问题：

[多选] Which three features are benefits of using GRE tunnels in conjunction with IPsec for building site-to-site VPNs？（）

A . allows dynamic routing over the tunnel
B . supports multi-protocol （non-IP） traffic over the tunnel
C . reduces IPsec headers overhead since tunnel mode is used
D . simplifies the ACL used in the crypto map
E . uses Virtual Tunnel Interface （VTI） to simplify the IPsec VPN configuratio