In the crux.
set system conntrack timeout custom rule 10 destination address '203.0.113.74' set system conntrack timeout custom rule 10 destination port '80' set system conntrack timeout custom rule 10 protocol tcp established '300' set system conntrack timeout custom rule 10 source address '192.0.2.168'
commit
vyos@r2-lts# commit [ system conntrack hash-size 32768 ] Updated conntrack hash size. This change will take affect when the system is rebooted.