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Domain Name System blocking, or DNS blocking / filtering, is a strategy for making it difficult for users to locate specific domains or websites on the Internet. It was first introduced in 1997 as a means to block spam email from known malicious IP addresses .
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]
Used for loopback addresses to the local host [1] 169.254.0.0/16 169.254.0.0–169.254.255.255 65 536: Subnet Used for link-local addresses [5] between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server 172.16.0.0/12 172.16.0.0–172.31.255.255 1 048 576: Private ...
A DNS query of a domain or IP address taken from a URI can be sent in the form of spamdomain.example.multi.surbl.org or 4.3.2.1.multi.surbl.org. The multi DNS zone return records contain codes that indicate which list contains the queried for domain or IP address. Many spam filters support use of SURBL.
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 ...
Specific address range(s) used by imgur.com Image hosting: Technical issue with content lock system EE: October 2013: 22 November 2013 (Technical problem resolved) WordPress.com: Several servers of wordpress.com Blog hosting: Mistake ISP(s) [36] 26 November 2013: 5 December 2013: Imgur: imgur.com Image hosting: Technical implementation [37] Sky ...
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.
Reverse DNS queries are used to map IP addresses to domain names. They are PTR queries for subdomains of in-addr.arpa (for IPv4 addresses) [ 3 ] and ip6.arpa (for IPv6 addresses). [ 4 ] For example, to find the domain name associated with the IP address 203.0.113.22, one would send a PTR query for 22.133.0.203.in-addr.arpa .