Networking Working Group Z. Ali Internet-Draft C. Filsfils Intended status: Standards Track N. Kumar Expires: September 26, 2019 C. Pignataro R. Gandhi F. Brockners Cisco Systems, Inc. J. Leddy Individual S. Matsushima SoftBank R. Raszuk Bloomberg LP D. Voyer Bell Canada G. Dawra LinkedIn B. Peirens Proximus M. Chen C. Li Huawei F. Iqbal Individual March 27, 2019 Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane (SRv6) draft-ali-6man-spring-srv6-oam-01.txt Abstract This document defines building blocks for Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane (SRv6). The document also describes some SRv6 OAM mechanisms. 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) 2019 IETF Trust and the persons identified as the 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. Ali, et al. Expires September 26, 2019 [Page 1] Internet-Draft SRv6 OAM March 2019 Table of Contents 1. Introduction.........................................................3 2. Conventions Used in This Document..............................3 2.1. Abbreviations.............................................3 2.2. Terminology and Reference Topology........................3 3. OAM Building Blocks............................................4 3.1. O-flag in Segment Routing Header..........................4 3.1.1. O-flag Processing....................................5 3.2. OAM Segments..............................................5 3.2.1. End.OP: OAM Endpoint with Punt.......................6 3.2.2. End.OTP: OAM Endpoint with Timestamp and Punt........6 3.3. SRH TLV...................................................7 4. OAM Mechanisms.................................................7 4.1. Ping......................................................7 4.1.1. Classic Ping.........................................7 4.1.2. Pinging a SID Function...............................9 4.2. Error Reporting..........................................11 4.3. Traceroute...............................................11 4.3.1. Classic Traceroute..................................12 4.3.2. Traceroute to a SID Function........................13 4.4. OAM Data Piggybacked in Data traffic.....................17 4.4.1. IOAM Data Field Encapsulation in SRH................17 4.4.2. Procedure...........................................18 4.5. Monitoring of SRv6 Paths.................................20 5. Security Considerations.......................................20 6. IANA Considerations...........................................21 6.1. ICMPv6 type Numbers Registry.............................21 6.2. SRv6 OAM Endpoint Types..................................21 6.3. SRv6 IOAM TLV............................................21 7. References....................................................22 7.1. Normative References.....................................22 7.2. Informative References...................................23 Ali, et al. Expires September 26, 2019 [Page 2] Internet-Draft SRv6 OAM March 2019 1. Introduction This document defines building blocks for Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane (SRv6). The document also describes some SRv6 OAM mechanisms. 2. Conventions Used in This Document 2.1. Abbreviations ECMP: Equal Cost Multi-Path. SID: Segment ID. 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. ICMPv6: multi-part ICMPv6 messages [RFC4884]. 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 Ali, et al. Expires September 26, 2019 [Page 3] Internet-Draft SRv6 OAM March 2019 In the reference topology: Nodes N1, N2, and N4 are SRv6 capable nodes. Nodes N3, N5 and N6 are classic IPv6 nodes. Node N100 is a controller. Node k has a classic IPv6 loopback address A:k::/128. A SID at node k with locator block B and function F is represented by B:k:F:: 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::. B:k:1:: is explicitly allocated as the END function at Node k. B:k::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., B:2:C31 represents END.X at N2 towards N3 via link3 (the 1st link between N2 and N3). Similarly, B:4: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 for implementing OAM mechanisms in SRv6 networks. 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 September 26, 2019 [Page 4] Internet-Draft SRv6 OAM March 2019 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. When N receives a packet whose IPv6 DA is S and S is a local SID, N executes the following the pseudo-code, before 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. Software (slow path) implements the required OAM mechanism. Timestamp is not carried in the packet forwarded to the next hop. 3.2. OAM Segments OAM Segment IDs (SIDs) is another component of the SRv6 OAM building Blocks. This document defines a couple of OAM SIDs. Additional SIDs will be added in the later version of the document. Ali, et al. Expires September 26, 2019 [Page 5] Internet-Draft SRv6 OAM March 2019 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) punts the packet. 