Linux Networking: DNS, HTTP, and TLS Testing

dig +short example.com A

# Fetch an A record in short output format.

dig +short example.com MX

# Fetch MX records in short format.

dig +trace example.com

# Follow delegation from root to authoritative answers.

dig @1.1.1.1 example.com

# Send a DNS query to a chosen DNS server.

host example.com

# Look up DNS records with the host command.

nslookup example.com 8.8.8.8

# Interactive or one-shot DNS lookup.

resolvectl status

# Inspect current DNS servers and search domains.

resolvectl query example.com

# Resolve a domain using resolvectl.

getent hosts example.com

# Query host resolution through glibc NSS.

cat /etc/resolv.conf

# Show the resolver configuration file.

curl -I https://example.com

# Make a HEAD request to inspect headers.

curl -v https://example.com

# Display request and response details.

curl --resolve example.com:443:203.0.113.10 https://example.com

# Pin a host:port to a chosen IP address.

curl --interface eth0 https://example.com

# Use a specific local interface for outbound traffic.

curl -x http://proxy.example.com:3128 https://example.com

# Send an HTTP request through a proxy.

openssl s_client -connect example.com:443 -servername example.com

# Open a TLS session and print certificate details.

openssl x509 -in cert.pem -noout -dates

# Print notBefore and notAfter fields from a certificate file.

wget --spider -S https://example.com

# Check whether a URL is reachable without downloading content.