内容来源：https://www.engadget.com/2271811/dont-throw-away-old-router-do-this-instead/

内容总结：

旧路由器别急着扔，它还能在新网络里发挥不少余热。与家中其他设备不同，路由器往往一用就是好几年，很多人容易忽略它是否还在接收固件更新、是否还支持最新Wi-Fi标准，这也让升级新路由器时多了一层顾虑——扔掉一台功能完好的设备总觉得浪费。实际上，旧路由器完全可以作为辅助设备继续使用。新机型在安全性、覆盖范围和性能上更胜一筹，适合担当主路由，但网络基础原理几十年来变化不大，旧路由器仍有多种再利用方式，不必直接送去填埋或回收。

改作Wi-Fi中继或网状节点：如果新路由器信号难以覆盖家中角落，旧路由器可充当专用接入点，省去另购无线扩展器的麻烦。有线连接更稳定、速度更快，但需要从主路由拉一根网线过来；无线方式则更灵活，但会占用旧路由的部分无线带宽，实际速度会打折扣。建议避免两个Wi-Fi信号近距离同时广播，以免干扰。可将旧路由设为仅广播2.4GHz频段，同时关闭新路由的2.4GHz，因为2.4GHz穿墙能力更强，而近十年Wi-Fi的主要提升集中在5GHz和6GHz等更高频段。不少路由器支持无线中继或桥接功能，可在管理面板或说明书中查找相关选项。少数路由器还能充当网状Wi-Fi节点，例如华硕的AiMesh允许不同型号混组统一网络，若旧路由支持该功能，购买新路由时可优先考虑同品牌产品。

利用LAN口充当网络交换机：如果新路由的LAN口不够用，无法连接智能电视、电脑、游戏机等高带宽设备，旧路由器可当作交换机使用，省下购买基础交换机的费用。设置方法很简单：用网线将新路由的LAN口与旧路由的LAN口相连，设备插在旧路由剩余LAN口上，注意不要插旧路由的WAN口。许多路由器在管理设置中提供接入点或交换机模式，直接启用即可；若没有，则需手动关闭DHCP服务器以及防火墙、NAT等路由功能。若只使用有线端口，应关闭旧路由的所有无线功能，避免信号干扰。

搭建文件与打印服务器：许多路由器带有容易被忽略的USB接口，可连接存储设备或打印机。连接打印机后，网络中任何设备都能发起打印任务，甚至无线打印，老旧的非Wi-Fi打印机也能借此实现网络打印。连接移动硬盘或U盘后，路由器就变成简易存储服务器，网络内设备均可读写。相比专用NAS设备及其硬盘的花费，这是低成本的起步方案，但路由器不具备可靠的备份与冗余功能，USB接口速度也有限，性能上不能要求太高。连接后可在管理面板中调整USB设备共享设置以获得更好体验。

变身专用VPN路由器：不少现代路由器支持VPN功能，但开启后所有流量都会走隧道。若在每个设备上单独安装VPN应用，长时间使用可能加剧电池消耗。将旧路由器改作VPN客户端就很有意义：让VPN独立于主网络运行，需要时连接即可，不必让所有流量都经过VPN，也无需移动设备承担额外负担。具体步骤因VPN服务商和路由器厂商而异，通常先将旧路由连接到新路由并启用接入点模式，然后在管理面板中找到VPN设置，开启功能并填入VPN凭据。

刷入第三方固件获得最大灵活性：路由器本质上是低功耗计算机，通常配备高效能CPU和少量内存，运行轻量级操作系统，专为路由网络流量而设计。当厂商停止提供最新固件，或原有系统限制过多时，问题就来了。好在开源社区专门为路由器开发了定制固件，例如OpenWRT，可替代厂商预装软件，让用户对设备拥有更大控制权，甚至安装BT客户端等第三方应用。这类固件能让旧路由器继续服役更久，上文不少方案在DD-WRT、FreshTomato等定制固件上也更容易实现。需要注意的是，并非所有路由器都受支持，型号繁多，需查阅各项目的文档确认自己的设备是否兼容。

