$ last -10 -i
user1  pts/0  150.xxx.100.yyy  Sat Mar 16 05:00   still logged in
user2  pts/2  220.xxx.243.yyy  Fri Mar 15 15:04 - 17:15  (02:11)
user3  pts/4  220.xxx.243.yyy  Fri Mar 15 13:46 - 16:05  (02:19)
user1  pts/3  220.xxx.243.yyy  Fri Mar 15 13:39 - 13:56  (00:16)
user4  pts/1  220.xxx.243.yyy  Fri Mar 15 13:22 - 16:53  (03:30)
user6  pts/0  150.xxx.121.yyy  Fri Mar 15 13:17 - 15:48  (02:31)
user1  pts/1  223.xxx.152.yyy  Fri Mar 15 13:04 - 13:05  (00:00)
user6  pts/2  150.xxx.121.yyy  Fri Mar 15 11:30 - 14:09  (02:39)
user1  pts/2  210.xxx.243.yyy  Fri Mar 15 10:51 - 10:51  (00:00)
user5  pts/0  150.xxx.121.yyy  Fri Mar 15 10:23 - 13:16  (02:52)

$ last -1000 -i | awk '{print $3}' | sort | uniq | grep '\.'
0.0.0.0
150.xxx.100.yy4
150.xxx.121.yy3
210.xxx.243.yy5
210.xxx.121.yy5
220.xx6.243.yy7
220.xx6.243.yy9
220.xx6.243.yy4
220.xx6.243.yy9
220.xx2.166.yy7
223.xxx.152.yy8
223.xxx.152.yy2