The BGP community is a value that you assign to routes. It is essentially a tag that is associated with the route so that someone else can evaluate the tag and make some processing decision based on the tag value.
In general the number before the colon in the community value (like 7020) would be your AS number. The number after the colon (like 20) is some arbitrary value that you pick.
So what this generally means is that you have agreed with some BGP neighbor that if they see routes from you with community (tag) value of 7020:20 that they should take some particular action about those routes.
Just to add a tiny detail on the prefect explaination by Rick, to add the community to the already existing communities you must use the "additive" keyword, in your example if the matched (in the ACL 99) routes has already got any communities it will be replaced with the "7020:20".
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.