Hello Alvaro,
thanks for your review.
Please see in-line regarding the two first points.
-m
Le 04/12/2017 à 22:49, Alvaro Retana a écrit :
Dear Authors:
I just finished reading this document (finally!). I have a some
comments (see below) which I think should be easy to address.
I also have some bigger issues that we’ll need the Chairs’ help to solve:
(1) Coordination with nv03
For the Chairs: Except for some clarification comments [1] related to
the current version, I see no other traffic in the nvo3 list related to
this document. Was there some other coordination that I’m missing? I
am not questioning having this document in bess (that’s perfectly fine);
I’m just raising the needed coordination with other WGs, from the
Charter: "The working group will also coordinate with...NVO3 working
group for coordination of protocols to support data center VPNs.”
What about Geneve (draft-ietf-nvo3-geneve)? The nvo3 WG is focusing on
Geneve as the Standard encapsulation, but this document doesn’t
even mention it.
Indeed. But The decision by NVO3 to work on Geneve is fairly recent.
I have indicated in the BESS report that we'll likely be working closeer
with NVO3 from now on. An individual draft on the applicability of EVPN
to NVO3 networks is targeting NVO3 WG. Conversely, an individual draft
on EVPN extensions for Geneve is targeting BESS. We have agreed that
we'll do cross reviews at the important milestones of these docs.
(2) Document Status
Why is this a Standards Track document? The Abstract/Introduction say
that “this document describes how Ethernet VPN (EVPN) can be used as an
NVO solution and explores applicability of EVPN functions and
procedures.” -- if it’s just a description (as the text clearly is),
and not a technical specification, then why it is not Informational?
I can see how we could call it an Applicability Statement (rfc2026) and
still publish it in the Standards Track. If we want to go that way, we
would need some minor updates to make it clear that this is an
Applicability Statement and is not intended to stand in for a Technical
Specification. I am not clear on the process as it related to possible
DownRefs (see below), but I’m willing to Last Call an Applicability
Statement in the Standards Track…if that is what you want.
Maybe the authors should s/describes/specifies/ to better reflect the
content of the document.
On the other hand, rfc2026 says "A Technical Specification is any
description of a protocol, service, procedure, convention, or format."
It seems to match as well.
Thanks!
Alvaro.
[1]
https://mailarchive.ietf.org/arch/msg/nvo3/cd0hOfb966ROcL4t8JCrBD28bBg/?qid=c9f632dc5d6aab5e4b22972bb242baf0
Major:
M1. Section 5.1.2.1 (Auto Derivation of RT) shows a “packet format” to
illustrate how the RT can be auto-derived. Without any context, the
description doesn’t make much sense: the fields are not described in
order, the reader is expected to know about global and
local administrative fields, the “A-bit” (or the Type field) are not
mentioned in the description, people could probably guess that “D-ID”
means “domain-id”, there’s no indication of what to do with that “packet
format”, etc. Please clean the description up, include clearer
explanations and some references can’t hurt.
M1.2. What about 4-byte ASNs?
M2. From 5.1.3 (Constructing EVPN BGP Routes): “...routes MAY be
advertised with multiple encapsulation types as long as they use the
same EVPN multi-homing procedures (section 8.3.1, Split Horizon)…”. Is
Split Horizon an example, or the only multi-homing procedure that should
be considered? Please be clear.
M3. From 5.2 (MPLS over GRE):
M3.1. “...when it is used in conjunction with EVPN the GRE key field
SHOULD be present, and SHOULD be used to provide a 32-bit entropy
field.” What are the cases when it is ok not to include the field, or
use it for that purpose? IOW, why are these SHOULDs not MUSTs? Or
maybe, when is the key field needed?
M3.2. "The Checksum and Sequence Number fields are not needed and their
corresponding C and S bits MUST be set to zero.” This is different than
what rfc4023 specifies (not a problem). If you’re specifying the
setting of the bits, then you should be more prescriptive with whether
the fields are included of not; suggestion: "The Checksum and Sequence
Number fields MUST NOT be included and the corresponding C and S bits in
the GRE Packet Header MUST be set to zero.”
