上一片里，💻小电脑学会了用命令行和电脑“说话”。可它想给远方的电脑发消息，先得找到对方。网络世界没有街道，门牌号就是 IP 地址。Last leaf, 💻 Little Computer learned to talk to its own machine. But to message a far-away computer, it must find that machine first. The network has no streets — its door numbers are IP addresses.
第 1 步：地址就是门牌号Step 1: An address is a door number
没有街道的世界里，地址长什么样？In a world with no streets, what does an address look like?
IP 地址就是门牌号。小电脑背起数据包，标签写着 192.168.1.3，就送到 3 号门。点可不能省：192.168.12.3 和 192.168.1.23 是两家。An IP address is a door number. Little Computer picks up a packet labelled 192.168.1.3 and carries it to door 3. Mind every dot: 192.168.12.3 and 192.168.1.23 are two different doors.
四段数字里，哪段是“街”，哪段是“门”？Of the four numbers, which ones name the “street”, and which the “door”?
第 2 步：四段数字，每段 0 到 255Step 2: Four numbers, each 0 to 255
IPv4 地址有 4 段，每段 0 到 255。前三段是“哪条街”（网络部分），最后一段是“几号门”（主机部分）。右下角还藏着下一代门牌：IPv6。An IPv4 address has 4 parts, each from 0 to 255. The first three name the street (network part); the last names the door (host part). Bottom-right hides the next-generation number: IPv6.
家里的地址和全网的地址，是一回事吗？Is the address at home the same as the one on the whole internet?
第 3 步：家里用私网，出门用公网Step 3: Private addresses at home, public ones outside
家里三台设备住内网（192.168.1.x），出门共用一个公网地址 203.0.113.7。IPv4 只有约 43 亿个，不够分了——更长的 IPv6 来接班。Three home devices live on private addresses (192.168.1.x) and go out under one public address, 203.0.113.7. IPv4 holds only about 4.3 billion numbers — not enough to share. The longer IPv6 takes over.
先在体检台改改地址，看它合不合规矩。再当快递员：合规的送到门，假地址退回。First tweak an address in the checker and see if it follows the rules. Then be the courier: deliver valid ones to the door, send fake ones back.
一句话记住它：IP 地址 = 网络世界的门牌号，数据包靠它找门。Remember it in one line: an IP address is the network world's door number — packets find doors with it.
IPv4 四段点分，每段 0 到 255，点不能省IPv4 is four dot-separated numbers, each 0–255 — mind every dot内网地址家里用，出门共用一个公网地址Private addresses serve the home; outside, all share one public address地址不够分了，更长的 IPv6 来接班The numbers ran short, so the longer IPv6 takes over
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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