[bmwg] Initial Reply to Publication Request on igp-dataplane drafts
Al Morton <acmorton@att.com> Fri, 25 May 2007 13:51 UTC
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Date: Fri, 25 May 2007 09:50:00 -0400
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From: Al Morton <acmorton@att.com>
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Subject: [bmwg] Initial Reply to Publication Request on igp-dataplane drafts
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BMWG, Below are Ron Bonica's comments on the terminology draft so far (through section 3.12). We have some work to do to clarify many of the definitions. It's good to have these comments from a fresh perspective -- significant improvements are now possible! Al bmwg co-chair The following are comments on draft-ietf-bmwg-igp-dataplane-conv-term-12. On the whole, this is a very good document. My comments are a bit lawyerish ;-) Please look for the prefix RB>> Ron Network Working Group INTERNET-DRAFT Expires in: August 2007 Intended Status: Informational Scott Poretsky Reef Point Systems Brent Imhoff Juniper Networks February 2007 Terminology for Benchmarking IGP Data Plane Route Convergence <draft-ietf-bmwg-igp-dataplane-conv-term-12.txt> Intellectual Property Rights (IPR) statement: By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. RB> Formatting issue Status of this Memo Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The IETF Trust (2007). ABSTRACT This document describes the terminology for benchmarking Interior Gateway Protocol (IGP) Route Convergence. The terminology is to be used for benchmarking IGP convergence time through externally observable (black box) data plane measurements. The terminology can be applied to any link-state IGP, such as ISIS and OSPF. Poretsky, Imhoff [Page 1] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence Table of Contents 1. Introduction .................................................2 2. Existing definitions .........................................3 3. Term definitions..............................................3 3.1 Convergence Event.........................................3 3.2 Route Convergence.........................................4 3.3 Network Convergence.......................................4 3.4 Full Convergence..........................................5 3.5 Convergence Packet Loss...................................5 3.6 Convergence Event Instant.................................6 3.7 Convergence Recovery Instant..............................6 3.8 Rate-Derived Convergence Time.............................7 3.9 Convergence Event Transition..............................7 3.10 Convergence Recovery Transition..........................8 3.11 Loss-Derived Convergence Time............................8 3.12 Sustained Forwarding Convergence Time....................9 3.13 Restoration Convergence Time.............................9 3.14 Packet Sampling Interval.................................10 3.15 Local Interface..........................................11 3.16 Neighbor Interface.......................................11 3.17 Remote Interface.........................................11 3.18 Preferred Egress Interface...............................12 3.19 Next-Best Egress Interface...............................12 3.20 Stale Forwarding.........................................13 3.21 Nested Convergence Events................................13 4. IANA Considerations...........................................13 5. Security Considerations.......................................14 6. Acknowledgements..............................................14 7. Normative References..........................................14 8. Author's Address..............................................15 1. Introduction This draft describes the terminology for benchmarking Interior Gateway Protocol (IGP) Route Convergence. The motivation and applicability for this benchmarking is provided in [Po07a]. The methodology to be used for this benchmarking is described in [Po07m]. The methodology and terminology to be used for benchmarking Route Convergence can be applied to any link-state IGP such as ISIS [Ca90] and OSPF [Mo98]. The data plane is measured to obtain black-box (externally observable) convergence benchmarking metrics. The purpose of this document is to introduce new terms required to complete execution of the IGP Route Convergence Methodology [Po07m]. These terms apply to IPv4 and IPv6 traffic and IGPs. An example of Route Convergence as observed and measured from the data plane is shown in Figure 1. The graph in Figure 1 shows Forwarding Rate versus Time. Time 0 on the X-axis is on the far right of the graph. The Offered Load to the ingress interface of the DUT SHOULD equal the measured maximum Throughput [Ba99][Ma98] of the DUT and the Forwarding Rate [Ma98] is measured at the egress interfaces of the DUT. The components of the graph and the metrics are defined in the Term Definitions section. Poretsky, Imhoff [Page 2] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence Convergence Convergence Recovery Event Instant Instant Time = 0sec Forwarding Rate = ^ ^ ^ Offered Load = Offered Load --> ------\ Packet /-------- <---Max Throughput \ Loss /<----Convergence Convergence------->\ / Event Transition Recovery Transition \ / \_____/<------Maximum Packet Loss X-axis = Time Y-axis = Forwarding Rate Figure 1. Convergence Graph 2. Existing definitions 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 BCP 14, RFC 2119 [Br97]. RFC 2119 defines the use of these key words to help make the intent of standards track documents as clear as possible. While this document uses these keywords, this document is not a standards track document. The term Throughput is defined in [Ba91] and [Ba99]. 