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Network Working Group                                        N. BrownleeRequest for Comments: 2721                    The University of AucklandCategory: Informational                                     October 1999RTFM: Applicability StatementStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1999).  All Rights Reserved.Abstract   This document provides an overview covering all aspects of Realtime   Traffic Flow Measurement, including its area of applicability and its   limitations.Table of Contents1  The RTFM Documents . . . . . . . . . . . . . . . . . . . . . .22  Brief Technical Specification (TS) . . . . . . . . . . . . . .33  Applicability Statement (AS) . . . . . . . . . . . . . . . . .34  Limitations  . . . . . . . . . . . . . . . . . . . . . . . . .45  Security Considerations  . . . . . . . . . . . . . . . . . . .56  Policy Considerations  . . . . . . . . . . . . . . . . . . . .67  Soundness  . . . . . . . . . . . . . . . . . . . . . . . . . .68Appendix A: WG Report on the Meter MIB . . . . . . . . . . . .89  References . . . . . . . . . . . . . . . . . . . . . . . . . .910 Author's Address . . . . . . . . . . . . . . . . . . . . . . .911 Full Copyright Statement . . . . . . . . . . . . . . . . . . .10Brownlee                     Informational                      [Page 1]

RFC 2721             RTFM: Applicability Statement          October 19991  The RTFM Documents   The RTFM Traffic Measurement System has been developed by the   Realtime Traffic Flow Measurement Working Group.  It is described in   six other documents, as follows:   [ACT-BKG] Internet Accounting: Background             (Informational)      Sets out the requirements for a usage reporting system for network      traffic.  Sketches out the RTFM Architecture (meters, meter      readers and managers) allowing for multiple meters and meter      readers, with asynchronous reading from the meters.  Proposes      methods of classifying traffic flows, the need for flows to be      bi-directional (with separate sets of counters for each direction)      and the need for each packet to be counted in a single flow (the '      count in one bucket' principle).   [RTFM-ARC] RTFM Architecture                          (Informational)      Defines the RTFM Architecture, giving descriptions of each      component.  Explains how traffic flows are viewed as logical      entities described in terms of their address-attribute values, so      that each is defined by the attributes of its end-points.  Gives a      detailed description of the RTFM traffic meter, with full details      of how flows are stored in the meter's flow table, and how packets      are matched in accordance with rules stored in a ruleset.   [RTFM-MIB] RTFM Meter MIB                         (Proposed Standard)      Describes the SNMP Management Information Base for an RTFM meter,      including its flow table, rule table (storing the meter's      rulesets) and the control tables used for managing a meter and      reading flow data from it.   [RTFM-SRL] SRL: A Language for Describing Traffic     (Informational)              Flows and Specifying Actions for Flow Groups      An RTFM ruleset is an array of rules, used by the meter to decide      which flows are of interest, which end-point is the flow source,      and how much detail (i.e. what attribute values) must be saved for      each flow.  SRL is a high-level language providing a clear,      logical way to write rulesets.  It should also be useful for other      applications which select flows and perform actions upon them,      e.g. packet-marking gateways, RSVP policy agents, etc.Brownlee                     Informational                      [Page 2]

