On Wed, Apr 8, 2009 at 4:06 PM, Roland Bless <[email protected]> wrote: >> Counterexample #2: The IP address of an anycasted DNS service. The IP >> address neither identifies an endpoint nor locates a particular >> interface's points of attachment to the network. Instead it identifies >> a service and specifies multiple locations via which that service can >> be obtained. > > Correct, but I don't think that this is really a counterexample: > The Anycast address identifies _an_ endpoint (though not a > particular/specific one) that hosts the DNS service.
Hi Roland, Nice try, but "an" is synonymous with "one" and "one endpoint" doesn't mean "a more or less random choice among the many endpoints eligible to respond." Even if it did, packets may be routed to different servers on a packet by packet basis depending on the metric and whether per-packet load sharing is enabled. The address can hardly be an endpoint identifier if a different endpoint is selected for every single packet. > Anycast > routing will locate _an_ interface belonging to such an endpoint. Nope. The anycast DNS servers are configured with unicast IP addresses on their network interfaces. The anycast address is assigned as a local machine alias, reachable only by packets that get routed to the machine through one of its unicast interfaces. Counter-example #3: Describe for me, if you will, the locator and endpoint identifier semantics associated with 127.0.0.1. Counter-example #4: At home, I duck bandwidth limits on my ISP's usenet server by configuring my Linux router to apply NAT and spread the source address for outbound requests to TCP port 119 among all of my static IP addresses on a connection by connection basis. It does this both for source IPs used by machines are tasked to other purposes and for IP addresses which are not assigned to any machine. In all of those cases, the NAT machine functions as a normal router and packet-filtering firewall in for packets except for the specific ones where the exterior TCP port is 119. It does not mangle or translate any other packets. In this configuration, the source IP address has no endpoint identifier semantics whatsoever, with Tony's definition or any other. The TCP connection ID looks a lot like an identifier but the source IP address by itself has only locator semantics, and then only until the entry into my network after which packets with an external port of 119 go one way and the other packets go one of a number of different directions. What was it Hamlet said? More things on heaven and earth? Regards, Bill Herrin -- William D. Herrin ................ [email protected] [email protected] 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
