Re: Fw: New Version Notification for draft-ietf-bfd-unaffiliated-echo-07.txt

xiao.min2@zte.com.cn Thu, 04 May 2023 07:28 UTC

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Subject: Re: Fw: New Version Notification for draft-ietf-bfd-unaffiliated-echo-07.txt
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Hi Greg,






Thank you for the detailed review and comments, although I don't think your comments justify your conclusion.


Please see inline...



Original



From: GregMirsky <gregimirsky@gmail.com>
To: 肖敏10093570;
Cc: rtg-bfd@ietf.org <rtg-bfd@ietf.org>;
Date: 2023年04月29日 03:42
Subject: Re: Fw: New Version Notification for draft-ietf-bfd-unaffiliated-echo-07.txt


















Hi Xiao Min,thank you for sharing updates. I've read the new version and have several questions and comments.
It is stated in the Abstract:



   BFD Async procedures can be executed over the BFD


   Echo port where the neighboring system only loops packets back to the

   local system.

Is this conclusion differs from the definition of the BFD Echo function in RFC 5880? If it is not, what is the value of such a re-statement? If it is, it seems like an explicit attribution of this conclusion to this document would be helpful.
[XM]>>> RFC 5880 doesn't say BFD Async procedures can be executed over the BFD Echo port because it classifies BFD Echo as an affiliated function. Would you please suggest some text you think helpful?


Is the following a requirement or an observation:



   a network device must be able to quickly detect


   faults in communication with adjacent devices.


If the former, please capitalize the normative language. If the latter, then it appears as an arguable view. Indeed, in some cases, local protection is a viable option, while in other environments, e2e path protection might be preferable.
[XM]>>> At the beginning of the sentence "in some cases" can be added, is that acceptable to you?


Further, in Introduction, I read:


   Section 5 of

   [RFC5880] indicates that the payload of a BFD Echo packet is a local

   matter and hence its contents are outside the scope of that

   specification.  This document, on the other hand, specifies the

   contents of the Echo packets and what to do with them.

It seems to me that this draft is positioned as the definition of the content of an Echo message and the processing of it, whether as an unaffiliated or affiliated (RTC5880-style) function. Is that correct?
[XM]>>> That's incorrect. This document specifies only Unaffiliated BFD Echo, and  it doesn't touch affiliated BFD Echo.

I hope you can help me understand the demultiplexing of Unaffiliated BFD sessions:


   Device A performs its

   initial demultiplexing of a Unaffiliated BFD Echo session using the

   source IP address or UDP source port, once the remote system echoes

   back the local discriminator, all further received packets are

   demultiplexed based on the "Your Discriminator" field only, which is

   conformed to the procedure specified in Section 6.3 of [RFC5880].

Does "initial demultiplexing" refers to the first BFD Control message transmitted in the Unaffiliated BFD Echo mode?

[XM]>>> Not exactly. Actually "initial demultiplexing" is applied to the received BFD Control packet(s) whose "Your Discriminator" is zero.

Considering that "device B would not intercept any received Unaffiliated BFD Echo packet", how "the remote system echoes back the local discriminator"?

[XM]>>> Here "echoes back" means "loops back", is "loops back" more clear?






A lengthy copy of a text from Section 4 of RFC 5881 seems like unnecessary:




   the destination address MUST be chosen in such a way as to



   cause the remote system to forward the packet back to the local



   system.  The source address MUST be chosen in such a way as to



   preclude the remote system from generating ICMP or Neighbor Discovery



   Redirect messages.  In particular, the source address SHOULD NOT be



   part of the subnet bound to the interface over which the BFD Echo



   packet is being transmitted, and it SHOULD NOT be an IPv6 link-local



   address, unless it is known by other means that the remote system



   will not send Redirects.



It seems that a reference to that section and something like "rules stated in Section 4 [RFC5881] are applicable to the encapsulation of an Unaffiliated BFD Echo Control message" could be sufficient.
[XM]>>> I'd like to follow your suggestion if there is no objection from Jeff.

What is the interpretation of "expected value"? It appears that none of these values are used, but are ignored. Right?

[XM]>>> As indicated by Jeff, "the desire is that we avoid unset values being a potential vector for disclosure of uninitialized memory".

