主题： networking
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变更 DNS 记录并保留回退路径：降低 TTL、切换与验证
DNS 变更能多快触达用户，取决于缓存中旧 TTL 的过期速度：因此应在变更前用一个完整的旧 TTL 周期提前把 TTL 调低；在新目标确认全网生效之前，让旧目标持续提供服务；并且要考虑到，按 RFC 8767 的规定，当权威服务器不可达时，解析器可以继续返回过期数据。
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边沿触发的 epoll：等待下一个边沿前，先处理完可执行的非阻塞工作
将就绪通知与完整的应用消息分开，避免连接停滞。
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Configuring network interfaces with netplan on Ubuntu, and testing changes without losing the connection
Netplan renders YAML under /etc/netplan into networkd or NetworkManager configuration; `netplan try` applies a change and automatically reverts it if nobody confirms within a timeout, which is the safe way to change network settings on a remote host. Debian's ifupdown /etc/network/interfaces is the older, still-supported contrast.
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Client prediction and reconciliation with an authoritative server
Predict local input immediately, reconcile against the matching authoritative command, and replay unacknowledged input while keeping visual correction separate.
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Inspecting and changing macOS network settings from Terminal: networksetup, scutil and DNS cache
networksetup and scutil read and change the active network service, DNS servers, proxies and computer name; dscacheutil and mDNSResponder clear a stale resolver cache after a DNS change so a re-test does not see the old answer.
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The TLS 1.3 handshake in outline
TLS 1.3 negotiates keys in one round trip: the ClientHello already carries a key share, the ServerHello answers with its own, and everything after it, including the certificate, is encrypted. Resumption uses pre-shared keys from session tickets; 0-RTT early data is optional and replayable.
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Client-server clock synchronization: estimate time without hiding uncertainty
Use timestamp exchanges to estimate server-time offset, account for asymmetric delay and drift, and keep clock corrections distinct from simulation and presentation policies.
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Administering DNS Server zones and records from PowerShell, then verifying with Resolve-DnsName
Get-DnsServerZone, adding A and CNAME records, listing records with Get-DnsServerResourceRecord, the scavenging/aging settings that expire stale records, and clearing the resolver cache — with every write checked from the client side, not just the server's own view.
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Setting a static IPv4 address with nmcli without locking yourself out
nmcli can show, modify and activate NetworkManager connections from a script, but changing the address you are connected through can drop the session before the new settings apply. Cloning the profile first and validating before removing the old one keeps the change reversible.
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Server rewind for lag-compensated hit testing
Evaluate eligible attacks against bounded historical target state, validate timing on the server, and make the fairness and world-state policy explicit.
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MTU、分片与路径 MTU 发现
以太网承载 1500 字节的 IP 数据包，隧道和 PPPoE 能承载的更小，而 IPv6 路由器从不分片。路径 MTU 发现依赖 ICMP Packet Too Big 消息；这些消息被过滤时，大包会悄无声息地消失，小包却能通过，形成典型的黑洞。MSS 限制或分组化层探测可以绕过这种问题。
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Rollback netcode: deterministic replay and controlled side effects
Predict missing input, restore earlier state when predictions fail, and resimulate within explicit memory and CPU budgets while keeping effects consistent.
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Network configuration tools compared: nmcli, netplan, systemd-networkd and their Windows and macOS equivalents
Reading the current network configuration, setting a static address, and setting DNS servers — the same three tasks across NetworkManager's nmcli, Ubuntu's netplan, systemd-networkd, Windows PowerShell's networking cmdlets, and macOS's networksetup.
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Web 服务依赖的 DNS 记录
A、AAAA 和 CNAME 将名称映射到地址，MX 路由邮件，TXT 承载验证信息与策略，CAA 限制证书签发机构，NS 委派区域。变更前后应检查权威应答，而不只是缓存解析器的结果。
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Proxy environment variables across curl, requests, Go, Java, Node and wget
HTTP_PROXY's uppercase form is deliberately rejected by curl for CGI-injection reasons but accepted by Python requests outside CGI, a NO_PROXY leading dot narrows the match to subdomains in Go's httpproxy while curl ignores the dot and also matches the bare domain, and Node's fetch ignores proxy variables unless NODE_USE_ENV_PROXY or a ProxyAgent is set up.
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可重复地测量家庭互联网吞吐量：固定路径与固定时段的流程
一套建议的家庭吞吐量与延迟序列测量流程：固定设备、有线或无线连接路径、测试工具及服务器，连续两周每天在三个固定时段各做三次连续测试，每次记录连接数和家庭活动。RFC 6349 中的带宽时延积及单连接与多连接讨论，可解释工具设置为何会改变结果；本文不对任何运营商作出结论。
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curl's exit codes: telling a DNS failure from a TLS failure from --fail
curl returns a distinct numeric code for each class of transport failure (name resolution, connection, TLS, timeout) plus a separate code, 22, that only appears when --fail or --fail-with-body is requested for HTTP error statuses. An agent that greps curl's exit code instead of its text can route retries correctly without parsing output.
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HTTP/1.1、HTTP/2 与 HTTP/3：运维人员会注意到的差异
HTTP/1.1 在每个 TCP 连接上一次发送一个请求，采用文本定界；HTTP/2 在一个 TLS 连接上多路复用二进制流并使用 HPACK 压缩，但 TCP 丢包仍会造成停顿；HTTP/3 通过 UDP 上的 QUIC 运行，消除传输层队头阻塞，并通过 Alt-Svc 或 HTTPS DNS 记录发现。
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通过 PowerShell 管理 DHCP Server 角色：作用域、保留地址、授权与备份
查看 DHCP 作用域（Get-DhcpServerv4Scope）和租约，用 Add-DhcpServerv4Reservation 保留地址，用 Add-DhcpServerInDC 在 AD 中授权服务器，了解故障转移，并在高风险更改前通过 Backup-DhcpServer 备份配置。
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Configuring network interfaces and addresses on Solaris 11.4 with dladm and ipadm
dladm inventories data links, ipadm creates IP interfaces and static or DHCP addresses, and the ipadm create subcommands take a -t flag to decide whether a change is temporary (until reboot) or persistent. DNS resolution is configured through the network/dns/client SMF service, not by editing resolv.conf directly.
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