I don't have one. I expect some people will just want the option of having more computers with actual IP addresses on their internal networks rather than just one externally-accessible address, just for convenience.
There's probably some benefit in the standard parts of IPv6 like QoS and IPsec which have been retrofitted onto IPv4 in various forms actually being guaranteed to be present on each host, but I'm not visionary to come up with a specific example at this time.
NAT's big shortcoming is that it's a hassle when you want one of your inside hosts to be able to receive connections from the outside like a server.
I think something will still exist like this for IPv6, but now you'll actually have more addresses when you want outside computers to be able to access an internal host. So it'll be up to you whether or not an outside host can diddle on the inside, which it wasn't before.
In IPv6, NAT will be to address the security issue you mention, rather than the shortage of address space that caused its inception in IPv4. It's the latter issue in which IPv6 is a solution.
It's not that they'll need an entire/64, but certainly more than one address. It's just a matter of not breaking the standard, and there really shouldn't be any reason an ISP would need to further subdivide their address space. After all, ISPs will typically be allocated a/32, which would give them 2^32/64s to allocate.
This is precisely why I said "in the current incarnation." Hopefully there will be enough consumer demand for/64s that it would be unwise for them to do this.
Whether or not your "prefix" changes each time will be much the same as whether or not your single IPv4 address changes each time you connect. Either your ISP statically assigns you one (perhaps for an extra fee), or it doesn't. But that 64-bit prefix will be your global identifier that gives you an address space, much as the single IPv4 address is your global identifier now, except your address space is only 1 address.
The intention with IPv6 is that you won't have "unroutable" networks, like we do with private nets such as 10.x.x.x and 192.168.x.x. Everything will have a globally unique IPv6 address. There was in the original spec what were called a "site-local" addresses, which were private addresses not routed to the outside much like their IPv4 analogues, but those have been deprecated.
However, you'll have plenty of addresses because, in the current incarnation, you're not allocated a single address, but rather you are allocated a subnetwork, which is currently 2^64 addresses. So the first 64 bits are assigned to you by your ISP, and then the second 64 bits are yours to do with as you like.
So that addresses the question of NAT: there won't be any lack of IP addresses necessitating its use. I am only addressing the use of NAT as a way around limited address space, and not any of the other uses for which NAT has.
But what about DHCP? IPv6 comes with something more elementary, called "stateless autoconfiguration." Basically, the router constantly broadcasts your "prefix" to the subnetwork, which is the first 64 bit half of your 128 bit address your ISP assigns you. The machine then takes its subnetwork ID (the MAC address), and sets the second 64 bits to a function of that. In the case of Ethernet, it isn't the 48-bit Ethernet MAC address verbatim, but a published function of it. It's called stateless because it's always a function of whatever the network's prefix is plus some kind of subnet ID, and there's no concept of leases, or any of the state a DHCP server maintains.
There is not yet an equivalent mechanism for "stateful autoconfiguration," which is more what DHCP is, where you can automatically assign an arbitrary address to a client. You can of course statically configure an interface to have a specific address, but there is no automated mechanism to always assign a particular autoconfigured client a particular address you designate. There are proposed standards for an IPv6 version of DHCP, however, and I expect eventually such a beast will eventually come around.
Students, faculty, and staff already have another unique identifier at UT-Austin called the Electronic Identifier (EID), which is already used to access most secure web services. The University is even in the process of replacing the SSN with this EID. It's just unfortunate that this happened before they had finished doing so.
Older EIDs are based off a person's name and might not be hard to guess, but at least you can't use it to apply for credit cards and loans.
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I don't have one. I expect some people will just want the option of having more computers with actual IP addresses on their internal networks rather than just one externally-accessible address, just for convenience.
There's probably some benefit in the standard parts of IPv6 like QoS and IPsec which have been retrofitted onto IPv4 in various forms actually being guaranteed to be present on each host, but I'm not visionary to come up with a specific example at this time.
NAT's big shortcoming is that it's a hassle when you want one of your inside hosts to be able to receive connections from the outside like a server.
I think something will still exist like this for IPv6, but now you'll actually have more addresses when you want outside computers to be able to access an internal host. So it'll be up to you whether or not an outside host can diddle on the inside, which it wasn't before.
In IPv6, NAT will be to address the security issue you mention, rather than the shortage of address space that caused its inception in IPv4. It's the latter issue in which IPv6 is a solution.
It's not that they'll need an entire /64, but certainly more than one address. It's just a matter of not breaking the standard, and there really shouldn't be any reason an ISP would need to further subdivide their address space. After all, ISPs will typically be allocated a /32, which would give them 2^32 /64s to allocate.
This is precisely why I said "in the current incarnation." Hopefully there will be enough consumer demand for /64s that it would be unwise for them to do this.
Oh, yeah, I forgot one more point:
Whether or not your "prefix" changes each time will be much the same as whether or not your single IPv4 address changes each time you connect. Either your ISP statically assigns you one (perhaps for an extra fee), or it doesn't. But that 64-bit prefix will be your global identifier that gives you an address space, much as the single IPv4 address is your global identifier now, except your address space is only 1 address.
The intention with IPv6 is that you won't have "unroutable" networks, like we do with private nets such as 10.x.x.x and 192.168.x.x. Everything will have a globally unique IPv6 address. There was in the original spec what were called a "site-local" addresses, which were private addresses not routed to the outside much like their IPv4 analogues, but those have been deprecated.
However, you'll have plenty of addresses because, in the current incarnation, you're not allocated a single address, but rather you are allocated a subnetwork, which is currently 2^64 addresses. So the first 64 bits are assigned to you by your ISP, and then the second 64 bits are yours to do with as you like.
So that addresses the question of NAT: there won't be any lack of IP addresses necessitating its use. I am only addressing the use of NAT as a way around limited address space, and not any of the other uses for which NAT has.
But what about DHCP? IPv6 comes with something more elementary, called "stateless autoconfiguration." Basically, the router constantly broadcasts your "prefix" to the subnetwork, which is the first 64 bit half of your 128 bit address your ISP assigns you. The machine then takes its subnetwork ID (the MAC address), and sets the second 64 bits to a function of that. In the case of Ethernet, it isn't the 48-bit Ethernet MAC address verbatim, but a published function of it. It's called stateless because it's always a function of whatever the network's prefix is plus some kind of subnet ID, and there's no concept of leases, or any of the state a DHCP server maintains.
There is not yet an equivalent mechanism for "stateful autoconfiguration," which is more what DHCP is, where you can automatically assign an arbitrary address to a client. You can of course statically configure an interface to have a specific address, but there is no automated mechanism to always assign a particular autoconfigured client a particular address you designate. There are proposed standards for an IPv6 version of DHCP, however, and I expect eventually such a beast will eventually come around.
Students, faculty, and staff already have another unique identifier at UT-Austin called the Electronic Identifier (EID), which is already used to access most secure web services. The University is even in the process of replacing the SSN with this EID. It's just unfortunate that this happened before they had finished doing so. Older EIDs are based off a person's name and might not be hard to guess, but at least you can't use it to apply for credit cards and loans.