SRPM Path Consistency over SRv6
draft-weng-ippm-srpm-path-consistency-over-srv6-00
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| Authors | Weiqiang Cheng , Changwang Lin | ||
| Last updated | 2022-03-02 | ||
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draft-weng-ippm-srpm-path-consistency-over-srv6-00
IPPM Working Group S. Weng
Internet Draft W. Cheng
Intended status: Informational China Mobile
Expires: Sep 3, 2022 C. Lin
New H3C Technologies
March 3, 2022
SRPM Path Consistency over SRv6
draft-weng-ippm-srpm-path-consistency-over-srv6-00
Abstract
Twamp can be used to measure the performance of end-to-end paths in
networks. Stamp [rfc8762] and twamp light are more lightweight
measurement methods. In the SRv6 network, it is also necessary to
measure the performance of SRv6 policy. This document describes a
method to measure srv6 policy through stamp and twamp light.
Status of this Memo
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This Internet-Draft will expire on September 3 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction ................................................ 2
1.1. Requirements Language .................................. 3
1.2. Terminology ............................................ 3
2. Requirement for consistent path ............................. 4
3. Correlate bidirectional path using Path Segment ............. 5
4. STAMP/TWAMP light Procedure with Path segment ............... 7
4.1. Stamp/twamp light Session-sender procedure ............. 7
4.2. Stamp/twamp light Session-reflector procedure .......... 8
5. IANA Considerations ........................................ 10
6. Security Considerations .................................... 10
7. References ................................................. 10
7.1. Normative References .................................. 10
Contributors .................................................. 12
Authors' Addresses ............................................ 13
1. Introduction
Segment Routing (SR) allows a headend node to steer a packet flow
along any path. Per-path states of Intermediate nodes are eliminated
thanks to source routing. The headend node steers a flow into an SR
Policy. The packets steered into an SR Policy carry an ordered list
of segments associated with that SR Policy. SR policy is used to
forward messages, so the quality of SR policy, such as packet loss
and delay, also needs to be measured.
The Simple Two-Way Active Measurement Protocol (STAMP) provides
capabilities for the measurement of various performance metrics in
IP networks [RFC8762] without the use of a control channel to pre-
signal session parameters. [RFC8972] defines optional extensions in
the form of TLVs for STAMP.
The STAMP test packets are transmitted along an IP path between a
Session-Sender and a Session-Reflector to measure performance delay
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and packet loss along that IP path. It may be desired in SRv6
networks that the consistent path (same set of links and nodes)
between the Session-Sender and Session-Reflector is used for the
STAMP test packets in both directions.
[ietf-ippm-stamp-srpm] defines the Return Path TLV, Using Return
Path TLV, The Session-Sender can request this in the test packet to
the Session-Reflector.
Twamp light is also widely deployed, and stamp supports interworking
with twamp light. So there are four possible combinations to deploy
stamp and twamp light:
STAMP Session-Sender with STAMP Session-Reflector.
STAMP Session-Sender with TWAMP Light Session-Reflector.
TWAMP Light Session-Sender with STAMP Session-Reflector.
TWAMP Light Session-Sender with TWAMP Light Session-Reflector.
Twamp light does not support the TLV of stamp, so in order to meet
various deployment combinations, this document proposes a method to
realize the same path between Session-Sender and session-reflector
using path segment, which is also applicable to all scenarios where
twamp light and stamp are deployed.
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.
1.2. Terminology
STAMP: Simple Two-way Active Measurement Protocol
TWAMP: Two-Way Active Measurement Protocol
PTP: Precision Time Protocol
SR: Segment Routing
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2. Requirement for consistent path
In the reference topology shown below, the procedure of stamp and
twamp light is similar. The Session-Sender S1 initiates a test
packet and the Session-Reflector R1 transmits a reply test packet.
The reply test packet may be transmitted to the Session-Sender S1 on
the consistent path (same set of links and nodes) or a different
path in the reverse direction from the path taken towards the
Session-Reflector R1.