中文翻译：

别急着扔掉旧路由器——不妨这样做
你的旧路由器在网络上还有很多潜力，给它安排个新任务吧。
和家里的许多设备不同，你大概很少会想到升级路由器这回事。路由器能用很久，很容易忽略它已经不再收到固件更新，或者不支持最新的Wi-Fi标准。这就让升级新Wi-Fi路由器变得有些为难，因为扔掉一台功能完好的设备总让人觉得浪费。
好在这个问题不难解决。旧路由器完全可以另作他用，哪怕只是当个二级或三级设备也很有价值。虽然新款路由器在安全性、覆盖范围和性能上更胜一筹，因而最适合作为主力设备，但旧路由器也有它的优势——大多数网络基础原理几十年来都没怎么变过。你有很多方法可以让旧路由器重获新生，而不是把它送进垃圾填埋场或回收站。
把旧路由器变成Wi-Fi中继器或Mesh节点
如果新Wi-Fi路由器信号覆盖不到家里的一些角落，可以考虑把旧路由器当作专用接入点。这样一来，你就不用再买无线扩展器或其他单一用途的设备了。
有两种方式可选：有线或无线。有线连接更稳定、速度更快，但你需要从主路由器拉一根网线过来。如果隔了好几个房间，这恐怕不太现实，除非你愿意在墙里走线。
我不建议在相近位置同时发射两个Wi-Fi信号，因为这会造成无线干扰，反而降低性能。好消息是，你可以在两台路由器上分别禁用特定频段来避免拥堵。一个不错的方案是让旧路由器只发射2.4GHz频段，同时在新路由器上禁用该频段。这是因为2.4GHz信号穿墙能力更强，而过去十年Wi-Fi的大部分改进都集中在5GHz和6GHz等更高频段上。
许多路由器支持无线中继或桥接功能，可以在管理面板或说明书中查找相关术语。在我那台老TP-Link路由器上，这个功能藏在WDS桥接标签下的好几层子菜单里。这种方式的缺点是，路由器得拿出一部分有限的无线带宽来和新路由器通信，导致你连接旧路由器时实际速度会打折扣。
少数路由器还能充当Mesh Wi-Fi节点。华硕在其路由器上把这项功能叫做AiMesh，允许你混搭不同型号来组建一个统一网络。如果你还没选好新路由器，而旧路由器恰好支持这个功能，那就买同一系列的，方便搭配使用。
利用LAN口轻松充当网络交换机
如果新路由器的LAN口不够用，没法连接智能电视、电脑和游戏主机等高带宽设备，你可以把旧路由器当交换机使。一个基本的网络交换机通常要10到20美元，既然手头有旧路由器，这种单一用途的设备就大可不必再买了。
把路由器设为交换机模式相对简单。只需用一根网线从新路由器的LAN口接到旧路由器的LAN口，再把设备插到旧路由器剩余的端口上就行。注意千万不要插到旧路由器的WAN口。
很多路由器在管理设置里提供了接入点（AP）或交换机模式，你需要进入路由器管理面板启用。如果找不到这些模式，就得手动关闭路由器的DHCP服务器，以及防火墙和NAT等其他路由功能。
关于无线干扰的提醒在这里同样适用。如果你只用旧路由器的有线网口，那就把所有无线功能都关掉。
搭建文件和打印服务器，享受无线便利
很多路由器上有一个容易被忽视的USB接口。但这个接口用途广泛，可以连接存储设备或打印机。连接打印机后，你可以从任何连接到路由器的设备发起打印任务，甚至无线打印。如果你有一台不支持Wi-Fi的老打印机，这就是一个简便的变通方案。
连接外置硬盘或U盘等存储设备，就能把路由器变成一个简易存储服务器。换句话说，你可以从网络上的任何设备读写这个存储设备。专用的网络附加存储（NAS）设备及其硬盘价格不菲，所以这是一个低成本的入门方式。只是要记住，路由器不具备任何可靠性或备份功能，而这正是真正的NAS设备的强项。而且路由器上的USB接口通常速度不快，性能会比较有限。
连接设备后，在路由器管理面板里找找USB设备共享设置，调一调以获得最佳体验。
把它变成专用VPN路由器
许多现代路由器支持VPN功能，但启用后意味着所有流量都要走VPN隧道。你也可以在单个设备上安装VPN应用，但长时间使用可能导致电池消耗过快。这时候，把旧路由器改造成VPN客户端就很有意义了。用一台独立于主网络的专用路由器来跑VPN，你就可以随时连接，既不用让所有流量都走VPN，也不用强迫移动设备承担这个负担。
具体操作步骤因VPN服务商和路由器厂商而异，但通常先要把旧路由器连接到新路由器，并启用接入点模式。然后，在路由器管理面板中找到VPN设置，打开该功能，填入你的VPN凭据。
刷入自定义固件，获得最大灵活性
虽然我们平时不这么想，但路由器本质上就是低功耗计算机，通常搭配一颗高效CPU和少量内存与存储。因此它们出厂时搭载的是轻量级操作系统，专为既定用途设计：路由网络流量以及与此相关的其他任务。当厂商停止为你的路由器提供最新固件，或者其局限性让你无法实现想要的功能时，问题就来了。
幸运的是，众多富有进取心的开源社区已经为路由器专门打造了自定义固件。像OpenWRT这样的项目，用更灵活的操作系统取代了厂商自带的软件，让你对设备拥有更大的控制权，包括安装种子客户端等第三方应用的能力。
这些是让旧路由器继续发挥余热的好选择。上面提到的许多建议，在DD-WRT或FreshTomato等自定义路由器固件上也更容易实现。我用的是OpenWRT，因为我觉得它比许多路由器的默认系统限制更少。
自定义固件的缺点是不是所有路由器都支持。鉴于型号数量庞大，你得逐一阅读各项目的文档，才能确定你的具体设备是否兼容。

