A2.3.4 · Data transmissions
A2.3.4 · 数据传输
Static and Dynamic Routing
静态路由与动态路由
A home network with two devices, set up once and never touched again, and a company network spanning dozens of routers where links fail and get added every month, need genuinely different approaches to deciding where traffic goes next.
一个只有两台设备、配置一次后再也不去动它的家庭网络,与一个横跨数十台路由器、链路每个月都会出现故障或新增的公司网络,在决定流量下一步走向时,确实需要截然不同的方法。
Explainer
讲解
Every router has to answer the same question for every packet that arrives: which way does this go next? The answer lives in the router's routing table, and there are two fundamentally different ways that table gets built and kept up to date.
每一台路由器对每个到达的数据包都必须回答同一个问题:接下来该往哪里走?答案存放在路由器的路由表中,而这张表的建立与更新方式,有两种根本不同的路径。
Routing is the process of choosing a path across a network for traffic to follow, using a routing table that maps destinations to the next router a packet should be sent to.
路由是指利用一张将目的地映射到数据包应发往的下一台路由器的路由表,为网络中的流量选择路径的过程。
Explainer
讲解
Static routing
静态路由
In static routing, a network administrator types every route into the routing table by hand. The table stays exactly as configured until a person deliberately changes it, the routers themselves never adjust anything on their own.
在静态路由中,网络管理员手动将每一条路由输入路由表。该表会一直保持配置时的样子,直到有人特意更改它为止,路由器本身从不自行调整任何内容。
Real example: a two-router home network, one path in, one path out, that will never realistically need a second route.
真实例子:一个只有两台路由器的家庭网络,一进一出,现实中永远不会需要第二条路由。
- Predictable and lightweight (a fixed table means traffic always follows a known path, and no processing power or bandwidth is spent on routers talking to each other to work anything out) 可预测且轻量 (固定的路由表意味着流量始终沿已知路径走,也不会有任何处理能力或带宽花在路由器之间互相沟通、协商结果上)
- No automatic response to failure (if the one configured path breaks, traffic simply stops, since nothing in static routing looks for an alternative on its own) 无法自动应对故障 (如果配置好的那条唯一路径中断,流量便会直接停止,因为静态路由中没有任何机制会自行寻找替代路径)
- Manual upkeep that doesn't scale (every new link or removed link across the whole network has to be typed in by hand, which becomes unmanageable well before a network reaches even a few dozen routers) 人工维护难以扩展 (整个网络中每一条新增或移除的链路都必须手动输入,这在网络规模远未达到数十台路由器之前就会变得无法管理)
Explainer
讲解
Dynamic routing
动态路由
In dynamic routing, routers build and update their own routing tables automatically, by continuously exchanging information about the network with each other and recalculating the best paths whenever something changes. No specific routing protocol needs to be named or explained, only the general idea that this exchange and recalculation happens algorithmically.
在动态路由中,路由器通过彼此持续交换网络信息,并在情况发生变化时重新计算最佳路径,来自动建立并更新自己的路由表。无需指名或解释任何具体的路由协议,只需理解这种交换与重新计算是以算法方式自动进行的这一总体概念即可。
Real example: a company's network spanning dozens of offices, where links are added, removed and occasionally fail on their own.
真实例子:一家公司横跨数十个办公室的网络,链路会被新增、移除,偶尔也会自行发生故障。
- Adapts on its own (when a link fails or a new one is added, the routers detect it and recalculate routes automatically, with no administrator needing to intervene) 自行适应 (当链路发生故障或新增链路时,路由器会自动侦测到并重新计算路由,无需管理员介入)
- Scales to large, changing networks (growth doesn't multiply the manual configuration workload the way it does with static routing) 可扩展到大型、多变的网络 (网络增长不会像静态路由那样成倍增加人工配置的工作量)
- Costs real resources (the constant exchange of routing information between routers uses processing power and bandwidth that static routing never spends) 消耗真实资源 (路由器之间持续交换路由信息,会占用静态路由从不消耗的处理能力和带宽)
- Convergence isn't instant (after a change, it takes time for every router to learn about it and agree on the new best paths, and during that window some routers can hold outdated, inconsistent information) 收敛并非瞬间完成 (变化发生后,每台路由器都需要一段时间才能得知并就新的最佳路径达成一致,在这段时间内,部分路由器可能持有过时、不一致的信息)
Convergence is the time it takes for every router in a network to update its own routing table and reach a shared, consistent understanding of the network after something changes. Static routing has no convergence delay at all (there's nothing to recalculate), which sounds like an advantage until you remember it also means static routing never adapts to the change in the first place.
