draft-ietf-6man-spring-srv6-oam-02.txt   draft-ietf-6man-spring-srv6-oam-03.txt 
6man Z. Ali 6man Z. Ali
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: May 23, 2020 S. Matsushima Expires: June 20, 2020 S. Matsushima
Softbank Softbank
D. Voyer D. Voyer
Bell Canada Bell Canada
M. Chen M. Chen
Huawei Huawei
November 20, 2019 December 18, 2019
Operations, Administration, and Maintenance (OAM) in Segment Routing Operations, Administration, and Maintenance (OAM) in Segment Routing
Networks with IPv6 Data plane (SRv6) Networks with IPv6 Data plane (SRv6)
draft-ietf-6man-spring-srv6-oam-02 draft-ietf-6man-spring-srv6-oam-03
Abstract Abstract
This document defines building blocks for Operations, Administration, This document defines building blocks for Operations, Administration,
and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane
(SRv6). The document also describes some SRv6 OAM mechanisms. (SRv6). The document also describes some SRv6 OAM mechanisms.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 23, 2020. This Internet-Draft will expire on June 20, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology and Reference Topology . . . . . . . . . . . 3 2.2. Terminology and Reference Topology . . . . . . . . . . . 3
3. OAM Building Blocks . . . . . . . . . . . . . . . . . . . . . 5 3. OAM Building Blocks . . . . . . . . . . . . . . . . . . . . . 5
3.1. O-flag in Segment Routing Header . . . . . . . . . . . . 5 3.1. O-flag in Segment Routing Header . . . . . . . . . . . . 5
3.1.1. O-flag Processing . . . . . . . . . . . . . . . . . . 6 3.1.1. O-flag Processing . . . . . . . . . . . . . . . . . . 6
3.2. OAM Segments . . . . . . . . . . . . . . . . . . . . . . 6 3.2. OAM Segments . . . . . . . . . . . . . . . . . . . . . . 6
3.3. End.OP: OAM Endpoint with Punt . . . . . . . . . . . . . 6 3.3. End.OP: OAM Endpoint with Punt . . . . . . . . . . . . . 7
3.4. End.OTP: OAM Endpoint with Timestamp and Punt . . . . . . 7 3.4. End.OTP: OAM Endpoint with Timestamp and Punt . . . . . . 7
3.5. SRH TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 7
4. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Ping . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. Ping . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . 8 4.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Pinging a SID Function . . . . . . . . . . . . . . . 10 4.1.2. Pinging a SID . . . . . . . . . . . . . . . . . . . . 9
4.1.3. Error Reporting . . . . . . . . . . . . . . . . . . . 12 4.2. Traceroute . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Traceroute . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.1. Classic Traceroute . . . . . . . . . . . . . . . . . 11
4.2.1. Classic Traceroute . . . . . . . . . . . . . . . . . 13 4.2.2. Traceroute to a SID . . . . . . . . . . . . . . . . . 12
4.2.2. Traceroute to a SID Function . . . . . . . . . . . . 15 4.3. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . 15
4.3. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . 18 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 16
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 7.1. ICMPv6 type Numbers RegistrySEC . . . . . . . . . . . . . 16
7.1. ICMPv6 type Numbers RegistrySEC . . . . . . . . . . . . . 20 7.2. SRv6 OAM Endpoint Types . . . . . . . . . . . . . . . . . 16
7.2. SRv6 OAM Endpoint Types . . . . . . . . . . . . . . . . . 20 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 22 10.2. Informative References . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
This document defines building blocks for Operations, Administration, This document defines building blocks for Operations, Administration,
and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane
(SRv6). The document also describes some SRv6 OAM mechanisms. (SRv6). The document also describes some SRv6 OAM mechanisms.
2. Conventions Used in This Document 2. Conventions Used in This Document
2.1. Abbreviations 2.1. Abbreviations
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SL: Segment Left. SL: Segment Left.
SR: Segment Routing. SR: Segment Routing.
SRH: Segment Routing Header. SRH: Segment Routing Header.
SRv6: Segment Routing with IPv6 Data plane. SRv6: Segment Routing with IPv6 Data plane.
TC: Traffic Class. TC: Traffic Class.
ICMPv6: multi-part ICMPv6 messages [RFC4884]. ICMPv6: ICMPv6 Specification [RFC4443].
2.2. Terminology and Reference Topology 2.2. Terminology and Reference Topology
This document uses the terminology defined in [I-D.ietf- spring-srv6- This document uses the terminology defined in [I-D.ietf- spring-srv6-
network-programming]. The readers are expected to be familiar with network-programming]. The readers are expected to be familiar with
the same. the same.
Throughout the document, the following simple topology is used for Throughout the document, the following simple topology is used for
illustration. illustration.
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O-flag: OAM flag. When set, it indicates that this packet is an O-flag: OAM flag. When set, it indicates that this packet is an
operations and management (OAM) packet. This document defines the operations and management (OAM) packet. This document defines the
usage of the O-flag in the SRH.Flags. usage of the O-flag in the SRH.Flags.
