Re: [vwrap] VWRAP and IPv6

[Richard Barnes <[e-mail]>]

The impact of IPv6 on VWs should be far less than you imagine, I  
think. :)

It has often been said that many, many things will be assigned IPv6  
addresses.  There will certainly be enough to go around, but that  
doesn't make them good application-layer identifiers.  If you want to  
use IP addresses with IP, they have to route, and that means that they  
have to be either (1) topologically assigned, or (2) overlay routed,  
e.g., with mobile IP.  So if you want to use an IP address to address  
something, you're going to have to either change that address when the  
thing gets connected differently, or you'll need some overlay routing  
scheme to route to a persistent address.  (And if you're not going to  
use the address with IP, then why would you use an IP address?)

VWRAP, as an application layer protocol, has a choice about what  
identifiers to use for things and how to use those identifiers.  ISTM  
that using IP addresses (again, of either type) remains a bad idea,  
compared with something that is decoupled from the routing layer.

As far as the DNS, I'm not sure what your point is:
(i) DNS caching has been around for decades
(ii) DNS names can already refer to multiple addresses
(iii) Depends on implementation.  Maybe there's some application-layer  
way to resolve names.  E.g., SIP endpoints don't need to have DNS  
records because the INVITE transaction maps from SIP URIs to IP  
addresses.
(iv) From RFC 4291: "IPv6 addresses are 128-bit identifiers for  
interfaces and sets of
interfaces"
(v) Seems like there's a use case lurking, hard to address without  
details.  But you're probably still at the application layer.  For  
instance, if you were telling your peer to send you an HTTP request,  
you would send an HTTP URI, which can already handle IPv6 addresses.

--Richard


On May 19, 2010, at 9:35 AM, Morgaine wrote:

