Articles
The history and evolution of networking technology: Ethernet, WiFi, and VPNs.
Network Troubleshooting: A Step-by-Step Diagnostic Method
When the network breaks, work in a logical order. Learn how to use ping, traceroute, DNS lookups and port checks to isolate a problem, and what each tool actually reveals.
How DNS Works: A Practical Guide to Domain Name Resolution
Understand how DNS turns a domain name into an IP address, the difference between recursive and authoritative servers, how caching and TTL work, and how to diagnose a resolution problem with a lookup tool.
Port Forwarding vs Port Scan: What Is the Real Difference?
Opening a port on your router is not the same as testing whether it is reachable. Learn the difference between port forwarding and port scanning, why people confuse them, and how to verify that a forwarding actually works.
IPv4 vs IPv6: Address Exhaustion, NAT and How to Diagnose Both
Two versions of the IP protocol run in parallel today. This guide explains how their addresses differ, why IPv4 ran out, what NAT does about it, and how to diagnose both on your network.
How a Speed Test Works: Download, Upload and Why Results Vary
The number from a speed test is the product of a short measurement against a remote server, not a fixed property of your connection. This guide explains what it measures, why it fluctuates, and how to get a reliable result.
SSL/TLS Certificates Explained: Trust Chains and the Most Common Errors
Certificates are what turn the padlock icon from a warning into a reassurance. This guide explains the chain of trust, how to verify a certificate, and what the common HTTPS errors actually mean.
WHOIS Explained: What a Domain Lookup Reveals
A WHOIS lookup shows the public record behind a domain: registrar, dates, nameservers and status. Learn what it reveals and what privacy often hides.
DNS Propagation Explained: Why Your DNS Change Takes Time
DNS changes do not appear instantly everywhere. Learn how TTL and caching servers control propagation, and how to check a change from multiple resolvers.
Subnetting Explained: How IP Subnet Masks Divide a Network
Learn how a subnet mask splits an IP network into smaller, manageable subnets - and how CIDR notation, host counts and supernetting all fit together.
Public vs Private IP Addresses: What Your IP Reveals and Why It Matters
Every device on a network has an IP, but only one kind is visible to the world. Understanding public versus private addressing explains what your IP reveals, what it hides, and why it changes.
How to Read a Traceroute: Every Hop, Every Asterisk, and When a Route Is Abnormal
Traceroute shows the path your packets take through the internet. Reading each hop - the latency, the asterisks, the private address - turns a route into a real diagnosis of where a problem lives.
How to Read a Port Scan: Open, Closed and Filtered Ports Explained
A port scan returns a wall of open, closed and filtered ports. Knowing what each state actually means turns a raw list into a real answer about what is exposed and what is safe.
DNS Record Types Explained: A, AAAA, CNAME, MX, TXT, NS and PTR
DNS is not one lookup but many, distinguished by record type. Knowing what each type answers turns 'the domain doesn't work' into a two-minute diagnosis - and explains half of what mail and verification tools do.
The Four HTTP Security Headers Every Site Should Send
HSTS, Content-Security-Policy, X-Frame-Options and X-Content-Type-Options cost an afternoon to deploy and quietly prevent whole classes of attacks. Here is what each one does and how to adopt them without breaking your site.
Blacklists (DNSBL): Why Your IP Gets Listed and How to Get Off
Mail servers check every sender against public blocklists. A single listing can silently drop your emails - here is how the system works, why innocent IPs end up on it, and what actually gets you delisted.
Ping vs Traceroute: Which One Answers Your Question?
Both tools test reachability, but they answer two different questions. Knowing which one to reach for turns a vague 'the site is slow' into a precise diagnosis in seconds.
Why These Tools Exist: Reading Results, Judging Warnings, and When You Actually Need a VPN
What each diagnostic tool is actually for, how to read a result without over- or under-reacting, concrete open-port risk examples, and when exposure genuinely calls for a VPN or firewall change - versus when it's normal.
