SPRING Working Group Z. Ali Internet-Draft C. Filsfils Intended status: Standards Track N. Kumar Expires: January 1, 2019 C. Pignataro F. Iqbal R. Gandhi Cisco Systems, Inc. J. Leddy Comcast S. Matsushima SoftBank R. Raszuk Bloomberg LP D. Voyer Bell Canada G. Dawra LinkedIn B. Peirens Proximus M. Chen Huawei G. Naik Drexel University July 2, 2018 Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane (SRv6) draft-ali-spring-srv6-oam-01.txt Abstract This document defines building blocks that can be used for Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane (SRv6). The document also describes some SRv6 OAM mechanisms that can be realized using these building blocks. 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the Ali, et al. Expires January 1, 2019 [Page 1] Internet-Draft OAM for SRv6 July 2, 2018 document authors. All rights reserved. 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 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction......................................................3 2. Conventions Used in This Document.................................3 2.1. Abbreviations.............................................3 2.2. Terminology and Reference Topology........................4 3. OAM Building Blocks...............................................5 3.1. O-flag in Segment Routing Header..........................5 3.1.1. O-flag Processing....................................6 3.1.2. Disabling Penultimate Segment Pop (PSP)..............7 3.2. OAM Segments..............................................7 Ali, et al. Expires January 1, 2019 [Page 2] Internet-Draft OAM for SRv6 July 2, 2018 3.2.1. End.OP: OAM Endpoint with Punt.......................7 3.2.2. End.OTP: OAM Endpoint with Timestamp and Punt........8 4. OAM Mechanisms....................................................8 4.1. Ping......................................................9 4.1.1. Classic Ping.........................................9 4.1.2. Pinging a SID Function..............................10 4.1.2.1. End-to-end ping using END.OP/ END.OTP..........11 4.1.2.2. Segment-by-segment ping using O-flag (Proof of Transit)................................................11 4.2. Error Reporting..........................................13 4.3. Traceroute...............................................13 4.3.1. Classic Traceroute..................................13 4.3.2. Traceroute to a SID Function........................15 4.3.2.1. Hop-by-hop traceroute using END.OP/ END.OTP....16 4.3.2.2. Tracing SRv6 Overlay...........................17 4.4. In-situ OAM..............................................19 4.5. Monitoring of SRv6 Paths.................................19 5. Security Considerations..........................................20 6. IANA Considerations..............................................20 6.1. Segment Routing Header Flags Register....................20 6.2. ICMPv6 type Numbers Registry.............................20 7. References.......................................................21 7.1. Normative References.....................................21 7.2. Informative References...................................22 8. Acknowledgments..................................................22 1. Introduction This document defines building blocks that can be used for Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane (SRv6). The document also describes some SRv6 OAM mechanisms that can be implemented using these building blocks. Additional OAM mechanisms will be added in a future revision of the document. 2. Conventions Used in This Document 2.1. Abbreviations ECMP: Equal Cost Multi-Path. SID: Segment ID. Ali, et al. Expires January 1, 2019 [Page 3] Internet-Draft OAM for SRv6 July 2, 2018 SL: Segment Left. SR: Segment Routing. SRH: Segment Routing Header. SRv6: Segment Routing with IPv6 Data plane. TC: Traffic Class. UCMP: Unequal Cost Multi-Path. 2.2. Terminology and Reference Topology This document uses the terminology defined in [I-D.draft-filsfils- spring-srv6-network-programming]. The readers are expected to be familiar with the same. Throughout the document, the following simple topology is used for illustration. +--------------------------| N100 |------------------------+ | | ====== link1====== link3------ link5====== link9------ ||N1||======||N2||======| N3 |======||N4||======| N5 | || ||------|| ||------| |------|| ||------| | ====== link2====== link4------ link6======link10------ | | | ------ | +-------| N6 |---------+ link7 | | link8 ------ Figure 1 Reference Topology In the reference topology: Nodes N1, N2, and N4 are SRv6 capable nodes. Nodes N3, N5 and N6 are classic IPv6 nodes. Node 100 is a