Hostname Resolver

Resolve hostnames to IP addresses and perform reverse DNS lookups instantly. Get comprehensive DNS records including A, AAAA, MX, TXT, NS, and CNAME with detailed technical information.

Instant Lookup
Multiple Records
Reverse Lookup
🌐
DNS Resolve
🔄
Reverse PTR
📧
MX Records
⚡
Batch Lookup
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Resolve Hostname or IP Address

Enter a hostname to resolve its IP addresses, or enter an IP address for reverse DNS lookup. Get comprehensive DNS records including A, AAAA, MX, TXT, NS, and CNAME records.

Enter a domain name (e.g., google.com) or hostname to resolve

Quick Examples

Free Hostname Resolver: DNS Lookup & Reverse PTR Checker Online

Resolve hostnames to IP addresses and perform reverse DNS lookups instantly with comprehensive DNS record queries for A, AAAA, MX, TXT, NS, and CNAME records. Professional network diagnostics tool for system administrators, developers, and security researchers.

What Is Hostname Resolution (And Why It Matters)?

Hostname resolution is the process of converting human-readable domain names (like google.com) into machine-readable IP addresses (like 142.250.185.46) that computers use to communicate over networks. This DNS (Domain Name System) translation is fundamental to internet connectivity—every web request, email delivery, and API call depends on accurate hostname resolution according to RFC 1034 (DNS Concepts).

Professional hostname resolution goes beyond simple lookups. Our tool performs comprehensive DNS queries including forward resolution (hostname → IP), reverse DNS lookups (IP → hostname via PTR records), MX record queries for mail server configuration, TXT records for domain verification and security policies (SPF, DKIM, DMARC), NS records for nameserver identification, and CNAME records for alias tracking—providing complete network intelligence in under 1 second.

Why Hostname Resolution Is Critical for Network Operations:

Network Diagnostics & Troubleshooting
  • • Diagnose connectivity issues: Identify DNS misconfigurations causing outages
  • • Verify DNS propagation: Confirm record changes propagated globally
  • • Trace network paths: Map IP addresses to hostnames for security audits
  • • Validate configurations: Ensure mail servers, nameservers configured correctly
Security & Infrastructure Management
  • • Security reconnaissance: Investigate suspicious IP addresses and domains
  • • Email authentication: Verify SPF, DKIM, DMARC records for deliverability
  • • Reverse DNS verification: Confirm server ownership via PTR records
  • • Infrastructure mapping: Document IP ranges and hostname patterns

Real Hostname Resolution Examples

→ Forward DNS Lookup: google.com → 142.250.185.46 Hostname resolves to IPv4 address
← Reverse DNS Lookup: 8.8.8.8 → dns.google IP address resolves to hostname via PTR
📧 MX Record Lookup: gmail.com → gmail-smtp-in.l.google.com Mail server hostname with priority 5
🌐 NS Record Lookup: cloudflare.com → ns1.cloudflare.com Authoritative nameserver hostname

How to Resolve Hostnames in 3 Simple Steps

1
Enter hostname or IP address: Type or paste any hostname (example.com), fully qualified domain name (www.example.com), or IP address (8.8.8.8, 2001:4860:4860::8888). Our tool auto-detects input type and sanitizes URLs by removing http://, www., and trailing paths automatically for RFC 1123 compliant processing.
2
Select lookup mode and options: Choose Forward Lookup (hostname to IP) or Reverse Lookup (IP to hostname via PTR). for forward lookups, customize which DNS record types to query—A (IPv4), AAAA (IPv6), MX (mail servers), TXT (domain verification), NS (nameservers), and CNAME (aliases). Enable all records for comprehensive diagnostics or select specific types for targeted queries.
3
Get instant detailed results: View all DNS records with record counts, query time metrics, and organized sections for each record type. Copy individual records to clipboard, export all results for documentation, or print for reports. Results include IPv4/IPv6 addresses, mail server priorities, TXT record contents, and nameserver details. Use our DNS lookup tool for advanced WHOIS queries.

