{% set nameservers = ["10.1.1.151","10.1.1.152"] %}

{% set nameserver1 = nameservers|random %}
{% set nameserver2 = nameservers|random %}
{% for _ in range(1,100) %}
  {% if not nameserver2 == nameserver1 %}
    {% break %}
  {% endif %}
  {% set nameserver2 = nameservers|random %}
{% endfor %}

nameserver1: {{ nameserver1 }}
nameserver2: {{ nameserver2 }}