Internet DRAFT - draft-yang-bfd-sbfd-proxy
draft-yang-bfd-sbfd-proxy
Internet Engineering Task Force Q. Yang, Ed.
Internet-Draft F. Zhu
Intended status: Standards Track V. Wen
Expires: 25 June 2023 Arista Networks Inc
J. Hu
B. Huang
N. Liu
ByteDance Inc
22 December 2022
S-BFD Proxy
draft-yang-bfd-sbfd-proxy-02
Abstract
This document proposes an extension to Seamless Bidirectional
Forwarding Detection (S-BFD).
The S-BFD initiator will send packets that carry extra information,
and this enables reflector to act as a proxy, and respond with the
extra information in consideration.
This document updates RFC 7880.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 June 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
Yang, et al. Expires 25 June 2023 [Page 1]
Internet-Draft S-BFD Proxy December 2022
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. S-BFD Proxy Reflector Overview . . . . . . . . . . . . . . . 3
3. Packet format . . . . . . . . . . . . . . . . . . . . . . . . 4
4. S-BFD Proxy Reflector Procedures . . . . . . . . . . . . . . 6
5. S-BFD Proxy Initiator Procedures . . . . . . . . . . . . . . 7
6. SBFDInitiator State Machine . . . . . . . . . . . . . . . . . 7
7. S-BFD Echo Function . . . . . . . . . . . . . . . . . . . . . 7
8. Co-existence with Classical S-BFD Sessions . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Seamless Bidirectional Forwarding Detection (S-BFD), as described in
[RFC7880] and related documents, has defined a mechanism for
liveliness detection of paths end-to-end.
However, in certain cases, such liveliness detection is not possible
end-to-end. There could be a number of reasons. For example, the
path termination point may not be able to perform S-BFD reflector
functionality, or it is not possible for the path termination point
to route back to the source IP address of the initiator.
In such cases, however, it may still be useful or essential for the
S-BFD initiator to detect the liveliness of the path.
In this draft, we propose a mechanism for an intermediate node in the
path to act as a proxy for the real end point, and the report S-BFD
status would be for the entire path.
Yang, et al. Expires 25 June 2023 [Page 2]
Internet-Draft S-BFD Proxy December 2022
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. S-BFD Proxy Reflector Overview
Similar to regular S-BFD sessions, in an S-BFD proxy session, the
initiator will determine, with help of configuration, which is
outside the scope of this specification, a proxy reflector, along the
path, to be the responder of the S-BFD packet. It then sends the
S-BFD packet terminating at the proxy reflector, and the proxy
reflector reflects the S-BFD packet with a status in consideration of
the remaining path.
In order for the proxy reflector to reflect the status of the entire
path, the initiator will have to include the information about the
remaining path in the S-BFD packet payload (see section 4).
When the reflector receives the S-BFD packet, instead of just
reflecting the packet as defined in RFC7880, it will retrieve the
remaining path information from S-BFD packet, and inspect the health
of the corresponding path (scope outside of this spec). It will then
respond with the appropriate status back to the initiator.
It is possible that the initiator may have multiple paths passing
through the proxy reflector. In order for the initiator to
differentiate the different sessions, the proxy reflector will have
to keep track of the discriminator combination. The reflector MAY
remove the auxiliary TLV from the S-BFD payload, except when required
otherwise. See section 4 for exception.
This is exemplified in Figure 1.
A---------B---------C---------D
^ ^
| |
System-ID System-ID
xxx yyy
BFD Discrim BFD Discrim
123 456
Figure 1: S-BFD Proxy
Yang, et al. Expires 25 June 2023 [Page 3]
Internet-Draft S-BFD Proxy December 2022
In this example, A is the head end, and has a path all the way to D.
But for some reason, an end to end S-BFD session to D is not
possible. Instead, A will attempt to have an S-BFD session using C
as the proxy reflector.
A will encode the remaining path corresponding to the last segment,
C-D, in the S-BFD packet payload. When C, acting as proxy reflector,
receives the packet, it decodes the path information for C-D and
inspects the health of that segment, through some means, and responds
to A. A will interpret the response as the status of the entire
tunnel end-to-end.
3. Packet format
S-BFD proxy reflector introduces new field in the BFD packet.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Vers | Diag |Sta|P|F|C|A|D|M| Detect Mult | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Your Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Min TX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min Echo RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Auth Len | Authentication Data... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aux Type | Aux Len | Aux Data… |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Packet format
The extra information is carried after the (optional) Auth Type, in
the Aux TLVs.
Yang, et al. Expires 25 June 2023 [Page 4]
Internet-Draft S-BFD Proxy December 2022
Since there is no bit available in the 2nd 8-bit header to indicate
the existence of this field, we will modify the decoding procedure as
the following: if, after decoding to the end of S-BFD packet,
including the optional Auth, the length consumed is less than the
total Length field in the first word, the remaining bytes will be
considered as Aux TLVs.
There might be multiple auxiliary TLVs from that point on. If at any
point, the Aux Len indicates a length bigger than the remaining
bytes, the packet will be considered malformed and MUST be discarded.
Aux Len must have a minimum value of 2 (in bytes). Packet with Aux
Len less than 2 MUST be discarded.
Otherwise, the Aux Len bytes will be consumed and its interpretation
will depend on the Aux Type specification. If somehow the packet end
is reached with still remaining length, the packet MUST be discarded.
The Aux Len denotes the length of the auxiliary path data. The Aux
Lens from all auxiliary TLVs are added to the BFD length field.
The Aux Type takes 8 bits, with the highest bit as the 'reflection
bit'.
