IETF Last Call Review of draft-ietf-lsr-anycast-flag-08
review-ietf-lsr-anycast-flag-08-opsdir-lc-schoenwaelder-2025-11-20-00

I have reviewed draft-ietf-lsr-anycast-flag-08. I have ticked "has
issues" since there is no "I have questions" choice - and what follows
may just show my lack of familiarity with OSPF.

While the abstract clearly states the purpose of the document
('defines a new flag in the OSPFv2 Extended Prefix TLV Flags to
advertise the anycast property'), the introduction does not really do
that but it goes right into technical details before stating the
purpose of the document. (And as a first time reader, I was not sure
why all these details matter - but more on that later). Anyway, this
is entirely stylistic.

I was not sure what the N-bit is, which is discussed in section 2. I
guess routing people know the N-bit by heart but for the less informed
reader, it may help to spell out what it is and where it is defined.
Perhaps also explain why it is a bad idea to set both the N-bit and
the new AC-flag. It seems that the words 'bit' and 'flag' are used
interchangeably here, but perhaps refer to things defined as -bit
always as bit and things defined as -flag always as flag? Again, this
is stylistic.

While searching for the definition of the N-bit, I ended up looking
into RFC 9513 and I found that there is also an AC-bit define where I
spotted an N-bit. Since this I-D also defines an AC-flag, can this
name clash lead to confusion? I guess I am bit lost on the context as
I am not deeply familiar with OSPF specifications. I guess this is
what the text in the introduction tried to explain. So probably it all
makes sense but on first read I did not get it. Anyway, what happens
to the older AC bit, is it they still needed? Can there be situations
where AC-bit and AC flag come together and may disagree?

The new YANG leaf 'anycast-flag' is augmenting an ospf interface. The
description says "Sets the prefix as an anycast address." Is it clear
which prefix is meant?

From an operational perspective, what is the effect of setting the
AC-flag on an anycast address versus not setting it (which is likely
the current behavior)? Does setting this flag cause other routers to
change their behavior? What should an operator do if some of the
routers support the new AC-flag but others don't?