draft-ietf-bfd-vxlan IESG status

Jeffrey Haas <jhaas@pfrc.org> Mon, 27 January 2020 22:12 UTC

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Date: Mon, 27 Jan 2020 17:17:05 -0500
From: Jeffrey Haas <jhaas@pfrc.org>
To: iesg@ietf.org
Cc: Greg Mirsky <gregimirsky@gmail.com>, bfd-chairs@ietf.org, draft-ietf-bfd-vxlan@ietf.org, rtg-bfd WG <rtg-bfd@ietf.org>
Subject: draft-ietf-bfd-vxlan IESG status
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Much like the BFD Working Group discussion on the BFD for vxlan feature, the
IESG review for the draft has reached a stage where it is difficult to
determine what the related actions are.  (IESG take note for tools
discussion!)

This email is an attempt to kick the conversation back into gear.

My notes here are based on the current status of the document tracked here:
https://datatracker.ietf.org/doc/draft-ietf-bfd-vxlan/ballot/

My comments on the draft are based on the -10 version of the draft as
currently published.

---

Open Issue 1: Discussion on TTL/Hop Limit = 1

Proposed Action: Greg has proposed text he will send to the working group
suggesting GTSM procedures be utilized.  The expected concern is how this
impacts existing implementations.

---

Open Issue 2: Document Status should be Informational rather than Proposed
Standard.

Proposed Action: Greg should make the document Informational.  Prior WG
discussion suggested that we don't really care what level it should be at,
and had actually requested IESG guidance long ago via our AD.

---

Open Issue 3: dst IP/MAC assignment procedures for inner VXLAN headers.
(DISCUSS via Benjamin K.)  Specifically per-VNI form rather than strictly
VTEP-to-VTEP mode.

Issue Comment 1 (Benjamin K.): This is "a namespace grab in what is
essentially the tenant's namespace".

Issue Comment 2 (Jeff H.): Joel Halpern flagged this repeatedly as well as
part of directorate review.

Issue Comment 3 (Benjamin K.): "management VNI does not suffer from this
namespacing issue".

Issue Comment 4 (Jeff H./Benjamin K.): The concept of a "management VNI" is
not supported by existing standards work, but is accepted as a common
implementation behavior.

Issue Comment 5: A significant exploration of this set of issues is
documented in the following thread:
https://mailarchive.ietf.org/arch/msg/rtg-bfd/SfXfu3pCh9BxaRFrXbEOgGt6xjE/

Proposed Action: Limit the Internet-Draft's applicability to verifying
connectivity to the management VNI.  "All other uses of the specification to
test toward other vxlan endpoints are out of scope."

In reviewing the thread, my reading of the comments from Santosh, Anoop, and
Dinesh are effectively "don't break existing implementations".  There is
acknowledge among those in the discusssion that numbering space collisions
between the protocol codepoints chosen to run as endpoints for the BFD for
vxlan session and the tenant space are undesirable.  It is generally agreed
in the thread (IMO) that for the "management VNI" case that this is not
problematic, although the details of provisioning are still specific to the
implementation.  

By setting the case aside where a test to a specific VTEP may have tenant
namespace collisions, the document can be cleaned of a lot of unnecessary
edge cases that are difficult to generally resolve.  Implementations that
may choose to permit sessions to non-management VNIs will have need to
resolve how to deal with collisions.  

---

Open Issue 4: "multicast service node" text (COMMENT via Benjamin K.)

Proposed Action: Incorporate suggested text from Benjamin K. to clarify text
in -10.

---

Open Issue 5: Comma parsing issue (COMMENT via Benjamin K.)

Proposed Action: Accept Benjamin's suggested changes.  (RFC Editor will win
the day here though!)

---

Open Issue 6: "Section 3, MUST NOT be forwarded to a VM" (COMMENT via
Benjamin K.)

Proposed Action: The fate of this issue is tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 7: "::FFFF:7F00:0/104 IPv6 range" (COMMENT via Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 8: "Section 4: MUST ensure that the BFD Control packet is not
forwarded to a tenant but is processed locally at the remote VTEP" (COMMENT
via Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 9: "Destination MAC: This MUST NOT be of one of tenant's MAC
addresses." (COMMENT via Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 10: "The details of how the MAC address is obtained are outside
the scope of this document." (COMMENT via Benjamin K.)

Proposed Action: None.  Reason 1: If we go with only the management VNI,
provisioning remains an easy answer.  Reason 2: If we go with VNI-to-VNI
mode, it's not unreasonable for the environment to claim a MAC address.
This is no different than a switch itself.  Collisions would be handled via
updated configuration.

---

Open Issue 11: "dst IP header MUST NOT be one of tenant's" (COMMENT via Benjamin
K.)

Comment 1 (Jeff H.): The loopback range as a destination would serve to
catch BFD traffic in either VNI-to-VNI or VTEP-to-VTEP mode.  I think this
is more clearly understood after the IESG reviewed the existing mechanisms
using the loopback address range in existing RFCs.

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 12: "Section 5, BFD dst mac collision with tenant" (COMMENT via
Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 13: "The UDP destination port and the TTL of the inner IP packet
MUST be validated to determine if the received packet can be processed by
BFD." (COMMENT via Benjamin K.)

Proposed Action: Provide reference to RFC 5880/5881 sections covering
existing BFD procedure.  Do not copy and paste from them.

---

Open Issue 14: "nits ... then the BFD session" (COMMENT via Benjamin K.)

Proposed Action: Accept grammar correction.

