Target server: use the address specified by the client.

"server_address": {
  "selection": "original"
}

Target server: use a fix address.

"server_address": {
  "address": "<fix-IP>",
  "port": 22,
  "selection": "fix"
}

Target server: configure inband destination selection, where the client can specify the target address in the username. The target can be either an IP range, or a domain.

"server_address": {
  "dns_server": "<ip-of-dns-server>",
  "dns_suffixes": null,
  "domains": [
    {
      "domain": {
        "selection": "address",
        "value": "<IP-range>"
      },
      "port": 22
    },
    {
      "domain": {
        "selection": "domain",
        "value": "*.example"
      },
      "port": 22
    }
  ],
  "selection": "inband"
}