The document does not define any other flag in the SRH.Flags and The document does not define any other flag in the SRH.Flags and
meaning and processing of any other bit in SRH.Flags is outside of meaning and processing of any other bit in SRH.Flags is outside of
the scope of this document. the scope of this document.
3.1.1. O-flag Processing 3.1.1. O-flag Processing
The SRH.Flags.O-flag implements the "punt a timestamped copy and The SRH.Flags.O-flag implements the "punt a timestamped copy of the
forward" behavior. packet" behavior. This enables an SRv6 Endpoint node to send a
timestamped copy of the packets marked with o-flag to a local OAM
process. To prevent multiple evaluations of the datagram, the OAM
process MUST NOT respond to any upper-layer header (like ICMP, UDP,
etc.) payload. However, the OAM process MAY export the time-stamped
copy of the packet to a controller using e.g., IPFIX [RFC7011]. To
avoid hitting any performance impact, the processing node SHOULD
rate-limit the number of packets punted to the OAM process.
Specification of the OAM process or the external controller
operations are beyond the scope of this document.
Implementation of the O-flag is OPTIONAL. If a node does not support Implementation of the O-flag is OPTIONAL. If a node does not support
the O-flag, then upon reception it simply ignores it. It is also the O-flag, then upon reception it simply ignores it.
possible that a node is capable of supporting the O-bit but based on
a local decision it MAY ignore it during processing on some local
SIDs.
If a node supports the O-flag, it can optionally advertise its If a node supports the O-flag, it can optionally advertise its
potential via node capability advertisement in IGP [I-D.ietf-isis- potential via node capability advertisement in IGP [I-D.ietf-isis-
srv6- extensions] and BGP-LS [I-D.ietf-idr-bgpls-srv6-ext]. srv6- extensions] and BGP-LS [I-D.ietf-idr-bgpls-srv6-ext].
When N receives a packet whose IPv6 DA is S and S is a local SID, the When N receives a packet whose IPv6 DA is S and S is a local SID, the
pseudo-code associated with the SID S, as defined in section 4.3.1.1 line S01 of the the pseudo-code associated with the SID S, as defined
of [I-D.ietf-6man-segment-routing-header], is modified as follows for in section 4.3.1.1 of [I-D.ietf-6man-segment-routing-header], is
the O-flag processing. modified as follows for the O-flag processing.
S01.1. IF SRH.Flags.O-flag is set and local configuration permits S01.1. IF SRH.Flags.O-flag is set and local configuration permits
O-flag processing THEN O-flag processing THEN
a. Make a copy of the packet. a. Make a copy of the packet.
b. Send the copied packet, along with an accurate timestamp b. Send the copied packet, along with a timestamp
to the OAM process. ;; Ref1, Ref2 to the OAM process. ;; Ref1
Ref1: An implementation SHOULD copy and record the timestamp as soon as Ref1: An implementation SHOULD copy and record the timestamp as soon as
possible during packet processing. Timestamp is not carried in the packet possible during packet processing. Timestamp is not carried in the packet
forwarded to the next hop. forwarded to the next hop.
Ref2: An implementation SHOULD NOT generate ICMP error during
local SID S processing. If local SID S processing requires generation
of an ICMP error, the error is generated by the local OAM process.
Please note that the O-flag processing happens before execution of Please note that the O-flag processing happens before execution of
regular processing of the local SID S. regular processing of the local SID S.
3.2. OAM Segments 3.2. OAM Segments
OAM Segment IDs (SIDs) is another component of the SRv6 OAM building The presence of an OAM SID in the Destination address of the IPv6
Blocks. This document defines a couple of OAM SIDs. header instructs the segment endpoint implementing the OAM SID that
the content of the packet is of interest to the node and to process
the upper-layer payload, accordingly.
3.3. End.OP: OAM Endpoint with Punt 3.3. End.OP: OAM Endpoint with Punt
Many scenarios require punting of SRv6 OAM packets at the desired
nodes in the network. The "OAM Endpoint with Punt" function (End.OP
for short) represents a particular OAM function to implement the punt
behavior for an OAM packet. It is described using the pseudocode as
follows:
When N receives a packet destined to S and S is a local End.OP SID, N When N receives a packet destined to S and S is a local End.OP SID, N
does: does:
1. Send the packet to the OAM process ;; Ref1 S01. Send the packet to the OAM process
Ref1: The local OAM process SHOULD NOT generate ICMP error during
local SID S processing.
Please note that in an SRH containing END.OP SID, it is RECOMMENDED The local OAM process further processes the packet, this MAY involve
to set the SRH.Flags.O-flag = 0. processing protocol layers above IPv6. For example, ping and
traceroute will require ICMP or UDP protocol processing. Once the
packet leaves the IPv6 layer the processing is considered host
processing and the upper layer protocols MUST be processed as such.