controller. Ali, et al. Expires January 1, 2019 [Page 4] Internet-Draft OAM for SRv6 July 2, 2018 Node Nk has a classic IPv6 loopback address Bk::/128 Node Nk has Ak::/48 for its local SID space from which Local SIDs are explicitly allocated. The IPv6 address of the nth Link between node X and Y at the X side is represented as 2001:DB8:X:Y:Xn::, e.g., the IPv6 address of link6 (the 2nd link) between N3 and N4 at N3 in Figure 1 is 2001:DB8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st link between N3 and N4) at node 3 is 2001:DB8:3:4:31::. Ak::0 is explicitly allocated as the END function at Node k. Ak::Cij is explicitly allocated as the END.X function at node k towards neighbor node i via jth Link between node i and node j. e.g., A2::C31 represents END.X at N2 towards N3 via link3 (the 1st link between N2 and N3). Similarly, A4::C52 represents the END.X at N4 towards N5 via link10. represents a SID list where S1 is the first SID and S3 is the last SID. (S3, S2, S1; SL) represents the same SID list but encoded in the SRH format where the rightmost SID (S1) in the SRH is the first SID and the leftmost SID (S3) in the SRH is the last SID. (SA, DA) (S3, S2, S1; SL) represents an IPv6 packet, SA is the IPv6 Source Address, DA the IPv6 Destination Address, (S3, S2, S1; SL) is the SRH header that includes the SID list . 3. OAM Building Blocks This section defines the various building blocks that can be used to implement OAM mechanisms in SRv6 networks. The following section describes some SRv6 OAM mechanisms that can be implemented using these building blocks. 3.1. O-flag in Segment Routing Header [I-D. draft-ietf-6man-segment-routing-header] describes the Segment Routing Header (SRH) and how SR capable nodes use it. The SRH contains an 8-bit "Flags" field [I-D. draft-ietf-6man-segment- routing-header]. This document defines the following bit in the SRH.Flags to carry the O-flag: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | |O| | +-+-+-+-+-+-+-+-+ Ali, et al. Expires January 1, 2019 [Page 5] Internet-Draft OAM for SRv6 July 2, 2018 Where: - O-flag: OAM flag. When set, it indicates that this packet is an operations and management (OAM) packet. This document defines the usage of the O-flag in the SRH.Flags. - 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 the scope of this document. 3.1.1. O-flag Processing Implementation of the O-flag is OPTIONAL. A node MAY ignore SRH.Flags.O-flag. It is also 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 does not support the O-flag, then upon reception it simply ignores it. If a node supports the O-flag, it can optionally advertise its potential via node capability advertisement in IGP [I-D.bashandy-isis-srv6- extensions] and BGP-LS [I-D.dawra-idr-bgpls-srv6-ext]. The SRH.Flags.O-flag implements the "punt a timestamped copy and forward" behavior. To avoid the head of the line processing of the packet, some implementation may implement the "forward and punt a timestamped copy" behavior, instead. In order to implement "punt a timestamped copy and forward" or "forward and punt a timestamped copy" behavior, the following instructions are inserted at the beginning or the end of the pseudo-code for all SID Functions, respectively. When N receives a packet whose IPv6 DA is S and S is a local SID, N executes the following the pseudo-code, either before or after the execution of the local SID S. 1. IF SRH.Flags.O-flag is True and SRH.Flags.O-flag is locally supported for S THEN a. Timestamp a local copy of the packet. ;; Ref1 b. Punt the time-stamped copy of the packet to CPU for processing in software (slow-path). ;; Ref2 Ref1: Timestamping is done in hardware, as soon as possible during the packet processing. As timestamping is done on a copy of the packet which is locally punted, timestamp value can be carried in the local packet (punt) header. Ref1: Hardware (microcode) just punts the packet. There is no requirement for the hardware to manipulate any TLV in SRH (or Ali, et al. Expires January 1, 2019 [Page 6] Internet-Draft OAM for SRv6 July 2, 2018 elsewhere). Software (slow path) implements the required OAM mechanism. Timestamp is not carried in the packet forwarded to the next hop. 3.1.2. Disabling Penultimate Segment Pop (PSP) Penultimate Segment Pop (PSP) needs to be disabled when SRH.Flags.O- flag is set. If a node supports SRH.Flags.O-flag, it adds the following check after executing the instruction 'update the IPv6 DA with SRH[SL]' during processing of a local SID as described in [I- D.draft-filsfils-spring-srv6-network-programming]: 1. IF updated SL = 0 & PSP is TRUE and SRH.Flags.O-bit is False 2. pop the top SRH ;; Ref1 Ref1: PSP behavior is disabled when SRH.Flags.O-flag is set. 3.2. OAM Segments OAM Segment IDs (SIDs) is another components of the building blocks needed to implement SRv6 OAM mechanisms. This document defines a couple of OAM SIDs. Additional SIDs will be added in the later version of the document. 