收敛是指网络中每一台路由器在情况发生变化后,更新自身路由表并就网络达成共享、一致理解所需要的时间。静态路由完全没有收敛延迟(因为根本没有什么需要重新计算),这听起来像是个优点,但别忘了这也意味着静态路由压根就不会对变化做出适应。
Explainer
讲解
Comparing all seven factors
比较全部七项因素
The statement names seven specific factors. A strong "explain" answer draws on several of these directly, rather than reducing the whole comparison to "dynamic is smarter."
该考纲陈述具体列出了七项因素。一份有力的"explain"答案会直接援引其中的几项,而不是把整个比较简化为"动态路由更聪明"。
| Factor因素 | Static routing静态路由 | Dynamic routing动态路由 |
|---|---|---|
| Configuration配置 | Entered manually, route by route逐条手动输入 | Set up once, then routes are discovered automatically设置一次后,路由便会自动被发现 |
| Maintenance维护 | Every change needs a manual edit每次变动都需要人工修改 | Adjusts itself as the network changes随网络变化自行调整 |
| Complexity复杂度 | Simple for a small, stable network对小型、稳定的网络而言很简单 | More to set up initially, but handles a complex network without growing harder to manage by hand初始设置更复杂,但处理复杂网络时不会随之变得更难人工管理 |
| Resource usage资源使用 | Minimal, no extra processing or bandwidth needed极少,无需额外的处理能力或带宽 | Higher, routers constantly exchange information with each other较高,路由器之间持续互相交换信息 |
| Convergence收敛 | Not applicable, routes never change on their own不适用,路由从不自行改变 | Takes real time after a change, and can briefly cause inconsistent routing while it happens变化后需要实际的时间,过程中可能短暂造成路由不一致 |
| Scalability可扩展性 | Poor, manual effort grows with every router added较差,每增加一台路由器人工工作量就随之增加 | Good, designed specifically to handle growth automatically良好,专为自动应对增长而设计 |
| Network size网络规模 | Best suited to small, rarely-changing networks最适合小型、极少变化的网络 | Best suited to larger networks that change often or need high availability最适合频繁变化或需要高可用性的大型网络 |
Notice the shape: every single row favours whichever option matches the network's actual size and rate of change, not one option overall. That's the "explain" this statement is really asking for.
注意这个规律:每一行都青睐与网络实际规模和变化速度相匹配的那个选项,而不是某个选项在整体上占优。这才是这条考纲陈述真正要求的"explain"。
Worked example
示例讲解
What happens when a link fails
链路故障时会发生什么
A retail chain's network connects its Store, Warehouse and Head Office. Normally the Store reaches Head Office directly. The clearest way to see the real difference between static and dynamic routing is to watch what each one does the moment that direct link breaks.
一家连锁零售商的网络连接着其门店、仓库与总部。通常情况下,门店直接与总部相连。要看清静态路由与动态路由之间的真正差异,最清楚的方式就是观察当这条直连链路中断的那一刻,两者各自会做什么。
Before the failure. All three sites are connected. The Store's routing table sends Head-Office-bound traffic straight down the direct link, since that's the only route anyone ever configured.
故障发生之前。三处场所全部相连。门店的路由表会将发往总部的流量直接沿这条直连链路发送,因为那是唯一配置过的路由。
The direct link fails. A cable fault takes down the Store-to-Head-Office link entirely. A route through the Warehouse still physically exists and could carry the traffic instead.
直连链路发生故障。一处线缆故障使门店与总部之间的链路完全中断。一条经由仓库的路由在物理上仍然存在,原本可以改为承载该流量。
Under static routing: nothing changes automatically. The Store's routing table still names the now-dead direct link as the only route, so every packet bound for Head Office is simply dropped, until an administrator notices and manually reconfigures the table to route via the Warehouse instead.
在静态路由下:没有任何东西会自动改变。门店的路由表仍然把这条已经失效的直连链路列为唯一路由,因此每一个发往总部的数据包都会直接被丢弃,直到管理员发现问题,并手动将路由表重新配置为经由仓库转发。
Under dynamic routing: the Store's router detects that the direct link is gone (it stops hearing from Head Office over it), exchanges updated information with the Warehouse's router, and recalculates: the Warehouse route becomes the new best path. There's a short convergence delay while this negotiation happens, but no person has to do anything.
在动态路由下:门店的路由器侦测到直连链路已经消失(不再通过它收到来自总部的信息),便与仓库的路由器交换更新后的信息,并重新计算:经由仓库的路由成为新的最佳路径。这一协商过程会有一段短暂的收敛延迟,但完全不需要任何人手动介入。
Check your understanding
检验你的理解
A university is expanding from 4 buildings to over 60 across a new campus, with new network links being added and occasionally failing on a weekly basis. Which routing approach fits better, and why?
一所大学正从 4 栋建筑扩展到新校区的 60 多栋建筑,新的网络链路每周都会新增,偶尔也会出现故障。哪种路由方式更合适,为什么?