3. Term Definitions 3.1 Convergence Event Definition: The occurrence of a planned or unplanned action in the network that results in a change in the egress interface of the Device Under Test (DUT) for routed packets. Discussion: Convergence Events include link loss, routing protocol session loss, router failure, configuration change, and better next-hop learned via a routing protocol. Measurement Units: N/A Issues: None See Also: Convergence Packet Loss Convergence Event Instant Poretsky, Imhoff [Page 3] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence 3.2 Route Convergence Definition: Recovery from a Convergence Event indicated by the DUT Throughput equal to the offered load. Discussion: Route Convergence is the action of all components of the router being updated with the most recent route change(s) including the Routing Information Base (RIB) and Forwarding Information Base (FIB), along with software and hardware tables. Route Convergence can be observed externally by the rerouting of data Traffic to a new egress interface. Measurement Units: N/A Issues: None See Also: Network Convergence Full Convergence Convergence Event RB> I'm not sure that I understand the difference between route convergence and full convergence. Does route convergence apply to a single route while full convergence applies to the entire FIB? You might want to clarify that. RB> Also, you might want to point out that route convergence isn't always the same as sustained route convergence. RB> Also, your definition of route convergence requires only that the DUT is sending packets *someplace*. There is no requirement that the DUT send the packet to *the right place*. Consider the following problem: RB> Let's say that the DUT has three interfaces, A, B, C. Before the convergence event, traffic enters the DUT through A and leaves through B. But B goes down, causing a transient condition in which the DUT forwards packets right back out through A. During this transient period, packets loop until the TTL expires. (This doesn't help anybody much!) At the end of the transient period, routing converges and the DUT forwards packets out through Interface C, whence they have a fighting chance of delivery. So, when did route convergence occur, at the beginning or the transient period or at the end? According to your definition, it happened at the beginning. 3.3 Network Convergence Definition: The completion of updating of all routing tables, including the FIB, in all routers throughout the network. Discussion: Network Convergence is bounded by the sum of Route Convergence for all routers in the network. Network Convergence can be determined by recovery of the Throughput to equal the offered load, with no Stale Forwarding, and no blenders [Ca01][Ci03]. RB> Above, you defined Route Convergence as "Recovery from a Convergence Event indicated by the DUT Throughput equal to the offered load". This is an event, not a quantity. So, you can't talk about the "the sum of Route Convergence". Measurement Units: N/A Issues: None See Also: Route Convergence Stale Forwarding Poretsky, Imhoff [Page 4] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence 3.4 Full Convergence Definition: Route Convergence for an entire FIB. Discussion: When benchmarking convergence, it is useful to measure the time to converge an entire FIB. For example, a Convergence Event can be produced for an OSPF table of 5000 routes so that the time to converge routes 1 through 5000 is measured. Full Convergence is externally observable from the data plane when the Throughput of the data plane traffic on the Next-Best Egress Interface equals the offered load. Measurement Units: N/A Issues: None See Also: Network Convergence Route Convergence Convergence Event 3.5 Convergence Packet Loss Definition: The amount of packet loss produced by a Convergence Event until Route Convergence occurs. RB> Units of measure? Discussion: Packet loss can be observed as a reduction of forwarded traffic from the maximum Throughput. Convergence Packet Loss includes packets that were lost and packets that were delayed due to buffering. RB> How will you count the packets that were delayed? Timestamping each packet? How much delay will you tolerate before you say that a packet is lost? RB> Isn't this metric influence by the rate at which you send packets into the DUT. If the pause between packets is long enough, you may not observe any loss between the convergence event and sustained route convergence. The maximum Convergence Packet Loss observed in a Packet Sampling Interval may or may not reach 100% during Route Convergence (see Figure 1). Measurement Units: number of packets RB> In 3.11 you say that the unit of measure is packets per second. Which is it? Issues: None See Also: Route Convergence Convergence Event Rate-Derived Convergence Time Loss-Derived Convergence Time Packet Sampling Interval Poretsky, Imhoff [Page 5] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence 3.6 Convergence Event Instant Definition: The time instant that a Convergence Event becomes observable in the data plane. Discussion: