mppe +H -M +S -L -D -C what each character mean.

根据Microsoft Point-To-Point Encryption (MPPE) Protocol的rfc3078文件中第2节Configuration Option Format：

H：使用stateless模式（this indicates that the sender wishes to negotiate the use of stateless mode）

M：使用56bit密钥(this indicates the desire of the sender to negotiate the use of 56-bit session keys)

S：使用128bit密钥(this indicates the desire of the sender to negotiate the use of 128-bit session keys)

L：使用40bit密钥(this indicates the desire of the sender to negotiate the use of 40-bit session keys)

D：已过期(The ‘D‘ bit is obsolete)

C：供MPPC使用(The ‘C‘ bit is used by MPPC)

参考：

https://www.ietf.org/rfc/rfc3078.txt

mppe +H -M +S -L -D -C中个字母意思