The Rise of the VPN: From Dial-Up Tunnels to WireGuard and Zero Trust
How VPNs evolved from a niche way to reach the corporate LAN into the default way anyone protects traffic on an untrusted network - and what each generation of protocol actually changed.
The Genesis of WiFi: From 2 Mbps to Multi-Gigabit, Generation by Generation
How WiFi went from a slow, unreliable 1997 curiosity to the multi-gigabit, multi-device backbone of every home and office network today.
From LAN to the Internet: Token Ring, Ethernet, and the Protocols That Won
How local networks went from proprietary token-passing rings to the switched Ethernet and TCP/IP stack that now underpins the entire Internet.
My IP Check
Your public IP address and network location, detected automatically.
Loads automatically when you open NetChecks — no input needed. Use the Refresh button to re-check after switching networks or reconnecting your VPN.
Your browser
All-in-One Scan
Runs every relevant check against one IP or hostname in a single pass: DNS, whois, ping, traceroute, a well-known-ports scan (1-1024), HTTP headers and the SSL certificate.
Enter a domain or IP address and run it to check DNS, whois, ping, traceroute, common ports, HTTP headers, and the SSL certificate all at once.
Most checks run in parallel - typically finishes in about 30 seconds, longer if the target is slow or unreachable.
The port scan step only runs once the consent checkbox above is checked - every other check runs regardless.
Ping
Send ICMP echo requests to a host to check reachability and latency.
Enter a hostname or IP address and press Ping to send ICMP echo requests and measure round-trip latency.
Learn more about Ping
What it is
Ping sends ICMP Echo Request packets to a host and measures how long it takes for ICMP Echo Reply packets to come back. It is the most basic network connectivity test there is: it answers exactly one question, "is this machine reachable, and how quickly?" The ICMP protocol (RFC 792) was designed back in 1981 specifically to carry control and diagnostic messages over IP networks, outside of any application traffic - Ping is its best-known and most universally available implementation, present on virtually every operating system and network device since their earliest versions.
How it works
Every ICMP packet carries a TTL (Time To Live) field decremented by one at each router it crosses; if it hits zero before reaching the target, the packet is dropped and an error is sent back to the sender. The round-trip time (RTT) measured in milliseconds reflects the cumulative network latency over the entire round trip, not just the last leg near the target - a point that is often misunderstood, since slow ping results can have their root cause anywhere along the path, not necessarily near the server being tested. A ping typically sends several packets in a row rather than just one, which lets you tell a one-off latency spike apart from a recurring problem and calculate a packet loss rate over the sample.
Reading the results
A stable, low RTT - a few milliseconds on a local network, 10 to 50 ms for a destination within the same country, and noticeably more for an intercontinental link - indicates a healthy connection. Even a small amount of packet loss (above 1-2%) is particularly damaging for latency-sensitive uses like VoIP or interactive remote sessions, where every dropped packet shows up as a glitch or audible cutout. Highly variable latency from one packet to the next (jitter) is often more of a problem for these same use cases than latency that is high but perfectly stable. "Request timed out" means no reply arrived within the allotted time - the host could genuinely be down, a firewall could be silently blocking ICMP, or a route could be broken somewhere along the path; "Destination unreachable" is different and more informative: an intermediate router explicitly sent back a message saying it could not forward the packet, which helps narrow down where the problem actually sits.
Common mistakes
The most common misreading is concluding a host is "down" the moment a ping fails, when in fact a great many servers and devices - especially behind a properly hardened firewall, or hosted with major cloud providers - deliberately block inbound ICMP as a matter of policy while being fully operational and reachable on their actual services (HTTP, a database, and so on). A missing ping reply is therefore only meaningful evidence of downtime when combined with other signals, such as the application itself also failing to respond. Conversely, a successful ping is no guarantee whatsoever that the application service hosted on that machine is working correctly - these are two entirely independent layers of the network stack.
