RFC: A proposed path towards OSPFv3 LSA Extensibility

[acooks-at-bda]

The is a Request For Comments on my approach for adding support for RFC 8362 OSPFv3 LSA Extensibility.

The main problem to solve is that ospf6d operates directly on the LSAs and the 'records' or 'descriptors' in each LSA, without much abstraction between the protocol logic and the format of data on the wire.

RFC 8362 adds new LSAs that nearly maps one-to-one to existing LSAs, but with the each of the 'descriptors' in each LSA wrapped in a TLV. This additional TLV header breaks all the pointer arithmetic used for handling the descriptors. To support the new LSAs, these descriptors need to be unwrapped from their TLVs - and they can then be processed more-or-less in the same way as the existing descriptors.

This change set contains Work-In-Progress for two separable chunks:

• to extract the functions that operate on descriptors from their LSA-handling scope, and insert an abstraction so that these functions can be used when processing the new E-LSAs.
• early work to show how E-LSAs would use the refactored descriptor functions.

It's a sizeable change that is hard to review as one PR, but I've tried to break it into reviewable commits. Depending on feedback and progress, I imagine this work would eventually be staged in multiple PRs.

Thank you for your consideration.