💡 Pro Tip: Batch Hostname Resolution

Resolve up to 50 hostnames simultaneously for network audits, infrastructure mapping, and bulk DNS verification. Perfect for checking entire server fleets, validating migration lists, or security reconnaissance. Results processed concurrently with 10-host parallelism for maximum speed while respecting DNS server rate limits.

6 DNS Record Types Our Tool Queries

A
A Record (Address Record - IPv4):

Maps hostnames to 32-bit IPv4 addresses defined in RFC 1035. The most fundamental DNS record type—returns IP addresses like 192.168.1.1 that computers use for direct network communication. Multiple A records indicate load balancing or geographic distribution. Essential for web servers, APIs, and any IPv4-accessible service.

AAAA
AAAA Record (IPv6 Address):

Maps hostnames to 128-bit IPv6 addresses (2001:4860:4860::8888) defined in RFC 3596. Critical for modern networks as IPv4 addresses exhaust—IPv6 provides 340 undecillion addresses for future growth. Many major services (Google, Facebook, Netflix) require AAAA records for IPv6 connectivity. Check both A and AAAA for dual-stack configurations.

MX
MX Record (Mail Exchange):

Specifies mail servers responsible for accepting email for a domain with priority values (lower = higher priority) per RFC 5321. Example: gmail.com has MX priority 5 pointing to gmail-smtp-in.l.google.com. Multiple MX records provide redundancy—if primary fails, mail routes to secondary. Essential for email deliverability diagnostics and spam filter configuration.

TXT
TXT Record (Text Record):

Stores arbitrary text data for domain verification, security policies, and configuration metadata per RFC 1464. Common uses: SPF records (v=spf1) for email authentication, DKIM keys for message signing, DMARC policies for phishing protection, domain ownership verification for Google/Microsoft services, and site verification tokens. Critical for email security audits.

NS
NS Record (Nameserver):

Delegates DNS authority for a domain to specific nameservers defined in RFC 1035. Example: cloudflare.com delegates to ns1.cloudflare.com and ns2.cloudflare.com. Changes to NS records affect all domain DNS—crucial for migrations, CDN setups, and DNS provider switches. Verify NS records match registrar configuration to prevent resolution failures.

CNAME
CNAME Record (Canonical Name):

Creates aliases that point one hostname to another canonical name per RFC 1035. Example: www.example.com CNAME → example.com (final A record). Used for subdomain management, CDN configurations (www → cdn.provider.com), and service redirection. CNAME cannot coexist with other record types at same name—use A records for apex domains (@).

8 Real-World Hostname Resolution Scenarios

1. Website Migration DNS Verification

Verify DNS records propagated after migrating to new hosting or CDN. Resolve hostnames to confirm A/AAAA records point to new IP addresses, check CNAME configurations for www redirection, and validate NS records updated to new provider. Reduces migration downtime by catching DNS misconfigurations before going live. Use with DNS propagation checker for global verification.

2. Email Deliverability Troubleshooting

Diagnose email delivery failures by querying MX records to verify mail servers exist, checking TXT records for SPF/DKIM/DMARC configuration, and performing reverse DNS on mail server IPs to confirm PTR records match. 90% of email deliverability issues stem from DNS misconfigurations— resolve MX records to identify missing or incorrect mail exchange servers immediately.

3. Security Reconnaissance and Threat Intelligence

Investigate suspicious domains and IP addresses by performing forward and reverse DNS lookups to map infrastructure. Resolve hostnames to uncover shared hosting (multiple domains on same IP), identify command-and-control servers via PTR records, and trace phishing campaigns through DNS patterns. Combine with IP geolocation for comprehensive threat analysis.

4. Load Balancer and CDN Configuration

Verify load balancer DNS round-robin configurations by querying A records—multiple IPs indicate distribution across servers. Check CDN edge node resolution by resolving hostnames from different geographic locations. Validate CNAME records point to CDN providers (Cloudflare, Fastly, Akamai) correctly. Essential for high-traffic infrastructure audits.

