Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6, and MPLS
draft-ietf-bfd-seamless-ip-06

[Ballot comment]
Section 5.1, 6.1:

The IPv4-mapped IPv6 prefix for the IPv4 loopback range 127.0.0.0/8 is incorrect.

It is currently written as 0:0:0:0:0:FFFF:7F00/104. It should instead be 0:0:0:0:0:FFFF:7F00:0/104.

Sections 5.1, 6.1:

The document just talks about the TTL field being set to 255. It does not talk about the Hop Limit field for IPv6. I would assume you want to do the same for IPv6 packets as for the IPv4 packets. Can you include the Hop Limit as well if you want the same behavior for IPv6. I have two suggested forms of changes. Pick whatever works better for you.

OLD:

TTL field of the IP header SHOULD be set to 255

NEW:

The TTL/Hop Limit field of the IP header SHOULD be set to 255

(or)

The TTL field of the IPv4 header or the Hop Limit field of the IPv6 header SHOULD be set to 255

[Ballot comment]
Elwyn Davies raised a question about why it is reasonable to require special-case TTL expiry treatment. Carlos Pignataro had a response relating to existing practice with similar treatment. Could that explanation/response and the logic why this is reasonable be added as a note to the document?

[Ballot comment]
Just a couple of small things.

I'm pretty sure I know why

      *  UDP destination port MUST be set to a well-known UDP
        destination port assigned for S-BFD: 7784.

      *  UDP source port MUST NOT be set to 7784.
     
the UDP source port has this restriction, but it might be helpful to people who can't guess, if you could add a phrase explaining why. We were all new protocol designers once.
     
It's a small thing, but

      BFD Chairs
     
we're phasing out @tools.ietf.org in favor of @ietf.org, aren't we?

[Ballot discuss]
Section 4, 2nd paragraph: "  If the port is not 7784, then the packet MUST be looked up to locate
  a corresponding SBFDInitiator session or classical BFD session based
  on the value from the "your discriminator" field in the table
  describing BFD discriminators.  "

Do I understand correctly that whether or not the destination port is 7784 tells you if this is an "initial" packet vs a "reflected" packet? If the destination port is not 7784, how do you know it’s not some competely different protocol? Do you assume the receiver has no other UDP based services?

[Ballot comment]
- 2: This doesn't seem to allow an administrator to configure different listening ports by administrative action. Is that the intent? Also, why does it matter if the source port is 7784?

- 6.1, first bullet: Does this imply that the initiator must listen for reflected packets at its source port? Was that explicitly mentioned somewhere that I missed?

Editorial:

-5.1.1, first paragraph: I had trouble parsing the last sentence in the paragraph.

[Ballot comment]
This part is unclear to me:
"It is, however, possible for an
  SBFDInitiator to carefully set "your discriminator" and TTL fields to
  perform a continuity test towards a target, but to a transit network
  node and not to the target itself. [...]
  This also requires S-BFD control packets not be dropped by the
  responder node due to TTL expiry.  Thus implementations on the
  responder MUST allow received S-BFD control packets taking TTL expiry
  exception path to reach corresponding reflector BFD session."

You basically perform a traceroute with (S-)BFD, right? Why do you need the last sentence? Wouldn't it be okay, if the packet get dropped by the responder, to simply re-send with a higher TTL?

[Ballot discuss]
I think that these are both simple fast issues to resolve.

1) Sec 3: "This document defines only the UDP port value
  for the S-BFD Echo function.  The source port and the procedures for
  the S-BFD Echo function are outside the scope of this document."
Please add a reference to the S-BFD base document for defining where the
procedures are found.

Where, precisely, is the source port defined?  It wasn't in the S-BFD base
document.  This seems like a hole.  Can you please clarify?

2) Sec 4:  " If the port is not 7784, then the packet MUST be looked up to locate
  a corresponding SBFDInitiator session or classical BFD session based
  on the value from the "your discriminator" field in the table
  describing BFD discriminators. "

I assume that you mean that UDP source port is used to look up the appropriate receiver.
If that receiver handles BFD and S-BFD packets, then the "your discriminator" field is used
to identify the BFD session.  PLEASE clarify that because this reads as if BFD is the only
application that uses UDP.

