SFC WG T. Ao
Internet-Draft ZTE Corporation
Intended status: Standards Track G. Mirsky
Expires: September 11, 2019 ZTE Corp.
Z. Chen
China Telecom
K. Leung
Cisco System
March 10, 2019
SFC OAM for path consistency
draft-ao-sfc-oam-path-consistency-05
Abstract
Service Function Chain (SFC) defines an ordered set of service
functions (SFs) to be applied to packets and/or frames and/or flows
selected as a result of classification. SFC Operation,
Administration and Maintenance can monitor the continuity of the SFC,
i.e., that all elements of the SFC are reachable to each other in the
downstream direction. But SFC OAM must support verification that the
order of traversing these SFs corresponds to the state defined by the
SFC control plane or orchestrator, the metric referred in this
document as the path consistency of the SFC. This document defines a
new SFC OAM method to support SFC consistency check, i.e.
verification that all elements of the given SFC are being traversed
in the expected order.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 11, 2019.
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Copyright Notice
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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. Consistency OAM: Theory of Operation . . . . . . . . . . . . 3
3.1. COAM packet . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. SFF Information Record TLV . . . . . . . . . . . . . . . 4
3.3. SF Information Sub-TLV . . . . . . . . . . . . . . . . . 5
3.4. SF Information Sub-TLV Construction . . . . . . . . . . . 6
3.4.1. Multiple SFs as hops of SFP . . . . . . . . . . . . . 6
3.4.2. Multiple SFs for load balance . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. COAM Message Types . . . . . . . . . . . . . . . . . . . 8
5.2. SFF Information Record TLV Type . . . . . . . . . . . . . 8
5.3. SF Information Sub-TLV Type . . . . . . . . . . . . . . . 8
5.4. SF Identifier Types . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informational References . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Service Function Chain (SFC) is a chain with a series of ordered
Service Functions (SFs). Service Function Path (SFP) is a path of a
SFC. SFC is described in detail in the SFC architecture document
[RFC7665]. The SFs in the SFC are ordered and only when one SF
processes traffic then it can be processed by the next SF. Changes
in the order may cause errors. Sometimes, an SF uses the metadata
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from its upstream SF process. That's why it's very important for the
operator to make sure that the order of traversing the SFs is exactly
as defined by the control plane or the orchestrator. This document
refers to the correspondence between the state of the control plane
and the SFP itself as the SFP consistency.
This document defines the method to check the path consistency of the
SFP. It is an extension of the SFC Echo-request/Echo-reply specified
in the [I-D.ietf-sfc-multi-layer-oam].
2. Conventions used in this document
2.1. Terminology
SFC(Service Function Chain): An ordered set of some abstract SFs.
SFF: Service Function Forwarder
SF: Service Function
OAM: Operation, Administration and Maintenance
SFP: Service Function Path
COAM(Consistency OAM): OAM that can be used to check the consistency
of the Service Function Path.
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. Consistency OAM: Theory of Operation
Consistency OAM(COAM) uses two functions: COAM Request and COAM
Reply. Every SFF that receives the COAM Request MUST perform the
following actions:
o Collect information of traversed by the COAM Request packet SFs
and send it to the ingress SFF as COAM Reply packet over IP
network [I-D.ietf-sfc-multi-layer-oam];
o Forward the COAM Request to next downstream SFF if the one exists.
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As result, the ingress SFF collects information about all traversed
SFFs and SFs, information of the actual path the COAM packet has
traveled, so that we can verify the path consistency of the SFC. The
mechanism for the SFP consistency verification is outside the scope
of this document.
3.1. COAM packet
Consistency OAM introduces two new types of messages to the SFC Echo
request/reply operation [I-D.ietf-sfc-multi-layer-oam] with the
following values detailed in Section 5.1:
o TBA1 - COAM Request
o TBA2 - COAM Reply
Upon receiving the COAM Request, the SFF MUST respond with the COAM
Reply. The SFF MUST include the SFs information, as described in
Section 3.3 and Section 3.2.