5. Network Inventory and Asset Discovery

Map internal and external network infrastructure by batch resolving hostname lists—resolve 50 hostnames simultaneously to inventory servers, identify naming patterns (web01, db02), and document IP address allocations. Perform reverse DNS on IP ranges to discover forgotten or shadow IT systems. Critical for network security audits and compliance documentation.

6. API and Webhook Endpoint Validation

Verify third-party API hostnames resolve correctly before integration—resolve endpoints to confirm they're active and reachable. Check webhook URLs resolve to expected IP ranges for security validation. Validate SSL certificate common names match resolved hostnames using SSL checker. Prevents integration failures from DNS misconfigurations.

7. VPN and Private Network Diagnostics

Troubleshoot VPN DNS resolution issues by verifying internal hostnames resolve to correct private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). Check split-tunnel DNS configurations route internal queries to private DNS servers. Identify DNS leaks by resolving public domains and verifying queries route through VPN tunnel. Use subnet calculator for private IP range validation.

8. Domain Expiration and Takeover Prevention

Monitor critical domain DNS records to detect unauthorized changes or expiration—resolve hostnames periodically to ensure A/MX/NS records remain consistent. Detect subdomain takeovers by identifying CNAME records pointing to deprovisioned services (Heroku, AWS S3, GitHub Pages). Check NS records to catch domain hijacking attempts. Automate monitoring with scheduled batch resolution for security alerting.

7 DNS Resolution Mistakes That Break Networks

1. Trusting Only A Records (Ignoring IPv6)

Checking only A records misses 40% of modern infrastructure running IPv6. Many services (Google, Facebook, Cloudflare) prefer AAAA records for IPv6 clients. Always query both A and AAAA records for complete network visibility—missing IPv6 addresses causes connectivity failures for dual-stack environments.

2. Not Verifying Reverse DNS (PTR Records)

Mail servers require valid PTR records matching forward DNS—90% of email servers reject messages from IPs without reverse DNS. SMTP servers perform reverse lookups to verify sender authenticity. Configure PTR records for all mail servers and verify with reverse DNS queries to prevent deliverability issues and spam classification.

3. Forgetting DNS Propagation Delays

DNS changes take 24-48 hours to propagate globally due to TTL (Time To Live) caching. Making DNS changes and immediately testing causes false positives—queries return cached old records. Lower TTL to 300 seconds (5 minutes) 24 hours before migrations, make changes, wait for TTL expiration, then verify with hostname resolution from multiple global locations.

4. Mixing CNAME with Other Record Types

CNAME records cannot coexist with A, MX, TXT, or other records at the same hostname per RFC 1034. Setting www as CNAME and adding MX record causes DNS resolution failures—one record overwrites the other unpredictably. Use A/AAAA records at apex (@) and CNAME for subdomains only.

5. Not Monitoring NS Record Changes

Unauthorized NS record changes redirect all domain traffic to attacker nameservers—domain hijacking through DNS. Monitor NS records daily by resolving hostnames and comparing against expected nameservers. Set up alerts for NS record modifications at registrar level to detect takeover attempts within minutes instead of days.

6. Ignoring TXT Record Security Policies

Missing SPF, DKIM, and DMARC TXT records allows email spoofing using your domain—attackers send phishing emails appearing from your address. Query TXT records to verify email authentication policies configured: SPF restricts sending servers, DKIM adds cryptographic signatures, DMARC instructs receivers how to handle failures. Essential for brand protection and email deliverability.

7. Overlooking CNAME Chain Loops

CNAME chains (A → B → C → D) add latency and can create loops (A → B → A) causing infinite resolution. RFC 1034 recommends maximum 8 CNAME redirects—excessive chaining degrades performance by 200-500ms per hop. Resolve CNAME records to identify chain depth and eliminate unnecessary aliases by pointing directly to final canonical hostname.

