BGP advertisements control

[ahmedabdelbaqi]

Hello Dears I want to ask about the following case : If I have router in AS 100 with 2 router neighbors ( Assume they are ISPs ) AS 200 & AS 300 and I have networks 192.168.2.0 - 192.168.7.0 I advertise 192.168.2.0 - 192.168.4.0 with one neighbor AS 200 & 192.168.2.0 - 192.168.4.0 with another AS 300 by using route-map . In my design I use default route ( with LSA and track ) ,the requests from these networks routed via the default route and returned from destination via BGP   .  what is the method to control advertisement of networks in case the public service of one ISPs goes down and I want to automatically advertise the networks for this down ISP on the other ISP ?

[Q S Tahmeed · Accepted solution]

Hi, 

You can prepend prefixes towards your ISPs. Suppose prefix X is transmitted via ISP-A. In that case you announce prefix X towards ISP-A without any prepending and towards ISP-B with prepending, using your own AS at least more than 2 times. This way when ISP-A goes down global traffic will shift through ISP-B for the prefix X. 

Regards / Tahmeed

[ahmedabdelbaqi]

It is very helpful for my purpose , Thank you very much