RFC 2721             RTFM: Applicability Statement          October 1999   [RTFM-NEW] RTFM New Attributes                         (Experimental)      There has been considerable interest from users in extending the      RTFM Architecture so as to allow a meter to report on an increased      number of flow-related measures.  This RFC documents work on      specifying such measures (the 'new' attributes) and reports on      experience of implementing them.   [RTFM-NTM] RTFM: Experiences with NeTraMet            (Informational)      NeTraMet is a free software implementation of the RTFM      Architecture which has been available since 1993.  This RFC      records RTFM implementation experience gained with NeTraMet up to      late 1996.  One particularly important result is the realisation      that groups of rules which test the same attribute using the same      mask can be implemented as a single hashed comparison, allowing      the meter to rapidly determine whether a packet belongs to one of      a large number of networks.2  Brief Technical Specification (TS)   RTFM provides for the measurement of network traffic 'flows', i.e.   - a method of specifying traffic flows within a network   - a hierarchy of devices (meters, meter readers, managers) for     measuring the specified flows   - a mechanism for configuring meters and meter readers, and for     collecting the flow data from remote meters   RTFM provides high time resolution for flow first- and last-packet   times.  Counters for long-duration flows may be read at intervals   determined by a manager.  The RTFM Meter is designed so as to do as   much data reduction work as possible, which minimizes the amount of   data to be read and the amount of processing needed to produce useful   reports from it.   RTFM flow data can be used for a wide range of purposes, such as   usage accounting, long-term recording of network usage (classified by   IP address attributes) and real-time analysis of traffic flows at   remote metering points.3  Applicability Statement (AS)   To use RTFM for collecting network traffic information one must first   consider where in the network traffic flows are to be measured.  Once   that is decided, an RTFM Meter must be installed at each chosen   measurement point.Brownlee                     Informational                      [Page 3]

RFC 2721             RTFM: Applicability Statement          October 1999   At least one Meter Reader is needed to collect the measured data from   the meters, and a single Manager is needed to control the meters and   meter readers.   RTFM Meters may be single- or multi-user hosts running a meter   program (one such program is available as free software, a second is   under development at IBM Research).  Alternatively, meters could be   run as firmware in switches or routers.  A hybrid approach in which   an RTFM meter takes raw traffic data from a router provides another   useful implementation path.   RTFM Managers are programs running on a host, communicating with   meters and meter readers via the network.  For this purpose meters   are SNMP agents implementing the RTFM Meter MIB, and managers are   SNMP clients using the Meter MIB to store and access the flow data.4  Limitations   RTFM is designed to measure traffic flows for traffic passing a point   in a network.  If packets for a flow pass the metering point in both   directions the meter will match them up, providing counters for each   direction.  If packets only pass in one direction the meter can only   provide counts for that direction.   Users of RTFM should note that installing meters, meter readers and   managers merely provides one with the capability to collect flow   data.  Further installation work will be needed to develop   configuration files (RTFM rulesets) for each meter, data processing   applications to analyse the flow data, and various scripts, cron   jobs, etc.  so as to create a useful production-quality measurement   system which suits a user's particular needs.   One of the strengths of RTFM is its ability to collect flow data at   whatever level of detail (or 'granularity') is required.  It can be   tempting to simply collect 'all possible data', but there are severe   resource constraints.  If one tries to save the complete address-   attribute value for all attributes of every possible flow a very   large amount of data may be produced rapidly, but the meter has only   a finite amount of memory for its flow table.  A better approach is   to save the minimum amount of data required to achieve the   measurement system goals.   For example, to collect usage data so as to bill subscribers   identified by their IP address one could just save the full IP   address, nothing more.  The RTFM meter would produce flow data for   each subscriber IP address, with PDU and Octet counts for data sent   and received, which would be the minimum needed to produce bills.  In   practice one would probably want to save at least part of theBrownlee                     Informational                      [Page 4]

