问题：

[单选] Which of the following is a characteristic of a data center core?（）

A . Server-to-server traffic always remains in the core layer.
B . The recommended practice is for the core infrastructure to be in Layer 3.
C . The boundary between Layer 2 and Layer 3 should be implemented in the aggregation layer.
D . The Cisco Express Forwarding hashing algorithm is the default, based on the IP address and Layer 4 port.
E . Core layer should run BGP along with an IGP becauseiBGP has a lower administrative distance than any IGP.