Network Working Group                                     Vishwas Manral
Internet Draft                                         Netplane Networks
                                                              Russ White
Expiration Date: June 2002                                 Cisco Systems
File Name: draft-manral-ospfconv-term-00.txt               December 2001

               OSPF Benchmarking Terminology and Concepts
                   draft-manral-ospfconv-term-00.txt


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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
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   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.


2. Abstract

   This draft explains the terminology and concepts used in [2] and
   future OSPF benchmarking drafts.















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3. Conventions used in this document

   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 [1].


4. Motivation

   This draft is a companion to [2], which describes basic Open Shortest
   Path First (OSPF [3]) testing methods. This draft explains
   terminology and concepts used in OSPF Testing Framework Drafts, such
   as [2].


5. Definitions


   o    Internal Measurements


         -    Definition

              Internal measurements are measurements taken on the Device
              Under Test (DUT) itself.


         -    Discussion

              These measurement rely on output and event recording,
              along with the clocking and timestamping available on the
              DUT itself. Internal measurements are preferred for all
              tests that can be completely contained on the DUT (which
              is very rare).


      o    External Measurements


         -    Definition

              External measurements infer the performance of the DUT
              through observation of its communications with other dev-
              ices.


         -    Discussion




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              One example of an external measurement is when a down-
              stream device receives complete routing information from
              the DUT, it can be inferred that the DUT has transmitted
              all the routing information available.

              For the purposes of this paper, external technique are
              more readily applicable. However, external measurements
              have their own problems because they include the time to
              advertise the new route downstream and transmission times
              for the advertisement within the device under test.


      o    Multi-device Measurements


         -    Definition

              Multi-device measurements require the measurement of
              events occuring on multiple devices within the testbed.


         -    Discussion

              For instance, the timestamp on a device generating an
              event could be used as the marker for the beginning of a
              test, while the timestamp on the DUT or some other device
              might be used to determine when the DUT has finished pro-
              cessing the event.

              These sorts of measurements are the most problematic, and
              are to be avoided where possible, since the timestamps of
              the devices in the test bed must be synchronized within
              milliseconds for the test results to be meaningful. Given
              the state of network time protocol implementation, expect-
              ing the timestamps on several devices to be within mil-
              liseconds of each other is highly optimistic.


      o    Point-to-Point links


         -    Definition

              A network that joins a single pair of routers is called a
              point-to-point link. For OSPF [3], point-to-point links
              are those on which a designated router are not elected.





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         -    Discussion

              A point-to-point link will take lesser time to converge
              than a braodcast link of the same speed because it does
              not have the overhead of DR election. Point-to-point links
              can be either numbered or unnumbered. However in the con-
              text of [2], the two can be regarded the same.


      o    Broadcast Link


         -    Definition

              Networks supporting many (more than two) attached routers,
              together with the capability to address a single physical
              message to all of the attached routers (broadcast). In the
              context of [2] and [3], broadcast links are taken as those
              on which a designated router is elected.


         -    Discussion

              The adjacency formation time on a broadcast link can be
              more than that on a point-to-point link of the same speed,
              because DR election has to take place. All routers on a
              broadcast network form adjacency with the DR and BDR.

              Async flooding also takes place thru the DR. In context of
              convergence, it may take more time for an LSU to be
              flooded from one DR-other router to another DR-other
              router, because the LSA has to be first processsed at the
              DR.


      o    Shortest Path First Time


         -    Definition

              The time taken by a router to complete the SPF process.


         -    Discussion

              This does not include the time taken by the router to give
              routes to the forwarding engine.




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         o    Measurement Units

              The LSA time is generally measured in milliseconds.


      o    Hello Interval


         -    Definition

              The length of time, in seconds, between the Hello Packets
              that the router sends on the interface.


         -    Discussion

              The hello interval should be the same for all routers on
              the network

              Decreasing the hello interval can allow the router dead
              interval (below) to be reduced, thus reducing convergence
              times in those situations where the router dead interval
              timing out causes an OSPF process to notice an adjacency
              failure. Very small router dead intervals accompanied by
              very small hello intervals can produce more problems than
              they resolve, as described in [4] & [5].


      o    Router Dead interval


         -    Definition

              After ceasing to hear a router's Hello Packets, the number
              of seconds before its neighbors declare the router down.


         -    Discussion

              This is advertised in the router's Hello Packets in the
              RouterDeadInterval field. The router dead interval should
              be some multiple of the HelloInterval (say 4 times the
              hello interval), and must be the same for all routers
              attached to a common network.







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6. Concepts


6.1.  A network is termed to be converged when all of the devices within
   the network have a loop free path to each possible destination. Since
   we are not testing network convergence, but performance for a partic-
   ular device within a network, however, this definition needs to be
   narrowed somewhat to fit within a single device view.

   In this case, convergence will mean the point in time when the DUT
   has performed all actions needed to react to the change in topology
   represented by the test condition; for instance, an OSPF device must
   flood any new information it has received, rebuild its shortest path
   first (SPF) tree, and install any new paths or destinations in the
   local routing information base (RIB, or routing table).


6.2. Measuring Convergence

   Obviously, there are several elements to convergence, even under the
   definition given above for a single device. We will try to provide
   tests to measure each of these:


      o    The time it takes for the DUT to pass the information about a
           network event on to its neighbors.


      o    The time it takes for the DUT to process information about a
           network event and calculate a new Shortest Path Tree (SPT).


      o    The time it takes for the DUT to make changes in its local
           rib reflecting the new shortest path tree.


