As a branch of the discussion [homenet] ULA scope [draft-ietf-6man-rfc3484-revise-05.txt], I would like some clear explanation of the actual issues related to routing between hosts in ULA subnets. Some people seems to be concerned for a reason that seems pretty unclear to me.
Here is my use case: ================= I have a new house. The electrician installs lighting devices from two vendors using different LLN technologies, e.g. power line and RF. The ISP has not installed a CER router yet, so there is no central source of prefixes or naming service. The electrician completes his installation by including devices with their respective border routers and testing with a stand-alone tool that all devices communicate correctly. Now a technician sets up advanced rules for how timers and sensors control lights and window blinds. He plugs a cable between the two LLN border routers and connects a PC. He uses mDNS to discover the devices via Resource Directories in the LLN border routers. Devices are configured to control other devices using some application protocol. Everything works when the technician leaves the house. A week later the ISP installs the CER router. Everything still works. Here is my question(s): ================== Why should homenet require the subnet ULAs to be distributed from another router? It works without extra routers in the scenario described above. (Actually, the technician's configuration would break if new ULAs were distributed by another router later on). Why cannot two border routers connected to the homenet LAN make routing protocol announcements for two different ULA prefixes - such as: "I am the router with LAN link-local address X and you can use me to reach ULA subnet XX" ? In a homenet case, why cannot the default ULA policy be boiled down to "Discard ULA packets trying to pass the CER"? Thanks, Anders
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