---

Open Issue 15: "Section 6" (COMMENT via Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.  In particular, this section attempts to
justify VNI-to-VNI mode poorly.  

---

Open Issue 16: "Section 9" regarding mis-forwarding/filtering of BFD traffic
toward tenant (COMMENT via Benjamin K.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

(Alvaro's DISCUSSes are covered by the above.)

(Alvaro acknowledged that his COMMENTS were cleared on December 25, 2019)

(Eric V's DISCUSS points are covered by prior open points regarding:
 - TTL (see Open Issue 1)
 - Mapped IPv6 addresses were covered in discussion with IESG about existing
   RFC behavior for this range.
 - The mismatch between document IANA action and shepherd writeup is an
   artifact of document changes since the shepherd writeup had happened.
   The document currently has no open IANA actions.
 - Section 9 issues about TTL were addressed in -09 of the document.)

---

Open Issue 17: "RFC 5881 (BFD) states that it applies to IPv4/IPv6 tunnels,
may I infer that this document is only required to address the Ethernet
encapsulation ? I.e.  specifying the Ethernet MAC addresses?" (COMMENT via
Eric V.)

Comment 1 (Jeff H.): RFC 5881 addresses single-hop "that is associated with
an incoming interface".  vxlan requires additional demultiplexing based on
packet contents and thus the comment is not fully applicable.  This document
(draft-ietf-bfd-vxlan) is intended to cover the vxlan protocol encapsulation
for BFD.

Proposed Action: No action required.

---

Open Issue 18: "BFD session per VXLAN VNI" (COMMENT via Eric V.)

Proposed Action: I believe this issue's fate is similarly tied to Open Issue 3.
If the proposal is limited solely to management VNI, this text is not
relevant and may be deleted.

---

Open Issue 19: "Section 4...FCS" (COMMENT via Eric V.)

Proposed Action: Accept suggested change to "Outer Ethernet FCS"?

---

Open Issue 20: "using the src mac as the dst mac" (COMMENT via Eric V.)

Proposed Action: ?  I'm unclear what the proposal and comment is here.

---

(TTL issues noted by Eric V. addressed in Open Issue 1.)

---

Open Issue 21: "throttling of BFD control packets" (COMMENT via Roman D.)

Proposed Action: The section on throttling is written in a confusing manner
and is in need of a re-write.

In particular, what's unclear is what is doing the throttling and why?  If
the comment is intended to say that some forms of rate-limiting of the vxlan
traffic between two systems is in place that it may impact BFD, it should
say that.  And perhaps once said, omit giving "advice".  "If it hurts, don't
do that."

---

(COMMENTS from Roman D. addressed in -10 and earlier:
 - citing specific security considerations applicability
 - nits
)

(COMMENT from Suresh K. covered in open issues above.)

(COMMENT from Warren K. regardig loopback network range discussed above.)

---

Open Issue 22: "terminology isn't" (COMMENT via Warren K.)

Proposed Action: Either rename the section "acronyms used in this document"
or expand the section to cover the terminology.

---

(Mirja K. indirects a number of issues to "See Olivier's TSV-ART review",
which is present in this message:
https://mailarchive.ietf.org/arch/msg/rtg-bfd/y3xDkvpT-ZodhcaBRHNOSDVByA8/)

Open Issue 23: "follow same lookup path needs more explanation"

Proposed Action: Add a sentence explaining that this is to ensure that the
encapsulated BFD traffic requires following the equivalent data path to
protect the resource"

---

Open Issue 24: "Discuss ECMP considerations" (TSV-ART via Olivier B.)

Comment 1 (Jeff H.): I believe this came up in the message thread, but base
BFD also has similar unclear ECMP behaviors.  The working group has avoided
trying to standardize anything regarding ECMP since it gets very
implementation specific.  Some vendors will go out of their way to do things
to mitigate ECMP considerations when BFD is in place; others simply ignore
it.

Proposed Action: Unclear.  None?

---

(Minor issues report by Olivier B. that have been addressed in -10 or
 earlier:
 - p2p vxlan tunnel wording
 - VNI has been added to section 2.1
 - "figure 1 could take less space" - not addressed.
 - section 4 flattened to remove unnecessary sub-sections
 - "dedicated mac" address no longer in current versions of document
 - "v4 in v6 / v6 in v4, etc." - intentionally unspecified since arbitrary
   encapsulations are supported by specification.  Implementations may have
   specific limitations.
 - "section 5 dedicated mac" no longer in the document
 - "decapsulation procedure reference" I believe has been clarified.)

(Mirja's comment on status is covered by Open Issue 2)

(Comments from Barry L. addressed:
 - "forming up"
 - bfd packet/vtep packets/vteps plurality agreement.
 - "may be configured" clarified.
 - Section 4.1 "of")

---

Open Issue 25: "leading to a false negative" (COMMENT via Barry L.)

Proposed Action: The underlying concern in this sentence is that BFD packets
must not be mis-delivered to VMs since there will be no BFD machinery
present in that VM to execute the BFD procedures and thus sessions will
drop.  Possible action is to simply delete this sentence since it
prematurely anticipates procedures later described in the document.

---

Open Issue 26: "loopback range through a firewall" (COMMENT via Barry L.)

Proposed Action: Accept suggested rewording.

---

Open Issue 27: "Section 4...addresses the scenario" (COMMENT via Barry L.)

Proposed Action: This sentence needs to be reworded.

---

(Comments from Adam R. addressed:
 - Form of ipv6 mapped address.
 - Usage of loopback network  addresses compared to prior RFCs discussed in
   thread with IESG.)





-- Jeff