how to find which ISP holds a given IP addr.block ?

[M K Saravanan <mksarav@xxxxxxxxxxxxxxxxx>]

hi,

My /var/log/secure shows:

Apr  4 14:48:08 aukbc3 in.ftpd[17528]: refused connect from 213.48.246.23
Mar 31 17:16:30 aukbc3 in.ftpd[2808]: refused connect from 203.79.221.51
Mar 24 02:02:00 aukbc3 in.ftpd[11448]: refused connect from 198.116.10.120

How to find out to which ISP these IP addr. belong?

Note: host/dig doesnot report any domain name for these addr.

I made traceroute to 213.48.246.23 and found the nearest router to this.  Then
did a "dig" to that router which shows "ns.cableinet.net" as the
nameserver. using nslookup changed the default server to that and did a lookup
which shows:

Name:    usr8379-kno.cableinet.co.uk
Address:  213.48.246.23

Now to whom I should report about this unauthorised access?

-- mks --