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(Unofficial) Google Refid used by Google NTP servers as time4.google.com For servers on stratum 2 and below, the refid is an encoded form of the upstream time server's IP address. For IPv4, this is simply the 32-bit address; for IPv6, it would be the first 32 bits of the MD5 hash of the source address.
Instead of returning the valid IP address of a requested site (for example, instead of 198.35.26.96 being returned by the DNS when "www.wikipedia.org" is entered into a browser, [2] if this IP were on a block list, the DNS might reply that the domain is unknown or with a different IP address that directs to a site with a page stating that the ...
Google Public DNS is a Domain Name System (DNS) service offered to Internet users worldwide by Google.It functions as a recursive name server.Google Public DNS was announced on December 3, 2009, [1] in an effort described as "making the web faster and more secure."
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 ...
The original list of IPv4 address blocks was published in September 1981. [3] In previous versions of the document, [19] [20] network numbers were 8-bit numbers rather than the 32-bit numbers used in IPv4. At that time, three networks were added that were not listed earlier: 42.rrr.rrr.rrr, 43.rrr.rrr.rrr, and 44.rrr.rrr.rrr.
There is an informal protocol for the addresses returned by DNSBL queries which match. Most DNSBLs return an address in the 127.0.0.0/8 IP loopback network. The address 127.0.0.2 indicates a generic listing. Other addresses in this block may indicate something specific about the listing—that it indicates an open relay, proxy, spammer-owned ...
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.
For example, to do a reverse lookup of the IP address 8.8.4.4 the PTR record for the domain name 4.4.8.8.in-addr.arpa would be looked up, and found to point to dns.google. If the A record for dns.google in turn pointed back to 8.8.4.4 then it would be said to be forward-confirmed.