Network Working Group P. Turaga Internet-Draft R. Raszuk Intended status: Standards Track Bloomberg LP Expires: September 17, 2016 March 16, 2016 MPLS Test Labels draft-turaga-mpls-test-labels-00 Abstract This document describes an underlying mechanism for automatic diagnostics of link quality between any two devices connected together by standard point to point link. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 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." This Internet-Draft will expire on September 17, 2016. Copyright Notice Copyright (c) 2016 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 Turaga & Raszuk Expires September 17, 2016 [Page 1] Internet-Draft draft-turaga-mpls-test-labels March 2016 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3 4. MPLS Special Purpose Loop Label . . . . . . . . . . . . . . . 4 4.1. Operation of MPLS Special Purpose Loop Label . . . . . . 6 4.2. Comparison with stated test requirements . . . . . . . . 8 4.3. Probe size and rate calculation . . . . . . . . . . . . . 8 5. MPLS Special Purpose Swap-to-Drop and Drop Labels . . . . . . 9 6. Probe's QOS marking . . . . . . . . . . . . . . . . . . . . . 9 7. Bandwidth Considerations for link under test . . . . . . . . 10 8. I2RS and YANG modelling . . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10. Security Considerations . . . . . . . . . . . . . . . . . . . 10 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 13.1. Normative References . . . . . . . . . . . . . . . . . . 11 13.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Terminology o RTT - Round Trip Time o TTL - Time to Live o BFD - BiDirectional Failure Detection o LFM - Link Fault Management o ICMP - Internet Control Message Protocol 2. Introduction Real time monitoring of WAN or MAN link quality presents a real operational challenge. The common use of circuit emulation techniques by carriers makes detection of the circuits degradation difficult. Very often such reduced link quality results in increased queuing times or packet drops beyond SLA guarantees. Furthermore, the characteristics of link degradation is different from link to link. The problem space described above is further complicated due to the following reasons: Turaga & Raszuk Expires September 17, 2016 [Page 2] Internet-Draft draft-turaga-mpls-test-labels March 2016 o Link anomalies may not occur at the same uniform rate or be of the same constant and continuous pattern. This transient characteristic maybe a function of load or other temporary problems for example transport network over-subscription. o Encountered degradated service behavior may not translate to link errors or packet discards on either end of the suspected link because the emulated link consisting of multiple independent L2 segments in the carrier's network. Currently available tools on the circuit endpoints (usually routers) do not allow easy way to diagnose circuit health. Tools used today to detect link issues include: o Creating hardware or software loops manually - this results in the actual link under test to be taken out of service. Test traffic is then sent through the link and based on the results of the test, link quality issues are detected. o Regular pings/probes on directly connected links between routers/ network devices - Depending on the size of the probe packets and the rate at which they are sent between the network devices and the loss, the link issues are detected. The issue with this approach is that network processor on the router has to process all these packets. This causes an additional processing load on the routers. o BFD, IP protocol hellos etc are based on detecting neighbor state based on tiny and lightweight hellos. Such probes were designed for fast detection of end-to-end link state events .. not to evaluate link quality. If say N hellos send in T interval are lost it is an indication about link or peer down event. o The layer 2 OAM tools are not capable of addressing the requirements since by definition an emulated link consists of number of different L2 links hidden by the emulation layer and its encapsulation. L2 OAM could only indicate potential problems within single layer 2 link. They are light weight and some of these issues can only be detected at various levels of data rates (within agreed SLAs) transiting via such links. 3. Requirements The following are some of the key considerations required to be addressed in an alternative diagnostics solutions: o The testing should be atomic in nature - the UUT in this document is a single p2p link. o The test should not be subject to any alterations by externally injected packets o The probe packets should never be able to transit L3 node to any other L3 node Turaga & Raszuk Expires September 17, 2016 [Page 3] Internet-Draft draft-turaga-mpls-test-labels March 2016 o The level of diagnostics data should be configurable such that operator is able to inject anywhere from 0.1% to 100% of test load of a given max link capacity with build in automatic consideration of existing average of production traffic load (unless link is considered as taken out-of-service). o The duration of the test traffic should be either configurable by the operator or controlled by built-in detection heuristics. o The frequency of the test traffic should be either configurable by the operator or controlled by built-in detection heuristics. o Probes should not be subject to process switching by the route processors on either end of the link during the burst. o The solution should strive to minimize amount of required protocol extensions for as easy as possible inter-operability characteristics. o In the topologies where Link Aggregation is used, the aggregated bandwidth of the link should be considered instead of the individual links. The probe accounting should be recorded as total of all link members. Probe's hashing should follow normal data plane load balancing rules as configured on the directly connected peering routers. 