If all the four TCP MSS options are configured simultaneously, then the order of preference is as follows:
* If TCP packet enters an IPsec VPN tunnel, then an ipsec-vpn mss value has high priority over all-tcp mss value, hence ipsec-vpn mss value is set.
Ref:
https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/security-edit-tcp-mss.html
* If TCP packet enters an IPsec VPN tunnel, then an ipsec-vpn mss value has high priority over all-tcp mss value, hence ipsec-vpn mss value is set.
Ref:
https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/security-edit-tcp-mss.html