3.4. End.OTP: OAM Endpoint with Timestamp and Punt 3.4. End.OTP: OAM Endpoint with Timestamp and Punt
Scenarios demanding performance management of an SR policy/ path
requires hardware timestamping before hardware punts the packet to
the software for OAM processing. The "OAM Endpoint with Timestamp
and Punt" function (End.OTP for short) represents an OAM SID function
to implement the timestamp and punt behavior for an OAM packet. It
is described using the pseudocode as follows:
When N receives a packet destined to S and S is a local End.OTP SID, When N receives a packet destined to S and S is a local End.OTP SID,
N does: N does:
1. Timestamp the packet ;; Ref1 S01.1. Timestamp the packet ;; Ref1
S01.2. Send the packet, along with a timestamp, to the
2. Send the packet, along with an accurate timestamp, to the OAM process
OAM process ;; Ref2
Ref1: Timestamping SHOULD be done in hardware, as soon as possible Ref1: Timestamping SHOULD be done in hardware, as soon as possible
during the packet processing. during the packet processing.
Ref2: The local OAM process SHOULD NOT generate ICMP error during
local SID S processing.
Please note that in an SRH containing END.OTP SID, it is RECOMMENDED The local OAM process further processes the packet, this MAY involve
to set the SRH.Flags.O-flag = 0. processing protocol layers above IPv6. For example, ping and
traceroute will require ICMP or UDP protocol processing. Once the
3.5. SRH TLV packet leaves the IPv6 layer the processing is considered host
processing and the upper layer protocols MUST be processed as such.
[I-D.ietf-6man-segment-routing-header] defines TLVs of the Segment
Routing Header.
SRH TLV plays an important role in carrying OAM and Performance
Management (PM) metadata.
4. OAM Mechanisms 4. OAM Mechanisms
This section describes how OAM mechanisms can be implemented using This section describes how OAM mechanisms can be implemented using
the OAM building blocks described in the previous section. the OAM building blocks described in the previous section.
Additional OAM mechanisms will be added in a future revision of the
document.
[RFC4443] describes Internet Control Message Protocol for IPv6 [RFC4443] describes Internet Control Message Protocol for IPv6
(ICMPv6) that is used by IPv6 devices for network diagnostic and (ICMPv6) that is used by IPv6 devices for network diagnostic and
error reporting purposes. As Segment Routing with IPv6 data plane error reporting purposes. As Segment Routing with IPv6 data plane
(SRv6) simply adds a new type of Routing Extension Header, existing (SRv6) simply adds a new type of Routing Extension Header, existing
ICMPv6 ping mechanisms can be used in an SRv6 network. This section ICMPv6 ping mechanisms can be used in an SRv6 network. This section
describes the applicability of ICMPv6 in the SRv6 network and how the describes the applicability of ICMPv6 in the SRv6 network and how the
existing ICMPv6 mechanisms can be used for providing OAM existing ICMPv6 mechanisms can be used for providing OAM
functionality. functionality.
The document does not propose any changes to the standard ICMPv6 The document does not propose any changes to the standard ICMPv6
[RFC4443], [RFC4884] or standard ICMPv4 [RFC792]. [RFC4443], [RFC4884] or standard ICMPv4 [RFC792].
4.1. Ping 4.1. Ping
There is no hardware or software change required for ping operation
at the classic IPv6 nodes in an SRv6 network. That includes the
classic IPv6 node with ingress, egress or transit roles.
Furthermore, no protocol changes are required to the standard ICMPv6
[RFC4443], [RFC4884] or standard ICMPv4 [RFC792]. In other words,
existing ICMP ping mechanisms work seamlessly in the SRv6 networks.
The following subsections outline some use cases of the ICMP ping in The following subsections outline some use cases of the ICMP ping in
the SRv6 networks. the SRv6 networks.
4.1.1. Classic Ping 4.1.1. Classic Ping
The existing mechanism to ping a remote IP prefix, along the shortest The existing mechanism to ping a remote IP prefix, along the shortest
path, continues to work without any modification. The initiator may path, continues to work without any modification. The initiator may
be an SRv6 node or a classic IPv6 node. Similarly, the egress or be an SRv6 node or a classic IPv6 node. Similarly, the egress or
transit may be an SRv6 capable node or a classic IPv6 node. transit may be an SRv6 capable node or a classic IPv6 node.
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processing. Specifically, it observes the END.X function processing. Specifically, it observes the END.X function
(B:4:C52) with PSP (Penultimate Segment POP) on the echo request (B:4:C52) with PSP (Penultimate Segment POP) on the echo request
packet and removes the SRH and forwards the packet across link10 packet and removes the SRH and forwards the packet across link10
to N5. to N5.
o The echo request packet at N5 arrives as an IPv6 packet without an o The echo request packet at N5 arrives as an IPv6 packet without an
SRH. Node N5, which is a classic IPv6 node, performs the standard SRH. Node N5, which is a classic IPv6 node, performs the standard
IPv6/ ICMPv6 processing on the echo request and responds, IPv6/ ICMPv6 processing on the echo request and responds,
accordingly. accordingly.
