Submarine Cable Systems · 海底电缆系统商

The companies that build and operate transoceanic fiber: who owns a cable system, how capacity is sold as wavelengths and IRUs, and where the landing stations connect to the rest of the network. 建设和运营跨洋光缆的公司：谁拥有一条海缆系统、容量怎么按波长和 IRU 出售、登陆站接到网络的哪一层。

A submarine cable is an L1 product sold in wavelengths and decades-long IRUs. 海缆是一层产品，按波长和几十年期的 IRU 出售。
Landing stations are where the ocean meets the terrestrial backbone. 登陆站是海洋与陆地骨干相接的地方。
Read with the OTN/ODF lab on this site. 配合本站的 OTN/ODF 光网络实验一起看。

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MPLS Label Switching · MPLS 标签交换 — How an MPLS label switched path is signalled and how packets are forwarded by label instead of by a destination lookup at every hop. Watch the label stack get pushed, swapped and popped hop by hop, including penultimate hop popping. MPLS 的标签交换路径是怎么建立的、报文怎么按标签转发而不用每跳查路由表：逐跳看标签栈的压入、交换、弹出，以及次末跳弹出（PHP）。
SR-TE Segment Routing · SR-TE 段路由 — Segment Routing traffic engineering: the path is carried in the packet as a label stack, so there is no per-hop signalling state to maintain. Compare an SR-TE explicit path against plain IGP shortest path and see which links actually carry the traffic. 段路由流量工程：路径以标签栈的形式写在报文里，中间节点不用维护每条路径的状态。把 SR-TE 显式路径和 IGP 最短路对照着看，流量到底走了哪几条链路。
eBGP · eBGP 跨自治系统路由 — How autonomous systems interconnect with external BGP: session establishment, route advertisement, and how AS_PATH prevents loops between providers. Includes the attribute decision process that picks the best path. 自治系统之间怎么用 eBGP 互通：会话怎么建立、路由怎么通告、AS_PATH 怎么在运营商之间防环，以及选路时属性的比较顺序。
iBGP · iBGP 自治系统内部路由 — Carrying externally learned routes inside an AS: why iBGP does not re-advertise routes between peers, why that forces either a full mesh or a route reflector, and how next-hop-self and the IGP underlay fit together. 外部路由怎么在 AS 内部传递：iBGP 为什么不在邻居之间转发路由、由此为什么必须全互联或者上路由反射器，以及 next-hop-self 和底层 IGP 的配合。
OSPF Link State · OSPF 链路状态路由 — Flood LSAs to build an identical map of the network on every router, then run Dijkstra on it. Step through adjacency states, LSA types, area design and the SPF run that produces the routing table. 泛洪 LSA 让每台路由器拼出同一张全网地图，再各自跑 Dijkstra：邻接状态机、LSA 类型、区域划分，以及算出路由表的那次 SPF。
IS-IS Link State · IS-IS 链路状态路由 — The other link-state IGP, the one carriers actually run: L1/L2 levels instead of areas, TLV-encoded LSPs that extend without a protocol revision, and a topology that rides directly on layer 2. 运营商网络里更常见的那个链路状态协议：用 L1/L2 两级代替区域、用 TLV 编码的 LSP 不改协议就能扩展，而且直接跑在二层上。
EIGRP Distance Vector · EIGRP 距离矢量路由 — DUAL in action: successors and feasible successors are computed before anything breaks, so failover is a table lookup rather than a re-convergence. See exactly when a router has to go active and query its neighbours. DUAL 算法实况：后继和可行后继在故障之前就算好了，切换只是查一次表而不是重新收敛。看清楚什么情况下路由器不得不进入 active 状态去查询邻居。
