下述结论均不考虑BGP联盟的情况。
1.Local_preference
"A BGP speaker MUST NOT include this attribute in UPDATE messages it sends to external peers, except in the case of BGP Confederations [RFC3065]. If it is contained in an UPDATE message that is received from an external peer, then this attribute MUST be ignored by the receiving speaker, except in the case of BGP Confederations" From RFC 4271.
2.MED.
MED is not propagated outside of a receiving autonomous system.
