I understand the concept of BGP communities and how they are used to flag routing updates. What I haven't been able to find is how the values of the communities are set. With a community value of 3275:100, the 3275 part is the ASN of the sending router, but what is the meaning of the 100 piece? Is that a well-known value or a value that is agreed upon by admins in each AS? What I'm asking here is whether the community values are unique in a relationship between a provider and customer. Can provider A agree that the 100 value represents a LOCAL_PREF of 220 with one customer and that it denotes a METRIC of 2 with a different customer?
Well, providers don't usually seek agreement from customers. They simply decide on a set of community values and publish them to make customers aware of them.
PS. Pls do rate posts that help