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In a BGP environment where Community is being utilised I read thay BT offers a service in where it can prevent customer routes being advertised to certain peers (EUROPE, ASIA....).

I wondered, why would you want to do this as a Customer AND as a SP?

As a Customer in UK why would I not want my route to be advertised to Asia?

Is it due to the fact that I might only want it to be local to the UK? Or on SP side would it cost additional resources to make this route visible to BGP neighbours in Asia?

I just don't get why you would want to prevent routes from being advertised.

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If you had multiple peerings with an ISP you may choose to advertise specific prefixes marked with the NO_EXPORT community as well as advertising an aggregate route. The specific prefixes would provide more detail for the ISP to route to those prefixes, providing a more efficient path and better fault tolerance. Outside of your upstream ISP those routes are less useful and it is best practice to aggregate, so they would not be advertise upstream to other ISPs, only the aggregate prefix would get advertised.

If you want a reason specific for not advertising to a geographic region, security would be one. You may have a VPN server that should only be accessed from the UK. You could mark that prefix with a community so that other countries have no routing information to reach that network. It's pretty easy to circumvent though. DDOS would be another reason. If you were being attacked by a botnet in a certain region it may be beneficial to stop advertising your prefixes to that region.

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  • Absolutely incredible source of information Karl, I have to ask, where do you find your information?
    – Daniel
    Nov 24 '16 at 20:07

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