3.2.1. 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 does: 1. Punt the packet to CPU for SW processing (slow-path) ;; Ref1 Ref1: Hardware (microcode) only punts the packet. There is no requirement for the hardware to manipulate any TLV in the SRH (or elsewhere). Software (slow path) implements the required OAM mechanisms. Please note that in an SRH containing END.OP SID, it is RECOMMENDED to set the SRH.Flags.O-flag = 0. Ali, et al. Expires January 1, 2019 [Page 7] Internet-Draft OAM for SRv6 July 2, 2018 3.2.2. 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, N does: 1. Timestamp the packet ;; Ref1 2. Punt the packet to CPU for SW processing (slow-path) ;; Ref2 Ref1: Timestamping is done in hardware, as soon as possible during the packet processing. As timestamping is done on a copy of the packet which is locally punted, timestamp value can be carried in the local packet (punt) header. Ref2: Hardware (microcode) only punts the packet. There is no requirement for the hardware to manipulate any TLV in the SRH (or elsewhere). Software (slow path) implements the required OAM mechanisms. Please note that in an SRH containing END.OTP SID, it is RECOMMENDED to set the SRH.Flags.O-flag = 0. 4. OAM Mechanisms This section describes how OAM mechanisms can be implemented using 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 (ICMPv6) that is used by IPv6 devices for network diagnostic and error reporting purposes. As Segment Routing with IPv6 data plane (SRv6) simply adds a new type of Routing Extension Header, existing ICMPv6 ping mechanisms can be used in an SRv6 network. This section describes the applicability of ICMPv6 in the SRv6 network and how the existing ICMPv6 mechanisms can be used for providing OAM functionality. Ali, et al. Expires January 1, 2019 [Page 8] Internet-Draft OAM for SRv6 July 2, 2018 Throughout this document, unless otherwise specified, the acronym ICMPv6 refers to multi-part ICMPv6 messages [RFC4884]. The document does not propose any changes to the standard ICMPv6 [RFC4443], [RFC4884] or standard ICMPv4 [RFC792]. 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 SRv6 networks. 4.1.1. Classic Ping The existing mechanism to ping a remote IP prefix, along the shortest path, continues to work without any modification. The initiator may 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. If an SRv6 capable ingress node wants to ping an IPv6 prefix via an arbitrary segment list , it needs to initiate ICMPv6 ping with an SR header containing the SID list . This is illustrated using the topology in Figure 1. Assume all the links have IGP metric 10 except both links between node2 and node3, which have IGP metric set to 100. User issues a ping from node N1 to a loopback of node 5, via segment list . Figure 2 contains sample output for a ping request initiated at node N1 to the loopback address of node N5 via a segment list . > ping B5:: via segment-list A2::C31, A4::C52 Sending 5, 100-byte ICMP Echos to B5::, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625 /0.749/0.931 ms Figure 2 A sample ping output at an SRv6 capable node Ali, et al. Expires January 1, 2019 [Page 9] Internet-Draft OAM for SRv6 July 2, 2018 All transit nodes process the echo request message like any other data packet carrying SR header and hence do not require any change. Similarly, the egress node (IPv6 classic or SRv6 capable) does not require any change to process the ICMPv6 echo request. For example, in the ping example of Figure 2: - Node N1 initiates an ICMPv6 ping packet with SRH as follows (B1::, A2::C31)(B1::, A4::C52, A2::C31, SL=2, NH: ICMPv6)(ICMPv6 Echo Request). - Node N2, which is an SRv6 capable node, performs the standard SRH processing. Specifically, it executes the END.X function (A2::C31) on the echo request packet. - Node N3, which is a classic IPv6 node, performs the standard IPv6 processing. Specifically, it forwards the echo request based on DA A4::C52 in the IPv6 header. - Node N4, which is an SRv6 capable node, performs the standard SRH processing. Specifically, it observes the END.X function (A4::C52) with PSP (Penultimate Segment POP) on the echo request packet and removes the SRH and forwards the packet across link10 to N5. - The echo request packet at N5 arrives as an IPv6 packet without a SRH. Node N5, which is a classic IPv6 node, performs the standard IPv6/ ICMPv6 processing on the echo request and responds, accordingly. 