Well I'm curious. I can't think of any significant way it is "broken by design", so either this is hyperbole or I'm so used to the brokenness I'm not even thinking about it.

1. Ethernet happens, is designed around bus topology with shared medium and everyone talks by filtering out messages for themselves (with half of the addresses for multicast)

2. Digital works on moving ethernet from bus to star topology, design explicitly disallows connecting stars to each other without L3 router

3. Unfortunately, a non-trivial product range ends up based on LAT - essentially serial port over ethernet - and supposedly because of miscommunication LAT is very... raw-ethernet solution. No way to route it sensibly.

4. Suddenly, there's a need for larger L2 segments, except Ethernet has no way to support them (it finally gained one around starting ~2005 by throwing everything you know about L2 switching out)

5. It's too late to add features to ethernet that would make it work in larger span than single star, and possibility of loops bringing down exists, so do multicast storms (those weren't fixed).

6. The budget doesn't allow to put in a lot of computing power, a z80 gets thrown in. Spanning Tree Protocol gets created in vague hope to mitigate the curse of large L2 ethernet zones. We get stuck with primitive MAC learning 7. Genie is out of the box, and since you can crap out a too-large ethernet network much cheaper than do a proper routed one, the curse continues. Since cheap is the king, you often do not even get STP. Large scale networks fail when interns misconnect cables, multigigabit backbones end up doing 10mbit because STP made an ancient switch in the cleaning closet into root of the tree. Cats and Dogs living together, etc.

8. From around ~2005, proposals to fix it proper show up. Solution? Put routing into ethernet, using IS-IS for routing. On the other side, increasingly crazy centralized "decentralized" SDNs also try to setup L2 forwarding to deal with applications that can't deal with real IP subnetting. Somehow passing ethernet over XMPP over TLS (with BGP involved somewhere) is still better than ethernet's mac-learning.

CISCO had a lot of early customers among universities because dedicated box ran better than random unix workstation pulled out from other duties (or even sharing them) running RIP and the like.

there is a reason evpn exists, and is it to solve this exact issue by making gateways handle all logic normally stretched across to the other side of a l2vpn.

It's how I deployed VM's at scale using BGP from the VM host to the top of rack switch. VM's could route to each other, but no layer 2 connectivity.

It allowed for easy migration of systems between VM hosts too, as the ToR would learn the /128 or /32 and traffic would route to the new VM host.

Larger L2 spans should be done only when required, and preferably with things like TRILL/SPB.

absolutely, but in ipv4, the breakage has the effect of some niche-applications like TV streaming to client-machines breaking whereas in ipv6 it has the effect of the whole network breaking.

The applications broken in v4 are so niche that most people won't notice.

>SSDP (the tech underlying UPNP) already covers IPv6, there's no need to add new one

yes, but it's very badly supported still. I have not seen this work in any home-network yet, be it because of broken OSes, broken applications or broken router software.

>This also includes proper handling of ICMPv6

You're making me hopeful. Back when I was setting things up in 2014, the situation was a minefield of brokenness, sometimes even with UI showing huge warnings about my explicit allow-ICMP-rule I had to add after the default was to block all ICMP.

Except when you’re building these applications. Then it’s infuriating! Maybe more often a feeling of hopelessness than anger.