英文来源：

Don't throw away your old router — Do this instead
Your old router has a lot of potential on your network, so give it a new job.
Unlike many devices in your home, you probably don't think much about upgrading your router. Routers can work for a long time, and it's easy to overlook when one isn't getting firmware updates anymore or doesn't support the latest Wi-Fi standards. This can make upgrading to a new Wi-Fi router more difficult, since throwing away a perfectly functioning piece of equipment feels wasteful.
Thankfully, this doesn't need to be an issue. Old routers can easily be repurposed to have use even as a secondary or tertiary device. While newer models offer better security, range, and performance and are thus the best for your primary device, old routers can take advantage of the fact that most networking fundamentals haven't changed in decades. You have many ways to repurpose an old router instead of sending it off to the landfill or for recycling.
Turn your old router into a Wi-Fi repeater or mesh node
If your new Wi-Fi router struggles to reach corners of your home, consider using your old router as a dedicated access point. With this method, you don't need to buy a wireless extender or another single-purpose piece of tech.
There are two approaches you can take: wired or wireless. A wired connection brings stable connectivity and fast speeds, but you need an Ethernet line running back to your primary router. This might not be possible several rooms away unless you're comfortable pulling cable through your walls.
I recommend against broadcasting two Wi-Fi signals in close proximity, since this can lead to wireless interference and worse performance. The good news is that you can disable specific frequencies on both routers to avoid congestion. A good option is configuring the old router to broadcast on the 2.4GHz band, while disabling that frequency on the newer router. This is because 2.4GHz signals penetrate walls better, while most of the Wi-Fi improvements over the past decade have applied to higher frequencies like 5GHz and 6GHz.
Many routers support wireless repeater or bridge functionality, so check the admin panel or manual for those terms. On my older TP-Link router, this feature is hidden within several sub-menus under the WDS bridging label. The downside with this approach is that your router has to use part of its limited wireless capacity to communicate with your router. This translates to slower real-world speeds when you're connected to the secondary router.
A small number of routers can also double up as a mesh Wi-Fi node. Asus calls this feature AiMesh on its routers, and it allows you to mix different models to create one unified network. If you haven't chosen a new router yet and your old one offers this, buy one in the same family to take advantage of it.
Use the LAN ports for an easy network switch
If your new router doesn't have enough LAN ports to connect high-bandwidth devices like smart TVs, computers and gaming consoles, you can use your old router as a switch. A basic network switch typically costs between $10 and $20, and is yet another single-use device you don't need to buy if you have an old router lying around.
Setting up a router in switch mode is relatively easy. Simply run an Ethernet cable from your new router to the old one, using LAN ports on each, and connect your devices to the remaining ports on the old router. Make sure you don't plug anything into the old router's WAN port.
Many routers offer Access Point (AP) or Switch modes in their administrative settings, which you'll have to enable by accessing the router's admin panel. If you don't see one of these modes, you'll have to disable the router's DHCP server, along with any other routing options like firewall and NAT, manually.
The same warning about wireless interference applies here as well. You should disable all wireless functionality on the old router if you only care about the onboard Ethernet ports.
Create file and print servers for wireless convenience
Many routers have a USB port that's easy to overlook. But you can use this in many ways, including to connect a storage device or printer. The latter allows you to initiate print jobs from any device connected to your router, even wirelessly. If you have an old printer that lacks Wi-Fi support, this can be an easy workaround.
Connecting a storage device like an external hard drive or thumb drive can turn your router into a rudimentary storage server. In other words, you can read and write to the storage device from any device on the network. Dedicated network-attached storage (NAS) machines and the drives for them cost a fair bit, so this is an inexpensive way to get started. Just keep in mind that routers don't include any reliability or backup features, which is where actual NAS devices shine. And the USB port on your router is likely not the fastest, so performance will be limited.
After connecting the device, poke around in your router's admin panel to check its USB device sharing settings for the best experience.
Turn it into a dedicated VPN router
Many modern routers support VPN functionality, but enabling this feature means routing all traffic through the tunnel. You can install your VPN app on individual devices instead, but that might lead to battery drain over long periods. This is where repurposing an old router into a VPN client makes a lot of sense. Using a dedicated router for the VPN that operates independently from your primary network means you can connect to it when you want, without running all traffic through it or forcing your mobile devices to handle the workload.
The exact instructions vary by VPN provider and router manufacturer, but you'll generally start by connecting your old router to the new one and enabling access point mode. Then, look for VPN settings in the router's administration panel, turn on the feature, and provide your VPN credentials.
Install custom firmware for maximum flexibility
While we don't always think about them in this way, routers are essentially low-power computers, typically pairing an efficient CPU with small amounts of RAM and memory. They accordingly ship with lightweight operating systems designed for their intended purpose: routing network traffic and everything else associated with that task. This creates problems when manufacturers stop providing the latest firmware for your router, or when its limited nature prevents you from doing what you want.
Luckily for us, entire enterprising open-source communities have built custom firmware designed specifically for routers. Projects like OpenWRT replace a router's manufacturer-provided software with a more flexible OS that gives you greater control over the device, including the ability to install third-party apps like torrent clients.
These are a great option to keep your old router going for longer. Many of the suggestions above are also easier to set up on custom router firmware like DD-WRT or FreshTomato. I use OpenWRT, as I find it less restrictive than many routers' default operating systems.
The downside to custom firmware is that not all routers are supported. Given the sheer number of models, you'll have to read through each project's documentation to narrow down compatibility for your specific device.