The COAM packet is displayed in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Reply mode | Return Code | Return S.code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: COAM Packet Header
3.2. SFF Information Record TLV
For COAM Request, the SFF MUST include the Information of SFs into
the SF Information Record TLV in the COAM Reply message. Every SFF
send back one COAM Reply Message with all the SFs that are attaching
to the SFF along the SFP indicated by the COAM Request.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SFF Record TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Identifier(SPI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SF Information Sub-TLV |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SFF Information Record TLV
Service Path Identifier(SPI): The identifier of SFP to which all the
SFs in this TLV belong.
SF Information Sub-TLV: The Sub-TLV as defined in Figure 3.
3.3. SF Information Sub-TLV
Every SFF receiving COAM Request packet MUST include the SF
characteristic data into the COAM Reply packet. The data format of
each SF includes in a COAM Reply packet as SF Information sub-TLV
that is displayed in Figure 3.
After the COAM traversed the SFP, all the information of the SFs on
the SFP are collected from the TLVs with COAM Reply.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SF sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Service Index | SF Type | SF ID Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SF Identifiers |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Service Function information sub-TLV
SF sub-TLV Type: Two octets long field. It indicates that the TLV is
a SF TLV which contains the information of one SF.
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Length: Two octets long field. The value of the field is the length
of the data following the Length field counted in octets.
Service Index: Indicates the SF's position on the SFP.
SF Type: Two octets long field. It is defined in
[I-D.ietf-bess-nsh-bgp-control-plane] and indicates the type of SF,
e.g., Firewall, Deep Packet Inspection, WAN optimization controller,
etc.
Reserved: For future use. MUST be zeroed on transmission and MUST be
ignored on receipt.
SF ID Type: One octet long field with values defined as Section 5.4.
SF Identifier: An identifier of the SF. The length of the SF
Identifier depends on the type of the SF ID Type. For example, if
the SF Identifier is its IPv4 address, the SF Identifier should be 32
bits. SF ID Type and SF Identifier may be a list, indicating the
list of the SFs are which are included in a load balance group.
3.4. SF Information Sub-TLV Construction
Each SFF in the SFP MUST send one and only one COAM Reply
corresponding to the COAM Request. If there is only one SF attached
to the SFF in such SFP, only one SF information sub-TLV is included
in the on COAM Reply. If there are several SFs attached to the SFF
in the SFP, SF Information Sub-TLV MUST be constructed as described
below in either Section 3.4.1 and Section 3.4.2.
3.4.1. Multiple SFs as hops of SFP
Multiple SFs attached to one SFF are the hops of the SFP, the service
indexes of these SFs are different. Service function types of these
SFs could be different or be the same. Information about all SFs MAY
be included in the COAM Reply message. Information about each SF
MUST be listed as separate SF Information Sub-TLVs in the COAM Reply
message.
An example of the COAM procedure for this case is shown in Figure 4.
The Service Function Path(SPI=x) is SF1->SF2->SF4->SF3. The SF1,SF2
and SF3 are attached to SFF1, and SF4 is attached to SFF2. The COAM
Request message is sent to the SFFs in the sequence of the
SFP(SFF1->SFF2->SFF1). Every SFF(SFF1,SFF2) replies with the
information of SFs belonging to the SFP. The SF information Sub-TLV
in Figure 3 contains information for each SF(SF1, SF2,SF3 and SF4).
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SF1 SF2 SF4 SF3
+------+------+ | |
COAM Req ......> SFF1 ......> SFF2 ......> SFF1
(SPI=x) . . .
<............ <.......... <...........
COAM Reply1(SF1,SF2) COAM Reply2(SF4) COAM Reply3(SF3)
Figure 4: Example 1 for COAM Reply with multiple SFs
3.4.2. Multiple SFs for load balance
Multiple SFs may be attached to one SFF to balance the load, in other
words, that means that the particular traffic flow will transmit only
one of these SFs . These SFs have the same Service Function Type and
Service Index. For this case, the SF identifiers and SF ID Type of
all these SFs will be listed in the SF Identifiers field and SF ID
Type in a single SF information sub-TLV of COAM Reply message. The
number of these SFs can be calculated according to SF ID Type and the
value of Length field of the sub-TLV.
An example of the COAM procedure for this case is shown in Figure 4.
