On 2009-10-14 03:38, Christian Huitema wrote: ... > > First, we wonder about the importance of the 64 bit boundary. > Addressing documents specify that the global address is > essentially formed of a 64 bit subnet prefix and a 64 bit > host identifier, with the host identifier compatible with > IEEE 802 identifiers. Does that mean that the "routing" > requirement of stateless translation can only be addressed if > the IPv4 bytes are entirely contained within the subnet > prefix? Different authors have different opinions, so WG > input would be beneficial.
As I understand it, routers should never treat /64 as special or as any kind of limit. It's just a convention that /64 is considered the longest normal subnet prefix, which happens to be compatible with SLAAC. So I can't see any fundamental reason why the IPv4 address bits can't straddle the /64 boundary. However, they should clearly skip over the UG bits so the resulting 64-bit IID is consistent with the IID rules. That will break byte alignment. > > Second, we wonder about the constraints of host identifiers. > A first question is whether an all null identifier would be > legitimate and practical. There is some evidence that it > works with most stacks. But there is also a statement in the > addressing document that the all null address is reserved for > the subnet anycast address. Do stacks actually implement the > subnet anycast function? Should the specification be removed > from the addressing RFC? Can we just ignore it? If we cannot > ignore it, we will have to specify some value different from > zero for the suffix. A "checksum neutrality" field might do > that, but please consider the second question. If you do straddle the /64 boundary, you will not have a null IID so the issue goes away. If not, using null feels wrong to me. Firstly, it conflicts with the current (harmless and possibly implemented) spec. Secondly, specifying a value is no big deal as far as I can see. > > The second question regards the uniqueness of host > identifiers. Suppose we define the address used for stateless > translation as: 32 bit "provider" prefix, 32 bit IPv4 > address, and a constant identifier, either 0 or the "checksum > neutrality" value, which is only a function of the provider > prefix. Suppose now that for some reason there are two "IPv4 > addressed" hosts on the same link, e.g. because many servers > are located in the same server room. The two hosts will have > different addresses, in different 64 bit subnets, but they > will also have different host identifiers. Is that OK? Why wouldn't it be OK? I can't see why it's a question. The normal expectation is that different hosts have different IIDs so I am curious why this matters. Brian > > -- Christian Huitema > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list ipv6@ietf.org > Administrative Requests: > https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- > > -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