4.1.2. Pinging a SID Function 4.1.2. Pinging a SID
The classic ping described in the previous section cannot be used to The classic ping described in the previous section cannot be used to
ping a remote SID function, as explained using an example in the ping a remote SID function, as explained using an example in the
following. following.
Consider the case where the user wants to ping the remote SID Consider the case where the user wants to ping the remote SID
function B:4:C52, via B:2:C31, from node N1. Node N1 constructs the function B:4:C52 from node N1. Node N1 constructs the ping packet
ping packet (A:1::, B:2:C31)(B:4:C52, B:2:C31, SL=1; (A:1::, B:4:C52)(ICMPv6 Echo Request). The ping fails because the
NH=ICMPv6)(ICMPv6 Echo Request). The ping fails because the node N4 node N4 receives the ICMPv6 echo request with DA set to B:4:C52 but
receives the ICMPv6 echo request with DA set to B:4:C52 but the next the next header is ICMPv6, instead of SRH.
header is ICMPv6, instead of SRH. To solve this problem, the
initiator needs to mark the ICMPv6 echo request as an OAM packet.
The OAM packets are identified either by setting the O-flag in SRH or To perform ICMPv6 ping to a target SID an echo request message is
by inserting the END.OP/ END.OTP SIDs at an appropriate place in the generated by the initiator with the END.OP or END.OTP SID in the
SRH. The following illustration uses END.OTP SID but the procedures segment-list of the SRH immediately preceding the target SID. There
are equally applicable to the END.OP SID. MAY or MAY NOT be additional segments preceding the END.OP/ END.OTP
SID.
In an SRv6 network, the user can exercise two flavors of the ping: When the node instantiating a SID S of type END.OP or END.OTP
end-to-end ping or segment-by-segment ping, as outlined in the receives a packet with S in the destination address of the IPv6
following subsection. header it sends it to the OAM process. The OAM process verifies the
segment following S is a locally instantiated SID. It then processes
the Upper layer header of the packet, as a host, responding to the
echo request message in the ICMPv6 payload.
4.1.2.1. End-to-end ping using END.OP/ END.OTP When the segment following S is not verified by the OAM process an
ICMPv6 error message type 4 (parameter problem) code 0 (erroneous
header field encountered) with pointer set to the segment following S
(the target SID) is generated for the packet and the packet is
discarded.
The end-to-end ping illustration uses the END.OTP SID but the An implementation of the OAM process SID verification SHOULD do the
following:
o Verify that the SID is locally instantiated.
o Verify that the SID is instantiated in the data plane (this may
include verification of the SID in NPUs or forwarding hardware, as
applicable).
4.1.2.1. Ping using END.OP/ END.OTP
This section uses END.OTP SID for the ping illustration but the
procedures are equally applicable to the END.OP SID. procedures are equally applicable to the END.OP SID.
Consider the same example where the user wants to ping a remote SID Consider the example where the user wants to ping a remote SID
function B:4:C52, via B:2:C31, from node N1. To force a punt of the function B:4:C52, via B:2:C31, from node N1. To force a punt of the
ICMPv6 echo request at the node N4, node N1 inserts the END.OTP SID ICMPv6 echo request at the node N4, node N1 inserts the END.OTP SID
just before the target SID B:4:C52 in the SRH. The ICMPv6 echo just before the target SID B:4:C52 in the SRH. The ICMPv6 echo
request is processed at the individual nodes along the path as request is processed at the individual nodes along the path as
follows: follows:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(A:1::, B:2:C31)(B:4:C52, B:4:OTP, B:2:C31; SL=2; (A:1::, B:2:C31)(B:4:C52, B:4:OTP, B:2:C31; SL=2;
NH=ICMPv6)(ICMPv6 Echo Request). NH=ICMPv6)(ICMPv6 Echo Request).
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o Node N3 receives the packet as follows (A:1::, B:4:OTP)(B:4:C52, o Node N3 receives the packet as follows (A:1::, B:4:OTP)(B:4:C52,
B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). Node B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). Node
N3, which is a classic IPv6 node, performs the standard IPv6 N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on processing. Specifically, it forwards the echo request based on
DA B:4:OTP in the IPv6 header. DA B:4:OTP in the IPv6 header.
o When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52, o When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52,
B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it
processes the END.OTP SID, as described in the pseudocode in processes the END.OTP SID, as described in the pseudocode in
Section 3. The packet gets time-stamped and punted to the ICMPv6 Section 3. The packet gets time-stamped and punted to the OAM
process for processing. The ICMPv6 process checks if the next SID process for processing. The OAM process checks if the next SID in
in SRH (the target SID B:4:C52) is locally programmed. SRH (the target SID B:4:C52) is locally programmed.
o If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA)", Code: "SID not locally
implemented (TBA)"); otherwise a success is returned.
