Understand the result. Choose the next check.
Practical guides to network, DNS, SSL, email, IPv6 and subnet troubleshooting, with worked examples and related tools.
Why Ping fails when a website still opens
Separate ICMP reachability from HTTPS availability before treating packet loss as an outage.
Why DNS resolvers return different answers
Compare DNS records while accounting for cache age, traffic distribution and resolver policies.
Understanding certificate-chain verification errors
Read expiry, hostname coverage and certificate-chain findings as separate pieces of evidence.
How to check MX, SPF, DKIM and DMARC records
Inspect email DNS publication without confusing a found record with successful message authentication.
AAAA record exists, but HTTPS over IPv6 fails
Separate IPv6 DNS publication, connectivity and TLS findings when diagnosing a dual-stack website.
Plan different-sized IPv4 subnets with VLSM
Allocate a parent network to different host requirements and check boundaries before exporting the plan.