How to get a list of questions from stackoverflow API based on search query?

You can get this information utilizing the questions/ route. In this call, you will pass the tag(s) you are interested in to the tagged parameter (separated by a semicolon (;)).

To constrain questions returned to those with a set of tags, use the tagged parameter with a semi-colon delimited list of tags. This is an and constraint, passing tagged=c;java will return only those questions with both tags. As such, passing more than 5 tags will always return zero results.

For your specific question (searching for ipv4), you can utilize this as a starting point:

http://api.stackexchange.com/docs/questions#order=desc&sort=activity&tagged=ipv4&filter=!BHMIbze0EPheMk572h0ktETsgnphhU&site=stackoverflow&run=true

The filter is optional, but I've stripped out some of the default fields to present a smaller example. The link above returns entries that look like this:

"items": [
{
  "tags": [
    "ruby-on-rails",
    "ipv4",
    "geokit"
  ],
  "link": "http://stackoverflow.com/questions/29460004/rails-geokit-incorrectly-converting-ipv4-address-to-latitude-and-longitude",
  "title": "Rails: Geokit incorrectly converting IPv4 address to latitude and longitude"
},
{
  "tags": [
    "networking",
    "ip",
    "ipv4",
    "maxmind",
    "cidr"
  ],
  "link": "http://stackoverflow.com/questions/28358851/merging-of-multiple-ipv4-address-blocks-on-the-basis-of-their-country-region",
  "title": "merging of multiple IPv4 address blocks on the basis of their country region"
},
...
}

Stackexchange offers https://api.stackexchange.com/docs/advanced-search endpoint.

So for example, get on https://api.stackexchange.com/search/advanced?site=stackoverflow.com&q=firebase would return you something like this:

This is simplest example but as you will find in the docs, there are numerous parameters based on which search can be performed. Some of them are:

• accepted - true to return only questions with accepted answers, false to return only those without. Omit to elide constraint.
• answers - the minimum number of answers returned questions must have.
• body - text which must appear in returned questions' bodies.
• tagged - a semicolon delimited list of tags, of which at least one will be present on all returned questions.
• title - text which must appear in returned questions' titles.
• user - the id of the user who must own the questions returned.
• ...

Hope this helps!

Cheers!