RFC 2721             RTFM: Applicability Statement          October 1999   Destination IP address, which would allow the production of usage   logs showing subscriber activity over time.   The simplest way to determine how much detail can be collected is to   create an initial ruleset which collects the minimum amount, then to   modify it step by step, gradually increasing the amount of   information saved for each flow.  An RTFM meter ought to provide some   measures of its own performance (e.g. number of active flows,   percentage idle processor time, packets metered, packets not   metered).  Such measures will be implementation-specific, but should   allow a user to assess the impact of each change to the ruleset.   If the network data rate is too high, i.e. the meter reports that it   cannot meter all the packets even with the initial ruleset above, one   may be able to use other strategies.  For example one could   - run the meter on a faster computer, e.g. move from a DOS PC to a     workstation, or perhaps use a meter implemented in firmware within     a switch or router.   - use sampling.  The details of such sampling are not defined within     the RTFM Architecture, but the Meter MIB provides one simple method     by allowing one to specify that only every nth packet on an     interface will be metered.   This would probably not be acceptable     for producing billing data, but might well be acceptable for     traffic engineering purposes.5  Security Considerations   These are discussed in detail in the Architecture and Meter MIB   documents.  In brief, an RTFM Meter is an SNMP agent which observes a   network and collects flow data from it.  Since it doesn't control the   network directly, it has no direct effect on network security.   On the other hand, the flow data itself may well be valuable - to the   network operator (as billing data) or to an attacker (who may wish to   modify that data, or the meter's ruleset(s)).  It is therefore   important to take proper precautions to ensure that access to the   meter and its data is sufficiently secure.   For example, a meter port attached to a network should be passive, so   that it cannot respond to login attempts of any kind.  Control and   data connections to a meter should be via a secure management   network.  Finally, suitable security should be established for the   meter, as it would be for any other SNMP agent.Brownlee                     Informational                      [Page 5]

RFC 2721             RTFM: Applicability Statement          October 1999   Meters may, like any other network component, be subjected to Denial   of Service and other attacks.  These are outside the RTFM   Architecture - countermeasures for them are available, but are also   outside RTFM.6  Policy Considerations   When collecting traffic data, one must have well-defined operations   policies covering points such as:   - Exactly what data is to be collected, at what level of detail?   - How long will the data be kept?   - What may the data be used for?   - Who will be allowed to see the raw data?   - May summaries of the data be shown to other people?   Policy issues such as these should normally be considered as part of   an organisation's Network Security Policy.   Other policy issues relating more directly to the traffic data are   essentially part of the measurement system design, such as:   - How much time resolution is required for the data?     (Less resolution implies longer collection intervals, but that may     require more memory in the meters to hold flow data between     collections).   - What level of hardware redundancy is needed?     (A single meter and meter reader is generally enough.  For greater     reliability, meters and meter readers can be duplicated).   - Who is allowed to use the system?     (Approved users will need permissions to download rulesets to the     meters, and to collect their data, possibly via their own meter     readers).7  Soundness   NeTraMet, the first implementation of the RTFM Architecture, has been   in use worldwide since 1994.  Currently there are many organisations,   large and small, using it to collect traffic data for billing   purposes.   One example of these is Kawaihiko, the New Zealand Universities'   Network, which has seven RTFM meters located at sites throughout New   Zealand.  One of the sites is NZIX, the New Zealand Internet eXchange   at the University of Waikato, where Kawaihiko has a meter (attached   to a 100baseT network) observing traffic flows across the exchange toBrownlee                     Informational                      [Page 6]

RFC 2721             RTFM: Applicability Statement          October 1999   each of Kawaihiko's three international Internet Service Providers.   5-minute Octet counts are collected from all the Kawaihiko meters by   a single meter reader at Auckland.  Traffic data from the meters is   used to determine the cost per month for each of the Kawaihiko sites.   It is difficult to estimate how many organisations are using RTFM   traffic measurement.  There are about 250 people on the NeTraMet   mailing list, which often carries questions like 'why doesn't this   ruleset do what I meant'?  Once new users have the system running,   however, they tend to simply use it without further comment.   From time to time the list provides useful feedback.  For example,   early in 1998 there were two very significant user contributions:   - Jacek Kowalski (Telstra, Melbourne) described an improved hash     algorithm for NeTraMet's flow table, which provided almost an order     of magnitude improvement in packet-handling performance.   - Kevin Hoadley (JANET, U.K.) reported having problems with very     large rulesets.  These were resolved, and better methods of     downloading rules developed, allowing NeTraMet to work well for     rulesets with more than 32,000 rules.   Perhaps one reason why there is little discussion of NeTraMet's use   in collecting billing data is that users may consider that the way   collect their data is a commercially sensitive matter.Brownlee                     Informational                      [Page 7]

