OSPFv2 requires functional extension beyond what can readily be done
with the fixed-format Link State Advertisements (LSAs) as described
in RFC 2328. This document defines OSPFv2 Opaque LSAs based on
Type-Length-Value (TLV) tuples that can be used to associate additional
attributes with prefixes or links. Depending on the application,
these prefixes and links may or may not be advertised in the fixed-format
LSAs. The OSPFv2 Opaque LSAs are optional and fully backward
compatible.