(Via drafts-lastcall-comment@iana.org): IESG/Authors/WG Chairs:

IANA has completed its review of draft-ietf-bfd-seamless-ip-03.txt. If any part of this review is inaccurate, please let us know.

IANA understands that, upon approval of this document, there is a single action which IANA must complete.

IANA notes that the authors have requested an early allocation of port 7784 in the Service Name and Transport Protocol Port Number Registry. The entry for that port number will be changed from the Internet Draft to [ RFC-to-be ] upon approval of this document. The Service Name and Transport Protocol Port Number Registry is located at:

https://www.iana.org/assignments/service-names-port-numbers/

IANA understands that this is the only action required to be completed upon approval of this document.

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is only to confirm what actions will be performed. 


Thank you,

Sabrina Tanamal
IANA Specialist
ICANN

The following Last Call announcement was sent out:

From: The IESG
To: "IETF-Announce"
CC: jhaas@pfrc.org, aretana@cisco.com, rtg-bfd@ietf.org, bfd-chairs@ietf.org, draft-ietf-bfd-seamless-ip@ietf.org
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6 and MPLS) to Proposed Standard


The IESG has received a request from the Bidirectional Forwarding
Detection WG (bfd) to consider the following document:
- 'Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6 and
  MPLS'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2016-04-12. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  This document defines procedures to use Seamless Bidirectional
  Forwarding Detection (S-BFD) for IPv4, IPv6 and MPLS environments.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-bfd-seamless-ip/

IESG discussion can be tracked via
https://datatracker.ietf.org/doc/draft-ietf-bfd-seamless-ip/ballot/


The following IPR Declarations may be related to this I-D:

  https://datatracker.ietf.org/ipr/2106/
  https://datatracker.ietf.org/ipr/2595/

This shepherd writeup covers three documents:
  draft-ietf-bfd-seamless-base
  draft-ietf-bfd-seamless-use-case
  draft-ietf-bfd-seamless-ip



: Document Writeup for Working Group Documents
:
: As required by RFC 4858, this is the current template for the Document Shepherd Write-Up.
:
: Changes are expected over time. This version is dated 24 February 2012.
:
: (1) What type of RFC is being requested (BCP, Proposed Standard, Internet
: Standard, Informational, Experimental, or Historic)? Why is this the proper
: type of RFC? Is this type of RFC indicated in the title page header?

draft-ietf-bfd-seamless-use-case is targeted for Informational status, which
is appropriate since it does not specify any normative changes to existing
protocols and simply describes the circumstances motivating the Seamless BFD
feature.

Both draft-ietf-bfd-seamless-base and draft-ietf-bfd-seamless-use-case are
targeted for Proposed Standard.  The -base document covers updates to the
core BFD protocol, RFC 5880.  The -ip document covers implementation details
specifically relevant to the IP implementations utilizing the extensions in
the -base document; these include IP environments terminating across MPLS
LSPs.

: (2) The IESG approval announcement includes a Document Announcement Write-Up.
: Please provide such a Document Announcement Write-Up. Recent examples can be
: found in the "Action" announcements for approved documents. The approval
: announcement contains the following sections:
:
: Technical Summary:

For -base:
  This document defines a simplified mechanism to use Bidirectional
  Forwarding Detection (BFD) with large portions of negotiation aspects
  eliminated, thus providing benefits such as quick provisioning as
  well as improved control and flexibility to network nodes initiating
  the path monitoring.

For -ip:
  Seamless BFD defines a simplified mechanism to use Bidirectional
  Forwarding Detection (BFD) with large portions of negotiation aspects
  eliminated, thus providing benefits such as quick provisioning as
  well as improved control and flexibility to network nodes initiating
  the path monitoring.

  This document defines procedures to use Seamless Bidirectional
  Forwarding Detection (S-BFD) for IPv4, IPv6 and MPLS environments.

