DNS for Dummies: Part 2

A recursive resolver handles the heavy lifting in the DNS process. It:

• Acts on behalf of the stub resolver to locate the requested IP address.
• Queries multiple DNS servers (root, TLD, authoritative).
• Caches responses to speed up subsequent lookups.

Example: Google’s 8.8.8.8 or your ISP’s DNS server.

An authoritative server holds the definitive information about a domain.

• Stores DNS records for domains it manages.
• Responds with the appropriate IP address or relevant record for a query.

Example: Cloudflare’s authoritative server for suhesh.com.np knows the exact IP (172.67.222.11).

If there is no entry for the domain in the hosts file then your PC checks it’s operation system’s local DNS cache for a cached record to avoid querying a server.

Sites are cached when you visit the site for a certain time(TTL) so that querying the server is not required.

If there is no entry for the domain locally cached in the PC as well then the DNS cache of your network gateway(router) is searched for a cached record to avoid querying a server.

Sites are cached when you visit the site for a certain time(TTL) so that querying the server is not required.

Public DNS servers are reliable, fast, and often provide added features.

Examples of Popular Public DNS Servers:

Use Case:

You switch to Cloudflare’s 1.1.1.1 to improve website load speed and ensure your DNS queries aren’t logged by the ISP.

Changing DNS Settings (Linux):

sudo nmcli dev show | grep 'IP4.DNS' # Show current DNS
sudo nano /etc/resolv.conf # Modify DNS

Pros:

• Speed and reliability.
• Advanced features like ad blocking (AdGuard) or better privacy (Cloudflare).

Cons:

• Dependency on external entities.

On-premise DNS servers offer control and security, often used by organizations or enthusiasts.

Corporate Use Case:

Businesses often host DNS servers internally to:

• Ensure faster name resolution within the company’s network.
• Control and monitor employee DNS requests for security purposes.

Pros:

• Full control over DNS records.
• Customization for specific network needs.

Cons:

• Requires technical expertise and maintenance.
• Higher setup costs.

# Installing Pi-Hole
curl -sSL https://install.pi-hole.net | bash

Country code TLDs represent specific countries or territories. They are assigned based on the ISO 3166-1 alpha-2 country codes.

Examples:

• United States: .us
• India: .in
• Nepal: .com.np

Uses of ccTLDs:

• Localization of services and products for specific countries.
• Trust-building among local users (e.g., businesses in Nepal prefer .com.np for local recognition).

Fun Fact:

Some ccTLDs, though country-specific, are widely used globally because of their uniqueness or relevance. For instance:

• .me (Montenegro): Often used for personal blogs or profiles.
• .tv (Tuvalu): Popular among video or streaming services.

These are a subset of gTLDs managed by specific organizations and are restricted to certain purposes.

Examples:

• .gov: Restricted to US government entities.
• .edu: Reserved for accredited educational institutions.
• .mil: Used exclusively by the US military.

An example is .arpa, which is reserved for technical infrastructure purposes, such as reverse DNS lookups.

Description:
The A record maps a domain name to an IPv4 address. It’s the most common record used for name-to-address resolution.

Example:

@   IN  A 192.0.2.1
www IN  A 192.0.2.2

Breakdown:

• @: Represents the root domain (suhesh.com.np in this case).
• www: Resolves the www.suhesh.com.np subdomain to 192.0.2.2.
• Usage: Critical for websites, APIs, or any service running on an IPv4 address.

Description:
The AAAA record is like the A record but maps domain names to IPv6 addresses.

Example:

@   IN  AAAA 2001:0db8::1
www IN  AAAA 2001:0db8::2

Breakdown:

• @: Maps the root domain to 2001:0db8::1.
• Why IPv6? IPv4 has limited addresses; IPv6 expands the pool massively.

Description:
The CNAME record creates an alias, redirecting one domain name to another without associating directly with an IP address.

Example:

www     IN  CNAME suhesh.pages.dev.
suhesh.com.np. IN  CNAME suhesh.pages.dev.

Breakdown:

• www.suhesh.com.np is an alias for suhesh.pages.dev.
• This allows updates to be managed centrally on suhesh.pages.dev.

Description:
The MX record directs email for a domain to a mail server. Priority determines the order mail servers are tried.

Example:

@   IN  MX   10 mail.suhesh.com.np.
@   IN  MX   20 backup-mail.example.com.

Breakdown:

• Priority 10: Mail server mail.suhesh.com.np has the highest priority.
• Priority 20: Backup server backup-mail.example.com.
• Tip: Lower priority number = Higher priority.

Description:
The PTR record is used in reverse DNS. It maps an IP address to a domain name for validation purposes.

Example:

1.2.0.192.in-addr.arpa. IN PTR suhesh.com.np.

Breakdown:

• The IP 192.0.2.1 maps to suhesh.com.np.
• Commonly used for verifying email sender authenticity.

Description:
The SRV record specifies a service’s location, including protocol, port, and priority.

Example:

_service._tcp.suhesh.com.np. IN SRV 10 5 5060 sip.suhesh.com.np.

Breakdown:

• _service: Service name (e.g., _sip for VoIP).
• _tcp: Protocol used.
• 10: Priority (lower is preferred).
• 5: Weight (higher gets more traffic).
• 5060: Port for the service.

Description:
The TXT record stores text data for verification or metadata purposes, such as SPF, DKIM, and site ownership verification.

Example:

@       IN  TXT  "v=spf1 ip4:192.0.2.0/24 ~all"
_dmarc  IN  TXT  "v=DMARC1; p=none; rua=mailto:[email protected]"

Breakdown:

• SPF: Ensures only IPs in 192.0.2.0/24 can send mail.
• DMARC: Policy for email authentication reporting.