Hi Elie,
first of all you need to know what BGP communities are accepted by your ISP's.
You should ask them, because sometimes they do not publish all BGP communities ļ.
You can use for example well known (if they are accepted):
- no-export - which means do not export to any eBGP neighbor
- no-advertise - which means, do not export to any BGP neighbor at all.--
Jarek