About the description of well-known attributes in BGP, which is correct? (Multiple Choice)
A . The well-known attributes are divided into two types: recognized mandatory and optional transition.
B . BGP must recognize all well-known attributes.
C . Well-known attributes are identifiled by all BGP routers and must exist in the Update message.
D . Well-known attributes are identifiled by all BGP routers, but it does not need to exist in the Update message.
Answer: BCD