6.3. Types of Network Events


      o    Link or Neighbor Device Up

           The time needed for an OSPF implementation to recoginize a
           new link coming up on the device, build any necessarily adja-
           cencies, synchronize its database, and perform all other
           needed actions to converge.


      o    Initialization



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           The time needed for an OSPF implemention to be initialized,
           recognize any links across which OSPF must run, build any
           needed adjacencies, synchronize its database, and perform
           other actions needed to converge.


      o    Adjacency Down

           The time needed for an OSPF implementation to recognize a
           link down/adjacency loss based on hello timers alone, propo-
           gate any information as necessary to its remaining adjacen-
           cies, and perform other actions needed to converge.


      o    Link Down

           The time needed for an OSPF implementation to recognize a
           link down based on layer 2 provided information, propogate
           any information information as needed to its remaining adja-
           cencies, and perform other actions needed to converge.


6.4. LSA and Destination mix

   In many OSPF benchmark tests, a generator injecting a number of LSAs
   is called for. There are several areas in which injected LSAs can be
   varied in testing:


      o    The number of destinations represented by the injected LSAs

           Each destination represents a single reachable IP network;
           these will be leaf nodes on the shortest path tree. The pri-
           mary impact to performance should be the time required to
           insert destinations in the local routing table and handling
           the memory required to store the data.


      o    The types of LSAs injected

           There are several types of LSAs which would be acceptable
           under different situations; within an area, for instance,
           type 1, 2, 3, 4, and 5 are likely to be received by a router.
           Within a not-so-stubby area, however, type 7 LSAs would
           replace the type 5 LSAs received. These sorts of characteri-
           zations are important to note in any test results.





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      o    The Number of LSAs injected

           Within any injected set of information, the number of each
           type of LSA injected is also important. This will impact the
           shortest path algorithms ability to handle large numbers of
           nodes, large shortest path first trees, etc.


      o    The Order of LSA Injection

           The order in which LSAs are injected should not favor any
           given data structure used for storing the LSA database on the
           device under test. The ordering can be changed in various
           tests to provide insight on the efficency of storage within
           the DUT. Any such changes in ordering should be noted in test
           results.


6.5. Tree Shape and the SPF Algorithm

   The shortest path first algorithm is a simple algorithm which handles
   complexity by breaking the problem of finding the shortest paths
   through a network into smaller parts and recursing (calling itself)
   to compute the best path within each smaller part. Because of this,
   moving along a single level of the tree, along the tree's width, is
   fundamentally different than moving along the depth of the tree.

               root        root
              /    \        |
             1      2       1
            / \    / \      |
           3   4  5   6     2
                            |
                            3
                            |
                            4
                            |
                            5
                            |
                            6

   For instance, the shortest path first algorithm would go through two
   recursions when finding the shortest paths on the left topology, with
   an average of two nodes processed per level. The topology on the
   right would produce five recursions, with one node processed per
   recursion.  While this may not produce dramatically different test
   results, there may be some apparent difference between the two.




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   In general, those benchmarking link state protocols which use the
   shortest path first algorithm to compute the best paths through the
   network need to be aware that the construction of the tree may impact
   the performance of the algorithm. Best practice would be to try and
   make any emulated network look as much like a real network as possi-
   ble, especially in the area of the tree depth, the meshiness of the
   network, the number of stub links verses transit links, and the
   number of connections and nodes to process at each recursion level.


7. Route Generation

   As the size of networks grows, it becomes more and more difficult to
   actually create a large scale network on which to test the properties
   of routing protocols and their implementations. In general, network
   emulators are used to provide emulated topologues which can be adver-
   tised to a device with varying conditions. Route generators either
   tend to be a specialized device, a piece of software which runs on a
   router, or a process that runs on another operating system, such as
   Linux or another variant of Unix.

   Some of the characteristics of this device should be:


 o    The ability to connect to the several devices using both point-
      to-point and broadcast high speed media. Point-to-point links can
      be emulated with high speed Ethernet as long as there is no hub or
      other device in between the DUT and the route generator, and the
      link is configured as a point-to-point link within OSPF.


 o    The ability to create a set of LSAs which appear to be a logical,
      realistic topology. For instance, the generator should be able to
      mix the number of point-to-point and broadcast links within the
      emulated topology, and should be able to inject varying numbers of
      externally reachable destinations.


 o    The ability to withdraw and add routing information into and from
      the emulated topology to emulate links flapping.


 o    The ability to randomly order the LSAs representing the emulated
      topology as they are advertised.


 o    The ability to log or otherwise measure the time between packets
      transmitted and received.



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 o    The ability to change the rate at which OSPF LSAs are transmitted.


8. Acknowedgements

   The authors would like to thank Aman Shaikh
   (ashaikh@research.att.com) for his comments and help on this draft.


9. References

[1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", RFC2119, March 1997.


[2]  Manral, V., "Benchmarking Methodology for Basic OSPF Convergence",
     draft-manral-ospconv-intraarea-00, November 2001


[3]  Moy, J., "OSPF Version 2", RFC 2328, April 1998.


[4]  draft-ash-ospf-isis-congestion-control-01.txt


[5]  draft-ietf-ospf-scalability-00.txt


10. Authors' Addresses

      Vishwas Manral,
      Netplane Networks,
      189 Prashasan Nagar,
      Road number 72,
      Jubilee Hills,
      Hyderabad.

      vmanral@netplane.com

      Russ White
      Cisco Systems, Inc.
      7025 Kit Creek Rd.
      Research Triangle Park, NC 27709

      riw@cisco.com






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