in contrast to the possibly expected response of the MX record attached to *.example.com. Example usages The following example is from section 2.2.1 and is useful in clarifying how wildcards work. Say there is a DNS zone with the following resource records: $ORIGIN example. example. 3600 IN SOA <SOA RDATA> example. 3600 NS ns.example.com. example. 3600 NS ns.example.net. *.example. 3600 TXT "this is a wildcard" *.example. 3600 MX 10 host1.example. sub.*.example. 3600 TXT "this is not a wildcard" host1.example. 3600 A 192.0.2.1 _ssh._tcp.host1.example. 3600 SRV <SRV RDATA> _ssh._tcp.host2.example. 3600 SRV <SRV RDATA> subdel.example. 3600 NS ns.example.com. subdel.example. 3600 NS ns.example.net. A look at the domain names in a tree structure is helpful: example ├─ * │ └─ sub ├─ host1 │ └─ _tcp │ └─ _ssh ├─ host2 │ └─ _tcp │ └─ _ssh └─ subdel The following responses would be synthesized from one of the wildcards in the zone: The following responses would not be synthesized from any of the wildcards in the zone: The final example highlights one common misconception about wildcards. A wildcard "blocks itself" in the sense that a wildcard does not match its own subdomains. That is, *.example. does not match all names in the example. zone; it fails to match the names below *.example.. To cover names under *.example., another wildcard domain name is needed—*.*.example.—which covers all but its own subdomains. In practice To quote from , many DNS implementations diverge, in different ways, from the original definition of wildcards. Some of the variations include: With djbdns, in addition to checking for wildcards at the current level, the server checks for wildcards in all enclosing superdomains, all of the way up to the root. In the examples listed above, the query for _telnet._tcp.host1.example for an MX record would match a wildcard despite the domain _tcp.host1.example existing. Microsoft's DNS server (if configured to do so) and MaraDNS (by default) have wildcards also match all requests for empty resource record sets; i.e., domain names for which there are no records of the desired type. In the examples listed above, the query for sub.*.example for an MX record would match *.example, despite sub.*.example explicitly existing with only a TXT Record. Registrants Wildcard domains are widely used by blogging websites that allow users to create sub-domains upon demand; e.g., sites such as WordPress or Blogspot. Another popular use is by Free Dynamic DNS websites that allow users to