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. 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. Ref2: Hardware (microcode) timestamps and punts the packet. 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. Ali, et al. Expires September 26, 2019 [Page 6] Internet-Draft SRv6 OAM March 2019 3.3 SRH TLV SRH TLV plays an important role in carrying OAM and Performance Management (PM) metadata. For example, when SRH TLV piggybacks OAM information onto the data traffic (i.e., for In-situ OAM (IOAM) and Performance Management (PM) data in SRv6. networks). 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. 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. Ali, et al. Expires September 26, 2019 [Page 7] Internet-Draft SRv6 OAM March 2019 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 A:5:: via segment-list B:2:C31, B:4: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 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 (A:1::, B:2:C31)(A:5::, B:4:C52, B:2: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 (B:2:C31) and forwards the packet on link3 to N3. - 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. - Node N4, which is an SRv6 capable node, performs the standard SRH processing. Specifically, it observes the END.X function (B:4: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 an SRH. Node N5, which is a classic IPv6 node, performs the standard IPv6/ ICMPv6 processing on the echo request and responds, accordingly. Ali, et al. Expires September 26, 2019 [Page 8] Internet-Draft SRv6 OAM March 2019 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 B:4:C52, via B:2:C31, from node N1. Node N1 constructs the ping packet (A:1::, B:2:C31)(B:4:C52, B:2:C31, SL=1; NH=ICMPv6)(ICMPv6 Echo Request). The ping fails because the node N4 receives the ICMPv6 echo request with DA set to B:4:C52 but the next 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 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. 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 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 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 follows: - 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; 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 (B:2:C31) on the echo request packet. - 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 N3, which is a classic IPv6 node, performs the standard IPv6 processing. Specifically, it forwards the echo request based on DA B:4:OTP in the IPv6 header. - 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 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 B:4:C52) is locally programmed. Ali, et al. Expires September 26, 2019 [Page 9] Internet-Draft SRv6 OAM March 2019 - 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: and - 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). - 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. - 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. - 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. Ali, et al. Expires September 26, 2019 [Page 10] Internet-Draft SRv6 OAM March 2019 - 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:2: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. 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 Ali, et al. Expires September 26, 2019 [Page 11] Internet-Draft SRv6 OAM March 2019 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. 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 A:5:: via segment-list B:2:C31, B:4:C52 Tracing the route to B5:: 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) 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) 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) 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 Ali, et al. Expires September 26, 2019 [Page 12] Internet-Draft SRv6 OAM March 2019 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 may use the address of the interface on which probe was received as the source address in the ICMPv6 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 B:2:C31 and B:4: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 B:2: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 B:4: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 B:4:C52, via B:2:C31, from node N1. The trace route fails at N4. This is because the node N4 trace route probe where next header is UDP or ICMPv6, instead of SRH (even though the hop limit is set to 1). 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 or END.OTP SID at an appropriate place in the SRH. Ali, et al. Expires September 26, 2019 [Page 13] Internet-Draft SRv6 OAM March 2019 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 B:4:C52, via B:2:C31, from node N1. The traceroute 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 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. 4.3.2.1. 