Wildcard DNS

Wildcard DNS uses an asterisk ( * ) as the host record to point all subdomains to a single IP address (the record value). For example, if you set a wildcard record *.example.com for the domain example.com, all of its subdomains, such as a.example.com and b.example.com, will resolve to the same IP address as *.example.com.

Scenarios

You can configure wildcard DNS to redirect an entire domain, specify a single entry point for subdomains, or resolve to a fallback service page.

Supported record types

A record, AAAA record, CNAME record, NS record, MX record, TXT record, CAA record, explicit URL/implicit URL, SVCB record, and HTTPS record.

Procedure

On the Alibaba Cloud DNS – Public Zone page, click the target domain to go to the Resolution Settings page.
On the Settings page, click the Add Record button.

In the Add Record panel, set record type to A - Maps a domain name to an IPv4 address, host record to * (wildcard, with the domain suffix .cloud-example.net), Resolution Request Source to default line, TTL to 10 minutes, and Record Value Load Balancing Policy to round-robin. Then, in the Record Value Set area, enter the target IPv4 address and click + Add Item.
Verify the record.

Run the dig a.example.net command and check that the returned DNS record matches the record value you added.

Wildcard DNS query rules

A DNS query first attempts to match a line, and then a domain name.
On the same line, an exact domain match takes precedence over a wildcard match. The DNS resolver uses a wildcard record only if no other records match the query.
If a wildcard query matches a smart line but an exact-match query matches the default line, the exact-match record on the default line is used for resolution.

Example 1

Host record	Type	Line	Value
www.example.com	A	default line	1.1.1.1
api.example.com	A	default line	2.2.2.2
*.example.com	A	default line	3.3.3.3

A query for www.example.com → returns 1.1.1.1 (matches the exact A record, not the wildcard record).
A query for api.example.com → returns 2.2.2.2 (matches the exact A record, not the wildcard record).
A query for test.example.com → returns 3.3.3.3 because it finds no exact-match record and falls back to the wildcard record.
A query for the second-level subdomain abc.def.example.com → returns 3.3.3.3 because it finds no exact-match record and falls back to the wildcard record.

Example 2

Wildcard DNS records are configured for example.com on the China Unicom, China Telecom, and China Mobile lines:

Host record	Type	Line	Value
*	A	China Unicom	1.1.x.x
*	A	China Telecom	1.1.x.x
*	A	China Mobile	1.1.x.x
www	A	default line	4.4.x.x

When users on the China Unicom, China Telecom, and China Mobile lines access www.example.com, the domain resolves to 4.4.x.x. Although the query matches a line with a wildcard record, an exact match exists on the default line. Therefore, the resolver returns the record from the default line.

If you want users from China Unicom, China Telecom, and China Mobile to resolve www.example.com to 1.1.XX.XX, you need to add a DNS record with www as the host record for example.com under each of the three ISP lines, as shown below.

Host record	Type	Line	Value
*	A	China Unicom	1.1.x.x
www	A	China Unicom	1.1.x.x
*	A	China Telecom	1.1.x.x
www	A	China Telecom	1.1.x.x
*	A	China Mobile	1.1.x.x
www	A	China Mobile	1.1.x.x
www	A	default line	4.4.x.x

Now, when users on the China Unicom, China Telecom, and China Mobile lines access www.example.com, the domain resolves to 1.1.x.x.