4.1.2.2. Segment-by-segment ping using O-flag (Proof of Transit)
Consider the same example where the user wants to ping a remote SID
function B:4:C52, via B:2:C31, from node N1. However, in this ping,
the node N1 wants to get a response from each segment node in the SRH
as a "proof of transit". In other words, in the segment-by-segment
ping case, the node N1 expects a response from node N2 and node N4
for their respective local SID function. When a response to O-bit is
desired from the last SID in a SID-list, it is the responsibility of
the ingress node to use USP as the last SID. E.g., in this example,
the target SID B:4:C52 is a USP SID.
To force a punt of the ICMPv6 echo request at node N2 and node N4,
node N1 sets the O-flag in SRH. The ICMPv6 echo request is processed
at the individual nodes along the path as follows:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(A:1::, B:2:C31)(B:4:C52, B:2:C31; SL=1, Flags.O=1;
NH=ICMPv6)(ICMPv6 Echo Request).
o When node N2 receives the packet (A:1::, B:2:C31)(B:4:C52,
B:2:C31; SL=1, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request) packet,
it processes the O-flag in SRH, as described in the pseudocode in
Section 3. A time-stamped copy of the packet gets punted to the
ICMPv6 process for processing. Node N2 continues to apply the
B:2:C31 SID function on the original packet and forwards it,
accordingly. As B:4:C52 is a USP SID, N2 does not remove the SRH.
The ICMPv6 process at node N2 checks if its local SID (B:2:C31) is
locally programmed or not and responds to the ICMPv6 Echo Request.
o If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA)", Code: "SID not locally
implemented (TBA)"); otherwise a success is returned. Please note
that, as mentioned in Section 3, if node N2 does not support the
O-flag, it simply ignores it and process the local SID, B:2:C31.
o Node N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on
DA B:4:C52 in the IPv6 header.
o When node N4 receives the packet (A:1::, B:4:C52)(B:4:C52,
B:2:C31; SL=0, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request), it
processes the O-flag in SRH, as described in the pseudocode in
Section 3. A time-stamped copy of the packet gets punted to the
ICMPv6 process for processing. The ICMPv6 process at node N4
checks if its local SID (B:4:C52) is locally programmed or not and
responds to the ICMPv6 Echo Request.
o If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA)", Code: "SID not locally
implemented (TBA)"); otherwise a success is returned.
Support for O-flag is part of node capability advertisement. That
enables node N1 to know which segment nodes are capable of responding
to the ICMPv6 echo request. Node N1 processes the echo responses and
presents data to the user, accordingly.
Please note that segment-by-segment ping can be used to address proof
of transit use-case.
4.1.3. Error Reporting
Any IPv6 node can use ICMPv6 control messages to report packet
processing errors to the host that originated the datagram packet.
To name a few such scenarios:
o If the router receives an undeliverable IP datagram, or
o If the router receives a packet with a Hop Limit of zero, or
o If the router receives a packet such that if the router decrements
the packet's Hop Limit it becomes zero, or
o If the router receives a packet with problem with a field in the
IPv6 header or the extension headers such that it cannot complete
processing the packet, or
o If the router cannot forward a packet because the packet is larger o If the next SID is not locally programmed, the OAM process returns
than the MTU of the outgoing link. an ICMPv6 error message type 4 (parameter problem) code 0
(erroneous header field encountered) with pointer set to the
target SID B:4:C52 and the packet is discarded.
In the scenarios listed above, the ICMPv6 response also contains the o If the next SID is locally programmed, the node processes the
IP header, IP extension headers and leading payload octets of the upper layer header. As part of the upper layer header (ICMPv6)
"original datagram" to which the ICMPv6 message is a response. processing node N4 sends the ICMPv6 Echo Reply message [RFC4443].
Specifically, the "Destination Unreachable Message", "Time Exceeded
Message", "Packet Too Big Message" and "Parameter Problem Message"
ICMPV6 messages can contain as much of the invoking packet as
possible without the ICMPv6 packet exceeding the minimum IPv6 MTU
[RFC4443], [RFC4884]. In an SRv6 network, the copy of the invoking
packet contains the SR header. The packet originator can use this
information for diagnostic purposes. For example, traceroute can use
this information as detailed in the following subsection.
4.2. Traceroute 4.2. Traceroute
There is no hardware or software change required for traceroute There is no hardware or software change required for traceroute
operation at the classic IPv6 nodes in an SRv6 network. That operation at the classic IPv6 nodes in an SRv6 network. That
includes the classic IPv6 node with ingress, egress or transit roles. includes the classic IPv6 node with ingress, egress or transit roles.
