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IPv4 and IPv6 are both complex protocols. Changing anything does mean that you have to replace all the routers, but if you only change the address length, the

by LukeShu 14y ago

IPv4 and IPv6 are both complex protocols. Changing anything does mean that you have to replace all the routers, but if you only change the address length, the new routers are almost the same as the old ones, nothing needs re-engineered. Nobody needs retrained. Most software just needs a struct in a header file modified. You do need to replace everything, but you don't need to re-engineer everything. (Not necessarily my opinion, but my interpretation of GP's opinion)

purephase 14y ago
That is sort of what I meant. I stick by my caveat at the end though and recognize that it is likely far more complex than that which is why we're in the situation we're currently in.
XorNot 14y ago
If you change the address length, no old router and route packets to a new longer address. Nor can they route packets from long addresses to short ones. Game over. You can't "just change the address length". They're hardware ICs. If the address is not 32 bits long, then its a malformed packet that should be ignored. They cannot handle it differently. They can't be reprogrammed. There's been some consternation over Cisco stuff in this capacity, since they use an ASIC for IPv4 and a software-mechanism for IPv6 which is not nearly as fast. The cost and complexity of changing hardware is enormous compared to every other part of the process. IPv6 in software has been solved, and where it can't be solved you can shim-it trivially by comparison. Software is not what's holding it back.
- mprovost 14y ago
  They could have made the change backwards compatible. Basically by doing something along the lines of designating a part of IPv4 space for use with the new protocol, and then stuffing the extra address into the optional header field. Then if you're running an older device that doesn't understand the new header it will just forward it along until it gets to a device that can.
  - XorNot 14y ago
    Which puts you in the same problem: to any device (i.e. one with a hard-wired ASIC - the largest and fastest hardware generally) the new address space does not exist. The internet goes to some lengths to avoid routing loops as well, so once a packet is passed one router we're not going to be able to easily spin it around and send it back to get to the right place. The net effect is going to be to randomly DDoS a bunch of devices which happen to be behind non IPv4.5 hardware, and so receive 50% of the internets traffic which doesn't get routed properly by an upstream router.

by LukeShu 14y ago

purephase 14y ago

That is sort of what I meant. I stick by my caveat at the end though and recognize that it is likely far more complex than that which is why we're in the situation we're currently in.

XorNot 14y ago

If you change the address length, no old router and route packets to a new longer address. Nor can they route packets from long addresses to short ones. Game over. You can't "just change the address length". They're hardware ICs. If the address is not 32 bits long, then its a malformed packet that should be ignored. They cannot handle it differently. They can't be reprogrammed. There's been some consternation over Cisco stuff in this capacity, since they use an ASIC for IPv4 and a software-mechanism for IPv6 which is not nearly as fast. The cost and complexity of changing hardware is enormous compared to every other part of the process. IPv6 in software has been solved, and where it can't be solved you can shim-it trivially by comparison. Software is not what's holding it back.

mprovost 14y ago
They could have made the change backwards compatible. Basically by doing something along the lines of designating a part of IPv4 space for use with the new protocol, and then stuffing the extra address into the optional header field. Then if you're running an older device that doesn't understand the new header it will just forward it along until it gets to a device that can.
- XorNot 14y ago
  Which puts you in the same problem: to any device (i.e. one with a hard-wired ASIC - the largest and fastest hardware generally) the new address space does not exist. The internet goes to some lengths to avoid routing loops as well, so once a packet is passed one router we're not going to be able to easily spin it around and send it back to get to the right place. The net effect is going to be to randomly DDoS a bunch of devices which happen to be behind non IPv4.5 hardware, and so receive 50% of the internets traffic which doesn't get routed properly by an upstream router.