Errors with a WAO-Error code of 21xx indicate that wao.io could not resolve
the domain name of the configured origin server into an IP address
via the Domain Name System (DNS).

Command line tools like host or dig may help you narrow down the problem:

$ host example.prg
Host example.prg not found: 3(NXDOMAIN)

2100 - "DNSResolveError"

wao.io could not resolve the origin's domain name.

First, you may want to check that you haven't mistyped the domain name
in the WAO Basic Setup of your site.

If your DNS configuration changed recently, the new records may not have been
propagated yet to all intermediate systems and caches. Setting a shorter
time to live (TTL) can help here to reduce the time needed for world-wide distribution.

Another reason for WAO error 2100 may simply be a misconfiguration on your
origin's DNS server.

2101 - "DNSResolveTimeout"

wao.io did not get a DNS response for the origin's domain name.

A common reason here is that the DNS server of the origin is not accessible because
the service is down or a firewall or another security system in front of the
DNS server is preventing wao.io from reaching it.

It is also possible that the DNS server is generally reachable but did not respond
in time, perhaps due to temporary high load or network errors.

2102 - "DestinationNotAllowed"

The origin's domain name was resolved into an IP address that is on wao.io's
black list. Connections to such addresses are forbidden.
Does your domain name resolve into an address of a private IP range?

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