4. MPLS Special Purpose Loop Label The mechanism for the set of proposed requirements can be constructed by combining two standards based protocol elements: TTL field processing and mpls label lookup. Special purpose mpls label will allow to setup a scoped link based loop and TTL field can be used to limit the loop duration. The MPLS local loop label can be either special purpose MPLS label (value 4-6 or 8-12) or Extended special purpose MPLS label (values 16-239). The use of the extended special purpose label would inherently increase the label stack to two for the probe packets with top most label to be of value 15 (extension label per [RFC7274]). By injecting N number of such probe packets (with max payload up to given MTU value) it is possible to control test load. The observation of the difference between number of injected probes and number of MPLS TTL expiration for a given test bundle would be equal to the number of packet drops observed. Similarly by calculating the time difference of time stamp from the moment of injection of the probe packet to its TTL expiration a good average of real RTT of a link can be calculated. The observation of such RTT times across number of test sequences will allow to model the aggregated queuing delays possibly allowing prediction of upcoming drops. Turaga & Raszuk Expires September 17, 2016 [Page 4] Internet-Draft draft-turaga-mpls-test-labels March 2016 It needs to be also observed that the above tests are completely orthogonal and would co-exit with current mechanism like LSP Ping [RFC4379] or MPLS BFD [RFC5884]. The proposed in this document procedures do not intend to verify control plane or control plane to data plane correctness. As stated already TTL handling or label lookup are both standards based and do not require any changes to the underlying hardware. However choice of MPLS special purpose label is proposed to simplify the test operation and remove significant new data plane requirements. The semantics of such label would be following: When packet is received with MPLS Local Loop Label TTL must be decremented and if > 0 the entire packet must be returned over the same interface over which it was received. If after decrementing TTL the resulting register value is 0 the probe packet should be dropped and local TTL-equal-zero error should be generated. If the probes header contain additional information (for example as described in LSP ping RFC) such header should be copied into the error message punted the the local control plane CPU for further processing. If implementation allows such local error could be optionally logged and handled in data plane only reporting the aggregated results to the local RE/RP. Such solutions has following advantages over possible alternative which would be use of regular IP packets: o The new mechanism with new type of MPLS label allows for defining a special handling which will not overlap with any of the possible interference with existing protocols ... for example ICMP traceroute o The new non transitive specification of mpls special purpose label allows for much stricter security and safer operation of the proposed testing model o The separate new label TTL expiration may be easily handled differently then general TTL expiration thus resulting in no data plane rate limiting or pacing o Use of signalling less special purpose MPLS LLL relaxes the solution from either additional control plane extensions or requirements to either extend opex with new static routes or to introduce new extensions to already established link local addresses. o The main principle of the tests are to be congruent with switching vectors of production traffic. Therefor it is important that probe packets use the same lookup LFIB structure as regular user data packets as far as egress and ingress line cards are concerned. Turaga & Raszuk Expires September 17, 2016 [Page 5] Internet-Draft draft-turaga-mpls-test-labels March 2016 The MPLS LLL label is to be auto assigned to FECs by either automated association with numbered IP addresses for the given link or with link local addresses. The resolution to MAC address of L2 rewrites (with 8847 ethertype) would be resolved locally through corresponding L3 adjacency addresses. 