Hi Peter,
I’ve reviewed the OSPF Segment Routing WG draft and have some comments.
1. Can you describe the usage of algorithm in the Segment Routing
domain? An SR capable router advertises the algorithms it supports and an
algorithm is associated with a Prefix-SID. However, the usage of this
information is not described anywhere and it is guaranteed that there will be
many different interpretations.
2. The usage of the advertised Weight references the “Segment Routing
Architecture”. However, there is no description of weight usage there.
3. Section 3.2 - the range advertisement seems a bit unnatural. Why is
it assumed that all the advertised ranges have the same size? It would seem
more intuitive that individual ranges are defined by the <size/starting SID>
tuple.
4. Section 4.2 - Can you please make the P-flag the NP-Flag since the
set value indicates not to perform the PHP operation? If you want to keep it
the P-Flag, the set value should mean to perform the PHP.
5. Section 4.2 and 5.2 - The Segment Routing architecture defines
adjacency SIDs as having local significance. Yet the L-Flag allows this to be
encoded as global. Similarly, it would seem that a prefix SID would normally
have global significance and local significance would be an exception (e.g.,
possibly a loopback address accessible only from the advertising OSPF router).
6. Section 4.2 - I really don’t like having his sub-TLV redefine the
subsuming top-level TLV as a range of prefixes of the same length rather than a
single prefix. Although this is my first serious reading of the draft, this
encoding seems really unwieldy and, in practice, I’d expect the range size
always advertised as 1. We can discuss this more in Toronto.
7. Section 4.2 - Shouldn’t the reference for the mapping server be the
“Segment Routing Architecture” rather than the “Segment Routing Use Cases”? In
general, the usage of a mapping server and the scope of assignment needs to be
described better somewhere (not in the OSPF encoding document).
8. Section 6 - It would seem that an entity calculating a multi-area SR
path would need access to the topology for all the areas and the SID would need
to be globally assigned? Right? So rules are primarily for the population of
the forwarding plane. Right?
9. Section 6.2 - In standard OSPF, inter-area summary propagation only
applies to inter-area routes learned over the backbone. Is this any different?
Thanks,
Acee
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