T1 T2
/ \
+-------+ Test Packet +-------+
| | - - - - - - - - - ->| |
| S1 |=====================| R1 |
| |<- - - - - - - - - - | |
+-------+ Reply Test Packet +-------+
\ /
T4 T3
Session-Sender Session-Reflector
Figure 1: reference topology1
By recording the time stamp in the test packet, the delay of one-way
and two-way path can be measured. In the interaction process of a
test, the sender inserts the sending timestamp T1 into the test
packet. The reflector records the receiving timestamp T2 when
receiving the request message. Then reflector creates a reply packet
and inserts T1, T2 and the sending timestamp T3 of the reply packet
into the reply packet. Finally the sender receives the reply packet
and records the receiving timestamp T4.
In this way, the sender gets four timestamps. Bidirectional delay
can be obtained through t4-t1. If the one-way delay is calculated
through t2-t1, PTP is required to be deployed between sender and
reflector to ensure high-precision time synchronization, which is
not easy to achieve for existing networks.
Therefore, if the test packets in both directions can be guaranteed
to pass along the consistent path, the two-way delay can be obtained
by T4-T1, minus the time of processing packet on the reflector
calculated by T3-T2, and the final data is the sum of the delays in
two directions of transmitting packets along the consistent path.
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3. Correlate bidirectional path using Path Segment
A Path Segment is defined to identify an SR path in [draft-ietf-
spring-srv6-path-segment]. SRv6 Path segments can be used to
correlate the two unidirectional SRv6 paths at both ends of the
path.
[draft-ietf-idr-sr-policy-path-segment] proposes an extension to BGP
SR Policy distribute SR policies carrying Path Segment and
bidirectional path information.
Through this extension, when distributing SRv6 policy to the
headend, reverse path information and path segment of segment list
can be carried together.
SID-B1 SID-B2 SID-C1 SID-C2
+--------B-----------------C-----------+
SID-A1/ \ SID-D1
/ \
A D
\ /SID-D2
SID-A2\ SID-E1 SID-E2 /
+-------------------E-------------------+
Figure 2: reference topology2
In this way, on the headend in both directions of the forward and
reverse paths, the path segment of the paths in both directions can
be obtained, and the paths in both directions use the same
intermediate link.
Refer to the reference topology2. There are two paths between NodeA
and NodeD, and All nodes allocate end.x Segments.
SRv6 policy is distributed to NodeA and NodeD respectively as the
headend to build symmetrical two-way paths. SRv6 policy includes a
candidate path, which contains two segment lists.
Each segment list contains both the corresponding path segment and
the reverse path segment of the reverse path:
NodeA NodeD
SRv6 Policy A-D SRv6 Policy D-A
Candidate Path1 Candidate Path1
Segment list1 Segment list1
SID-A1, SID-B2, SID-C2 SID-D1, SID-C1, SID-B1
Path Segment: SID-Path-A1 Path Segment: SID-Path-D1
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Reverse Path Segment: Reverse Path Segment:
SID-Path-D1 SID-Path-A1
Segment list2 Segment list2
SID-A2, SID-E2 SID-D2, SID-E1
Path Segment: SID-Path-A2 Path Segment: SID-Path-D2
Reverse Path Segment: Reverse Path Segment:
SID-Path-D2 SID-Path-A2
The headend can use path segment in two directions to establish a
mapping table. Using this mapping table, the headend can index the
reverse path through the path segment of the forward path.
NodeA:
+-----------------+ +--------------------+
| Path Segment | |Reverse Path Segment|
+-----------------+ +--------------------+
| SID-Path-A1 |-+ | SID-Path-D1 |--+
+-----------------+ | +--------------------+ |
| SID-Path-A2 | | | SID-Path-D2 |--|-+
+-----------------+ | +--------------------+ | |
| | | |
| | +-----------------------+ | |
| | | segment List | | |
| | +-----------------------+ | |
| +->|SID-A1, SID-B2, SID-C2 |<----+ |
| +-----------------------+ |
+-------------->|SID-A2, SID-E2 |<------+
+-----------------------+
NodeD:
+-----------------+ +--------------------+
| Path Segment | |Reverse Path Segment|
+-----------------+ +--------------------+
| SID-Path-D1 |-+ | SID-Path-A1 |--+
+-----------------+ | +--------------------+ |
| SID-Path-D2 | | | SID-Path-A2 |--|-+
+-----------------+ | +--------------------+ | |
| | | |
| | +-----------------------+ | |
| | | segment List | | |
| | +-----------------------+ | |
| +->|SID-D1, SID-C1, SID-B1 |<----+ |
| +-----------------------+ |
+-------------->|SID-D2, SID-E1 |<------+
+-----------------------+
Figure 3: mapping table
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4. STAMP/TWAMP light Procedure with Path segment
This document proposes that the test packets in the two directions
of stamp/twamp light are transmitted along the consistent path
through path segment.
