Ralph Droms wrote: > Tony - (assuming "they" == IPv6LL) can you explain why IPv6LL > will work while "they don't work in IPv4"? My experience > with IPv4LL has been uniformly bad; I've never intentionally > used an IPv4LL address and the automatic assignment of an > IPv4LL address has on several (many?) occasions silently > interfered with my ability to assign a non-LL address and use > greater internet connectivity. I will admit ignorance and am > happy to hear success stories about IPv4LL.
Not having been there when your interference issues occurred, I can only guess that they were related to the default IPv4 perspective that an interface only has one dynamic address at a time. In that environment it takes explicit effort (user initiated or stack timer) to change the available address. There is no such restriction in an IPv6 environment, so the existence of an IPv6 LL can't interfere with global connectivity. In fact it is much more likely that intermittent global access (such as changing radio attachment points) would interfere with the stablility of an app that is running locally.
Certainly some of my problems with IPv4LL have resulted, as you suggest, from the restriction that an interface have just one dynamic IPv4 address at a time. I think there's more to the problem - my experience has been that the IPv4LL address is configured *silently*, so I have no expectation that the interface is configured in an unexpected way and that, because of that configuration, none of my applications will work.
Perhaps the "configured silently" problem is a UI issue? I'd also like, as a UI issue I guess, the ability to turn off the configuration of IPv4LL addresses. Personally, I don't have any convenient way to use an IPv4LL address, and I'd rather not have any address configured at all than an IPv4LL address. (Note that I'm still talking about IPv4 here and not making any predictions about the availability of applications that can use IPv6LL addresses.)
So, will this problem be solved in IPv6LL addressing? Will I either get some indication from the stack that "no global addresses are configured" or will applications work as usual within the constraints of the network resources that can be reached on the LL?
In any event, I should be a little more precise when I say "applications can't use LL addresses". What I mean here is that the applications won't work in the way I expect. That is, I can't use DNS to identify hosts the application should communicate with, so I have to use an out of band (shout-down-the-hall?) protocol to ask "What's the address of your host" so I have an IP address to give to the application. I don't see where IPv6LL addressing works any differently in this regard than IPv4LL addressing, so I don't see how applications will work any better with IPv6LL addresses.
> I don't know that some folks "don't want to make the scenario > work".
Just to be clear - I think I'm in the "I'd like to know how the scenario will work" camp and am trying to tease out all the pieces that have to be in place so that it can work. I don't think IPv6LL addresses taken alone are the whole story (based on my experience with IPv4LL addresses)...
I don't understand the advantage to IPv6LL from the > scenario you described. We can assign IPv4LL addresses today > in a one-link, no router ad-hoc network. But we have to > enter the addresses manually and those addresses get in the > way when full Internet connectivity becomes available. > What's different with IPv6LL?
There is no 'get in the way' limitation. Simultaneous support for multiple dynamically acquired addresses is a major advantage of IPv6, as it enables scenarios that are simply not possible in the IPv4 model of a single address at a time. What this bumps into here is the fallacious assumption by some app developers that the routing space is globally flat, so if by chance there is more than one address, every available address can be treated equally. This is not a real problem in the market when only their apps fail, but it is a real problem when they try to prevent other app developers from taking advantage of the opportunities through limitations in the standards.
I may have misunderstood your part of your original message, in which you wrote:
So you are going to tell the army private that is ducking the barrage of gunfire that he can get the critical info he needs from the marine he just bumped into, if he only types these (what to him are pseudo-random) 32 hex characters for both the src & dst.
Are you describing configuring the interface, configuring the src and dst in a specific datagram or specifying addresses to an application?
- Ralph
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