> The impact of IPv6 on VWs is going to be far greater than you  
> imagine, I believe.  As things stand, VWRAP is being designed around  
> the features and limitations of IPv4 networking.  It will of course  
> be able to ride on top of IPv6 as a transport, but unable to benefit  
> from its improved feature set, unless we provide the means to do so.
>
> The question "Why is there ever a need to carry an IP address in  
> this application-layer protocol, as opposed to, say, a DNS name or a  
> URI?" suggests an IPv4 mindset, because in IPv6 it has a variety of  
> possible answers:  (i) When the DNS lookup has already been done and  
> does not need to be done again, (ii) When a FQDN maps to multiple  
> addresses, but you want to refer to a specific one, (iii) When an  
> IPv6 address does not have an external address record, (iv) When the  
> host is already known and the IP address denotes something other  
> than a physical NIC interface, or (v) When listeners are allocated  
> locally and dynamically for the current session only, and their IP  
> addresses need to be communicated to a peer --- this will be an  
> extremely common use case with IPv6.
>
> In today's IPv4-based systems, it is normal for a user's machine to  
> have a single IP address, and for a client on that machine to talk  
> to a server that has a single customer-facing IP address too  
> (although it may also have others that are not public).  In IPv6- 
> based systems, this simple scenario is still possible but represents  
> only a special case among a new and vastly expanded set of IPv6 use  
> cases.
>
> The smallest allocatable block of IPv6 address space is a /64, so  
> 2^(128-64) IP addresses is the number that most normal IPv6 users  
> will have, although the much larger /48 blocks of 2^80 addresses are  
> commonly assigned to users as well.  With such IP riches client- 
> side, it is certain that they will be used for something, and the  
> obvious suggestion is to give every VW object an IPv6 address of its  
> own.
>
> Lest we forget, one of the most important properties of the REST  
> paradigm is addressability, but the benefits of high addressability  
> go far beyond the Web.  This is a property that will become  
> ubiquitous throughout networked computing with IPv6.  It's probably  
> no exaggeration to say that *everything* will be getting its own IP  
> address. :-)
>
> Faced with that future, it's a mistake to think in IPv4 terms and  
> consider IPv6 addresses as merely denoting a host which can be  
> obtained from its FQDN.  That's IPv4 thinking, and represents only a  
> very basic use case for IPv6.  In more extended use cases, IPv6  
> addresses will become much more like active local UUIDs than like  
> today's host IP addresses.  They will be used for inner-application  
> addressing, for example to make every object in an application an  
> addressable micro-server.
>
> VWRAP is being born into an IPv6 world, and it would be a mistake to  
> hardwire IPv4 thinking into its design.  We continually refer to the  
> need for extensibility and a desire to future-proof the protocol,  
> but lip service is not enough.  Adding IPv6 addresses to the  
> underlying ADT would provide a bare minimum level of thinking ahead  
> to support VWRAP implementations that embrace large numbers of  
> communicating objects.  (A generally extensible ADT would of course  
> achieve the same thing, and more.)
>
>
> Morgaine.
>
>
>
>
>
>
>
> ==============================================
>
> On Mon, May 17, 2010 at 3:50 PM, David W Levine <[e-mail]>  
> wrote:
>
>
> [e-mail] wrote on 05/17/2010 10:08:26 AM:
>
> > [image removed]
> >
> > Re: [vwrap] VWRAP and IPv6
> >
> > Richard Barnes
> >
> > to:
> >
> > Morgaine
> >
> > 05/17/2010 10:09 AM
> >
> > Sent by:
> >
> > [e-mail]
> >
> > Cc:
> >
> > vwrap
> >
> > In the spirit of good layering, it seems like we should be talking
> > about avoiding direct reliance on IP addresses instead of how we can
> > accommodate different addresses in the protocol.  Why is there  
> ever a
> > need to carry an IP address in this application-layer protocol, as
> > opposed to, say, a DNS name or a URI?
> >
> > --Richard
> >
> +1
>
> We may from time to time have a IP address stuck in the form of a URI
> which has the dotted decimal form of an resource. The spec should make
> sure that form can be an IPV6 address, but that should be very  
> straight
> forward.
>
> There may be some IPV6 features which eventually impact us at the  
> protocol
> design level, but the entire VWRAP specification has been written in  
> terms of
> URIs and Capabilities, not in terms of low level IP addresses. It  
> would take an
> incredibly powerful argument to suggest that this should change.  
> Likewise, while
> IPV6 changes addressing at the bottom of the stack, it doesn't  
> appreciably change
> the cost of holding open sessions, of managing sockets and buffers  
> inside of
> clients (especially lightweight devices) Further while we can all  
> devoutly hope
> that IPV6 finally deploys broadly, making it a dependancy in the  
> near term feels
> rather like a roadblock to possible adoption.
>
> - David
> ~ Zha
>
>
>
> >
> > On May 14, 2010, at 7:32 AM, Morgaine wrote:
> >
> > > Despite exceedingly low takeup of IPv6 so far, it's coming, and in
> > > the context of IETF WG rates of progress, it is really  
> imminent.  Of
> > > special relevance to us is that IPv4 addresses are projected to  
> run
> > > out within roughly the same time frame as VWRAP materializes.
> > >
> > > There is little point in creating a new VW protocol today purely  
> in
> > > the context of IPv4 without thinking about tomorrow's IPv6
> > > environment.  By the time that VWRAP is fully defined, we should
> > > expect a substantial and rapidly increasing proportion of VWRAP
> > > implementations to occur in IPv6-accessible worlds.  This is a
> > > situation for which we need to plan now, otherwise the protocol  
> will
> > > be obsolete before it's even ready.
> > >
> > > To get the ball rolling, here are a few IPv6-related issues that  
> we
> > > could usefully address in the group:
> > >
> > >    • The 128-bit IP address of IPv6 is likely to become a common
> > > payload, so it should be supported natively.  LLSD already  
> supports
> > > one 128-bit data type of course, the UUID.  IPv6 addresses should
> > > not be transported in UUID fields however, since their statistical
> > > properties and semantics are totally different.  In any case, the
> > > two spaces are disjoint so confusing them would be a mistake.  The
> > > IPv6 address seems a good candidate for its own defined type, in  
> the
> > > absence of wide integers.
> > >    • The extremely large address space of IPv6 has often been
> > > portrayed as allowing everything around us to have its own IP
> > > address.  In the context of virtual worlds, this idea can actually
> > > be put to good use, with each virtual object bearing its own IPv6
> > > address.  One candidate application for this has already been
> > > described in earlier discussions --- for example, implementing
> > > virtual object simulation in two parts, one client-side and one
> > > world-side, the two parts communicating directly.  IPv6 addressing
> > > of objects makes this relatively easy to achieve efficiently, so  
> its
> > > implementation in IPv6-based worlds is almost inevitable before
> > > long.  VWRAP should be ready for this.
> > >    • The event queue in current implementations provides an  
> indirect
> > > and highly inefficient way of achieving world-to-client
> > > communications.  IPv6 offers opportunities for direct  
> communication
> > > that can make the event queue approach obsolete, so it's worth
> > > examining IPv6-oriented alternatives.
> > >    • We recently discussed feature and protocol negotiation within
> > > VWRAP.  IPv6 provides much opportunity for new features and  
> protocol
> > > pathways to be negotiated between endpoints, so it gives us a very
> > > real and imminent set of use cases for negotiation.
> > >
> > > It would also be a feather in VWRAP's cap to be considered an  
> "IPv6-
> > > capable application protocol" in a stronger sense than just to be
> > > carried by IPv6 networks.  IPv6 does after all bring new abilities
> > > to the table, such as the huge addressing, and it would be a  
> mistake
> > > to ignore them.
> > >
> > >
> > > Morgaine.
> > >
> > >
> > >
> > > _______________________________________________
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> > > [e-mail]
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> >
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