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@SystemsAppr@discuss.systems

2026-04-21 00:44 UTC

This exposed two issues: first, is there a difference between an L3 switch and a router? And second, when modern switches can be configured to forward on either the Ethernet header or the IP header, how do we best talk about them? On the first question, we ultimately decided to let context be the determining factor. Even while there is no technical difference between an L3 switch and a router, the most common usage in the datacenter context favors "switch". For ISPs, router is still the preferred term. The configurability of modern devices, especially those based on programmable forwarding silicon, means we have to be clear in our discussions to separate what a device is capable of doing versus what it is configured to do. 3/n

Replies (3)

  • @SystemsAppr@discuss.systems 2026-04-21 00:45

    The more important issue here is that the Internet has changed a lot since our first edition. While the Internet Protocol was invented to allow interconnection of different network technologies and the networks of different organizations, its success has meant that IP is often just used to forward packets among homogeneous links inside a single organization. That doesn't change the meaning of "router", it just illustrates one of many ways the Internet has changed. The adoption of BGP for routing inside datacenters is another example of how different the Internet and its protocols are today. This is the challenge we face in writing this new edition: to be correct and precise in our descriptions of technology while admitting that the Internet of today is different than the one we described in our first edition. And to do that in a way that leaves the reader understanding the technology without being overwhelmed by the complexity of today's networks. More in the newsletter: https://systemsapproach.org/2026/04/20/not-your-fathers-internet/ 4/4

    Open ##2207366

  • @nbailey@mstdn.ca 2026-04-21 02:26

    @SystemsAppr@discuss.systems one of the definitions I’ve seen for routers is not to separate networks but act as a responsibility barrier. Everything in an L3 switched domain belongs to “us” but everything on the other side of the router is “them”. A bit more social/political than technical ;)

    Open ##2207367

  • @revk@toot.me.uk 2026-04-21 06:51

    @SystemsAppr@discuss.systems @aspensmonster@tenforward.social I may be old school, but deciding where to send packets based on MAC is a switch, and based on IP is a router. Clearly some things are a switch/router I guess.

    Open ##2207370