TCP vs UDP: How They Work and When to Use Each
A practical comparison of reliability, latency, and overhead in the internet's two core transport protocols.
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ネットワークとインターネット基盤を分かりやすく解説する実践的なガイドです。
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Protocols, routing, addressing, and the infrastructure that powers the internet.
What Is a Firewall and How Does It Work?
From packet filtering to stateful inspection and NGFWs: a practical model of network perimeter protection.
How to Check If an IP Is Blacklisted and Get Delisted
A practical workflow for DNSBL checks, root-cause analysis, and responsible delisting requests.
What Is a Proxy Server and When Should You Use One?
How proxies relay traffic, which types exist, and how a proxy differs from a VPN.
What Is Port Forwarding and How Does It Work?
How NAT sends inbound traffic to a LAN device and which security trade-offs that creates.
Router vs Switch: What Is the Difference?
A router connects networks with IP; a switch connects devices inside a LAN with MAC addresses.
What Is ICMP?
Why ICMP matters for ping, traceroute, error reporting, and healthy IP networking.
What Is a Subnet Mask and How Do You Read It?
How a subnet mask splits network and host bits, what CIDR means, and how ranges are calculated.
What Is a MAC Address?
The role of hardware identifiers on a LAN, how they differ from IPs, and why randomization exists.
The dig Command: DNS Troubleshooting Without Guesswork
How to query specific resolvers, read response sections, and trace DNS delegation.
How SSL/TLS Protects Internet Traffic
Encryption, server authentication, data integrity, and the role of TLS 1.2 and 1.3.
What Is Ping and How Do You Read the Result?
How ICMP Echo measures reachability and RTT, why packets disappear, and when ping can mislead.
Public vs Private IP Addresses
How public and local addresses differ, how NAT works, and what CGNAT and IPv6 change.
What Is an IP Address and How Does It Work?
A clear guide to network addressing, routing, IPv4, IPv6, and public addresses.
Traceroute and MTR: Watching the Packet Path
Traceroute takes a route snapshot; MTR adds latency and loss statistics over time.
How to Use MTR to Find Packet Loss and Latency
A practical way to read hop-by-hop statistics without mistaking ICMP rate limiting for real loss.
What Is DNS and How Does It Work?
How domain names become IP addresses, where caching happens, and why record types matter.