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 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 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 as follows. - Node N1 initiates a traceroute probe packet with a monotonically increasing value of hop count and SRH as follows (A:1::, B:2:C31)(B:4:C52, B:4:OTP, B:2: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 (B:2:C31) on the traceroute probe. Ali, et al. Expires September 26, 2019 [Page 14] Internet-Draft SRv6 OAM March 2019 - When node N3, which is a classic IPv6 node, receives the packet (A:1::, B:4:OTP)(B:4:C52, B:4:OTP, B:2: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 B:4:OTP in the IPv6 header. - 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 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 B:4:C52) is locally programmed. If the target SID B:4:C52 is locally programmed, node N4 responses with the ICMPv6 message (Type: Destination unreachable, Code: Port Unreachable). If the target SID B:4: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 B:4:C52 via segment-list B:2:C31 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=2) 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) 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) 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. Ali, et al. Expires September 26, 2019 [Page 15] Internet-Draft SRv6 OAM March 2019 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. - 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. - 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. - 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. - 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. - 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. 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. Ali, et al. Expires September 26, 2019 [Page 16] Internet-Draft SRv6 OAM March 2019 > traceroute srv6 B:4:C52 via segment-list B:2:C31 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=2) 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=1) Figure 5 A sample output for overlay traceroute to a SID function 4.4 OAM Data Piggybacked in Data traffic OAM and PM information from the intermediate SR endpoints can be piggybacked in the data packet. The OAM and PM information piggybacking in the data packets is also known as In-situ OAM (IOAM). This section describes iOAM functionality in SRv6 network. The IOAM data is carried in SRH.TLV. This enables the IOAM mechanism to build on the network programmability capability of SRv6. The ability for an intermediate SRv6 endpoint to determine whether to process or ignore some specific SRH TLVs is based on the SID function. This enables collection of the IOAM information from the intermediate endpoint nodes of choice. The nodes that are not capable of supporting the IOAM functionality does not have to look or process SRH TLV (i.e., such nodes can simply ignore the SRH IOAM TLV). 4.4.1 IOAM Data Field Encapsulation in SRH The SRv6 encapsulation header (SRH) is defined in [I-D.6man-segment-routing-header]. IOAM data fields are carried in the SRH, using a single pre-allocated SRH TLV. The different IOAM data fields defined in [I-D.ietf-ippm-ioam-data] are added as sub-TLVs. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SRH-TLV-Type | LEN | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | IOAM-Type | IOAM HDR LEN | RESERVED | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I ! | O ! | A ~ IOAM Option and Data Space ~ M | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<-+ | | | | | Payload + Padding (L2/L3/...) | Ali, et al. Expires September 26, 2019 [Page 17] Internet-Draft SRv6 OAM March 2019 | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: IOAM data encapsulation in SRH SRH-TLV-Type: IOAM TLV Type for SRH is defined as TBA1. The fields related to the encapsulation of IOAM data fields in the SRH are defined as follows: IOAM-Type: 8-bit field defining the IOAM Option type, as defined in Section 7.2 of [I-D.ietf-ippm-ioam-data]. IOAM HDR LEN: 8-bit unsigned integer. Length of the IOAM HDR in 4-octet units. RESERVED: 8-bit reserved field MUST be set to zero upon transmission and ignored upon receipt. IOAM Option and Data Space: IOAM option header and data is present as defined by the IOAM-Type field, and is defined in Section 4 of [I-D.ietf-ippm-ioam-data]. 