Internet DRAFT - draft-ao-sfc-oam-return-path-specified
draft-ao-sfc-oam-return-path-specified
SFC WG G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track T. Ao
Expires: 1 October 2021 Individual contributor
Z. Chen
China Telecom
G. Mishra
Verizon Inc.
30 March 2021
Controlled Return Path for Service Function Chain (SFC) OAM
draft-ao-sfc-oam-return-path-specified-09
Abstract
This document defines an extension to the Service Function Chain
(SFC) Operation, Administration and Maintenance (OAM) that enables
control of the Echo Reply return path directing it over a Reverse
Service Function Path. Enforcing the specific return path can be
used to verify the bidirectional connectivity of SFC and increase the
robustness of SFC OAM.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Extension . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SFC Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 4
5. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 5
5.1. Bi-directional SFC Case . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7.1. SFC Return Path Type . . . . . . . . . . . . . . . . . . 6
7.2. New Return Codes . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
While Service Function Chain (SFC) Echo Request, defined in
[I-D.ietf-sfc-multi-layer-oam], always traverses the SFC it directed
to, the corresponding Echo Reply is sent over IP network
[I-D.ietf-sfc-multi-layer-oam]. There are scenarios when it is
beneficial to direct the responder to use a path other than the IP
network. This document extends Service Function Chain (SFC)
Operation, Administration and Maintenance (OAM) by enabling control
of the Echo Reply return path to be directed over a Reply Service
Function Path (SFP). Such an extension is based on the analysis of
SFC OAM, active OAM protocols, in particular, provided in [RFC8924].
This document defines a new Type-Length-Value (TLV), Reply Service
Function Path TLV, for Reply via Specified Path mode of SFC Echo
Reply (Section 4).
The Reply Service Function Path TLV can provide an efficient
mechanism to test SFCs, such as bidirectional and hybrid SFC, as
defined in Section 2.2 [RFC7665]. For example, it allows an operator
to test both directions of the bidirectional or hybrid SFP with a
single SFC Echo Request/Echo Reply operation.
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2. Conventions used in this document
2.1. Acronyms
SF - Service Function
SFF - Service Function Forwarder
SFC - Service Function Chain, an ordered set of some abstract SFs.
SFP - Service Function Path
SPI - Service Path Index
OAM - Operation, Administration, and Maintenance
MAC - Message Authentication Code
2.2. 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.
3. Extension
The following reply modes had been defined in
[I-D.ietf-sfc-multi-layer-oam]:
* Do Not Reply
* Reply via an IPv4/IPv6 UDP Packet
* Reply via Application Level Control Channel
* Reply via Specified Path
The Reply via Specified Path mode is intended to enforce the use of
the particular return path specified in the included TLV. This mode
may help verify bidirectional continuity or increase SFC monitoring's
robustness by selecting a more stable path. In SFC's case, the
sender of Echo Request instructs the destination SFF to send Echo
Reply message along the SFP specified in the SFC Reply Path TLV, as
described in Section 4.
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4. SFC Reply Path TLV
The SFC Reply Path TLV carries the information that sufficiently
identifies the return SFP that the SFC Echo Reply message is expected
to follow. The format of SFC Reply Path TLV is shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SFC Reply Path | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Service Function Path |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SFC Reply TLV Format
where:
* Reply Path TLV Type: is a one-octet-long, indicates the TLV that
contains information about the SFC Reply path.
* Reserved - one-octet-long field.
* Length: is two octets long, MUST be equal to 4
* Reply Service Function Path is used to describe the return path
that an SFC Echo Reply is requested to follow.
The format of the Reply Service Function Path field displayed in
Figure 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Service Function Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Reply Service Function Path Field Format
where:
* Reply Service Function Path Identifier: SFP identifier for the
path that the SFC Echo Reply message is requested to be sent over.
* Service Index: the value for the Service Index field in the NSH of
the SFC Echo Reply message.
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5. Theory of Operation
[RFC7110] defined mechanism to control return path for MPLS LSP Echo
Reply. In SFC's case, the return path is an SFP along which the SFC
Echo Reply message MUST be transmitted. Hence, the SFC Reply Path
TLV included in the SFC Echo Request message MUST sufficiently
identify the SFP that the sender of the Echo Request message expects
the receiver to use for the corresponding SFC Echo Reply.
When sending an Echo Request, the sender MUST set the value of Reply
Mode field to "Reply via Specified Path", defined in
[I-D.ietf-sfc-multi-layer-oam], and if the specified path is SFC
path, the Request MUST include SFC Reply Path TLV. The SFC Reply
Path TLV includes the identifier of the reverse SFP and an
appropriate Service Index.
The Message Authentication Code (MAC) Context Header that is defined
in [I-D.ietf-sfc-nsh-integrity] MAY be used to protect the SFC Echo
Request's integrity when using the SFC Return Path TLV. If the NSH
of the received SFC Echo Request includes the MAC Context Header, the
packet's authentication MUST be verified before using any data. If
the verification fails, the receiver MUST stop processing the SFC
Return Path TLV and MUST send the SFC Echo Reply with the Return
Codes value set to the value Authentication failed from the IANA's
Return Codes sub-registry of the SFC Echo Request/Echo Reply
Parameters registry.