RFC 2721             RTFM: Applicability Statement          October 19998Appendix A: WG Report on the Meter MIB   The Meter MIB (in its current form) was developed early in 1996.  It   was produced as an SNMPv2 MIB, following a number of detailed (and   continuing) discussions with David Perkins beginning at the Dallas   IETF meeting in December 1995.   There are two current implementations:   - NeTraMet (Nevil Brownlee, The University of Auckland)   - IBM Meter (Sig Handelman & Stephen Stibler, IBM Research, N.Y, Bert     Wijnen provided further help with SNMP)   The NeTraMet meter is a stand-alone SNMP agent using an SNMPv2C   implementation derived from CMU SNMPv2.   The IBM meter runs as a sub-agent on an AIX system.  All the meter   code has been written by Stephen Stibler - it was not derived from   the NeTraMet code.  Stephen has found it useful to use nifty, one of   NeTraMet's manager/reader programs, to test the IBM meter.   As indicated above, there have only been two implementors to date,   and the Working Group consensus has been very strong.   The MIB has one unusual aspect:  the method used to read large   amounts of data from its Flow Table.  An earlier SNMPv1 version of   the MIB was in use from 1992 to 1997; it used opaque objects to read   column slices from the flow table for flows which had been active   since a specified time.  This was very non-standard (or at least very   application-specific).   With the change to SNMPv2 we were able to use 64-bit counters for   PDUs and Octets, RowStatus variables for control tables and GETBULK   requests to read rows from the flow table.  We also use the   TimeFilter convention from the RMON2 MIB to select flows to be read;   this gives the meter MIB a strong resemblance to RMON2.   The current MIB introduces a better way of reading large amounts of   data from the flow table.  This is the 'DataPackage' convention,   which specifies the attribute values to be read from a flow table   row.  The meter returns the values for each required attribute within   a BER-encoded sequence.  This means there is only one object   identifier for the whole sequence, greatly reducing the number of   bytes required to retrieve the data.  The combination ofBrownlee                     Informational                      [Page 8]

RFC 2721             RTFM: Applicability Statement          October 1999   TimeFilter:  to select the flows to be read   DataPackage: to select the attributes required for each flow   GetBulk:     to read many flows with a single SNMP PDU   provides a very effective way to read flow data from a traffic meter.9  References   [ACT-BKG]  Mills, C., Hirsch, G. and G. Ruth, "Internet Accounting              Background",RFC 1272, November 1991.   [RTFM-ARC] Brownlee, N., Mills, C. and G. Ruth, "Traffic Flow              Measurement: Architecture",RFC 2722, October 1999.   [RTFM-MIB] Brownlee, N., "Traffic Flow Measurement: Meter MIB",RFC2720, October 1999.   [RTFM-NEW] Handelman, S., Stibler, S., Brownlee, N. and G. Ruth,              "RTFM: New Attributes for Traffic Flow Measurement",RFC2724, October 1999.   [RTFM-NTM] Brownlee, N., "Traffic Flow Measurement: Experiences with              NeTraMet",RFC 2123, March 1997.   [RTFM-SRL] Brownlee, N., "SRL: A Language for Describing Traffic              Flows and Specifying Actions for Flow Groups",RFC 2723,              October 1999.10  Author's Address   Nevil Brownlee   Information Technology Systems & Services   The University of Auckland   Private Bag 92-019   Auckland, New Zealand   Phone: +64 9 373 7599 x8941   EMail: n.brownlee@auckland.ac.nzBrownlee                     Informational                      [Page 9]

RFC 2721             RTFM: Applicability Statement          October 199911  Full Copyright Statement   Copyright (C) The Internet Society (1999).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Brownlee                     Informational                     [Page 10]