Understand the result. Choose the next check.
Practical network troubleshooting guides for all tools: DNS, IP, TLS, email, HTTP, subnetting and monitoring, with examples and next steps.
Network
Why Ping fails when a website still opens
Separate ICMP reachability from HTTPS availability before treating packet loss as an outage.
Read guide →How to read Traceroute hops, timeouts and latency
Read Traceroute results without mistaking a silent router for an outage. Compare hop timing, destination responses and IPv4 or IPv6 paths.
Read guide →TCP port checker: open, refused or timed out?
Understand TCP port-check results, separate reachability from application health, and diagnose firewall or listener problems one step at a time.
Read guide →DNS & Domain
Why DNS resolvers return different answers
Compare DNS records while accounting for cache age, traffic distribution and resolver policies.
Read guide →DNS lookup guide: A, AAAA, CNAME, MX, NS and TXT
Choose the right DNS record type, interpret missing answers and TTLs, and verify website or email changes with focused follow-up checks.
Read guide →Reverse DNS lookup: PTR records and forward checks
Find the hostname published for an IP address, understand missing PTR records, and check forward and reverse DNS together for mail troubleshooting.
Read guide →WHOIS and RDAP: read domain and IP registration data
Interpret registrar, registration dates and domain status fields without confusing redacted data, DNS hosting or website availability.
Read guide →DNSSEC and SERVFAIL: investigate DNS resolution failures
Separate resolver failures, unsigned DNS and validation problems before changing nameservers or registrar DS records.
Read guide →Web & TLS
Understanding certificate-chain verification errors
Read expiry, hostname coverage and certificate-chain findings as separate pieces of evidence.
Read guide →Security headers: review CSP, HSTS and browser policies
Interpret missing security headers in context, inspect policy values, and plan safe follow-up checks instead of treating a score as a security audit.
Read guide →HTTP status codes: diagnose website response problems
Interpret HTTP responses, separate web errors from DNS or TLS failures, and compare IPv4 and IPv6 without confusing a response with a working application.
Read guide →HTTP headers: inspect caching and response metadata
Read Content-Type, Cache-Control, Location and other response headers, compare like-for-like requests, and identify the next check for stale or unexpected content.
Read guide →Redirect checker: find chains and HTTP/HTTPS loops
Trace server redirects, recognize loops and unnecessary hops, and verify a stable final URL after changing a proxy, domain or HTTPS configuration.
Read guide →CSR decoder: check subject, SANs and public-key details
Inspect a certificate signing request before issuance, verify the requested names and public key, and understand what decoding cannot validate.
Read guide →Certificate decoder: read PEM and DER certificate fields
Inspect certificate subject, issuer, validity, SANs and extensions, and distinguish a decoded certificate file from a trusted live HTTPS connection.
Read guide →OpenSSL made simple: create a CSR and convert PEM or PFX
Choose the right certificate files, request domain and IP SANs, and generate OpenSSL commands without uploading private keys.
Read guide →Email Security
How to check MX, SPF, DKIM and DMARC records
Inspect email DNS publication without confusing a found record with successful message authentication.
Read guide →IP blacklist check: investigate email delivery problems
Check the correct sending IPv4 address, distinguish listed from unavailable results, and investigate reputation without assuming a clean result guarantees delivery.
Read guide →IP & IPv6
AAAA record exists, but HTTPS over IPv6 fails
Separate IPv6 DNS publication, connectivity and TLS findings when diagnosing a dual-stack website.
Read guide →IP lookup: location, network provider and ASN explained
Understand what an IP lookup can tell you about a public address, why location can differ from your device, and when to use registration data.
Read guide →Calculators
Plan different-sized IPv4 subnets with VLSM
Allocate a parent network to different host requirements and check boundaries before exporting the plan.
Read guide →Subnet calculator: CIDR, masks and IPv4/IPv6 ranges
Understand network addresses, host ranges and prefix lengths, with a worked IPv4 example and the key differences for IPv6.
Read guide →Operations
Troubleshooting
Website not reachable: a step-by-step troubleshooting guide
Follow DNS, connection, TLS and HTTP evidence to locate a website problem and choose the next useful test.
Read guide →Move a website safely: DNS, TLS, data and rollback
Plan a hosting migration with verified backups, a single writer, destination checks and evidence-based DNS cutover.
Read guide →