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When you requested explicit A records for three subdomains (sub1.example.com, sub2.example.com, sub3.example.com) but received a wildcard record (*.example.com), your host essentially implemented this DNS configuration:

; Zone file snippet
example.com.    IN  A      192.0.2.1
*.example.com.  IN  A      192.0.2.1

While functionally equivalent for your stated needs, this approach creates several technical considerations.

1. Phishing Vulnerabilities:
Attackers could register login.example.com or admin.example.com and host phishing pages that appear legitimate.

2. Cookie Scope Issues:
Modern browsers implement same-site cookies, but wildcards can still cause problems with:

Set-Cookie: session=abc123; Domain=.example.com; Path=/; Secure

Search engines may index multiple variations of your content under different subdomains:

• random123.example.com/about
• foo.example.com/about

This can trigger Google's duplicate content penalties despite canonical tags.

1. Debugging Challenges:
Wildcards make it harder to diagnose DNS-related issues in development environments:

# Troubleshooting becomes ambiguous when
curl -v http://test.example.com
# and
curl -v http://dev.example.com 
# resolve identically

2. Certificate Complications:
Wildcard SSL certificates require careful handling in CI/CD pipelines:

# Let's Encrypt wildcard cert example
certbot certonly \
  --manual \
  --preferred-challenges=dns \
  -d *.example.com \
  -d example.com

Request your host replace the wildcard with explicit records:

; Correct zone file implementation
example.com.    IN  A      192.0.2.1
sub1.example.com. IN A     192.0.2.1
sub2.example.com. IN A     192.0.2.1
sub3.example.com. IN A     192.0.2.1

Wildcards become appropriate when:

• Running multi-tenant SaaS platforms
• Developing dynamic staging environments
• Implementing domain-based routing for microservices

# Kubernetes Ingress example using wildcards
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: wildcard-ingress
spec:
  rules:
  - host: "*.example.com"
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: main-service
            port:
              number: 80

---

When your hosting provider implements a wildcard DNS record (*.yourdomain.tld) instead of specific A records as requested, it creates both technical and security considerations that developers should evaluate carefully.

Here's what typically happens in DNS configuration:

# What you requested (specific A records)
sub1.yourdomain.tld.  IN  A  192.0.2.1
sub2.yourdomain.tld.  IN  A  192.0.2.1
sub3.yourdomain.tld.  IN  A  192.0.2.1

# What you got (wildcard record)
*.yourdomain.tld.     IN  A  192.0.2.1

The wildcard approach introduces several security considerations:

• Potential for phishing attacks using arbitrary subdomains
• Cookie scope vulnerabilities (domain=.yourdomain.tld)
• Unexpected CORS behavior
• SSL certificate complications when using wildcard certs

Search engines may index random subdomains created by third parties, potentially leading to:

• Duplicate content issues
• Negative SEO attacks
• Brand reputation damage from malicious subdomains

For most production environments, explicit DNS records are preferable. Here's how to implement proper controls:

# Recommended approach (Nginx example)
server {
    listen 80;
    server_name sub1.yourdomain.tld sub2.yourdomain.tld sub3.yourdomain.tld;
    
    # Block all other subdomains
    if ($host !~* ^(sub1|sub2|sub3)\.yourdomain\.tld$) {
        return 444;
    }
    
    # Your normal configuration
    ...
}

Wildcard DNS can be appropriate for:

• Development/staging environments
• SaaS platforms with customer-specific subdomains
• Legacy systems requiring dynamic subdomains

Use DNS lookup tools to verify your configuration:

# Command line verification
dig +short randomsub.yourdomain.tld
dig +short sub1.yourdomain.tld

For strict enforcement, consider implementing these measures:

# Web server configuration (Apache example)
<VirtualHost *:80>
    ServerName yourdomain.tld
    ServerAlias *.yourdomain.tld
    RewriteEngine On
    RewriteCond %{HTTP_HOST} !^(sub1|sub2|sub3)\.yourdomain\.tld$
    RewriteRule ^ - [F]
</VirtualHost>