DNS Resolution Technical Deep Dive

RFC 1123 Hostname Validation

Our tool implements strict RFC 1123 hostname validation: labels (segments between dots) limited to 63 characters, total hostname max 253 characters, labels start/end with alphanumeric characters, hyphens allowed mid-label, and case-insensitive normalization. Rejects invalid formats like double dots (..), trailing hyphens (test-.com), or numeric-only TLDs preventing DNS poisoning vulnerabilities.

DNS Query Optimization with Retry Logic

Implements exponential backoff retry mechanism—initial query uses 5-second timeout, failed queries retry with 100ms * attempt delay (100ms, 200ms), maximum 2 retries. Skips retry for permanent failures (NXDOMAIN, server misbehaving) to avoid unnecessary delays. Concurrent batch processing uses semaphore with 10-host parallelism, preventing DNS server overload while maximizing throughput for infrastructure audits resolving 50 hosts in under 10 seconds.

IPv4 and IPv6 Dual-Stack Support

Full IPv4 (32-bit) and IPv6 (128-bit) address family support per RFC 4291. Queries A records for IPv4 using "ip4" network, AAAA records for IPv6 using "ip6" network, handles IPv4-mapped IPv6 addresses (::ffff:192.0.2.1), and validates both address formats with proper CIDR notation support. Essential for dual-stack environments and modern cloud infrastructure requiring IPv6 connectivity.

Reverse DNS PTR Record Format

PTR records use reverse DNS zones: IPv4 addresses reversed with .in-addr.arpa suffix (8.8.8.8 → 8.8.8.8.in-addr.arpa), IPv6 addresses nibblized (hex digits reversed) with .ip6.arpa suffix (2001:db8::1 → 1.0.0.0...d.b.8.0.1.0.0.2.ip6.arpa). Our tool automatically generates correct PTR domain formats and performs lookups, returning hostnames for IP addresses when PTR records exist—critical for mail server validation and security investigations.

Input Sanitization and Normalization

Automatically cleans user input: strips http:// and https:// protocols, removes www. prefix for consistent apex resolution, trims trailing slashes and paths (/about, /api), converts to lowercase for case-insensitive matching, and validates against injection attacks. Accepts hostnames, FQDNs, IP addresses, and even full URLs—extracts hostname component automatically for seamless user experience without format requirements.

Frequently Asked Questions

What's the difference between forward and reverse DNS lookup?

Forward DNS resolves hostnames to IP addresses (google.com → 142.250.185.46) using A/AAAA records—this is standard DNS resolution. Reverse DNS resolves IP addresses back to hostnames (8.8.8.8 → dns.google) using PTR records stored in reverse zones (in-addr.arpa for IPv4, ip6.arpa for IPv6). Reverse DNS is critical for email server verification, network security investigations, and server ownership validation.

How long does DNS resolution take?

Our tool typically resolves hostnames in under 1 second for cached queries, 2-5 seconds for uncached queries requiring recursive DNS lookups through root servers, TLD servers, and authoritative nameservers. Batch operations resolving 50 hosts complete in 8-12 seconds using 10 concurrent workers. Network latency, DNS server responsiveness, and record types queried affect total resolution time—querying all 6 record types takes longer than A records only.

Why do some hostnames have multiple IP addresses?

Multiple A/AAAA records indicate load balancing, geographic distribution, or redundancy. DNS round-robin returns different IPs in rotating order for traffic distribution across servers. CDNs use geo-DNS to return edge nodes closest to the query origin. High-traffic sites (Google, Facebook) have 20+ IP addresses for global availability. Query hostname resolution multiple times to see different IPs returned—confirms load balancing configuration works correctly.

What are MX record priorities and how do they work?

MX records include priority values (0-65535) where lower numbers = higher priority. Mail servers attempt delivery to lowest priority MX first—if unavailable, retry next priority. Example: Priority 5 (primary), Priority 10 (backup), Priority 20 (fallback). Multiple MX records with same priority provide load balancing. Always configure at least 2 MX records for redundancy—if single mail server fails, emails queue and retry backup servers preventing delivery loss.

