Solved.
For benefit of all you guys… Vyos does reply pings on every IP declared here…
interfaces ethernet eth0 {
address 1.1.1.2/24
address 1.1.1.3/24
address 1.1.1.4/24
The problem I had was simply a misconfiguration on my ISP’s side who didn’t reset the second IP to be assigned to the new MAC address of my newly installed box.
However system gateway-address must to be declared on Vyos configuration for internet access. After that no need to do something special on routes .
And NAT translations remain just the same as I had on my CISCO router.
Cheers 