4.1.2. Pinging a SID Function The classic ping described in the previous section cannot be used to ping a remote SID function, as explained using an example in the following. Consider the case where the user wants to ping the remote SID function A4::C52, via A2::C31, from node N1. Node N1 constructs the ping packet (B1::0, A2::C31)( A4::C52, A2::C31, SL=1; NH=ICMPv6)(ICMPv6 Echo Request). When the node N4 receives the ICMPv6 echo request with DA set to A4::C52 and next header set to ICMPv6, it silently drops it (see [I-D.filsfils-spring-srv6- network-programming] for details). 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 by inserting the END.OP/ END.OTP SIDs at an appropriate place in the SRH. The following illustration uses END.OTP SID but the procedures are equally applicable to the END.OP SID. Ali, et al. Expires January 1, 2019 [Page 10] Internet-Draft OAM for SRv6 July 2, 2018 In an SRv6 network, the user can exercise two flavors of the ping: end-to-end ping or segment-by-segment ping, as outlined in the following. 4.1.2.1. End-to-end ping using END.OP/ END.OTP The end-to-end ping illustration uses the END.OTP SID but the procedures are equally applicable to the END.OP SID. Consider the same example where the user wants to ping a remote SID function A4::C52 , via A2::C31, from node N1. To force a punt of the ICMPv6 echo request at the node N4, node N1 inserts the END.OTP SID just before the target SID A4::C52 in the SRH. The ICMPv6 echo request is processed at the individual nodes along the path as follows: - Node N1 initiates an ICMPv6 ping packet with SRH as follows (B1::0, A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2; NH=ICMPv6)(ICMPv6 Echo Request). - Node N2, which is an SRv6 capable node, performs the standard SRH processing. Specifically, it executes the END.X function (A2::C31) on the echo request packet. - Node N3 receives the packet as follows (B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). Node N3, which is a classic IPv6 node, performs the standard IPv6 processing. Specifically, it forwards the echo request based on DA A4::OTP in the IPv6 header. - When node N4 receives the packet (B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it processes the END.OTP SID, as described in the pseudocode in Section 3. The packet gets punted to the ICMPv6 process for processing. The ICMPv6 process checks if the next SID in SRH (the target SID A4::C52) is locally programmed. - 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 A4::C52, via A2::C31, from node N1. However, in this ping, the node N1 wants to get a response from each segment node in the SRH. 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. Ali, et al. Expires January 1, 2019 [Page 11] Internet-Draft OAM for SRv6 July 2, 2018 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: - Node N1 initiates an ICMPv6 ping packet with SRH as follows (B1::0, A2::C31)(A4::C52, A2::C31; SL=1, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request). - When node N2 receives the packet (B1::0, A2::C31)(A4::C52, A2::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 A2::C31 SID function on the original packet and forwards it, accordingly. As SRH.Flags.O=1, Node N2 also disables the PSP flavour, i.e., does not remove the SRH. The ICMPv6 process at node N2 checks if its local SID (A2::C31) is locally programmed or not and responds to the ICMPv6 Echo Request. - 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, A2::C31. - Node N3, which is a classic IPv6 node, performs the standard IPv6 processing. Specifically, it forwards the echo request based on DA A4::C52 in the IPv6 header. - When node N4 receives the packet (B1::0, A4::C52)(A4::C52, A2::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 (A2::C31) is locally programmed or not and responds to the ICMPv6 Echo Request. 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 discussed earlier. Ali, et al. Expires January 1, 2019 [Page 12] Internet-Draft OAM for SRv6 July 2, 2018 4.2. 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: - If the router receives an undeliverable IP datagram, or - If the router receives a packet with a Hop Limit of zero, or - If the router receives a packet such that if the router decrements the packet's Hop Limit it becomes zero, or - 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 - If the router cannot forward a packet because the packet is larger than the MTU of the outgoing link. In the scenarios listed above, the ICMPv6 response also contains the IP header, IP extension headers and leading payload octets of the "original datagram" to which the ICMPv6 message is a response. 