M4. In 7.1 (Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE
Encapsulation)
M4.1. These 2 MUSTs seem out of place as they are used to explain, and
not in a Normative way: “ ..the RD must be a unique value per EVI or per
NVE as described in [RFC7432]. In other words, whenever there is more
than one administrative domain for global VNI, then a unique RD MUST
be used, or whenever the VNI value have local significance, then
a unique RD MUST be used.” s/MUST/must
M4.2. This SHOULD is also out of place because the standardization was
already done in rfc7432 (this document is just mentioning it): “...as
noted in section 8.6 of [RFC7432]...the single-homing ingress NVE SHOULD
be able to…”. s/SHOULD/should
M4.3. Section 10.2.1 then points back at the text in 7.1 using another
SHOULD…again, s/SHOULD/should
M5. 7.2 (Impact on EVPN Procedures for VXLAN/NVGRE Encapsulation) also
includes a superfluous SHOULD: “...as noted in section 8.6 of
[RFC7432]...a single-homing ingress NVE SHOULD implement…”. s/SHOULD/should
M6. The introductory paragraph in Section 8.1 (EVPN Multi-Homing
Features) says that it is used to "recap the multi-homing features of
EVPN to highlight the encapsulation dependencies. The section only
describes the features and functions at a high-level. For more details,
the reader is to refer to [RFC7432].” However some of the 8.1.*
sub-sections contain Normative language. Is that Normative language
specifying new behavior introduced in this document, or highlighting the
recap from rfc7432? If there’s no new behavior, then please use lower
cases. If there is new behavior, then it would be nice to clarify that
in 8.1.
M7. In 8.3.1 (Split Horizon), this MUST is out of place because it is
not specifying anything: “...other means of performing the split-horizon
filtering function MUST be devised.” s/MUST/must
M8. References
M8.1. TUNNEL-ENCAP (aka draft-ietf-idr-tunnel-encaps) should be
Normative, which btw is marked to Obsolete rfc5512; I mention this
because both are listed in several parts, so you should take rfc5512 out.
M8.2. These should also be Normative: RFC7348, NVGRE, VXLAN-GPE, RFC4023
Minor:
P1. Please use the new Normative Language boilerplate (rfc8174).
P2. From 7.1 (Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE
Encapsulation): “...reduces the required routes and attributes to the
following subset of four out of eight”. Please either list the
attributes that are not needed, or put in a reference to where those can
be found. (rfc7432 ??)
P3. From 8.3.1 (Split Horizon): "In order to prevent unhealthy
interactions…”. I would really like to see more here: what does
“unhealthy interactions” mean? Can it result in loops or lost traffic
or some other “bad” thing? I note that even through you “prohibit” the
configuration, you don’t go as far as mandating that it not to be used
(MUST NOT), which makes me want to understand more the potential
effects…if it happens, what are the risks?
P4. In 8.3.3 (Unknown Unicast Traffic Designation): “...the ingress PE
MAY use a flag-bit in the VxLAN header to indicate BUM traffic type. Bit
6 of flag field in the VxLAN header is used for this purpose per section
3.1 of [VXLAN-GPE].” Suggestion: “…the ingress PE MAY set the BUM
Traffic Bit (B bit) [VXLAN-GPE] to indicate BUM traffic.”
P5. Security Considerations: I find that the suggestion of IPSec may be
out of place in this document; this document pretty much just talks
about how to use EVPN, it doesn’t really introduce new capabilities, so
unless IPSec is mentioned in rfc7432 (which is not — and not even
mentioned in this section), or recommended in rfc4271 (which is not)
then I would refrain from including such recommendation here. In fact,
I think that pointing at the Security Considerations of existing RFCs
should be enough.
P5.1. The reference to rfc4301 (beyond what VXLAN/NVGRE) mention seems
like you’re trying too hard. I would just put explicit references to
the encapsulations since they should be dealing with security themselves.
P6. References: [KEYWORDS] shows up twice. I think that the reference
to rfc4271 can be made Informative.
Nits:
N1. Section 3 (Terminology) literally transcribes several definitions
from rfc7432/rfc7365 — while it is ok, I personally prefer just pointing
at the definitions: it’s just easier to have the other RFCs be the
authoritative source and not rely on maintaining the definitions in sync
should they ever change. Suggestion: “The reader is expected to be
familiar with the terminology in …”.
N2. s/the VNI value have local significance/the VNI value has local
significance
N3. s/it is recommend/it is recommended
N4. Please be consistent in naming references, some list the RFC number,
while others a name...
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