Hi! I’m no expert on SFC so I spent some time reviewing RFC7665 and Simon Josefsson’s secdir review [0] as well as RFC 8300 and 8393.  It looks like all the things I was going to pick on are addressed by the references.

I’ll let somebody else on the IESG debate whether Figure 4 is trying to be a little different than the rest of this architectural document by specify some protocols bits; informational still?

[0] https://datatracker.ietf.org/doc/review-ietf-sfc-architecture-08-secdir-lc-josefsson-2015-05-28/