Re: Site to site VPN not able to use the second public IP address

I don't really understand why you don't want to use 218.255.187.42 for the VPN.

The IP 218.255.187.43 is already used for static NAT. You cannot use that IP.

What you should is add a secondary IP to your external interface like below:

Tthe 218.255.187.X IP will be used fore the VPN (with local-addess statement inside the IKE gateway definition)

interfaces {
    ge-0/0/0 {
        unit 0 {
            family inet {
                address 218.255.187.42/29 {
                  preferred;
                  primary;
                }
                address 218.255.187.X/29;
            }
        }
    }
}