The Service Function Path(SPI=x) is SF1a/SF1b->SF2a/SF2b. The
Service Functions SF1a and SF1b are attached to SFF1 which are load
balance for each other, and the Service Functions SF2a and SF2b are
attached to SFF2 which are load balance for each other as well. The
COAM Request message is sent to the SFFs in the sequence of the SFP
(i.e. SFF1->SFF2). Every SFF(SFF1,SFF2) replies with the
information of SFs belonging to the SFP. The SF information Sub-TLV
in Figure 3 contains information for all SFs at that hop.
/SF1a /SF2a
\SF1b \SF2b
| |
SFF1 SFF2
COAM Req .........> . .........> .
(SPI=x) . .
<............ <...............
COAM Reply1({SF1a,SF1b}) COAM Reply2({SF2a,SF2b})
Figure 5: Example 2 for COAM Reply with multiple SFs
4. Security Considerations
Security considerations discussed in [RFC8300] and
[I-D.ietf-sfc-multi-layer-oam] apply to this document.
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Also, since Service Function sub-TLV discloses information about the
SFP the spoofed COAM Request packet may be used to obtain network
information, it is RECOMMENDED that implementations provide a means
of checking the source addresses of COAM Request messages, specified
in SFC Source TLV [I-D.ietf-sfc-multi-layer-oam], against an access
list before accepting the message.
5. IANA Considerations
5.1. COAM Message Types
IANA is requested to assign values from its Message Types sub-
registry in SFC Echo Request/Echo Reply Message Types registry as
follows:
+-------+------------------------------+---------------+
| Value | Description | Reference |
+-------+------------------------------+---------------+
| TBA1 | SFP Consistency Echo Request | This document |
| TBA2 | SFP Consistency Echo Reply | This document |
+-------+------------------------------+---------------+
Table 1: SFP Consistency Echo Request/Echo Reply Message Types
5.2. SFF Information Record TLV Type
IANA is requested to assign new type value from SFC OAM TLV Type
registry as follows:
+-------+-----------------------------+---------------+
| Value | Description | Reference |
+-------+-----------------------------+---------------+
| TBA3 | SFF Information Record Type | This document |
+-------+-----------------------------+---------------+
Table 2: SFF-Information Record
5.3. SF Information Sub-TLV Type
IANA is requested to assign new type value from SFC OAM TLV Type
registry as follows:
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+-------+----------------+---------------+
| Value | Description | Reference |
+-------+----------------+---------------+
| TBA4 | SF Information | This document |
+-------+----------------+---------------+
Table 3: SF-Information Sub-TLV Type
5.4. SF Identifier Types
IANA is requested to create in the registry SF Types the new sub-
registry SF Identifier Types. All code points in the range 1 through
191 in this registry shall be allocated according to the "IETF
Review" procedure as specified in [RFC8126] and assign values as
follows:
+------------+-------------+-------------------------+
| Value | Description | Reference |
+------------+-------------+-------------------------+
| 0 | Reserved | This document |
| TBA6 | IPv4 | This document |
| TBA7 | IPv6 | This document |
| TBA8 | MAC | This document |
| TBA8+1-191 | Unassigned | IETF Review |
| 192-251 | Unassigned | First Come First Served |
| 252-254 | Unassigned | Private Use |
| 255 | Reserved | This document |
+------------+-------------+-------------------------+
Table 4: SF Identifier Type
6. Acknowledgements
Thanks to John Drake for his review and the reference to the work on
BGP Control Plane for NSH SFC.
Thanks to Joel M. Halpern for his suggestion about the load balance
scenario.
Thansk to Dirk von Hugo for his useful comments.
7. References
7.1. Normative References
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[I-D.ietf-bess-nsh-bgp-control-plane]
Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess-
nsh-bgp-control-plane-09 (work in progress), March 2019.
[I-D.ietf-sfc-multi-layer-oam]
Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Active
OAM for Service Function Chains in Networks", draft-ietf-
sfc-multi-layer-oam-02 (work in progress), March 2019.
[I-D.ietf-sfc-nsh-tlv]
Quinn, P., Elzur, U., and S. Majee, "Network Service
Header TLVs", draft-ietf-sfc-nsh-tlv-00 (work in
progress), January 2018.
[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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
7.2. Informational References
[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>.
Authors' Addresses
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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
Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai 201203
China
Phone: +86 18918588897
Email: 18918588897@189.cn
Kent Leung
Cisco System
170 West Tasman Drive
San Jose, CA 95134
USA
Email: kleung@cisco.com
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