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. 4.3. Traceroute There is no hardware or software change required for traceroute 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 traceroute operations. In other words, existing traceroute mechanisms work seamlessly in the SRv6 networks. The following subsections outline some use cases of the traceroute in the SRv6 networks. 4.3.1. Classic Traceroute The existing mechanism to traceroute a remote IP prefix, along the shortest path, continues to work without any modification. The initiator may be an SRv6 node or a classic IPv6 node. Similarly, the egress or transit may be an SRv6 node or a classic IPv6 node. Ali, et al. Expires January 1, 2019 [Page 13] Internet-Draft OAM for SRv6 July 2, 2018 If an SRv6 capable ingress node wants to traceroute to IPv6 prefix via an arbitrary segment list , it needs to initiate traceroute probe with an SR header containing the SID list . That is illustrated using the topology in Figure 1. Assume all the links have IGP metric 10 except both links between node2 and node3, which have IGP metric set to 100. User issues a traceroute from node N1 to a loopback of node 5, via segment list . Figure 3 contains sample output for the traceroute request. > traceroute B5:: via segment-list A2::C31, A4::C52 Tracing the route to B5:: 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec SRH: (B5::, A4::C52, A2::C31, SL=2) 2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec SRH: (B5::, A4::C52, A2::C31, SL=1) 3 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec SRH: (B5::, A4::C52, A2::C31, SL=1) 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 Please note that information for hop2 is returned by N3, which is a classic IPv6 node. Nonetheless, the ingress node is able to display SR header contents as the packet travels through the IPv6 classic node. This is because the "Time Exceeded Message" ICMPv6 message can contain as much of the invoking packet as possible without the ICMPv6 packet exceeding the minimum IPv6 MTU [RFC4443]. The SR header is also included in these ICMPv6 messages initiated by the classic IPv6 transit nodes that are not running SRv6 software. Specifically, a node generating ICMPv6 message containing a copy of the invoking packet does not need to understand the extension header(s) in the invoking packet. The segment list information returned for hop1 is returned by N2, which is an SRv6 capable node. Just like for hop2, the ingress node is able to display SR header contents for hop1. There is no difference in processing of the traceroute probe at an IPv6 classic node and an SRv6 capable node. Similarly, both IPv6 classic and SRv6 capable nodes use the address of the interface on which probe was received as the source address in the ICMPv6 Ali, et al. Expires January 1, 2019 [Page 14] Internet-Draft OAM for SRv6 July 2, 2018 response. ICMP extensions defined in [RFC5837] can be used to also display information about the IP interface through which the datagram would have been forwarded had it been forwardable, and the IP next hop to which the datagram would have been forwarded, the IP interface upon which a datagram arrived, the sub-IP component of an IP interface upon which a datagram arrived. The information about the IP address of the incoming interface on which the traceroute probe was received by the reporting node is very useful. This information can also be used to verify if SID functions A2::C31 and A4::C52 are executed correctly by N2 and N4, respectively. Specifically, the information displayed for hop2 contains the incoming interface address 2001:DB8:2:3:31:: at N3. This matches with the expected interface bound to END.X function A2::C31 (link3). Similarly, the information displayed for hop5 contains the incoming interface address 2001:DB8:4:5::52:: at N5. This matches with the expected interface bound to the END.X function A4::C52 (link10). 4.3.2. Traceroute to a SID Function The classic traceroute described in the previous section cannot be used to traceroute a remote SID function, as explained using an example in the following. Consider the case where the user wants to traceroute the remote SID function A4::C52, via A2::C31, from node N1. Node N1 constructs the traceroute packet (B1::0, A2::C31, HC=1)( A4::C52, A2::C31, SL=1; NH=UDP)(traceroute probe). Even though Hop Count of the packet is set to 1, when the node N4 receives the traceroute probe with DA set to A4::C52 and next header set to UDP, it silently drops it (see [I- D.draft-filsfils-spring-srv6-network-programming] for details). To solve this problem, the initiator needs to mark the traceroute probe as an OAM packet. The OAM packets are identified either by