I'm trying to get my head round IPv6. I've stumbled on something which surprised me, and I'm looking to understand this better in terms of networking:
Do Link Local addresses remove the need for a router to have multiple routable IP addresses?
As I understand it: IPv4 subnets are used to identify addresses which could be found using ARP. Beyond that they are used as logical groups of IP addresses for routing, where all IP addresses in a group can be contacted via the same route (next hop). All setups that I've seen have given each router multiple IP addresses, one for each subnet it's attached to. That is, each physical subnet needed its own logical IP subnet and a router attached to multiple subnets would need an IP address in each.
However under IPv6 ARP is gone and replaced by NDP. When I look on my own VM, it doesn't even know how big it's subnet really is. It thinks it's on a
/64 but in fact it's in a much larger subnet. The entire
/64 subnet is dedicated to my VM and its gateway is already outside that.
This suggests to me that IP subnets are subtly different under IPv6. It suggests that unlike ARP, NDP can detect physically connected routers without the routers having an IP on the same subnet.
My question is really this: If a physical subnet is composed entirely of routers, does the subnet need its own IPv6 subnet, or can / will the routers just use Link Local Addresses for that subnet:
Subnet-With-IP <--Router--> Subnet-no-IP <--Router--> Subnet-With-IP