RIP Distance Vector · RIP 距离矢量原型 — The simplest distance vector protocol, kept here because it is the clearest way to watch the count-to-infinity problem happen — and to see exactly which of split horizon, route poisoning and hold-down timers stops it. 最简单的距离矢量协议。留着它是因为「计数到无穷」在这里看得最清楚，也最容易看出水平分割、毒性逆转、抑制计时器分别挡住了哪一步。
Data Center Spine-Leaf · 数据中心 Spine-Leaf 架构 — How a fat-tree data center fabric is actually dimensioned: oversubscription ratio, ECMP hashing across spines, and what an elephant flow does to a hash-based load spread. 胖树数据中心网络到底怎么算容量：收敛比、跨 spine 的 ECMP 哈希，以及一条大象流会把基于哈希的负载分担压成什么样。
OTN/ODF Optical Network · OTN/ODF 光网络 — How data centers actually interconnect over the physical optical layer: which devices a layer-1 circuit passes through from router to router, how a ROADM decides to add, drop or express a wavelength, and how ring protection survives a fiber cut. IDC 之间在物理光层到底是怎么互联的：一条一层电路从路由器到路由器经过哪些设备、ROADM 怎么决定一个波长是上路、下路还是直通，以及环网保护怎么扛住一次光缆挖断。
IDC Topology · IDC 拓扑 — How a region's data centers are laid out and related: core, aggregation, business, satellite, interconnect, scrubbing, PoP and colocation sites, active-active vs active-standby pairs, fiber distance and RTT computed from real coordinates, order-of-magnitude traffic, and a failover drill — take a DC or a backbone span down and watch who gets isolated, promoted or detoured. Modeled on AWS global regions and China's multi-region layout. 一个 region 里的数据中心怎么布局、怎么相连：核心、汇聚、业务、卫星、三方互联、高防、PoP、托管，双活与主备关系，按真实经纬度算出的光缆距离和往返时延，数量级的流量，以及故障演练——打掉一个机房或一段骨干，看谁被孤立、谁备升主、出口怎么绕行。以 AWS 全球 region 和中国多 region 为蓝本。
Layer 2 Switching · 网络二层交换 — What a switch actually does with a frame: learn the source MAC, look up the destination, flood when it is unknown. Includes ARP resolution and the broadcast domain that ties it all together. 交换机拿到一个帧到底做了什么：学源 MAC、查目的 MAC、查不到就泛洪。顺带把 ARP 解析和广播域这条主线串起来。
STP Spanning Tree · STP 生成树协议 — Redundant links plus a flat layer 2 equals a broadcast storm. STP computes a loop-free tree and blocks the rest: root bridge election, port roles and states, and what a topology change actually costs. 二层冗余链路等于广播风暴。STP 算出一棵无环的树，把多余的链路阻塞掉:根桥选举、端口角色和状态，以及一次拓扑变更真正的代价。
Layer 3 Static Routing · 网络三层静态路由 — Longest prefix match decided hop by hop, plus the classic trap that catches everyone once: routing is one-way, so a reachable destination with no return route still fails. 逐跳的最长前缀匹配，外加那个人人都会踩一次的经典坑:路由是单向的，目的地可达但没有回程路由照样不通。
DNS · DNS 域名系统 — Walk a name resolution the way a resolver does: root → TLD → authoritative, one referral at a time. Recursive vs iterative queries, the roles of authoritative, recursive and forwarding servers, and where caching and TTL change the answer. 像解析器那样走一遍域名解析：根 → 顶级域 → 权威，一次一个委派。递归查询与迭代查询、权威/递归/转发三种角色，以及缓存和 TTL 在哪一步改变了结果。
Load Balancing · 负载均衡 — Three decision granularities side by side: L3 sends a client to a server, L4 pins a connection, L7 can route every single request. See what each one can and cannot see, and where session persistence has to come from. 三种决策粒度并排看：三层把客户端指到某台服务器，四层锁定一条连接，七层可以每个请求单独调度。看清各自能看到什么、看不到什么，以及会话保持只能从哪一层来。