When the reflection bit is not set, the reflector which supports this
specification is required to inspect the content, and reflects the
packet accordingly. If the reflector does not recognize this
particular type, it MUST drop it without reflecting back. This rule
shall trump the next. I.e, if there are multiple Aux TLVs, and a mix
of TLVs with reflection bit set and not set, the 'reflection bit
clear' rule shall take precedence.
When this bit is set, i.e, for type in ranges of 128-255, it is
required to reflect back the packet even without understanding the
content of the type and TLV. Inspecting the TLV contents, when the
reflector recognizes the type, is optional and reflecting status back
is at the discretion of the reflector.
If authentication is included, then it is still assumed that the
authentication is done on the entire packet, including the auxiliary
TLV portion.
For each Aux Type, there SHOULD be at most one TLV associated with.
If more than one is sent, undefined behavior may follow.
The following Aux types are defined:
Aux Type (8 bit):
Yang, et al. Expires 25 June 2023 [Page 5]
Internet-Draft S-BFD Proxy December 2022
0 reserved
1 MPLS label stack for purpose of additional check
2 MPLS label stack for purpose of return path
When the type is set to 1, it denotes a stack of labels. The labels
may or may not have global significance, and its allocation and
communication between the S-BFD initiator and S-BFD proxy reflector
is outside the scope of this document. Each label will take the
entire 32 bit (including TOS, BOS, and TTL field, but these may not
be used). The purpose of type 1 is for proxy functionality, that the
reflector may check reachability of the label stack
When the type is set to 2, it again denotes a stack of labels. The
labels are encoded the same way as 1. Here the reflector is expected
to use the label stack as the return path back to initiator, as
versus going over the IP forwarding.
4. S-BFD Proxy Reflector Procedures
The reflector, or responder, upon reception of proxy S-BFD Control
packets (type 1 above), after verifying the validity of the packets,
will look into payload and inspect the health of the remaining path,
and respond with the appropriate status.
If the remaining tunnel path is down, the responder must set the
bfd.SessionState to Down. Else it should set to Up. Notice here,
when the remaining path is down, the responder should not drop the
packet and let the initiator time out. This will help the initiator
to detect the failure faster.
For backward compatibility purposes, we propose to set the
bfd.SessionState to Down, as versus AdminDown, as specified in
RFC7880.
In addition it shall also respond to the initiator with a diagnostic
code of '6 -- Concatenated Path Down' in the S-BFD reply.
The reflector, or responder, upon reception of S-BFD control packets
with type 2 above, after verifying the validity of the packets, shall
respond with the appropriate status. In addition, it shall
encapsulate the packet with the specified label stack, and forward
accordingly. The label stack here will represent a potentially
traffic engineered path back to the initiator.
Yang, et al. Expires 25 June 2023 [Page 6]
Internet-Draft S-BFD Proxy December 2022
5. S-BFD Proxy Initiator Procedures
Changes to RFC7880 is when an initiator receives a packet with
bfd.SessionState to be Down, it should immediately turn the S-BFD
state to be Down.
6. SBFDInitiator State Machine
The following diagram provides the RECOMMENDED state machine for
stateful SBFDInitiators.
DOWN, +--+
ADMIN DOWN, | |
TIMER | V
+------+ UP +------+
| |----------------->| |----+
| DOWN | | UP | | UP
| |<-----------------| |<---+
+------+ DOWN,ADMIN DOWN,+------+
TIMER
Figure 3: SBFDInitiator Finite State Machine
Note that the above state machine is different from the S-BFD
specification [RFC7880]. This is because the proxy reflector may
send a packet with DOWN state.
7. S-BFD Echo Function
Since the operation outlined here requires cooperation of the
reflector, echo mode is not supported for S-BFD proxy.
8. Co-existence with Classical S-BFD Sessions
It is possible for S-BFD proxy sessions to coexist with regular S-BFD
sessions, even between the same initiator-reflector pair.
9. IANA Considerations
This memo includes no request to IANA.
10. Security Considerations
The same security considerations as those described in RFC7880 will
apply to this document.
Yang, et al. Expires 25 June 2023 [Page 7]
Internet-Draft S-BFD Proxy December 2022
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[RFC7881] Pignataro, C., Ward, D., and N. Akiya, "Seamless
Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016,
<https://www.rfc-editor.org/info/rfc7881>.
[RFC7882] Aldrin, S., Pignataro, C., Mirsky, G., and N. Kumar,
"Seamless Bidirectional Forwarding Detection (S-BFD) Use
Cases", RFC 7882, DOI 10.17487/RFC7882, July 2016,
<https://www.rfc-editor.org/info/rfc7882>.
[RFC7885] Govindan, V. and C. Pignataro, "Seamless Bidirectional
Forwarding Detection (S-BFD) for Virtual Circuit
Connectivity Verification (VCCV)", RFC 7885,
DOI 10.17487/RFC7885, July 2016,
<https://www.rfc-editor.org/info/rfc7885>.
Acknowledgements
The authors of this document would like to thank Joseph Swaminathan,
Zhen Xue, Hanchen Zheng, Kelvin Liu and Mamen Xu for the discussion
and comments of this document.
Authors' Addresses
Qing Yang (editor)
Arista Networks Inc
Yang, et al. Expires 25 June 2023 [Page 8]
Internet-Draft S-BFD Proxy December 2022
Email: qyang@arista.com
Feng Zhu
Arista Networks Inc
Email: fzhu@arista.com
Victor Wen
Arista Networks Inc
Email: vwen@arista.com
Jianwei Hu
ByteDance Inc
Email: hujianwei@bytedance.com
Beixin Huang
ByteDance Inc
Email: huangbeixin@bytedance.com
Nian Liu
ByteDance Inc
Email: liunian@bytedance.com
Yang, et al. Expires 25 June 2023 [Page 9]
