Post #1739635 · Elektrine

2026-04-21 00:41 UTC

We had a spirited debate in recent weeks regarding the right way to refer to modern networking devices, particularly those found in datacenters. One of us (Bruce) argued that, if it forwards IP packets, it&#39;s a router. Larry pushed back: shouldn&#39;t a router interconnect heterogeneous networks, or sit on the border between different autonomous systems? Further confounding the discussion is conflicting usage by industry players: most networking devices in datacenters, even those forwarding IP packets, are called switches. Put a similar device inside a service provider&#39;s backbone? Most people call those things routers—so what&#39;s the rule for when to use each term? This might seem like a trivial thing, but when writing a textbook, it&#39;s important that we use terminology precisely and consistently if we want our readers to understand the technology fully. Being inconsistent with standard industry practice would help no-one, even if we believe our stance to be &quot;correct&quot;. The good news is that we resolved the issue to our satisfaction, and along the way we gained some insights into how much the Internet has changed since we wrote our first edition in 1995. More in this week&#39;s newsletter: https://systemsapproach.org/2026/04/20/not-your-fathers-internet/ 🧵 1/n

Replies (6)

@SystemsAppr@discuss.systems 2026-04-21 00:43

Here are two images by the two authors representing different views of the naming issues: 2/n

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@jtk@infosec.exchange 2026-04-21 01:20

@SystemsAppr@discuss.systems I'm probably more aligned with Bruce by the sound of it. I used to explain to students that even their Windows laptops do IP routing, and they have routing tables! But cautioned, I wouldn't call them routers, even though they might have a really elaborate set of routes from their VPN. All hosts make forwarding decisions by examining the destination address and at least decide to deliver 1) locally, 2) to a directly attached host, or 3) a gateway. But decrementing the TTL/hop-limit is a basic requirement, as is updating the checksum in v4. I call a router connecting autonomous systems a "border" router. Even if it is pointing default and not doing BGP. I think @jeroen@secluded.ch is essentially right, the original usage of terms is still fundamentally precise and correct. The evolution of terms in the "market" has just confused things considerably. I often need more context to understand what people are talking about because a router to them is often not what I think of as a router.

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@dlakelan@mastodon.sdf.org 2026-04-21 02:08

@SystemsAppr@discuss.systems It seems pretty simple to say a router is a computer connected to more than one network which forwards packets between the networks based on routing tables and IP addresses. A switch is a device that determines which ports to send a packet out based on MAC or hardware addresses. An L3 switch is a switch that can also be configured as a router.

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@brouhaha@mastodon.social 2026-04-21 04:13

@SystemsAppr@discuss.systems Hill I'll die on: "Switch" is a nonsense marketing term made up by Kalpana Inc. in 1990. A multiport networking product can operate at layer 2, in which case it is a bridge, or at layer 3, in which case it is a router. Does it offer both capabilities? If so, it's a bridge and a router. Kalpana called their bridges "switches" because bridges had a poor reputation at the time. There was, and still is, no actual defined meaning to "switch". It was a "marketing breakthrough."

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@ted_h@mastodon.social 2026-04-21 09:43

@SystemsAppr@discuss.systems Harald Alvestrand, at the time chair of the IETF, defined the difference this way: if it decrements the TTL it is a router and if it doesn’t it is a switch. Kind of self determination, I guess.

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@fivetonsflax@tilde.zone 2026-04-22 08:23

@SystemsAppr@discuss.systems @ricci@discuss.systems Radia Perlman’s solution was bluntly simple: it’s always a “switch”. I use both words, but if I were writing a textbook, I’d give serious consideration to her approach.

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