RDMA · RDMA 远程直接内存访问 — Zero copy and kernel bypass: the NIC writes straight into remote memory, so the CPU and the kernel network stack are not on the path at all. That is also why RDMA traffic needs a lossless fabric and does not tolerate the drops TCP shrugs off. 零拷贝加内核旁路：网卡直接写进对端内存,CPU 和内核协议栈根本不在路径上。这也正是 RDMA 需要无损网络、受不了 TCP 满不在乎的那点丢包的原因。
InfiniBand · InfiniBand 高性能互联 — Ethernet vs RoCE vs InfiniBand, compared three ways. Inside the host the verbs interface is identical — every real difference lives in the network: credit-based flow control, a centralized subnet manager, and link-level reliability instead of end-to-end retries. 以太网、RoCE、InfiniBand 三路对比。主机内部的 verbs 接口完全一样,差别全在网络这一侧：基于信用的流控、集中式子网管理器，以及链路级可靠而不是端到端重传。
VLAN Layer 2 Isolation · VLAN 二层隔离 — 802.1Q tagging: many independent broadcast domains sharing one physical wire. Access ports, trunk ports, the native VLAN, and why two hosts on the same switch with the same subnet still cannot reach each other. 802.1Q 标签：一根线上跑多个互不打扰的广播域。接入口、trunk 口、native VLAN,以及为什么同一台交换机上同网段的两台主机照样不通。
VPN Encrypted Tunnels · VPN 加密隧道 — Site-to-site and remote access side by side: how the tunnel is negotiated, what the encapsulated packet looks like on the wire, and which traffic the split-tunnel policy actually sends through it. 站点互联和远程接入并排看：隧道怎么协商出来、封装后的报文在线路上长什么样,以及分离隧道策略实际把哪些流量送了进去。
SSL/TLS · SSL/TLS 加密 — The handshake in full: how the certificate chain is validated up to a trusted root, how the session key is agreed without ever sending it, and what actually changed in TLS 1.3. 完整的握手过程：证书链怎么一级级验到可信根、会话密钥怎么在从不传输的前提下协商出来,以及 TLS 1.3 到底改了什么。
Network Products by Layer · 网络产品总览 L1-L7 — A vendor-neutral map of networking products from layer 1 to layer 7: what capability lives at each layer, which vendors worldwide sell it, and the order of magnitude of price and performance. 不分厂商的网络产品地图：一到七层每一层有哪些能力、全球哪些厂商在做、价位和性能的数量级。
Security Products by Layer · 安全产品总览 L1-L7 — Security capabilities placed by layer: firewall, IPS, WAF, DDoS scrubbing, zero trust, DNS security, and which vendors offer each. 安全能力按层归位：防火墙、IPS、WAF、DDoS 清洗、零信任、DNS 安全，各由谁提供。
Network Equipment Vendors L1-L7 · 网络设备厂商 L1-L7 — Cisco, Arista, Juniper, Huawei, H3C, Ruijie, Ciena, Nokia, F5, A10, Extreme, Aruba, Ubiquiti, NETGEAR, TP-Link, Calix, Accton / Edgecore: each vendor's product lines from optical transport to application delivery, with company background and flagship layers. 思科、Arista、Juniper、华为、H3C、锐捷、Ciena、Nokia、F5、A10、Extreme、Aruba、Ubiquiti、NETGEAR、TP-Link、Calix、Accton：各家从光传输到应用交付的产品线、公司背景与主力层。
Networking Silicon L1-L7 · 网络芯片 L1-L7 — Broadcom, NVIDIA, Marvell and the other chip makers inside the switches and NICs: what merchant silicon changed about the equipment business, and which layers each vendor's chips implement. Broadcom、NVIDIA、Marvell……交换机和网卡里面那颗芯片的厂商：商用芯片改变了设备业的什么，各家芯片实现的是哪几层。
Carriers L1-L7 · 运营商 L1-L7 — AT&T, Verizon, NTT, Comcast, Cogent, Colt, Lumen, Telstra, China Telecom and two dozen more: what a carrier sells at each layer, from dark fiber and wavelengths to private lines, IP transit and cloud on-ramps. AT&T、Verizon、NTT、Comcast、Cogent、Colt、Lumen、Telstra、中国电信等二十多家：运营商在每一层卖什么——从暗光纤、波长到专线、IP 中转和云互联。
