> And once you go over 16 bits, you really need to start dealing with routing.
Disagree. you don't want to be routing unless you actually have to. A large flat network is more desirable a lot of the time (e.g thousands of devices in a DC) than a bunch of artificially carved up subnets.
The reason you don't see them very often is because people have had to use IPv4, which means ARP, which just doesn't scale. At some point in size, ARP chatter becomes the majority of the traffic on your network, which isn't great.
ND fixes this, and allows for ridiculously large networks (the way our good maker intended).
> Disagree. you don't want to be routing unless you actually have to. A large flat network is more desirable a lot of the time (e.g thousands of devices in a DC) than a bunch of artificially carved up subnets.
First, a /16 network is 65536 devices, which is pretty big as-is. And like in V4, you'll be able to disregard recommendations and choose a larger local net size (just change the netmask).
> ND fixes this, and allows for ridiculously large networks (the way our good maker intended).
ND doesn't solve it. It works in practice using the same old broadcast, just like ARP. Some switches might do ND snooping, but if you have thousands of devices, they'll overflow their internal tables and fall back to regular broadcasts.
ND also has unsolvable issues, like the neighbors cache size problems. Since you have a freaking /64 for your local network, you can't easily store the mapping for ALL hosts, and you're susceptible to various cache exhaustion attacks (including negative entries).
Snooping table sizes are typically around 16k entries. IGMP/ND packets are almost always punted to the CPU, so once the CPU is saturated, switches typically either fall back to broadcast or stop forwarding multicasts.
This varies widely by switch model, and 16k is on the low end. I looked at a few random Cisco and Arista switch datasheets just now and saw numbers ranging from 16k to 768k (usually 25% to 100% of the unicast MAC table size of the same switch).
Unicast MAC table space is scarce, too, and suffers the same failure modes when filled. You don't see people claiming this makes IPv4 over Ethernet infeasible. Do proper capacity planning, and this isn't a problem. Oversubscribe your network, and this is a problem even without multicast in the picture.
> Actually, people DO claim that [MAC table limits make IPv4 over Ethernet infeasible]. Flat Ethernet doesn't scale, and you need to use routing to break up broadcast domains.
This has nothing to do with unicast MAC table limits, and everything to do with ARP's O(n^2) scaling property. You use just as many MAC table entries in a network with 10 VLANs of 100 hosts as you do with 1 VLAN of 1000 hosts. Ethernet scales fine; ARP doesn't.
Disagree. you don't want to be routing unless you actually have to. A large flat network is more desirable a lot of the time (e.g thousands of devices in a DC) than a bunch of artificially carved up subnets.
The reason you don't see them very often is because people have had to use IPv4, which means ARP, which just doesn't scale. At some point in size, ARP chatter becomes the majority of the traffic on your network, which isn't great.
ND fixes this, and allows for ridiculously large networks (the way our good maker intended).