For -use-case:
  Seamless BFD defines a simplified mechanism to use Bidirectional
  Forwarding Detection (BFD) with large portions of negotiation aspects
  eliminated, thus providing benefits such as quick provisioning as
  well as improved control and flexibility to network nodes initiating
  the path monitoring.

  This document provides various use cases for Bidirectional Forwarding
  Detection (BFD) such that extensions could be developed to allow for
  simplified detection of forwarding failures.


: Relevant content can frequently be found in the abstract and/or introduction
: of the document. If not, this may be an indication that there are deficiencies
: in the abstract or introduction.
:
: Working Group Summary:

(For all documents.)
This document was discussed at length with significant participation of the
active members of the Bidirectional Forwarding Detection (BFD) Working
Group.  The use cases are seen to enable the use of core BFD technologies in
a fashion that leverages existing implementations and protocol machinery
while providing a simplified and largely stateless infrastructure for
continuity testing.  The high participation of the Working Group has ensured
that the technical aspects of this mechanism have been thoroughly discussed.

: Document Quality:

This document has been subject to multiple Working Group reviews and
includes participation from several large vendors.  Many of these vendors
have implementations in progress for this feature.

: Personnel:
:
: Who is the Document Shepherd? Who is the Responsible Area Director?

Document Shepherd: Jeffrey Haas, co-chair BFD.
Responsible Area Director: Alvaro Retana.

: (3) Briefly describe the review of this document that was performed by the
: Document Shepherd. If this version of the document is not ready for
: publication, please explain why the document is being forwarded to the IESG.

The shepherd has participated in multiple review cycles of the documents
with the authors with attention toward reviewing technical detail and
cleanliness of language.  The consensus of the Working Group is that the
documents are ready to progress.

: (4) Does the document Shepherd have any concerns about the depth or breadth
: of the reviews that have been performed?

Review of the documents has included discussion in the context of running
this feature in an MPLS LSP environment.  Several of the authors are also
regular participants in the IETF mpls Working Group.  It is the shepherd's
belief that this area has been adequately reviewed.

The security aspects of these documents have been discussed at length, with
attention given toward spoofing attacks that may elicit bad behaviors in the
protocol.  It is the shepherd's belief that security aspects have received
sufficient Working Group scrutiny.  Since these documents utilize existing
BFD security mechanisms, it is generally believed that those mechanism
continue to provide appropriate security in the context of Seamless BFD.

Transport considerations were also part of the extended discussion of
Seamless BFD.  In particular, since Seamless BFD is effectively stateless,
the existing mechanisms documented in RFC 5880 to regulate the rate of
packets is less effective.  Implementations of Seamless BFD Reflectors are
free to provide rate limiting of their responses, but must do so with regard
to a peak and potentially unknown load from an unknown number of Seamless
BFD Initiators.

Seamless BFD Reflectors may further control their load through filtering on
Source IP or validation of Destination IP (e.g. via consulting routing or
access control lists).  See draft-ietf-bfd-seamless-ip, Security
Considerations.

: (5) Do portions of the document need review from a particular or from broader
: perspective, e.g., security, operational complexity, AAA, DNS, DHCP, XML, or
: internationalization? If so, describe the review that took place.

Since Seamless BFD is largely building on experience gained in security and
transport considerations from the core BFD standards, no specific additional
review had been previously requested.

: (6) Describe any specific concerns or issues that the Document Shepherd has
: with this document that the Responsible Area Director and/or the IESG should be
: aware of? For example, perhaps he or she is uncomfortable with certain parts of
: the document, or has concerns whether there really is a need for it. In any
: event, if the WG has discussed those issues and has indicated that it still
: wishes to advance the document, detail those concerns here.

No issues.  It is the Shepherd's opinion that the issues have been
thoroughly discussed.

: (7) Has each author confirmed that any and all appropriate IPR disclosures
: required for full conformance with the provisions of BCP 78 and BCP 79 have
: already been filed. If not, explain why?

Yes.

: (8) Has an IPR disclosure been filed that references this document? If so,
: summarize any WG discussion and conclusion regarding the IPR disclosures.

