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For one, all IPv4 addresses could also be IPv6 addresses. There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just b

by Asooka 9y ago

For one, all IPv4 addresses could also be IPv6 addresses. There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just by prepending the address with 0s. You could enable backbone routers to speak only IPv6 and then translate those packets to IPv4 packets only when sending them to the endpoint devices. In short, IPv6 could have been designed as a backwards-compatible extension of IPv4, not a completely new network.

growse 9y ago
> For one, all IPv4 addresses could also be IPv6 addresses You mean how you can map from IPv4 addresses to IPv6 addresses? See RFC4291 section 2.5.5. https://www.ietf.org/rfc/rfc4291.txt https://www.ietf.org/rfc/rfc4291.txt
zAy0LfpBZLC8mAC 9y ago
> For one, all IPv4 addresses could also be IPv6 addresses. You have that today, all IPv4 addresses are also dualstack addresses, which is how IPv6 is normally deployed for the transition. > There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just by prepending the address with 0s. Which doesn't help you anything because it doesn't enable IPv4 hosts to communicate with IPv6 hosts. > You could enable backbone routers to speak only IPv6 and then translate those packets to IPv4 packets only when sending them to the endpoint devices. That's called a tunnel, you can have that today. > IPv6 could have been designed as a backwards-compatible extension of IPv4, not a completely new network. What exactly is the backwards compatibility if none of that allows IPv4 and IPv6 hosts to interoperate?
stephen_g 9y ago
That still doesn't work though, because an IPv4 host still can't address an IPv6 host, and an IPv4 router still wouldn't be able to route to an IPv6 network (without hacks far uglier than NAT). And they couldn't just upgrade every router in every backhaul network to the new protocol at once (assuming what you describe could actually work) - that took a decade, because lots of it used custom silicon for routing and switching.
jcranmer 9y ago
> There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just by prepending the address with 0s. I'm guessing you're unaware that this is what you do right now. The IPv4 address space has a map in IPv6 at ::ffff:0:0/96 for being able to listen to both IPv4 and IPv6 on an IPv6 address space. There's also a few other different maps of the entire IPv4 address space for other mixed IPv4/IPv6 schemes. The problem with any addressing enhancement to IPv4 is you still have to change every software ever (at the very least, you need to know how to craft new addresses), and you still have to change almost all hardware as well. Maybe you can devise schemes that could let some of the hardware in the middle be IPv6-unaware, but you still have to route the resulting packets to the correct location, which means you'd want to update most of the middle hops anyways.

by Asooka 9y ago

growse 9y ago

> For one, all IPv4 addresses could also be IPv6 addresses You mean how you can map from IPv4 addresses to IPv6 addresses? See RFC4291 section 2.5.5. https://www.ietf.org/rfc/rfc4291.txt https://www.ietf.org/rfc/rfc4291.txt

zAy0LfpBZLC8mAC 9y ago

> For one, all IPv4 addresses could also be IPv6 addresses. You have that today, all IPv4 addresses are also dualstack addresses, which is how IPv6 is normally deployed for the transition. > There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just by prepending the address with 0s. Which doesn't help you anything because it doesn't enable IPv4 hosts to communicate with IPv6 hosts. > You could enable backbone routers to speak only IPv6 and then translate those packets to IPv4 packets only when sending them to the endpoint devices. That's called a tunnel, you can have that today. > IPv6 could have been designed as a backwards-compatible extension of IPv4, not a completely new network. What exactly is the backwards compatibility if none of that allows IPv4 and IPv6 hosts to interoperate?

stephen_g 9y ago

That still doesn't work though, because an IPv4 host still can't address an IPv6 host, and an IPv4 router still wouldn't be able to route to an IPv6 network (without hacks far uglier than NAT). And they couldn't just upgrade every router in every backhaul network to the new protocol at once (assuming what you describe could actually work) - that took a decade, because lots of it used custom silicon for routing and switching.

jcranmer 9y ago

> There could be a straightforward translation between an IPv4 packet and an IPv6 packet and back just by prepending the address with 0s. I'm guessing you're unaware that this is what you do right now. The IPv4 address space has a map in IPv6 at ::ffff:0:0/96 for being able to listen to both IPv4 and IPv6 on an IPv6 address space. There's also a few other different maps of the entire IPv4 address space for other mixed IPv4/IPv6 schemes. The problem with any addressing enhancement to IPv4 is you still have to change every software ever (at the very least, you need to know how to craft new addresses), and you still have to change almost all hardware as well. Maybe you can devise schemes that could let some of the hardware in the middle be IPv6-unaware, but you still have to route the resulting packets to the correct location, which means you'd want to update most of the middle hops anyways.