You could use http://ipinfo.io (a service I built) for this. Here's some example output from the API:
$ curl ipinfo.io/128.32.0.1
{
"ip": "128.32.0.1",
"hostname": "No Hostname",
"city": "Berkeley",
"region": "California",
"country": "US",
"loc": "37.8668,-122.2536",
"org": "AS25 University of California at Berkeley",
"postal": "94720"
}
Notice the org field, "AS25 University of California at Berkeley". You can get just those details by appending /org to the URL:
$ curl ipinfo.io/128.32.0.1/org
AS25 University of California at Berkeley
You can do a bulk lookup of your IP addresses by putting them in a file and running the following command:
$ cat ips.txt | xargs -I% curl -s http://ipinfo.io/%/org | paste ips.txt -
128.32.0.1 AS25 University of California at Berkeley
128.62.76.244 AS18 University of Texas at Austin
24.32.142.2 AS7018 AT&T Services, Inc.
171.64.84.194 AS32 Stanford University
18.9.44.47 AS3 Massachusetts Institute of Technology
67.188.232.130 AS7922 Comcast Cable Communications, Inc.
You can find out more details about the API at http://ipinfo.io/developers.