I am unsure about how extensions are handled in TLS v1.2.
During the handshake, the client is able to add some extensions during ClientHello. As far I understood, the server can pick arbitrary subsets from this list in ServerHello similar to picking the cipher suite, the client provided during ClientHello.
Another possibility would be, that the server can either take all those extensions into account or must abort the handshake. I am not sure, what is true.
I was looking for an adequate answer here, but didn't really find the one statement I am looking for.