passer's post in агрегация портов на олте was marked as the answer
lacp c DGS-3120-24SC заработал:
aggregator-group load-balance both-ip
!
!
interface Port-aggregator1
switchport trunk vlan-allowed 7,9,20
switchport trunk vlan-untagged none
switchport mode trunk
!
interface GigaEthernet0/1
switchport trunk vlan-allowed 7,9,20
switchport trunk vlan-untagged none
switchport mode trunk
aggregator-group 1 mode lacp
!
interface GigaEthernet0/2
switchport trunk vlan-allowed 7,9,20
switchport trunk vlan-untagged none
switchport mode trunk
aggregator-group 1 mode lacp