Twamp light does not need to parse the TLV of stamp. Neither stamp
nor twamp light needs to modify the packet structure. Using SRH to
carry path segment, stamp and twamp light need to add some relevant
adaptation processing to meet the requirement.
4.1. Stamp/twamp light Session-sender procedure
For instance, the session-sender is Node A in Figure 2, and the
session is bounded with Segment List1 of Policy A-D. The test packet
is as follow:
+-----------------------------------------------------------+
| IPv6 Header |
. Source IP Address = Session-Sender IPv6 Address .
. Destination IP Address = SegmentList[SL] .
. Next-Header = SRH (43) .
. .
+-----------------------------------------------------------+
| SRH as specified in RFC 8754 |
. Next-Header = IPv6 .
. <PathSegment, Segment List> .
. .
+-----------------------------------------------------------+
| IPv6 Header |
. Source IP Address = Session-Sender IPv6 Address .
. Destination IP Address = Session-Reflector IPv6 Address .
. Next-Header = UDP .
. .
+-----------------------------------------------------------+
| UDP Header |
. .
+-----------------------------------------------------------+
| Payload |
. .
+-----------------------------------------------------------+
Figure 4: Encapsulation format of test packet
NodeA Encapsulates the path segment of segment list1 in SRH, and set
SRH.P-Flag.
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The test packet is as follows:
A------------->B------------>C---------->D
+-----------------+ +-----------------+
| SA=A's Ipv6Addr | | SA=A's Ipv6Addr |
+-----------------+ +-----------------+
| DA=SID-A1 | | DA=D's ipv6Addr |
+-----------------+ +-----------------+
| SL=3 | P-Flag=1 | | SL=0 | P-Flag=1 |
+-----------------+ +-----------------+
| D's ipv6Addr | | D's ipv6Addr |
+-----------------+ +-----------------+
| SID-C2 | | SID-C2 |
+-----------------+ +-----------------+
| SID-B2 | | SID-B2 |
+-----------------+ +-----------------+
| SID-A1 | | SID-A1 |
+-----------------+ +-----------------+
| SID-Path-A1 | | SID-Path-A1 |
+-----------------+ +-----------------+
| test-payload | | test-payload |
| | | |
+-----------------+ +-----------------+
Figure 5: Example of test packet
4.2. Stamp/twamp light Session-reflector procedure
The test packet is forwarded along the path A->B->C-D. While packet
arrives at nodeD, SRH.SL is 0 and the destination address is the
IPv6 address of NodeD. Packet is delivered up to the stamp/twamp
light module in control plane.
Stamp/twamp light module on NodeD detects SRH.P-flag is set,
extracts the path segment of the forward path from SRH, gets the
path segment of the reverse path through the mapping table. When
reply test packet, stamp/twamp light module use the segment list
associated with path segment of the reverse path to encapsulate SRH.
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+-----------------------------------------------------------+
| IPv6 Header |
. Source IP Address = Session-Reflector IPv6 Address .
. Destination IP Address = SegmentList[SL] .
. Next-Header = SRH (43) .
. .
+-----------------------------------------------------------+
| SRH as specified in RFC 8754 |
. Next-Header = IPv6 .
. <Segment List> .
. .
+-----------------------------------------------------------+
| IPv6 Header |
. Source IP Address = Session-Reflector IPv6 Address .
. Destination IP Address = Session-Sender IPv6 Address .
. Next-Header = UDP .
. .
+-----------------------------------------------------------+
| UDP Header |
. .
+-----------------------------------------------------------+
| Payload |
. .
