Hi, Sorry to dig this one up again, but although there has been a fair bit of discussion around the topic, I don't think that we have so far reached an agreement on how to provision sw CPEs with the address of the concentrator for MAP-E and lw4o6. We need to get a final answer on this as there's a few drafts (softwire-unified-cpe, softwire-map-dhcp, softwire-lw4over6) that are relying on it.
To try and summarise what's already out there: The Unified CPE & lw4o6 drafts propose the use of DHCPv6 Option 64 (the DS-Lite AFTR FQDN option) Map-dhcp describes the use of the default mapping rule (DMR) to provide the /128 of the BR I think that it's reasonable to say that both work – I.e. They contain enough information to provision the client with the /128 of the concentrator so that it can send traffic. Here are the arguments for/against each that I've seen. I've tried to list all the ones that I've seen, so if I've missed any, then please add them: DHCPv6 Option 64 Pros FQDN means that DNS round-robin load balancing could be used Reuse of an existing option Cons Can not be extended with additional sub-options map-dhcp DMR Pros Option has an 'encapsulated options' field, so could be extended with additional functionality (although no additional functionality has currently been proposed at this stage) Cons Only one DMR /128 can be provisioned to a client, so round robin load balancing can't be used May conflict with the MAP-T (</128 prefix) DMR – Could be considered to be out of scope for this discussion, but if we are following the mechanisms described in Unified CPE so that a CPE can work out which SW mode to configure, then a dedicated MAP-T sub-option (not shared by any other mode) is needed. This is related to conversations that I've had around extending the Unified CPE model for other softwire approaches. My view: If there is additional functionality required in this option, over an above the provisioning of a /128 prefix for the concentrator, then the MAP DMR (limited to MAP-E) is the clear choice. However, if no such functionality is needed, then we should re-use Option 64. Cheers, Ian
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