A zero value of the Required Min Echo RX Interval field per RFC 5880 is interpreted as no support for the Echo function. But it is the recommended value. Although it is ignored. Thus, what is the benefit of initializing the field after all?

[XM]>>> As indicated by Jeff, "the desire is that we avoid unset values being a potential vector for disclosure of uninitialized memory".

In the description



   Afterwards, the


   provisioned transmission interval is used.


What is the event that triggers the "afterward" transition?
[XM]>>> The preceding text says "The slow transmission rate SHOULD be no less then
 one second per packet, until the session is Up.".
With the high number of "this value MUST be ignored on receipt", "the Unaffiliated BFD Echo packet reuses the format of the BFD Control packet defined in [RFC5880]" seems like a severe overstatement.

[XM]>>> I don't think so. Ignoring some fields on receipt doesn't break the truth that BFD Control packet is reused here.


Which event triggers the transition in




   *  Your Discriminator MUST be set to 0 initially, and then MUST be



      set to the same as My Discriminator echoed back.



[XM]>>> The event is that "My Discriminator" is echoed/looped back.
What happens if Desired Min TX Interval, Required Min RX Interval, or Required Min Echo is not set to "the expected value"?

[XM]>>> Unset values can be a potential vector for disclosure of uninitialized memory.




Best Regards,

Xiao Min




In conclusion. As we learned from the BBF Liason, the Broadband Forum is not seeking standardization of the mechanism described in TR-146. Also, I learned about the implementation of the mechanism described in BBF's TR-146, and the authors are not interested in standardization either, as, in their opinion, there's no externally noticeable behavior that requires specification. So, I still don't see any value in standardizing what is described in the document.



Regards,
Greg







On Sun, Apr 23, 2023 at 7:16 PM <xiao.min2@zte.com.cn> wrote:


Dear BFD WG,





A -07 revision of draft-ietf-bfd-unaffiliated-echo has been posted, attempting to address all the WGLC comments.

The main updates are as below.

* add a sentence to clarify that this document doesn't change the affiliated BFD Echo function.

* change the order of section 2 "Updates to RFC 5880" and section 3 "Unaffiliated BFD Echo Procedures".

* add a summary on the Unaffiliated BFD Echo packet fields setting into the end of section "Unaffiliated BFD Echo Procedures".

* change the text on IP address setting to the same as specified in section 4 of RFC 5881.

* some editorial changes, e.g., s/BFD Unaffiliated Echo packet/Unaffiliated BFD Echo packet/g.






Best Regards,


Xiao Min



Original


From: internet-drafts@ietf.org <internet-drafts@ietf.org>
To: Raj Boddireddy <rchetan@juniper.net>;Raj Chetan Boddireddy <rchetan@juniper.net>;Reshad Rahman <reshad@yahoo.com>;Ruixue Wang <wangruixue@chinamobile.com>;Weiqiang Cheng <chengweiqiang@chinamobile.com>;肖敏10093570;
Date: 2023年04月24日 10:09
Subject: New Version Notification for draft-ietf-bfd-unaffiliated-echo-07.txt


A new version of I-D, draft-ietf-bfd-unaffiliated-echo-07.txt
has been successfully submitted by Xiao Min and posted to the
IETF repository.
 
Name:        draft-ietf-bfd-unaffiliated-echo
Revision:    07
Title:        Unaffiliated BFD Echo
Document date:    2023-04-23
Group:        bfd
Pages:        12
URL:            https://www.ietf.org/archive/id/draft-ietf-bfd-unaffiliated-echo-07.txt
Status:         https://datatracker.ietf.org/doc/draft-ietf-bfd-unaffiliated-echo/
Htmlized:       https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unaffiliated-echo
Diff:           https://author-tools.ietf.org/iddiff?url2=draft-ietf-bfd-unaffiliated-echo-07
 
Abstract:
   Bidirectional Forwarding Detection (BFD) is a fault detection
   protocol that can quickly determine a communication failure between
   two forwarding engines.  This document proposes a use of the BFD Echo
   where the local system supports BFD but the neighboring system does
   not support BFD.  BFD Async procedures can be executed over the BFD
   Echo port where the neighboring system only loops packets back to the
   local system.
 
   This document updates RFC 5880.
 
                                                                                   
 
 
The IETF Secretariat