Convergence Event Instant is observable from the data plane as the precise time that the device under test begins to exhibit packet loss. Measurement Units: hh:mm:ss:nnn, where 'nnn' is milliseconds Issues: None See Also: Convergence Event Convergence Packet Loss Convergence Recovery Instant 3.7 Convergence Recovery Instant Definition: The time instant that Full Convergence is measured and then maintained for an interval of duration equal to the Sustained Forwarding Convergence Time Discussion: Convergence Recovery Instant is measurable from the data plane as the precise time that the device under test achieves Full Convergence. Measurement Units: hh:mm:ss:uuu Issues: None See Also: Sustained Forwarding Convergence Time Convergence Packet Loss Convergence Event Instant Poretsky, Imhoff [Page 6] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence 3.8 Rate-Derived Convergence Time Definition: The amount of time for Convergence Packet Loss to persist upon occurrence of a Convergence Event until occurrence of Route Convergence. Rate-Derived Convergence Time can be measured as the time difference from the Convergence Event Instant to the Convergence Recovery Instant, as shown with Equation 1. Equation 1 - Rate-Derived Convergence Time = Convergence Recovery Instant - Convergence Event Instant. Discussion: Rate-Derived Convergence Time should be measured at the maximum Throughput. Failure to achieve Full Convergence results in a Rate-Derived Convergence Time benchmark of infinity. Measurement Units: seconds/milliseconds Issues: None See Also: Convergence Packet Loss Convergence Recovery Instant Convergence Event Instant Full Convergence 3.9 Convergence Event Transition Definition: The characteristic of a router in which Throughput gradually reduces to zero after a Convergence Event. RB> Is this a period of time or the characteristic of a router? If it is a characteristic, why does it have units of measure. RB> If it is a period of time, doesn't the packet sampling interval and data rate of the test stream influence it? Discussion: The Convergence Event Transition is best observed for Full Convergence. The Convergence Event Transition may not be linear. Measurement Units: seconds/milliseconds Issues: None See Also: Convergence Event Rate-Derived Convergence Time Convergence Packet Loss Convergence Recovery Transition Poretsky, Imhoff [Page 7] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence 3.10 Convergence Recovery Transition Definition: The characteristic of a router in which Throughput gradually increases to equal the offered load. RB> Same comments as above. Discussion: The Convergence Recovery Transition is best observed for Full Convergence. The Convergence Event Transition may not be linear. Measurement Units: seconds/milliseconds Issues: None See Also: Full Convergence Rate-Derived Convergence Time Convergence Packet Loss Convergence Event Transition 3.11 Loss-Derived Convergence Time Definition: The amount of time it takes for Route Convergence to to be achieved as calculated from the Convergence Packet Loss. Loss-Derived Convergence Time can be calculated from Convergence Packet Loss that occurs due to a Convergence Event and Route Convergence as shown with Equation 2. Equation 2 - Loss-Derived Convergence Time = Convergence Packets Loss / Offered Load NOTE: Units for this measurement are packets / packets/second = seconds Discussion: Loss-Derived Convergence Time gives a better than actual result when converging many routes simultaneously. Rate-Derived Convergence Time takes the Convergence Recovery Transition into account, but Loss-Derived Convergence Time ignores the Route Convergence Recovery Transition because it is obtained from the measured Convergence Packet Loss. Ideally, the Convergence Event Transition and Convergence Recovery Transition are instantaneous so that the Rate-Derived Convergence Time = Loss-Derived Convergence Time. However, router implementations are less than ideal. For these reasons the preferred reporting benchmark for IGP Route Convergence is the Rate-Derived Convergence Time. Poretsky, Imhoff [Page 8] INTERNET-DRAFT Benchmarking Terminology for February 2007 IGP Data Plane Route Convergence Guidelines for reporting Loss-Derived Convergence Time are provided in [Po07m]. Measurement Units: seconds/milliseconds Issues: None See Also: Route Convergence Convergence Packet Loss Rate-Derived Convergence Time Convergence Event Transition Convergence Recovery Transition 3.12 Sustained Forwarding Convergence Time Definition: The amount of time for which Full Convergence is maintained without additional packet loss. Discussion: The purpose of the Sustained Forwarding Convergence Time is to produce Convergence benchmarks protected against fluctuation in Throughput after Full Convergence is observed. The Sustained Forwarding Convergence Time to be used is calculated as shown in Equation 3. Equation 3 - Sustained Forwarding Convergence Time = 5*(Convergence Packet Loss/Offered Load) units are packets/pps = sec RB> Not sure that I understand where the constant 5 came from. for which at least one packet per route in the FIB for all routes in the FIB MUST be offered to the DUT per second. Measurement Units: seconds or milliseconds Issues: None See Also: Full Convergence Convergence Recovery Instant _______________________________________________ bmwg mailing list bmwg@ietf.org https://www1.ietf.org/mailman/listinfo/bmwg