4.4.2. Procedure This section summarizes the procedure for IOAM data encapsulation in SRv6 networks. Ali, et al. Expires September 26, 2019 [Page 18] Internet-Draft SRv6 OAM March 2019 4.4.2.1 Ingress Node As part of the SRH encapsulation, the ingress node of an SR domain or an SR Policy [I-D.spring-segment-routing-policy] MAY add the IOAM TLV in the SRH of the data packet. If an ingress node supports IOAM functionality and, based on a local configuration, wants to collect IOAM data, it adds IOAM TLV in the SRH. Based on the size of the segment list (SL), the ingress node preallocates space in the IOAM TLV. When IOAM data from the last node in the segment-list (Egress node) is desired, the ingress uses an Ultimate Segment Pop (USP) SID at the Egress node. The ingress node may also insert the IOAM data about the local information in the IOAM TLV in the SRH at index 0 of the preallocated IOAM TLV. 4.4.2.2 Intermediate SR Segment Endpoint Node The SR segment endpoint node is any node receiving an IPv6 packet where the destination address of that packet is a local SID or a local interface address. As part of the SR Header processing as described in [I-D.6man-segment-routing-header] and [I-D.spring-srv6-network-programming], the SR Segment Endpoint node performs the following IOAM operations. If an intermediate SR segment endpoint node is not capable of processing IOAM TLV, it simply ignores it. I.e., it does not have to look or process SRH TLV. If an intermediate SR segment endpoint node is capable of processing IOAM TLV and the local SID supports IOAM data recording, it checks if any SRH TLV is present in the packet using procedures defined in [I-D.6man-segment-routing-header]. If the node finds IOAM TLV in the SRH, based on Segment Left (SL), it finds the local index at which it is expected to record the IOAM data. The node records the IOAM data at the desired preallocated space. 4.4.2.3 Egress Node The Egress node is the last node in the segment-list of the SRH. When IOAM data from the Egress node is desired, a USP SID advertised by the Egress node is used. The processing of IOAM TLV at the Egress node is similar to the processing of IOAM TLV at the SR Segment Endpoint Node. The only difference is that the Egress node may telemeter the IOAM data to an external entity. Ali, et al. Expires September 26, 2019 [Page 19] Internet-Draft SRv6 OAM March 2019 4.6. 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. In the above reference topology, N100 is the centralized monitoring system implementing an END function B:100:1::. In order to verify a segment list , N100 generates a probe packet with SRH set to (B:100:1::, B:4:C52, B:2:C31, SL=2). The controller routes the probe packet towards the first segment, which is B:2:C31. N2 performs the standard SRH processing and forward it over link3 with the DA of IPv6 packet set to B:4:C52. N4 also performs the normal SRH processing and forward it over link10 with the DA of IPv6 packet set to B:100:1::. 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. Ali, et al. Expires September 26, 2019 [Page 20] Internet-Draft SRv6 OAM March 2019 6. IANA Considerations 6.1. ICMPv6 type Numbers Registry This document defines one ICMPv6 Message, a type that has been allocated from the "ICMPv6 'type' Numbers" registry of [RFC4443]. 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 6.2. SRv6 OAM Endpoint Types This I-D requests to IANA to allocate, within the "SRv6 Endpoint Behaviors Registry" 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 Behavior | Reference | | Value) | | | +------------------+-------------------+-----------+ | TBA (40) | End.OP | [This.ID] | | TBA (41) | End.OTP | [This.ID] | +------------------+-------------------+-----------+ 6.3. SRv6 IOAM TLV Ali, et al. Expires September 26, 2019 [Page 21] Internet-Draft SRv6 OAM March 2019 IANA is requested to allocate SRH TLV Type for IOAM TLV data fields under registry name "Segment Routing Header TLVs" requested by [I- D.6man-segment-routing-header]. +--------------+--------------------------+---------------+ | SRH TLV Type | Description | Reference | +--------------+--------------------------+---------------+ | TBA1 | TLV for IOAM Data Fields | This document | +--------------+--------------------------+---------------+ 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 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. [I-D.ietf-ippm-ioam-data] Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, P., Chang, R., and Bernier, D., "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-data, work in progress. Ali, et al. Expires September 26, 2019 [Page 22] Internet-Draft SRv6 OAM March 2019 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 The authors would like to thank Gaurav Naik for his review comments. 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 Ali, et al. Expires September 26, 2019 [Page 23] Internet-Draft SRv6 OAM March 2019 Carlos Pignataro Cisco Systems, Inc. Email: cpignata@cisco.com Rakesh Gandhi Cisco Systems, Inc. Canada Email: rgandhi@cisco.com Frank Brockners Cisco Systems, Inc. Germany Email: fbrockne@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 Gaurav Dawra LinkedIn Email: gdawra.ietf@gmail.com Bart Peirens Proximus Email: bart.peirens@proximus.com Ali, et al. Expires September 26, 2019 [Page 24] Internet-Draft SRv6 OAM March 2019 Mach Chen Huawei Email: mach.chen@huawei.com Cheng Li Huawei Email: chengli13@huawei.com Faisal Iqbal Individual Email: faisal.ietf@gmail.com Ali, et al. [Page 25]