setting the O-flag in SRH or by inserting the END.OTP SID at an appropriate place in the SRH. In an SRv6 network, the user can exercise two flavors of the traceroute: hop-by-hop traceroute or overlay traceroute. - In hop-by-hop traceroute, user gets responses from all nodes including classic IPv6 transit nodes, SRv6 capable transit nodes as well as SRv6 capable segment endpoints. E.g., consider the example where the user wants to traceroute to a remote SID function A4::C52 , via A2::C31, from node N1. The traceroute Ali, et al. Expires January 1, 2019 [Page 15] Internet-Draft OAM for SRv6 July 2, 2018 output will also display information about node3, which is a transit (underlay) node. - The overlay traceroute, on the other hand, does not trace the underlay nodes. In other words, the overlay traceroute only 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 A4::C52 , via A2::C31, from node N1, the overlay traceroute would only display the traceroute information from node N2 and node N2 and will not display information from node 3. 4.3.2.1. Hop-by-hop traceroute using END.OP/ END.OTP In this section, hop-by-hop traceroute to a SID function is exemplified using UDP probes. However, the procedure is equally applicable to other implementation of traceroute mechanism. Furthermore, the illustration uses the END.OTP SID but the procedures are equally applicable to the END.OP SID Consider the same example where the user wants to traceroute to a remote SID function A4::C52 , via A2::C31, from node N1. To force a punt of the traceroute probe only at the node N4, node N1 inserts the END.OTP SID just before the target SID A4::C52 in the SRH. The traceroute probe is processed at the individual nodes along the path as follows. - Node N1 initiates a traceroute probe packet with a monotonically increasing value of hop count and SRH as follows (B1::0, A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2; NH=UDP)(Traceroute probe). - When node N2 receives the packet with hop-count = 1, it processes the hop count expiry. Specifically, the node N2 responses with the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live exceeded in Transit"). - When Node N2 receives the packet with hop-count > 1, it performs the standard SRH processing. Specifically, it executes the END.X function (A2::C31) on the traceroute probe. - When node N3, which is a classic IPv6 node, receives the packet (B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; HC=1, SL=1; NH=UDP)(Traceroute probe) with hop-count = 1, it processes the hop count expiry. Specifically, the node N3 responses with the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live exceeded in Transit"). - When node N3, which is a classic IPv6 node, receives the packet with hop-count > 1, it performs the standard IPv6 processing. Specifically, it forwards the traceroute probe based on DA A4::OTP in the IPv6 header. Ali, et al. Expires January 1, 2019 [Page 16] Internet-Draft OAM for SRv6 July 2, 2018 - When node N4 receives the packet (B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it processes the END.OTP SID, as described in the pseudocode in Section 3. The packet gets punted to the traceroute process for processing. The traceroute process checks if the next SID in SRH (the target SID A4::C52) is locally programmed. If the target SID A4::C52 is locally programmed, node N4 responses with the ICMPv6 message (Type: Destination unreachable, Code: Port Unreachable). If the target SID A4::C52 is not a local SID, node N4 silently drops the traceroute probe. Figure 4 displays a sample traceroute output for this example. > traceroute srv6 A4::C52 via segment-list A2::C31 Tracing the route to SID function A4::C52 1 2001:DB8:1:2:21 0.512 msec 0.425 msec 0.374 msec SRH: (A4::C52, A4::OTP, A2::C31; SL=2) 2 2001:DB8:2:3:31 0.721 msec 0.810 msec 0.795 msec SRH: (A4::C52, A4::OTP, A2::C31; SL=1) 3 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec SRH: (A4::C52, A4::OTP, A2::C31; SL=1) Figure 4 A sample output for hop-by-hop traceroute to a SID function 4.3.2.2. 