8 ms·

In your world, I have a service that speaks only ip4v2 and a client that speaks ip4v1. How does my packet get there? Everything in between me and them needs to

In your world, I have a service that speaks only ip4v2 and a client that speaks ip4v1. How does my packet get there? Everything in between me and them needs to understand how to handle this conversation. Old routers and switches may drop or misroute packets. What about prefixes. The vast majority of ipv4 has been allocated. It we just have more octets then we haven't actually made more available allocations because they will be under already assigned prefixes. The smallest globally routable allocations in ipv4 is a /24. Routing hardware has a limit on the number of prefixes it can route. Just changing that to a smaller size would ease pressure, but even that is impossible without upgrading all switching infrastructure to handle the space. The next version of IP was always going to be a brand new protocol. There wasn't even a realistic option besides that.

jmyeet 3y ago
The point of an IP4v2 (to borrow your naming convention) address is that because it's prefixed with an IP4v1 address, then it can still get somewhere useful if an intervening router or even the destination gateway doesn't understand IP4v2. Think of IP4v2 as essentially embedding a NAT field into the IP header. This might work or it might not in any given circumstance but the path to make it work is a lot more straightforward. As for the routing table size issue, it's not really an issue at all. Assuming extra octets, a /24 block holds 16M addresses instead of 256 (or 254 realistically). You don't need a larger routing table. This would also allow an organization that might've had a /16 or /8 block or multiple blocks to get by with 1 (or a few) /24 blocks, allowing you to reclaim blocks without making external routing tables any larger.
- growse 3y ago
  How does the ip4v1 device know how to address the ip4v2 device in order to send a packet back? > As for the routing table size issue, it's not really an issue at all. Assuming extra octets, a /24 block holds 16M addresses instead of 256 (or 254 realistically). You don't need a larger routing table. If you want to subdivide those 16M addresses in any useful way, you're going to need a larger routing table.

jmyeet 3y ago

The point of an IP4v2 (to borrow your naming convention) address is that because it's prefixed with an IP4v1 address, then it can still get somewhere useful if an intervening router or even the destination gateway doesn't understand IP4v2. Think of IP4v2 as essentially embedding a NAT field into the IP header. This might work or it might not in any given circumstance but the path to make it work is a lot more straightforward. As for the routing table size issue, it's not really an issue at all. Assuming extra octets, a /24 block holds 16M addresses instead of 256 (or 254 realistically). You don't need a larger routing table. This would also allow an organization that might've had a /16 or /8 block or multiple blocks to get by with 1 (or a few) /24 blocks, allowing you to reclaim blocks without making external routing tables any larger.

growse 3y ago
How does the ip4v1 device know how to address the ip4v2 device in order to send a packet back? > As for the routing table size issue, it's not really an issue at all. Assuming extra octets, a /24 block holds 16M addresses instead of 256 (or 254 realistically). You don't need a larger routing table. If you want to subdivide those 16M addresses in any useful way, you're going to need a larger routing table.