Common mistake
常见错误
RecurringA common weak answer treats dynamic routing as simply "the better, more modern option," missing that the statement explicitly asks for advantages AND disadvantages of both. Dynamic routing's automatic adaptation is real, but it comes at a genuine resource cost that static routing simply doesn't pay, and for a small, stable network that cost buys nothing useful.
反复出现一种常见的薄弱答案,会把动态路由简单地当作"更好、更现代的选项",却没注意到该考纲陈述明确要求同时说明两者的优点和缺点。动态路由的自动适应能力确实是真实存在的优点,但它要付出静态路由完全不需要付出的真实资源代价,而对于一个小型、稳定的网络来说,这份代价买不到任何有用的东西。
One-sided: "Dynamic routing is better than static routing because it automatically adapts to changes." States a real advantage, but never mentions dynamic routing's own costs, or any situation where static routing is genuinely the right choice.
只讲一面: "动态路由比静态路由更好,因为它能自动适应变化。" 陈述了一个真实的优点,却完全没有提到动态路由自身的代价,也没有提到任何静态路由真正更合适的情况。
Both sides, tied to a context: "Dynamic routing adapts automatically to network changes, which suits a large, frequently-changing network, but this costs extra processing power and bandwidth that a small, stable network doesn't need to spend. Static routing avoids that cost entirely, but only works well while the network stays small and rarely changes." Gives a genuine advantage and disadvantage for each, tied to when each one actually applies.
两面兼顾,并结合具体情境: "动态路由能自动适应网络变化,适合大型、频繁变化的网络,但这需要付出额外的处理能力和带宽,而小型、稳定的网络并不需要付出这些代价。静态路由则完全避免了这一代价,但只有在网络保持小型且极少变化时才能良好运作。" 为两者各给出了真实的优点和缺点,并结合了各自实际适用的情境。
Revision questions
复习题
Past-paper style. Write an answer, then reveal the marking points and mark yourself.
采用历年真题风格。写下答案,然后展开评分要点给自己打分。
[2]Define the term convergence in the context of dynamic routing.
[2]在动态路由的语境下,定义术语收敛(convergence)。
Marking points
评分要点
- Convergence is the time it takes for every router in a network to update its routing table and reach a shared, consistent view of the network after something changes (such as a link failing).
- 收敛是指在发生变化(例如一条链路故障)之后,网络中每台路由器更新自己的路由表、并对网络达成一致、统一认识所需的时间。
[4]Explain a benefit and a drawback of using static routing on a network.
[4]解释在网络中使用静态路由的一项好处和一项缺点。
Marking points
评分要点
- Benefit: static routing is predictable and lightweight; traffic always follows a known path, and no processing power or bandwidth is spent on routers exchanging information.
- Drawback: it has no automatic response to failure (if the configured path breaks, traffic just stops), and every change must be typed in by hand, which does not scale.
- 优点:静态路由可预测且轻量;流量总是沿已知路径走,没有处理能力或带宽花在路由器之间交换信息上。
- 缺点:它无法自动应对故障(配置的路径中断时,流量直接停止),而且每次变动都必须手动输入,不可扩展。
[6]A small business network with three devices is expected to grow to over 100 devices across multiple sites within two years. Explain which routing approach would better suit the network now, and whether that recommendation would change as it grows.
[6]一个只有三台设备的小型企业网络,预计在两年内将扩展到跨多个场所、超过 100 台设备。解释目前哪种路由方式更适合该网络,以及随着网络增长这一建议是否会改变。
Marking points
评分要点
- Now, with three devices, static routing suits the network: it is small and stable, so a hand-configured table is simple and adds no overhead.
- As it grows to over 100 devices across multiple sites, the recommendation should change to dynamic routing.
- Dynamic routing adapts automatically when links fail or are added, and the manual configuration work of static routing would become unmanageable at that size.
- The extra processing and bandwidth dynamic routing costs is worth it for a large, changing, multi-site network that needs high availability.
- 现在只有三台设备,静态路由适合这个网络:它小而稳定,所以手工配置的路由表简单,不增加开销。
- 当它增长到跨多个站点、超过 100 台设备时,建议应改为动态路由。
- 动态路由在链路故障或新增时自动适应,而静态路由的人工配置工作在那种规模下会变得无法管理。
- 对于一个需要高可用性的大型、多变、多站点网络,动态路由多出的处理和带宽开销是值得的。
Flashcards
记忆卡片
Active recall for this statement’s key terms.
针对本条考纲陈述关键术语的主动回忆练习。
Keep this statement’s practice with you
把这条考纲陈述的练习保存下来
Free account: unlock every revision question and flashcard for A2.3.4, and every other IB CS 2027 statement.
免费账户:解锁 A2.3.4 以及所有其他 IB CS 2027 考纲陈述的全部复习题和记忆卡片。