4.1. Operation of MPLS Special Purpose Loop Label The following is considered as a high level description of proposed solution: o Two routers R1 and R2 connected together by link L1 o The RTT between R1 and R2 on link L1 is 5ms o R1 and R2 have IP connectivity with each other on 10.10.10.0/30 numbered link. R1 has been configured with IP an address of 10.10.10.1 and R2 has been configured with an IP address of 10.10.10.2 o A MPLS local loop label is allocated to match the corresponding FECs of the link addresses (or link local when applicable). The following IPv4 probe packet has been injected from R1 towards the FEC of R2: o Source IP address: 10.10.10.1 o Destination IP address: 10.10.10.100 o TTL = 254 o payload optional ... (to be discussed by WG) o Proposed format: o R1 sends probe of the following format: 0 1 2 3 +-------------+-------------+-------------+-------------+ | LLL Label |EXP |S| TTL | +-------------+-------------+-------------+-------------+ | | | Packet payload (TBD) | | | Header - IP v4/v6 or perhaps lift from MPLS echo RFC) | | Data - filled with data up to MTU if needed | +-------------+-------------+-------------+-------------+ Figure 1: MPLS Label Stack Object Label: 20 bits Exp: Experimental Use, 3 bits S: Bottom of Stack, 1 bit TTL: Time to Live, 8 bits Figure 1: MPLS LLL probe format Turaga & Raszuk Expires September 17, 2016 [Page 6] Internet-Draft draft-turaga-mpls-test-labels March 2016 Such test packet would be resolve and encapsulated into MPLS LLL label and directed towards R2 with even TTL value. Test sequence: o Packet arrives at R2 and TTL is decremented following MPLS LLL label lookup and reinjection towards R1 o Packet keeps looping till TTL expires on R1. o Upon TTL expiration an ICMP TTL-eq-zero error message is being logged on R1 (originator of probe sequence). The ICMP message contains the header information of the original packet is being send to local control plane processor. o The local implementation may optionally optimize the accounting for the received vs missed in flight probe packets in the data plane layer and only report the aggregated sequence history o The analysis of the packets header would be logged in local or remote database and become very valuable source of the link's behavioral metrics. Observations: o A test probe packet has potential to be amplified up to 254 times o An ICMP TTL expired message is indicative of successful test - healthy link o No ICMP TTL message implies that the original packet was lost while it was getting looped between two routers. So, No ICMP TTL message means that test for a specific probe has failed. Let's note that this would have no bearing on the local control plane of either end of the test. Any reaction associated and triggered by the test results would be driven by controller (residing together or separate from participating routers. o Ability to send multiple packets of different sizes on the link with inherently controlled TTL loop can results in expected burst of control/probe traffic on the link under test o Such probe burst can be programmed to get to a certain % of the link speed for a short time Based on fine tuned testing scenario allowing to fill the bandwidth up to a certain % of link capacity the count of packets originally sent by router R1 should be the same as the number of ICMP TTL expired messages. If the count of packets originally sent by router is the same as the number of ICMP TTL expired messages then the test is successful. If however the number of ICMP TTL expired messages is less than the count of packets originally sent by the router then the test is unsuccessful proving potential problems with the link. A test probe packet with even initial TTL value will generate a TTL time expired ICMP message on the originating router. A test probe Turaga & Raszuk Expires September 17, 2016 [Page 7] Internet-Draft draft-turaga-mpls-test-labels March 2016 packet with odd initial TTL value will generate a TTL time expired ICMP message on the neighboring router. It is RECOMMENDED that the test probe is sent with even initial TTL value. So, ICMP messages are not traversing the link under test. It is RECOMMENDED that a special payload structure is built for these test probes with sequence numbers. When the TTL expires and an ICMP message is generated, the IP header + 64 bits from original packet gets copied to ICMP message. [ RFC 792 ]. This can be used for associating the ICMP message and the test. 4.2. Comparison with stated test requirements Analysis of the proposed solution against the actual new test methodology requirements: o Provides means to potentially fill up the part of link bandwidth very rapidly because of inherent amplification due to high initial TTL value. The fill level of the test traffic is a function of: Initial packet size (higher the packet size the higher the fill level), Initial TTL value (higher the TTL value, higher the multiplicative factor for packets and hence higher the fill level), Initial number of packets sent (the more the packets sent the more the fill level). o Test can be run together with production traffic. There is no impact on production traffic neither there is any requirement to stop production traffic in order to perform the test. o The amplification of the packets and looping happens as a part of inherent forwarding in the routers. This solution does not require a special process in software or hardware to send the test probes between the two routers. o The link is not required to be taken offline for testing. This testing can co-exist with production traffic. o This mechanism is light-weight and does not require a lot of protocol programming or significant enhancements. 