Host A                              Host B 
               |              Middlebox M            |
               |                   |                 |
               | SYN (MP_CAPABLE)  |        SYN      |
               |-------------------|---------------->|
               |                SYN/ACK              |
               |<------------------------------------|
           a) MP_CAPABLE option stripped on outgoing path
         
             Host A                                Host B 
               |           SYN (MP_CAPABLE)            |
               |-------------------------------------->|
               |             Middlebox M               |
               |                  |                    |
               |    SYN/ACK       |SYN/ACK (MP_CAPABLE)|
               |<-----------------|--------------------|
           b) MP_CAPABLE option stripped on return path