Furthermore, no protocol changes are required to the standard Furthermore, no protocol changes are required to the standard
traceroute operations. In other words, existing traceroute traceroute operations. In other words, existing traceroute
mechanisms work seamlessly in the SRv6 networks. mechanisms work seamlessly in the SRv6 networks.
skipping to change at page 14, line 7 skipping to change at page 11, line 36
traceroute probe with an SR header containing the SID list <S1, S2, traceroute probe with an SR header containing the SID list <S1, S2,
S3>. That is illustrated using the topology in Figure 1. Assume all S3>. That is illustrated using the topology in Figure 1. Assume all
the links have IGP metric 10 except both links between node2 and the links have IGP metric 10 except both links between node2 and
node3, which have IGP metric set to 100. User issues a traceroute node3, which have IGP metric set to 100. User issues a traceroute
from node N1 to a loopback of node 5, via segment list <B:2:C31, from node N1 to a loopback of node 5, via segment list <B:2:C31,
B:4:C52>. Figure 3 contains sample output for the traceroute B:4:C52>. Figure 3 contains sample output for the traceroute
request. request.
> traceroute A:5:: via segment-list B:2:C31, B:4:C52 > traceroute A:5:: via segment-list B:2:C31, B:4:C52
Tracing the route to B5:: Tracing the route to A:5::
1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
SRH: (A:5::, B:4:C52, B:2:C31, SL=2) SRH: (A:5::, B:4:C52, B:2:C31, SL=2)
2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec 2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec
SRH: (A:5::, B:4:C52, B:2:C31, SL=1) SRH: (A:5::, B:4:C52, B:2:C31, SL=1)
3 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec 3 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec
SRH: (A:5::, B:4:C52, B:2:C31, SL=1) SRH: (A:5::, B:4:C52, B:2:C31, SL=1)
4 2001:DB8:4:5::52:: 0.879 msec 0.916 msec 1.024 msec 4 2001:DB8:4:5::52:: 0.879 msec 0.916 msec 1.024 msec
Figure 3 A sample traceroute output at an SRv6 capable node Figure 3 A sample traceroute output at an SRv6 capable node
skipping to change at page 15, line 9 skipping to change at page 12, line 39
useful. This information can also be used to verify if SID functions useful. This information can also be used to verify if SID functions
B:2:C31 and B:4:C52 are executed correctly by N2 and N4, B:2:C31 and B:4:C52 are executed correctly by N2 and N4,
respectively. Specifically, the information displayed for hop2 respectively. Specifically, the information displayed for hop2
contains the incoming interface address 2001:DB8:2:3:31:: at N3. contains the incoming interface address 2001:DB8:2:3:31:: at N3.
This matches with the expected interface bound to END.X function This matches with the expected interface bound to END.X function
B:2:C31 (link3). Similarly, the information displayed for hop5 B:2:C31 (link3). Similarly, the information displayed for hop5
contains the incoming interface address 2001:DB8:4:5::52:: at N5. contains the incoming interface address 2001:DB8:4:5::52:: at N5.
This matches with the expected interface bound to the END.X function This matches with the expected interface bound to the END.X function
B:4:C52 (link10). B:4:C52 (link10).
4.2.2. Traceroute to a SID Function 4.2.2. Traceroute to a SID
The classic traceroute described in the previous section cannot be The classic traceroute described in the previous section cannot be
used to traceroute a remote SID function, as explained using an used to traceroute a remote SID function, as explained using an
example in the following. example in the following.
Consider the case where the user wants to traceroute the remote SID Consider the case where the user wants to traceroute the remote SID
function B:4:C52, via B:2:C31, from node N1. The trace route fails function B:4:C52 from node N1. The trace route fails at N4. This is
at N4. This is because the node N4 trace route probe where next because the node N4 receives a trace route probe where next header is
header is UDP or ICMPv6, instead of SRH (even though the hop limit is UDP or ICMPv6, instead of SRH (even though the hop limit is set to
set to 1). To solve this problem, the initiator needs to mark the 1).
ICMPv6 echo request as an OAM packet.
The OAM packets are identified either by setting the O-flag in SRH or To traceroute a target SID a probe message is generated by the
by inserting the END.OP or END.OTP SID at an appropriate place in the initiator with the END.OP or END.OTP SID in the segment-list of the
SRH. SRH immediately preceding the target SID. There MAY or MAY NOT be
additional segments preceding the END.OP/ END.OTP SID.
In an SRv6 network, the user can exercise two flavors of the The node instantiating a SID S of type END.OP or END.OTP receives a
traceroute: hop-by-hop traceroute or overlay traceroute. packet with S in the destination address of the IPv6 header and sends
it to the OAM process (before processing the TTL). The OAM process
verifies the segment following S is a locally instantiated SID. It
then processes the Upper layer header of the packet, as a host,
responding to the probe message.
o In hop-by-hop traceroute, user gets responses from all nodes When the segment following S is not verified by the OAM process an
including classic IPv6 transit nodes, SRv6 capable transit nodes ICMPv6 error message type 4 (parameter problem) code 0 (erroneous
as well as SRv6 capable segment endpoints. E.g., consider the header field encountered) with pointer set to the segment following S
example where the user wants to traceroute to a remote SID (the target SID) is generated for the packet and the packet is
function B:4:C52, via B:2:C31, from node N1. The traceroute discarded.
output will also display information about node3, which is a
transit (underlay) node.
o The overlay traceroute, on the other hand, does not trace the An implementation of the OAM process SID verification SHOULD do the
underlay nodes. In other words, the overlay traceroute only following:
displays the nodes that acts as SRv6 segments along the route.
