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A Domain Name System blocklist, Domain Name System-based blackhole list, Domain Name System blacklist (DNSBL) or real-time blackhole list (RBL) is a service for operation of mail servers to perform a check via a Domain Name System (DNS) query whether a sending host's IP address is blacklisted for email spam. [1]
The list includes wide networks of computers sharing the same IP address using network address translation which are also affected (If one computer behind the NAT is allowed to send spam, the whole network will be blacklisted if the NAT IP is ever blacklisted.) This is a common method of pre-emptive blocking as most legitimate mail servers are ...
However, IP addresses should almost never be indefinitely blocked. Many IP addresses are dynamically assigned and change frequently from one person to the next, and even static IP addresses are periodically reassigned or have different users. In cases of long-term vandalism from an IP address, consider blocks over a period of months or years ...
As of 10:31:56 UTC on 31 January 2021, the domain and all sub-domains of spamcop.net resolved to a domain parking service due to the domain being expired. Later that day the domain was renewed and the service was again running. The outage resulted in messages being rejected due to the blacklist DNS entries all directing to the domain parking ...
Specific OTX components include a dashboard with details about the top malicious IPs around the world and to check the status of specific IPs; notifications should an organization's IP or domain be found in a hacker forum, blacklist or be listed by in OTX; and a feature to review log files to determine if there has been communication with known ...
Unix-like operating systems commonly implement IP address blocking using a TCP wrapper, configured by host access control files /etc/hosts.deny and /etc/hosts.allow.. Both companies and schools offering remote user access use Linux programs such as DenyHosts or Fail2ban for protection from unauthorized access while allowing permitted remote access.
The most common form of black hole is simply an IP address that specifies a host machine that is not running or an address to which no host has been assigned. Even though TCP/IP provides a means of communicating the delivery failure back to the sender via ICMP , traffic destined for such addresses is often just dropped.
These may change owner and need to be unblocked in the future, and so should remain tagged. IP addresses are usually added to this category with {{blocked proxy|indef=yes}} or a similar template. This category is not complete. For other lists of indefinitely blocked IP addresses which include open proxies, see BlockList or Database reports