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 A4::C52 , via A2::C31, from node N1. - Node N1 initiates a traceroute probe with SRH as follows (B1::0, A2::C31)(A4::C52, A2::C31; HC=64, SL=1, Flags.O=1; NH=UDP)(Traceroute Probe). Please note that the hop-count is Ali, et al. Expires January 1, 2019 [Page 17] Internet-Draft OAM for SRv6 July 2, 2018 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. - When node N2 receives the packet (B1::0, A2::C31)(A4::C52, A2::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 A2::C31 SID function on the original packet and forwards it, accordingly. As SRH.Flags.O=1, Node N2 also disables the PSP flavor, i.e., does not remove the SRH. The traceroute process at node N2 checks if its local SID (A2::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. - 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, A2::C31. - When node N3 receives the packet (B1::0, A4::C52)(A4::C52, A2::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 A4::C52 in the IPv6 header. Please note that there is no hop-count expiration at the transit nodes. - When node N4 receives the packet (B1::0, A4::C52)(A4::C52, A2::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 (A2::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. 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. > traceroute srv6 A4::C52 via segment-list A2::C31 Tracing the route to SID function A4::C52 Ali, et al. Expires January 1, 2019 [Page 18] Internet-Draft OAM for SRv6 July 2, 2018 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec SRH: (A4::C52, A4::OTP, A2::C31; SL=2) 2 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec SRH: (A4::C52, A4::OTP, A2::C31; SL=1) Figure 5 A sample output for overlay traceroute to a SID function 4.4. In-situ OAM [I-D.brockners-inband-oam-requirements] describes motivation and requirements for In-situ OAM (iOAM). iOAM records operational and telemetry information in the data packet while the packet traverses the network of telemetry domain. iOAM complements out-of- band probe based OAM mechanisms such ICMP ping and traceroute by directly encoding tracing and the other kind of telemetry information to the regular data traffic. [I-D.brockners-inband-oam-transport] describes transport mechanisms for iOAM data including IPv6 and Segment Routing traffic. To address iOAM requirements in an SRv6 network, the draft describes iOAM TLV in SRH and its usage. 4.5. Monitoring of SRv6 Paths In the recent past, network operators are interested in performing network OAM functions in a centralized manner. Various data models like YANG are available to collect data from the network and manage it from a centralized entity. SR technology enables a centralized OAM entity to perform path monitoring from centralized OAM entity without control plane intervention on monitored nodes. [I.D-draft-ietf-spring-oam-usecase] describes such a centralized OAM mechanism. Specifically, the draft describes a procedure that can be used to perform path continuity check between any nodes within an SR domain from a centralized monitoring system, with minimal or no control plane intervene on the nodes. However, the draft focuses on SR networks with MPLS data plane. The same concept applies to the SRv6 networks. This document describes how the concept can be used to perform path monitoring in an SRv6 network. This document describes how the concept can be used to perform path monitoring in an SRv6 network as follows. Ali, et al. Expires January 1, 2019 [Page 19] Internet-Draft OAM for SRv6 July 2, 2018 In the above reference topology, N100 is the centralized monitoring system implementing an END function A100::. In order to verify a segment list , N100 generates a probe packet with SRH set to (A100::, A4::C52, A2::C31, SL=2). The controller routes the probe packet towards the first segment, which is A2::C31. N2 performs the standard SRH processing and forward it over link3 with the DA of IPv6 packet set to A4::C52. N4 also performs the normal SRH processing and forward it over link10 with the DA of IPv6 packet set to A100::. This makes the probe loops back to the centralized monitoring system. In the reference topology in Figure 1, N100 uses an IGP protocol like OSPF or ISIS to get the topology view within the IGP domain. N100 can also use BGP-LS to get the complete view of an inter-domain topology. In other words, the controller leverages the visibility of the topology to monitor the paths between the various endpoints without control plane intervention required at the monitored nodes. 5. Security Considerations This document does not define any new protocol extensions and relies on existing procedures defined for ICMP. This document does not impose any additional security challenges to be considered beyond security considerations described in [RFC4884], [RFC4443], [RFC792] and RFCs that updates these RFCs. 6. IANA Considerations 6.1. Segment Routing Header Flags Register This document requests the creation of a new IANA managed registry to identify SRH Flags Bits. The registration procedure is "Expert Review" as defined in [RFC8126]. Suggested registry name is "Segment Routing Header Flags". SRH.Flags is an 8 bits field; the following bit is defined in this document: Suggested Bit Description Reference ----------------------------------------------------- 2 OAM This document 6.2. ICMPv6 type Numbers Registry This document defines one ICMPv6 Message, a type that has been allocated from the "ICMPv6 'type' Numbers" registry of [RFC4443]. Ali, et al. Expires January 1, 2019 [Page 20] Internet-Draft OAM for SRv6 July 2, 2018 Specifically, it requests to add the following to the "ICMPv6 Type Numbers" registry: TBA (suggested value: 162) SRv6 OAM Message. The document also requests the creation of a new IANA registry to the "ICMPv6 'Code' Fields" against the "ICMPv6 Type Numbers TBA - SRv6 OAM Message" with the following codes: Code Name Reference ------------------------------------------------------- 0 No Error This document 1 SID is not locally implemented This document 2 O-flag punt at Transit This document 6.3. SRv6 OAM Endpoint Types This I-D requests to IANA to allocate, within the "SRv6 Endpoint Types" sub-registry belonging to the top-level "Segment-routing with IPv6 dataplane (SRv6) Parameters" registry [I-D.filsfils-spring- srv6-network-programming], the following allocations: +-------------+-----+-------------------+-----------+ | Value (Suggested | Endpoint function | Reference | | Value) | | | +------------------+-------------------+-----------+ | TBA (25) | End.OTP | [This.ID] | | TBA (30) | End.OTP | [This.ID] | +------------------+-------------------+-----------+ 7. References 7.1. Normative References [RFC792] J. Postel, "Internet Control Message Protocol", RFC 792, September 1981. [RFC4443] A. Conta, S. Deering, M. Gupta, Ed., "Internet Control Ali, et al. Expires January 1, 2019 [Page 21] Internet-Draft OAM for SRv6 July 2, 2018 Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [RFC4884] R. Bonica, D. Gan, D. Tappan, C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, April 2007. [RFC5837] A. Atlas, Ed., R. Bonica, Ed., C. Pignataro, Ed., N. Shen, JR. Rivers, "Extending ICMP for Interface and Next-Hop Identification", RFC 5837, April 2010. [I-D.filsfils-spring-srv6-network-programming] C. Filsfils, et al., "SRv6 Network Programming", draft-filsfils-spring-srv6-network-programming, work in progress. [I-D.6man-segment-routing-header] Previdi, S., Filsfils, et al, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing-header, work in progress. 7.2. Informative References [I-D.bashandy-isis-srv6-extensions] IS-IS Extensions to Support Routing over IPv6 Dataplane. L. Ginsberg, P. Psenak, C. Filsfils, A. Bashandy, B. Decraene, Z. Hu, draft-bashandy-isis-srv6-extensions, work in progress. [I-D.dawra-idr-bgpls-srv6-ext] G. Dawra, C. Filsfils, K. Talaulikar, et al., BGP Link State extensions for IPv6 Segment Routing (SRv6), draft-dawra-idr-bgpls-srv6-ext, work in progress. [I-D.ietf-spring-oam-usecase] A Scalable and Topology-Aware MPLS Dataplane Monitoring System. R. Geib, C. Filsfils, C. Pignataro, N. Kumar, draft-ietf-spring-oam-usecase, work in progress. [I-D.brockners-inband-oam-data] F. Brockners, et al., "Data Formats for In-situ OAM", draft-brockners-inband-oam-data, work in progress. [I-D.brockners-inband-oam-transport] F.Brockners, at al., "Encapsulations for In-situ OAM Data", draft-brockners-inband-oam-transport, work in progress. [I-D.brockners-inband-oam-requirements] F.Brockners, et al., "Requirements for In-situ OAM", draft-brockners-inband-oam-requirements, work in progress. [I-D.spring-segment-routing-policy] Filsfils, C., et al., "Segment Routing Policy for Traffic Engineering", draft-filsfils-spring-segment-routing-policy, work in progress. 8. Acknowledgments To be added. Ali, et al. Expires January 1, 2019 [Page 22] Internet-Draft OAM for SRv6 July 2, 2018 Authors' Addresses Clarence Filsfils Cisco Systems, Inc. Email: cfilsfil@cisco.com Zafar Ali Cisco Systems, Inc. Email: zali@cisco.com Nagendra Kumar Cisco Systems, Inc. Email: naikumar@cisco.com Carlos Pignataro Cisco Systems, Inc. Email: cpignata@cisco.com Faisal Iqbal Cisco Systems, Inc. Email: faiqbal@cisco.com Rakesh Gandhi Cisco Systems, Inc. Canada Email: rgandhi@cisco.com John Leddy Comcast Email: John_Leddy@cable.comcast.com Robert Raszuk Bloomberg LP 731 Lexington Ave New York City, NY10022, USA Email: robert@raszuk.net Satoru Matsushima SoftBank Japan Email: satoru.matsushima@g.softbank.co.jp Daniel Voyer Bell Canada Email: daniel.voyer@bell.ca Ali, et al. Expires January 1, 2019 [Page 23] Internet-Draft OAM for SRv6 July 2, 2018 Gaurav Dawra LinkedIn Email: gdawra.ietf@gmail.com Bart Peirens Proximus Email: bart.peirens@proximus.com Mach Chen Huawei Email: mach.chen@huawei.com Gaurav Naik Drexel University United States of America Email: gn@drexel.edu Ali, et al. Expires January 1, 2019 [Page 24] Internet-Draft OAM for SRv6 July 2, 2018