I.e., in the example where the user wants to traceroute to a
remote SID function B:4:C52, via B:2:C31, from node N1, the
overlay traceroute would only display the traceroute information
from node N2 and node N4; it will not display information from
node 3.
4.2.2.1. Hop-by-hop traceroute using END.OP/ END.OTP o Verify that the SID is locally instantiated.
o Verify that the SID is instantiated in the data plane (this may
include verification of the SID in NPUs or forwarding hardware, as
applicable).
4.2.2.1. Traceroute using END.OP/ END.OTP
In this section, hop-by-hop traceroute to a SID function is In this section, hop-by-hop traceroute to a SID function is
exemplified using UDP probes. However, the procedure is equally exemplified using UDP probes. However, the procedure is equally
applicable to other implementation of traceroute mechanism. applicable to other implementation of traceroute mechanism.
Furthermore, the illustration uses the END.OTP SID but the procedures Furthermore, the illustration uses the END.OTP SID but the procedures
are equally applicable to the END.OP SID. are equally applicable to the END.OP SID.
Consider the same example where the user wants to traceroute to a Consider the same example where the user wants to traceroute to a
remote SID function B:4:C52, via B:2:C31, from node N1. To force a remote SID function B:4:C52, via B:2:C31, from node N1. To force a
punt of the traceroute probe only at the node N4, node N1 inserts the punt of the traceroute probe only at the node N4, node N1 inserts the
END.OTP SID just before the target SID B:4:C52 in the SRH. The END.OTP SID just before the target SID B:4:C52 in the SRH. The
traceroute probe is processed at the individual nodes along the path traceroute probe is processed at the individual nodes along the path
as follows: as follows:
skipping to change at page 16, line 44 skipping to change at page 14, line 29
Transit"). Transit").
o When node N3, which is a classic IPv6 node, receives the packet o When node N3, which is a classic IPv6 node, receives the packet
with hop-count > 1, it performs the standard IPv6 processing. with hop-count > 1, it performs the standard IPv6 processing.
Specifically, it forwards the traceroute probe based on DA B:4:OTP Specifically, it forwards the traceroute probe based on DA B:4:OTP
in the IPv6 header. in the IPv6 header.
o When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52, o When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52,
B:4:OTP, B:2:C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it B:4:OTP, B:2:C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it
processes the END.OTP SID, as described in the pseudocode in processes the END.OTP SID, as described in the pseudocode in
Section 3. The packet gets timestamped and punted to the Section 3. Before hop-limit processing, the packet gets
traceroute process for processing. The traceroute process checks timestamped and punted to the OAM process for processing. The OAM
if the next SID in SRH (the target SID B:4:C52) is locally process checks if the next SID in SRH (the target SID B:4:C52) is
programmed. locally programmed.
o If the target SID B:4:C52 is locally programmed, node N4 responses o If the next SID is not locally programmed, the OAM process returns
with the ICMPv6 message (Type: Destination unreachable, Code: Port an ICMPv6 error message type 4 (parameter problem) code 0
Unreachable). If the target SID B:4:C52 is not a local SID, node (erroneous header field encountered) with pointer set to the
N4 silently drops the traceroute probe. target SID B:4:C52 and the packet is discarded.
o If the next SID is locally programmed, the node processes the
upper layer header. As part of the upper layer header processing
node N4 responses with the ICMPv6 message (Type: Destination
unreachable, Code: Port Unreachable).
Figure 4 displays a sample traceroute output for this example. Figure 4 displays a sample traceroute output for this example.
> traceroute srv6 B:4:C52 via segment-list B:2:C31 > traceroute srv6 B:4:C52 via segment-list B:2:C31
Tracing the route to SID function B:4:C52 Tracing the route to SID function B:4:C52
1 2001:DB8:1:2:21 0.512 msec 0.425 msec 0.374 msec 1 2001:DB8:1:2:21 0.512 msec 0.425 msec 0.374 msec
SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=2) SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=2)
2 2001:DB8:2:3:31 0.721 msec 0.810 msec 0.795 msec 2 2001:DB8:2:3:31 0.721 msec 0.810 msec 0.795 msec
SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1) SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1)
3 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec 3 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec
SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1) SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1)
Figure 4 A sample output for hop-by-hop traceroute to a SID function Figure 4 A sample output for hop-by-hop traceroute to a SID function
4.2.2.2. Tracing SRv6 Overlay
The overlay traceroute does not trace the underlay nodes, i.e., only
displays the nodes that acts as SRv6 segments along the path. This
is achieved by setting the SRH.Flags.O bit.
