DNSBL (DNS-based Blackhole List):Services that hold lists of SPAM emitting IP addresses.These services provide protection against spam IP addresses.
Example:xbl.spamhaus.org, b.barracudacentral.org etc.Sample log lines are shown below
Code:
[Wed Jan 18 15:24:09 2017] [error] [client 110.172.188.21*] denied by DNSBL: b.barracudacentral.org for:/abstract/800, referer: http://site.com/dizin
[Wed Jan 18 15:24:31 2017] [error] [client 156.194.8.25*] denied by DNSBL: zen.spamhaus.org for:/abstract/147, referer: http://www.site.com/dizin2