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