When to use it
The first thing to check before escalating a ticket: does the machine respond at all, before digging any further? Confirming connectivity after a firewall rule or routing table change, to make sure the change did not break access. Establishing a baseline latency measurement before a VoIP rollout or a carrier link failover, so there is an objective point of comparison if call quality complaints come in later. A lightweight, low-overhead periodic health check for an MSP monitoring several client sites in parallel, always as a complement to - never a replacement for - deeper application-level monitoring.
Traceroute
Trace the network path (hop by hop) to a destination host.
Enter a hostname or IP address and run it to see every network hop between this server and the destination, with latency per hop.
DNS Lookup (Nslookup)
Query DNS records: A, AAAA, MX, TXT, NS, CNAME, SOA, PTR, SRV, CAA.
Enter a domain, choose a record type (A, AAAA, MX, TXT, NS, CNAME, SOA, PTR, SRV, or CAA), then look it up.
Whois
Look up registration information for a domain or IP address.
Enter a domain or IP address to look up its registration details — registrar, owner organization, and important dates.
Blacklist Check
Check whether an IP address or domain is listed on public spam/abuse blocklists (DNSBL).
Enter an IPv4 address or domain and run it to check 7 public DNSBL/RBL blocklists at once - each shows as listed, not listed, or check failed.
TCP Port Scan
Check whether TCP ports are open on a host or IP: common ports, a custom list, or the full 1-65535 range.
Enter a host or IP, pick common ports, a custom list, or the full range, then scan to see which TCP ports respond.
A full range scan can take up to ~100 seconds. Large scans (more than 100 ports, including custom ranges/lists) are limited to 1 per minute per visitor.
Open ports (0)
HTTP Header Inspector
Fetch the HTTP response status and headers for a URL.
Enter a URL to fetch its HTTP response status code and every response header the server sends back.
SSL / TLS Certificate Checker
Inspect a host's TLS certificate: issuer, validity dates, and days remaining.
Enter a hostname to inspect its TLS certificate — issuer, validity dates, and days remaining before it expires.
Geo-IP Lookup
Look up the geographic location and network info for an IP address. Leave empty to look up your own public IP.
Enter any IP address, or leave it empty to look up your own, to see its approximate location and network/ISP info.
Subnet / CIDR Calculator
Computed entirely in your browser — no data sent to the server.
Enter an IP address and CIDR prefix (e.g. 192.168.1.0/24) to instantly compute the network range, broadcast address, and usable host count.
Speed Test
Basic download/upload throughput test against this server (accuracy depends on the server's own uplink).
Press Start to measure download and upload throughput against this server. Accuracy depends on this server's own connection.
Country Code Dictionary
ISO 3166-1 alpha-2 country codes — searched entirely in your browser.
Search or browse the list of ISO 3166-1 alpha-2 country codes, looked up entirely in your browser.
| Country | ISO Code |
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Phone Dialing Code Dictionary
International calling codes by country — searched entirely in your browser.
Search or browse international calling codes by country, looked up entirely in your browser.
| Country | Dial Code |
|---|
World Clock
Pick a time zone to see the current time — drag the globe to spin it.
Pick a time zone from the list, or drag the globe, to see the current time there.
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Drag to rotate the globe.
French Mobile Network Status
Mobile antenna sites down or under maintenance in France, by operator (Orange, Free, SFR, Bouygues Telecom), from ARCEP's public data. Snapshot updated once a day by ARCEP - not a minute-by-minute feed.
Browse mobile antenna and fibre outage data by French operator — no input needed, updated automatically from ARCEP's public data.
Most affected departments
Number of sites currently down or under maintenance, by department. Click an operator above to filter.
Data: Arcep — Sites indisponibles · Official network status map
Fixed Network (Fibre)
Fibre (FTTH) network quality by operator: reported-outage rate and connection-failure rate, from ARCEP's public data. Monthly indicators, 6-month rolling average - not a live feed like the mobile section.
By operator (parent group)
Averages over the last 6 available months, per infrastructure-operator parent group.