4.3. Probe size and rate calculation Initial packet size and rate are important to determine the test fill level for the link. The test packet loops the same number of times as the original TTL value of the original packet. The time it takes for the original packet to come back to the original router is the RTT (Round Trip Time) value between two routers. Under the assumptions that: RTT of link under test is 1ms, link speed 1 Gb/s, packet size of test packet is 1536 bytes, TTL on original packet is 254, then the test packets would loop on the link for next 254ms. Turaga & Raszuk Expires September 17, 2016 [Page 8] Internet-Draft draft-turaga-mpls-test-labels March 2016 Under the above assumptions it is easy to calculate that in order fill the 1 Gb/s link to 100% 81 such probe packets need to be injected into any link under test. Likewise in order to fill the link to 20% of its capacity 16 probe packets are required. Link Simmering - To be able to set non user impacting graceful link removal from IGP topology and conduct full bandwidth test then return the link to the topology. 5. MPLS Special Purpose Swap-to-Drop and Drop Labels While tests described in the former sections are addressing most of the link health monitoring cases there is additional class of tests which may require quite different data plane pattern characteristics. Specifically there is requirement for injection of large number of full MTU echo probes which will only be able to be received by peer's ingress line card and returned once to the sender without even processing the TTL field. For such purpose this document also defines two additional types of Special Purpose MPLS labels: Swap-to-Drop and Drop Labels. The semantics of Swap-to-Drop label requires the network device which received packets with Swap-to-Drop label to decrement TTL and swap the label with Drop label and return it over the same interface over which it arrived. The semantics of Drop Label means to drop the packet received with such special purpose label while incrementing either global interface drop counters or defining the new counters dedicated to logging the received packets with drop label. Similar to MPLS Special purpose loop label the swap-to-drop as well as drop labels are local to the link. Packets containing such labels should be never switched via a network node. 6. Probe's QOS marking Since injected test packets are regular IP packets encapsulated in MPLS they can be marked with any class of service inserted into EXP field. As a result the test probes similar to actual data will be processed based on the real QoS configuration and will be subject to treatment defined for a given packet class. That allows both prioritization as well as de-prioritization of a given set of test probes. Turaga & Raszuk Expires September 17, 2016 [Page 9] Internet-Draft draft-turaga-mpls-test-labels March 2016 7. Bandwidth Considerations for link under test The payload of the test packets can be of any IP protocols. The link fill levels is also a function of Inter-packet gap of the test and the RTT of that link. Deterministic fill levels can only be derived by accounting for RTT of the link under test. 8. I2RS and YANG modelling It is expected that link testing methodology described in this document will be accessible by I2RS channel as well as YANG models will be defined for both setting and retrieval of the data. 9. IANA Considerations This document requires IANA to define new Special purpose mpls label or extended special purpose MPLS label values subject to WG recommendation. The following special purpose labels are to be allocated: o Local Loop Label o Swap-to-Drop Label o Drop Label 10. Security Considerations While the proposed mechanism does not define any new protocols nor protocol extensions of already existing specifications it does relay on the TTL-expiry notifications. Such notifications must be enabled and must not be limited in any way for the specific class of probe packets. It is highly recommended that test destinations addresses to be not routeable beyond their locally attached devices. 11. Contributors Authors would like to thank Truman Boyes and Leo Pang for their valuable input. 12. Acknowledgments Turaga & Raszuk Expires September 17, 2016 [Page 10] Internet-Draft draft-turaga-mpls-test-labels March 2016 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . 13.2. Informative References [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, September 1981, . [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic Configuration of IPv4 Link-Local Addresses", RFC 3927, DOI 10.17487/RFC3927, May 2005, . [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, . [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, DOI 10.17487/RFC4379, February 2006, . [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, June 2010, . [RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating and Retiring Special-Purpose MPLS Labels", RFC 7274, DOI 10.17487/RFC7274, June 2014, . Authors' Addresses Partha Turaga Bloomberg LP 731 Lexington Ave New York City, NY 10022 USA Email: pturaga@bloomberg.net Turaga & Raszuk Expires September 17, 2016 [Page 11] Internet-Draft draft-turaga-mpls-test-labels March 2016 Robert Raszuk Bloomberg LP 731 Lexington Ave New York City, NY 10022 USA Email: robert@raszuk.net Turaga & Raszuk Expires September 17, 2016 [Page 12]