Echo Reply is expected to be sent by the destination SFF of the SFP
being tested or by the SFF at which SFC TTL expires as defined
[RFC8300]. The processing described below equally applies to both
cases and is referred to as responding SFF.
If the Echo Request message with SFC Reply Path TLV, received by the
responding SFF, has Reply Mode value of "Reply via Specified Path"
but no SFC Reply Path TLV is present, then the responding SFF MUST
send Echo Reply with Return Code set to "Reply Path TLV is missing"
value (TBA2). If the responding SFF cannot find the requested SFP it
MUST send Echo Reply with Return Code set to "Reply SFP was not
found" (TBA3) and include the SFC Reply Path TLV from the Echo
Request message.
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Suppose the SFC Echo Request receiver cannot determine whether the
specified return path SFP has the route to the initiator. In that
case, it SHOULD set the value of the Return Codes field to
"Unverifiable Reply Path" (TBA4). The receiver MAY drop the Echo
Request when it cannot determine whether SFP's return path has the
route to the initiator. That means, when sending Echo Request, the
sender SHOULD choose a proper source address according to specified
return path SFP to help the receiver to make the decision.
5.1. Bi-directional SFC Case
The ability to specify the return path for an Echo Reply might be
used in the case of bi-directional SFC. The egress SFF of the
forward SFP might not be co-located with a classifier of the reverse
SFP, and thus the egress SFF has no information about the reverse
path of an SFC. Because of that, even for bi-directional SFC, a
reverse SFP needs to be indicated in a Reply Path TLV in the Echo
Request message.
6. Security Considerations
Security considerations discussed in [RFC8300] apply to this
document.
The SFC Return Path extension, defined in this document, can be used
for potential "proxying" attacks. For example, the Echo Request
initiator may specify a return path with a destination different from
that of the initiator. Such attacks will usually not happen in an
SFC domain where the initiators and receivers belong to the same
domain, as specified in [RFC7665]. Even if the attack occurs, to
prevent using the SFC Return Path extension for proxying any possible
attacks, the return path SFP SHOULD have a path to reach the sender
of the Echo Request, identified in SFC Source TLV
[I-D.ietf-sfc-multi-layer-oam]. The MAC Context Header that is
defined in [I-D.ietf-sfc-nsh-integrity] MAY be used to protect the
integrity of the SFC Echo Request/Reply when using the SFC Return
Path TLV.
7. IANA Considerations
7.1. SFC Return Path Type
IANA is requested to assign from its SFC Echo Request/Echo Reply TLV
registry new type as follows:
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+=======+======================+===============+
| Value | Description | Reference |
+=======+======================+===============+
| TBA1 | SFC Reply Path Type | This document |
+-------+----------------------+---------------+
Table 1: SFC Return Path Type
7.2. New Return Codes
IANA is requested to assign new return codes from the SFC Echo
Request/Echo Reply Return Codes sub-registry of the SFC Echo Request/
Echo Reply Parameters registry as defined in Table 2.
+=======+============================+===============+
| Value | Description | Reference |
+=======+============================+===============+
| TBA2 | Reply Path TLV is missing | This document |
+-------+----------------------------+---------------+
| TBA3 | Reply SFP was not found | This document |
+-------+----------------------------+---------------+
| TBA4 | Unverifiable Reply Path | This document |
+-------+----------------------------+---------------+
Table 2: SFC Echo Reply Return Codes
8. References
8.1. Normative References
[I-D.ietf-sfc-multi-layer-oam]
Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Active
OAM for Service Function Chaining", Work in Progress,
Internet-Draft, draft-ietf-sfc-multi-layer-oam-09, 11
February 2021, <https://tools.ietf.org/html/draft-ietf-
sfc-multi-layer-oam-09>.
[I-D.ietf-sfc-nsh-integrity]
Boucadair, M., Reddy, T., and D. Wing, "Integrity
Protection for the Network Service Header (NSH) and
Encryption of Sensitive Context Headers", Work in
Progress, Internet-Draft, draft-ietf-sfc-nsh-integrity-05,
23 March 2021, <https://tools.ietf.org/html/draft-ietf-
sfc-nsh-integrity-05>.
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[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>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
8.2. Informative References
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<https://www.rfc-editor.org/info/rfc7110>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC8924] Aldrin, S., Pignataro, C., Ed., Kumar, N., Ed., Krishnan,
R., and A. Ghanwani, "Service Function Chaining (SFC)
Operations, Administration, and Maintenance (OAM)
Framework", RFC 8924, DOI 10.17487/RFC8924, October 2020,
<https://www.rfc-editor.org/info/rfc8924>.
Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com, gregory.mirsky@ztetx.com
Ting Ao
Individual contributor
No.889, BiBo Road
Shanghai
201203
China
Phone: +86 17721209283
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Email: 18555817@qq.com
Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai
201203
China
Phone: +86 18918588897
Email: 18918588897@189.cn
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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