SFC WG T. Ao
Internet-Draft ZTE Corporation
Intended status: Standards Track G. Mirsky
Expires: December 31, 2017 ZTE Corp.
Z. Chen
China Telecom
June 29, 2017
Controlled Return Path for Service Function Chain (SFC) OAM
draft-ao-sfc-oam-return-path-specified-00
Abstract
This document defines extensions to the Service Function Chain (SFC)
Operation, Administration and Maintenance (OAM) that enable control
of the Echo Reply return path by specifying it as Reverse Service
Function Path. Enforcing the specific return path can be used to
verify bidirectional connectivity of SFC and increase 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Extension . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SFC Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 4
5. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 5
5.1. Case of Bi-directional SFC . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. SFC Return Path Type . . . . . . . . . . . . . . . . . . 6
7.2. New Return Codes . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
While Echo Request, defined in [I-D.ooamdt-rtgwg-demand-cc-cv],
always traverses the Service Function Chain (SFC) it directed to, the
corresponding Echo Reply is sent over IP network
[I-D.wang-sfc-multi-layer-oam]. There are scenarios when it is
beneficial to direct the responder to use path other than the IP
network. This document defines extensions to the Service Function
Chain (SFC) Operation, Administration and Maintenance (OAM) that
enable control of the Echo Reply return path by specifying it as
Reply Service Function Path. This document defines a new Type-
Length-Value (TLV), Reply Service Function Path TLV, for Reply via
Specified Path mode of Overlay Echo Reply (Section 4).
The Reply Service Function Path TLV provides efficient mechanism to
test bidirectional and hybrid SFCs, as these were defined in
Section 2.2 [RFC7665], that allows an operator to test both
directions of the bidirectional or hybrid SFP with a single Overlay
Echo Request/Echo Reply operation.
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2. Conventions used in this document
2.1. Terminology
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
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
Following reply modes had been defined in
[I-D.ooamdt-rtgwg-demand-cc-cv]:
o Do Not Reply
o Reply via an IPv4/IPv6 UDP Packet
o Reply via Application Level Control Channel
o Reply via Specified Path
The Reply via Specified Path mode is intended to enforce use of the
particular return path specified in the included TLV. This mode may
help to verify bidirectional continuity or increase robustness of the
monitoring of the SFC by selecting more stable path. In case of SFC,
the sender of Echo Request instructs the egress SFF to send Echo
Reply message along the SFP specified in the SFC Reply Path TLV
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 Overlay Echo Reply message is
expected to follow. The format of SFC Reply Path TLV is display 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 Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Service Function Path |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SFC Reply TLV Format
where:
o Reply Path TLV Type: is 2 octets long, indicates the TLV that
contains a information about the SFC Reply path.
o Length: is 2 octets long, MUST be equal to 4
o Reply Service Function Path is used to describe the return path
that an Overlay 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 Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Reply Service Function Path Field Format
where:
o Reply Service Path Identifier: is SFP identifier for the path that
the Overlay Echo Reply message is requested to be sent over.
o Service Index: used for forwarding in the reply SFP.
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5. Theory of Operation
[RFC7110] defined mechanism to control return path for MPLS LSP Echo
Reply. In case of SFC, the return path is a SFP along which Overlay
Echo Reply message MUST be transmitted. Hence, the SFC Reply Path
TLV included in the Overlay Echo Request message MUST sufficiently
identify the SFP that the sender of the Echo Request message expects
the receiver to use for the corresponding Overlay 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.ooamdt-rtgwg-demand-cc-cv], and MUST include SFC Reply Path TLV.
The SFC Reply Path TLV includes identifier of the reverse SFP and an
appropriate Service Index.
Echo Reply is expected to be sent by the egress SFF of the SFP being
tested or by the SFF at which SFC TTL expires as defined
[I-D.ietf-sfc-nsh]. Processing described below equally applies in
both cases and referred 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 requested SFP it
MUST send Echo Reply with Return Code set to "Reply SFP was not
found" and include the SFC Reply Path TLV from the Echo Request
message.
5.1. Case of Bi-directional SFC
Ability to specify the return path to be used for Echo Reply is very
useful in bi-directional SFC. For bi-directional SFC, since the last
SFF of the forward SFP may not co-locate with classifier of the
reverse SFP,it is assumed that last SFF doesn't know the reply path
of a SFC. So even for bi-directional SFC, a reverse SFP also need to
be indicated in reply path TLV in echo request message.
6. Security Considerations
Will be added in the future updates.
7. IANA Considerations
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7.1. SFC Return Path Type
IANA is requested to assign from its Overlay Echo Request/Echo Reply
TLV registry new type as following:
+-------+----------------------+---------------+
| 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 Overlay Echo
Request/Echo Reply Return Codes registry as following:
+-------+----------------------------+---------------+
| Value | Description | Reference |
+-------+----------------------------+---------------+
| TBA2 | Reply Path TLV is missing | This document |
| TBA3 | Reply SFP was not found | This document |
+-------+----------------------------+---------------+
Table 2: SFC Overlay Echo Reply Return Codes
8. References
8.1. Normative References
[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-12 (work in progress), February 2017.
[I-D.ooamdt-rtgwg-demand-cc-cv]
Mirsky, G., Kumar, N., Kumar, D., Chen, M., Yizhou, L.,
and D. Dolson, "Echo Request and Echo Reply for Overlay
Networks", draft-ooamdt-rtgwg-demand-cc-cv-03 (work in
progress), March 2017.
[I-D.wang-sfc-multi-layer-oam]
Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Multi-
Layer OAM for Service Function Chains in Networks", draft-
wang-sfc-multi-layer-oam-09 (work in progress), June 2017.
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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,
<http://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, <http://www.rfc-editor.org/info/rfc8174>.
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,
<http://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,
<http://www.rfc-editor.org/info/rfc7665>.
Authors' Addresses
Ting Ao
ZTE Corporation
No.889, BiBo Road
Shanghai 201203
China
Phone: +86 21 68897642
Email: ao.ting@zte.com.cn
Greg Mirsky
ZTE Corp.
1900 McCarthy Blvd. #205
Milpitas, CA 95035
USA
Email: gregimirsky@gmail.com
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Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai 201203
China
Phone: +86 18918588897
Email: 18918588897@189.cn
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