Can I resolve private IP addresses and internal hostnames?

Our tool runs client-side in your browser, so it queries your local DNS resolver—can resolve internal hostnames if your DNS server knows them (corporate intranets, VPN environments). Private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are detected and flagged automatically. Reverse DNS for private IPs requires PTR records configured on internal DNS servers. for public internet, private IPs don't resolve via public DNS—only public hostnames and routable IPs work.

How do CNAME records affect resolution?

CNAME records create aliases—www.example.com CNAME → example.com causes DNS resolver to follow chain until finding A/AAAA record. Each CNAME adds 50-100ms latency for additional lookup. Maximum 8 CNAME redirects per RFC 1034—deeper chains fail. CNAME cannot coexist with other record types at same hostname (causes conflicts). Our tool shows full CNAME chain and warns about excessive hops affecting performance. Use A records for apex domains, CNAME for subdomains only.

What TXT records should I check for email security?

Query TXT records for three email authentication mechanisms: SPF (starts with v=spf1) lists authorized mail servers, DKIM (selector._domainkey.domain.com) provides public keys for signature verification, and DMARC (_dmarc.domain.com) sets policies for authentication failures. Our tool displays all TXT records—look for these patterns to audit email security configuration. Missing or misconfigured records enable email spoofing and harm deliverability.

Is hostname resolution data private and secure?

All DNS queries execute server-side using Go's standard library net resolver with no data logging, storage, or tracking. Queries use your server's configured DNS resolvers (typically ISP or public DNS like 8.8.8.8). DNS queries are inherently observable by DNS servers in resolution path—use DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT) for encrypted queries. Our tool provides diagnostic results only—no personal data collected, no cookies set, no query history retained after page close.

Advanced Hostname Resolution Strategies

Automating DNS Monitoring with Scheduled Queries

Set up cron jobs or scheduled tasks to resolve critical hostnames every 15-60 minutes, comparing results against baseline configuration. Alert when A/MX/NS records change unexpectedly—catches domain hijacking, DNS misconfigurations, and infrastructure failures within minutes. Export JSON results for programmatic comparison and integrate with monitoring systems (Nagios, Zabbix, Datadog) for automated incident response.

Geo-Distributed DNS Resolution Testing

Test hostname resolution from multiple geographic locations to verify CDN edge node distribution and geo-DNS configuration. Different regions should resolve to different IP addresses for optimized latency. Use VPN or cloud servers in EU, Asia, Americas to query hostnames—confirms traffic routes to nearest data center. Critical for global applications ensuring worldwide users receive low-latency responses.

Combining DNS with Certificate Validation

Cross-reference resolved IP addresses with SSL certificate common names and SANs (Subject Alternative Names) to detect mismatches indicating man-in-the-middle attacks or misconfigurations. Resolve hostname to IP, connect to IP:443, retrieve certificate, verify CN matches original hostname. Use alongside SSL checker for comprehensive HTTPS validation—ensures encrypted connections reach correct servers.

DNS-Based Infrastructure Mapping

Perform bulk reverse DNS on entire IP ranges (CIDR blocks) to discover all hostnames—maps complete infrastructure topology. Resolve all discovered hostnames back to IPs for bidirectional mapping. Identify naming conventions (prod-web-01, staging-db-02) revealing server purposes. Essential for network documentation, security audits, and decommissioning old assets—find forgotten servers by systematic IP range scanning.

Detecting DNS Cache Poisoning

Query same hostname from multiple DNS resolvers (8.8.8.8, 1.1.1.1, ISP resolver) and compare IP address results—discrepancies indicate cache poisoning attacks redirecting traffic. Verify A record TTL matches authoritative server settings—abnormally low TTLs (< 60 seconds) or high values (> 86400) suggest manipulation. Check DNSSEC validation status if enabled—failed validation confirms tampering. Repeat queries to detect inconsistent responses over time.

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