You have 2 options, using Django templates built-in features:

1. If you want to set the first host as the default select option
2. If you want to set an specific host as the default select option

Here are the 2 possible solutions:

<select id="ip_addr">
    {% for host in hosts %}
        <option value="{{ host.ipaddress }}" {% if forloop.first %}selected{% endif %}>{{ host.ipaddress }}</option>
    {% endfor %}
</select>
<select id="ip_addr">
    {% for host in hosts %}
        <option value="{{ host.ipaddress }}" {% if host.ipaddress == '0.0.0.0' %}selected{% endif %}>{{ host.ipaddress }}</option>
    {% endfor %}
</select>

Note: foorloop.first is a special template loop variable, that is True during the first iteration of a loop.