All IPR has been disclosed.  The only IPR considerations placed against
these specifications is by Cisco Systems:
https://datatracker.ietf.org/ipr/2402/
https://datatracker.ietf.org/ipr/2107/
https://datatracker.ietf.org/ipr/2595/
https://datatracker.ietf.org/ipr/2106/

These appear to be Cisco's usual RAND terms and did not elicit any concern
from the Working Group.

: (9) How solid is the WG consensus behind this document? Does it represent the
: strong concurrence of a few individuals, with others being silent, or does the
: WG as a whole understand and agree with it?

Strong consensus from active members of the Working Group.

: (10) Has anyone threatened an appeal or otherwise indicated extreme
: discontent? If so, please summarise the areas of conflict in separate email
: messages to the Responsible Area Director. (It should be in a separate email
: because this questionnaire is publicly available.)

No.

: (11) Identify any ID nits the Document Shepherd has found in this document.
: (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts Checklist).
: Boilerplate checks are not enough; this check needs to be thorough.

None of substance.  The open nits are against referenced I-Ds of later
versions.

: (12) Describe how the document meets any required formal review criteria,
: such as the MIB Doctor, media type, and URI type reviews.

Not applicable.

: (13) Have all references within this document been identified as either
: normative or informative?

Yes.

: (14) Are there normative references to documents that are not ready for
: advancement or are otherwise in an unclear state? If such normative references
: exist, what is the plan for their completion?

draft-geib-segment-routing-oam-usecase is referenced by the Seamless BFD use
case document and is targeted for the spring Working Group.  The status of
that document is Informational.  It is unclear to the Shepherd whether that
document will eventually be adopted and progressed within the spring Working
Group as its purpose is to similarly document use cases appropriate to that
Working Group's charter.

Two things may be done:
1. Hold the Seamless BFD Use Case document in REF state pending resolution.
2. Move the reference to that document in the Seamless BFD Use Case document
to be an Informative reference.

It is the Shepherd's belief that 2 may be the appropriate response.

: (15) Are there downward normative references references (see RFC 3967)? If
: so, list these downward references to support the Area Director in the Last
: Call procedure.

No.

: (16) Will publication of this document change the status of any existing
: RFCs? Are those RFCs listed on the title page header, listed in the abstract,
: and discussed in the introduction? If the RFCs are not listed in the Abstract
: and Introduction, explain why, and point to the part of the document where the
: relationship of this document to the other RFCs is discussed. If this
: information is not in the document, explain why the WG considers it
: unnecessary.

The Seamless BFD base document will update RFC 5880 and is correctly flagged
as having done so.

: (17) Describe the Document Shepherd's review of the IANA considerations
: section, especially with regard to its consistency with the body of the
: document. Confirm that all protocol extensions that the document makes are
: associated with the appropriate reservations in IANA registries. Confirm that
: any referenced IANA registries have been clearly identified. Confirm that newly
: created IANA registries include a detailed specification of the initial
: contents for the registry, that allocations procedures for future registrations
: are defined, and a reasonable name for the new registry has been suggested (see
: RFC 5226).

The Seamless BFD IP document has gone through early allocation for a UDP
port number.  This number is stably being used by implementors for this
feature.  It is not expected that there will be further Considerations in
that document.

The other two documents have no IANA Considerations.

: (18) List any new IANA registries that require Expert Review for future
: allocations. Provide any public guidance that the IESG would find useful in
: selecting the IANA Experts for these new registries.

None.

: (19) Describe reviews and automated checks performed by the Document Shepherd
: to validate sections of the document written in a formal language, such as XML
: code, BNF rules, MIB definitions, etc.

Not applicable.

It should be noted that there will be impact on BFD Yang module work that is
in progress with the BFD Yang Design Team.  They have been notified to
consider the impact of these drafts upon their work.

While there is a BFD MIB (RFCs 7330, 7331) covering BFD functionality, no
Working Group work is currently targeted for the management of Seamless BFD
via SNMP.  It is the Shepherd's opinion that if such work is of interest
that there exists sufficient flexibility in the published MIBs to
accommodate the inclusion of management for Seamless BFD, although there
would be an augmentation MIB required to cover the Seamless BFD Reflector
configuration and transport policy.