Comment by orangeboats
1 month ago
I am tired of people claiming that you can make a "new Internet protocol that is compatible with IPv4".
No, backwards compatibility is not the problem here: IPv6-only hosts can easily connect to IPv4 hosts. Just append "64:ff9b::" to an existing IPv4 address, like so: 64:ff9b::8.8.8.8. Even prior to NAT64, we have plenty of schemes like 6to4 to bridge IPv4 and IPv6.
But no IPv4 hosts can ever connect to IPv6 hosts, or IPv7, or IPvInfinite for that matter. I will refer to my previous comment on why that is: https://news.ycombinator.com/item?id=46469336
I think the people complaining about compatibility are more talking about the concepts in IPv4 and IPv6. IPv6 could have been "everything is the same except the IP address is 16 bytes instead of 4". Instead there are new ways to do everything.
Addressing works differently (no broadcast, multicast everywhere, link-local is mandatory). Configuration works differently (SLAAC, RA, DHCPv6 is not a drop-in replacement for regular DHCP). Neighbor discovery replaces ARP and depends on ICMPv6 working. Fragmentation behavior changed. NAT is “not a thing” by design, which breaks a bunch of assumptions people built entire networks around.