Data Center Operators L1-L7 · 数据中心运营商 L1-L7 — Equinix, Digital Realty, CoreSite, Colt DCS and others: what a data center operator actually provides — space, power, cooling, cross-connects, interconnection fabrics — and what it leaves to you. Equinix、Digital Realty、CoreSite、Colt DCS 等：数据中心运营商到底提供什么——机房、电力、制冷、交叉连接、互联平台——以及什么留给你自己。
Internet Exchanges L1-L7 · IXP 互联网交换中心 L1-L7 — DE-CIX, AMS-IX, LINX, Equinix IX and other Internet exchanges: how an IXP works, what a port and a peering session cost, and where the route servers sit. DE-CIX、AMS-IX、LINX、Equinix IX 等互联网交换中心：IXP 怎么运作、一个端口和一条 peering 会话多少钱、路由服务器在哪。
Submarine Cable Systems · 海底电缆系统商 — The companies that build and operate transoceanic fiber: who owns a cable system, how capacity is sold as wavelengths and IRUs, and where the landing stations connect to the rest of the network. 建设和运营跨洋光缆的公司：谁拥有一条海缆系统、容量怎么按波长和 IRU 出售、登陆站接到网络的哪一层。
Cloud Providers L1-L7 · 云服务商 L1-L7 — AWS, Azure, Google Cloud, Alibaba Cloud and Oracle Cloud: what each public cloud turned every layer into as a product — from dedicated interconnects and VPCs to load balancers, WAFs and DNS. AWS、Azure、Google Cloud、阿里云、Oracle Cloud：公有云把每一层各做成了什么产品——从专线接入、VPC 到负载均衡、WAF 和 DNS。
Neocloud / AI Cloud Providers · AI 云服务商 — CoreWeave, Lambda, Crusoe, Nebius, Nscale, Together AI, FluidStack: clouds built around GPU clusters, and why their network layers — InfiniBand, RoCE, high-radix fabrics — look nothing like a general-purpose cloud's. CoreWeave、Lambda、Crusoe、Nebius、Nscale、Together AI、FluidStack：围绕 GPU 集群建的云，为什么它们的网络层——InfiniBand、RoCE、高基数交换——和通用云完全不一样。
Satellite & LEO Internet · 卫星互联网 — Starlink and other LEO and GEO satellite Internet providers: what the access layer looks like, where the latency comes from, and how the ground segment joins the terrestrial Internet. Starlink 等低轨与静止轨道卫星互联网：接入层长什么样、时延从哪来、地面段怎么接入陆地互联网。
CDN & Edge Providers L4-L7 · CDN 与边缘 L4-L7 — Akamai, Cloudflare and Fastly: what content delivery and edge compute do at layers 4 to 7 — caching, TLS termination, WAF, DDoS absorption, edge functions — and how they are priced. Akamai、Cloudflare、Fastly：内容分发与边缘计算在四到七层做了什么——缓存、TLS 终结、WAF、DDoS 吸收、边缘函数——以及怎么计费。
DNS Providers · DNS 服务商 — Cloudflare DNS, Quad9, Cisco Umbrella, DNSFilter and others: authoritative DNS, recursive resolvers and DNS security as products — features, pricing and what each one can see. Cloudflare DNS、Quad9、Cisco Umbrella、DNSFilter 等：权威 DNS、递归解析和 DNS 安全作为产品——功能、定价、各自能看到什么。
Security Vendors L1-L7 · 安全厂商 L1-L7 — Palo Alto Networks, Fortinet, Zscaler, Check Point, Qihoo 360 and others: each security vendor's products placed at the layer where they operate — NGFW, SASE, ZTNA, EDR, DNS security — with company background. Palo Alto、Fortinet、Zscaler、Check Point、奇安信/360 等：每家安全厂商的产品放到它工作的那一层——NGFW、SASE、ZTNA、EDR、DNS 安全——并附公司背景。

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