+-----------------------------------------------------------+
Figure 6: Encapsulation format of reply test packet
The Example of reply test packet is as follows:
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D------------->C------------>B---------->A
+-----------------+ +-----------------+
| SA=D's Ipv6Addr | | SA=D's Ipv6Addr |
+-----------------+ +-----------------+
| DA=SID-D1 | | DA=A's ipv6Addr |
+-----------------+ +-----------------+
| SL=3 | P-Flag=0 | | SL=0 | P-Flag=0 |
+-----------------+ +-----------------+
| A's ipv6Addr | | A's ipv6Addr |
+-----------------+ +-----------------+
| SID-B1 | | SID-B1 |
+-----------------+ +-----------------+
| SID-C1 | | SID-C1 |
+-----------------+ +-----------------+
| SID-D1 | | SID-D1 |
+-----------------+ +-----------------+
| reply test | | reply test |
| payload | | payload |
+-----------------+ +-----------------+
Figure 7: Example of reply test packet
The reply test packet will be forward along the path D->C->B->A. In
this way, the forward and reverse paths of test packet are
guaranteed to be consistent.
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
The security requirements and mechanisms described in [RFC8402] and
[RFC8754] also apply to this document.
This document does not introduce any new security consideration.
7. References
7.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C.,
Talaulikar, K., Mattes, P.,Rosen, E., Jain, D., and S.
Lin, "Advertising Segment Routing Policies in BGP", draft-
ietf-idr-segment-routing-te-policy-11 (work in progress),
November 2020
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[I-D.ietf-spring-mpls-path-segment] Cheng, W., Li, H., Chen, M.,
Gandhi, R., and R. Zigler, "Path Segment in MPLS Based
Segment Routing Network",draft-ietf-spring-mpls-path-
segment-07 (work in progress), December 2021.
[I-D.ietf-spring-segment-routing-policy] Filsfils, C., Talaulikar,
K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment
Routing Policy Architecture", draft-ietf-spring-segment-
routing-policy-17 (work in progress),February 2022.
[I-D.ietf-spring-srv6-path-segment] Li, C., Cheng, W., Chen, M.,
Dhody, D., and Y. Zhu, "Path Segment for SRv6 (Segment
Routing in IPv6)", draft-ietf-spring-srv6-path-segment-03
(work in progress),November 2021.
[I-D.ietf-idr-sr-policy-path-segment] Li, C., Li, Z., Yin, Y.,
Cheng, W., Talaulikar, K., "SR Policy Extensions for Path
Segment and Bidirectional Path", draft-ietf-idr-sr-policy-
path-segment-05(work in progress), January 2022.
[I-D.ietf-spring-stamp-srpm] Gandhi, R., Filsfils, C., Voyer, D.,
Chen, M., Janssens, B., and R. Foote, "Performance
Measurement Using Simple TWAMP (STAMP) for Segment Routing
Networks", Work in Progress, Internet-Draft, draft-ietf-
spring-stamp-srpm-03, 1 February 2022,
<https://www.ietf.org/archive/id/draft-ietf-spring-stamp-
srpm-03.txt>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg,
L.,Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,July
2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy,
J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing
Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8762] Greg Mirsky, Guo Jun, Henrik Nydell, Richard Foote,
"Simple Two-Way Active Measurement Protocol", RFC 8762,
DOI: 10.17487/RFC8762, March 2020, <https://www.rfc-
editor.org/info/rfc8762>.
[RFC8972] Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
and E. Ruffini, "Simple Two-Way Active MeasurementProtocol
Optional Extensions", RFC 8972, DOI 10.17487/RFC8972,
January 2021, <https://www.rfc-editor.org/info/rfc8972>.
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[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986, DOI
0.17487/RFC8986, February 2021, <https://www.rfc-
editor.org/info/rfc8986>.
Contributors
Yisong Liu contributed to the content of this document.
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Authors' Addresses
Wengsijun
China Mobile
Beijing
CN
Email: wengsijun@chinamobile.com
Weiqiang Cheng
China Mobile
Beijing
CN
Email: chengweiqiang@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Hao Li
New H3C Technologies
Beijing
China
Email: lihao@h3c.com
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