In this section, overlay traceroute to a SID function is exemplified
using UDP probes. However, the procedure is equally applicable to
other implementation of traceroute mechanism.
Consider the same example where the user wants to traceroute to a
remote SID function B:4:C52, via B:2:C31, from node N1.
o Node N1 initiates a traceroute probe with SRH as follows (A:1::,
B:2:C31)(B:4:C52, B:2:C31; HC=64, SL=1, Flags.O=1;
NH=UDP)(Traceroute Probe). Please note that the hop-count is set
to 64 to skip the underlay nodes from tracing. The O-flag in SRH
is set to make the overlay nodes (nodes processing the SRH)
respond.
o When node N2 receives the packet (A:1::, B:2:C31)(B:4:C52,
B:2:C31; SL=1, HC=64, Flags.O=1; NH=UDP)(Traceroute Probe), it
processes the O-flag in SRH, as described in the pseudocode in
Section 3. A time-stamped copy of the packet gets punted to the
traceroute process for processing. Node N2 continues to apply the
B:2:C31 SID function on the original packet and forwards it,
accordingly. The traceroute process at node N2 checks if its
local SID (B:2:C31) is locally programmed. If the SID is not
locally programmed, it silently drops the packet. Otherwise, it
performs the egress check by looking at the SL value in SRH.
o As SL is not equal to zero (i.e., it's not egress node), node N2
responses with the ICMPv6 message (Type: "SRv6 OAM (TBA)", Code:
"O-flag punt at Transit (TBA)"). Please note that, as mentioned
in Section 3, if node N2 does not support the O-flag, it simply
ignores it and processes the local SID, B:2:C31.
o When node N3 receives the packet (A:1::, B:4:C52)(B:4:C52,
B:2:C31; SL=0, HC=63, Flags.O=1; NH=UDP)(Traceroute Probe),
performs the standard IPv6 processing. Specifically, it forwards
the traceroute probe based on DA B:4:C52 in the IPv6 header.
Please note that there is no hop-count expiration at the transit
nodes.
o When node N4 receives the packet (A:1::, B:4:C52)(B:4:C52,
B:2:C31; SL=0, HC=62, Flags.O=1; NH=UDP)(Traceroute Probe), it
processes the O-flag in SRH, as described in the pseudocode in
Section 3. A time-stamped copy of the packet gets punted to the
traceroute process for processing. The traceroute process at node
N4 checks if its local SID (B:2:C31) is locally programmed.
o If the SID is not locally programmed, it silently drops the
packet. Otherwise, it performs the egress check by looking at the
SL value in SRH. As SL is equal to zero (i.e., N4 is the egress
node), node N4 tries to consume the UDP probe. As UDP probe is
set to access an invalid port, the node N4 responses with the
ICMPv6 message (Type: Destination unreachable, Code: Port
Unreachable)
Figure 5 displays a sample overlay traceroute output for this
example. Please note that the underlay node N3 does not appear in
the output.
Tracing the route to SID function B:4:C52
1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1)
2 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec
SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=0)
Figure 5 A sample output for overlay traceroute to a SID function
4.3. Monitoring of SRv6 Paths 4.3. Monitoring of SRv6 Paths
In the recent past, network operators are interested in performing In the recent past, network operators are interested in performing
network OAM functions in a centralized manner. Various data models network OAM functions in a centralized manner. Various data models
like YANG are available to collect data from the network and manage like YANG are available to collect data from the network and manage
it from a centralized entity. it from a centralized entity.
SR technology enables a centralized OAM entity to perform path SR technology enables a centralized OAM entity to perform path
monitoring from centralized OAM entity without control plane monitoring from centralized OAM entity without control plane
intervention on monitored nodes. [RFC 8403] describes such a intervention on monitored nodes. [RFC 8403] describes such a
skipping to change at page 22, line 25 skipping to change at page 18, line 39
[I-D.ietf-6man-segment-routing-header] [I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019. progress), October 2019.
[I-D.ietf-spring-srv6-network-programming] [I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming", Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-05 (work in draft-ietf-spring-srv6-network-programming-06 (work in
progress), October 2019. progress), December 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References 10.2. Informative References
[I-D.matsushima-spring-srv6-deployment-status] [I-D.matsushima-spring-srv6-deployment-status]
Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6 Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6
Implementation and Deployment Status", draft-matsushima- Implementation and Deployment Status", draft-matsushima-
spring-srv6-deployment-status-02 (work in progress), spring-srv6-deployment-status-04 (work in progress),
October 2019. December 2019.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981, RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>. <https://www.rfc-editor.org/info/rfc792>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89, Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006, RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>. <https://www.rfc-editor.org/info/rfc4443>.
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