On Aug 17, 2010, at 8:47 AM, Eric Gray wrote: > Jared, > > Actually, if you look at the question from a slightly different > perspective, there is more than one "legitimate operational reason." > > The "recast" version of the question is what is the cost to the > network if a host IS required to know this information (for reasons > having not a lot to do with making the host itself work correctly), > and "knows" incorrect information? > > The first (and probably most important) reason why networks > should not depend on hosts having the correct information, is the > likelihood that a host (which may or may not be under the operational > control of the network operator) might be misconfigured. > > DHCP has done much to fix this problem, at least for the hosts > that are cooperative. But there is always the possibility that the > need to keep the host updated (via DHCP, for instance) may be less > than healthy for the host. And - quite frankly - the host does not > really need to know this information in most cases.
Poorly configured and behaving network elements (hosts, routers) will always exist. Building a fault-tolerant system should be a goal, but this requires cooperation. > A second reason is more philosophical (though the above reason > is one aspect of this higher-level "philosophical" reason) - it is > not a good idea in general to force a "need-to-know" on entities that > do not themselves have an existing "need-to-know." Doing so has the > undesirable effect of increasing the amount of knowledge that needs > to be correctly "spread around." Correct, so spreading network topology information via redirects is not an ideal situation as they don't need to know. As a host, I need to know what is on-net and what should be forwarded to my router (default gateway). As a router, I need to know my topology, and in the event "I don't know", there may exist a higher level authority (default) to direct my packets/frames/cells/modulation to. - Jared -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
