RFC3535
Network Working Group J. Schoenwaelder Request for Comments: 3535 International University Bremen Category: Informational May 2003
Overview of the 2002 IAB Network Management Workshop
Status 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 (2003). All Rights Reserved.
Abstract
This document provides an overview of a workshop held by the Internet Architecture Board (IAB) on Network Management. The workshop was hosted by CNRI in Reston, VA, USA on June 4 thru June 6, 2002. The goal of the workshop was to continue the important dialog started between network operators and protocol developers, and to guide the IETFs focus on future work regarding network management. This report summarizes the discussions and lists the conclusions and recommendations to the Internet Engineering Task Force (IETF) community.
Contents
Introduction
The IETF has started several activities in the operations and management area to develop technologies and standards that aim to help network operators manage their networks. The main network management technologies currently being developed within the IETF are:
o The Simple Network Management Protocol (SNMP) RFC3410 was
created in the late 1980s. The initial version (SNMPv1) is widely deployed, while the latest version (SNMPv3), which addresses security requirements, is just beginning to gain significant deployment.
o The Common Information Model (CIM) [CIM], developed by the
Distributed Management Task Force (DMTF), has been extended in cooperation with the DMTF to describe high-level policies as rule sets (PCIM) RFC3060. Mappings of the CIM policy extensions to LDAP schemas have been defined and work continues to define specific schema extension for QoS and security policies.
o The Common Open Policy Service (COPS) RFC2748 protocol has been
extended to provision configuration information on devices (COPS- PR) RFC3084. Work is underway to define data definitions for specific services such as Differentiated Services (DiffServ).
During 2001, several meetings have been organized at various events (NANOG-22 May 2001, RIPE-40 October 2001, LISA-XV December 2001, IETF-52 December 2001) to start a direct dialog between network operators and protocol developers. During these meetings, several operators have expressed their opinion that the developments in the IETF do not really address their requirements, especially for configuration management. This naturally leads to the question of whether the IETF should refocus resources, and which strategic future activities in the operations and management area should be started.
The Internet Architecture Board (IAB), on June 4 thru June 6, 2002, held an invitational workshop on network management. The goal of the workshop was to continue the important dialog started between network operators and protocol developers, and to guide the IETFs focus on future work regarding network management.
The workshop started with two breakout session to (a) identify a list of technologies relevant for network management together with their strengths and weaknesses, and to (b) identify the most important operator needs. The results of these discussions are documented in Section 2 and Section 3. During the following discussions, many more specific characteristics of the current SNMP framework were identified. These discussions are documented in Section 4. Section 5 defines a combined feature list that was developed during the discussions following the breakout sessions. Section 6 gives concrete recommendations to the IETF.
The following text makes no explicit distinction between different versions of SNMP. For the majority of the SNMP related statements, the protocol version is irrelevant. Nevertheless, some statements are more applicable to SNMPv1/SNMPv2c environments, while other statements (especially those concerned with security) are more applicable to SNMPv3 environments.
Network Management Technologies
During the breakout sessions, the protocol developers assembled a list of the various network management technologies that are available or under active development. For each technology, a list of strong (+) and weak (-) points were identified. There are also some characteristics which appear to be neutral (o).
The list does not attempt to be complete. Focus was given to IETF specific technologies (SNMP, COPS-PR, PCIM) and widely used proprietary technologies (CLI, HTTP/HTML, XML). The existence of other generic management technologies (such as TL1, CORBA, CMIP/GDMO,
TMN) or specific management technologies for specific problem domains (such as RADIUS, DHCP, BGP, OSPF) were acknowledged, but were not the focus of discussion.
SNMP / SMI / MIBs
The SNMP management technology was created in the late 1980s and has since been widely implemented and deployed in the Internet. There is lots of implementational and operational experience, and the characteristics of the technology are thus well understood.
+ SNMP works reasonably well for device monitoring. The stateless
nature of SNMP is useful for statistical and status polling.
+ SNMP is widely deployed for basic monitoring. Some core MIB
modules, such as the IF-MIB RFC2863, are implemented on most networking devices.
+ There are many well defined proprietary MIB modules developed by
network device vendors to support their management products.
+ SNMP is an important data source for systems that do event
correlation, alarm detection, and root cause analysis.
o SNMP requires applications to be useful. SNMP was, from its early
days, designed as a programmatic interface between management applications and devices. As such, using SNMP without management applications or smart tools appears to be more complicated.
o Standardized MIB modules often lack writable MIB objects which can
be used for configuration, and this leads to a situation where the interesting writable objects exist in proprietary MIB modules.
- There are scaling problems with regard to the number of objects in
a device. While SNMP provides reasonable performance for the retrieval of a small amount of data from many devices, it becomes rather slow when retrieving large amounts of data (such as routing tables) from a few devices.
- There is too little deployment of writable MIB modules. While
there are some notable exceptions in areas, such as cable modems where writable MIB modules are essential, it appears that router equipment is usually not fully configurable via SNMP.
- The SNMP transactional model and the protocol constraints make it
more complex to implement MIBs, as compared to the implementation of commands of a command line interface interpreter. A logical operation on a MIB can turn into a sequence of SNMP interactions
where the implementation has to maintain state until the operation is complete, or until a failure has been determined. In case of a failure, a robust implementation must be smart enough to roll the device back into a consistent state.
- SNMP does not support easy retrieval and playback of
configurations. One part of the problem is that it is not easy to identify configuration objects. Another part of the problem is that the naming system is very specific and physical device reconfigurations can thus break the capability to play back a previous configuration.
- There is often a semantic mismatch between the task-oriented view
of the world usually preferred by operators and the data-centric view of the world provided by SNMP. Mapping from a task-oriented view to the data-centric view often requires some non-trivial code on the management application side.
- Several standardized MIB modules lack a description of high-level
procedures. It is often not obvious from reading the MIB modules how certain high-level tasks are accomplished, which leads to several different ways to achieve the same goal, which increases costs and hinders interoperability.
A more detailed discussion about the SNMP management technology can be found in Section 4.
COPS-PR / SPPI / PIBs
The COPS protocol RFC2748 was defined in the late 1990s to support policy control over QoS signaling protocols. The COPS-PR extension allows provision policy information on devises.
+ COPS-PR allows high-level transactions for single devices,
including deleting one configuration and replacing it with another.
+ COPS-PRs non-overlapping instance namespace normally ensures that
no other manager can corrupt a specific configuration. All transactions for a given instance namespace are required to be executed in-order.
+ Both manager and device states are completely synchronized with
one another at all times. If there is a failure in communication, the state is resynchronized when the network is operating properly again and the device's network configuration is valid.
+ The atomicity of transactions is well-defined. If there is any
failure in a transaction, that specific failure is reported to the manager, and the local configuration is supposed to be automatically rolled-back to the state of the last "good" transaction.
+ Capability reporting is part of the framework PIB which must be
supported by COPS-PR implementations. This allows management applications to adapt to the capabilities present on a device.
+ The focus of COPS-PR is configuration, and the protocol has been
optimized for this purpose (by using for example TCP as a transport mechanism).
o Only a single manager is allowed to have control, at any point in
time, for a given subject category on a device. (The subject category maps to a COPS Client-Type.) This single manager assumption simplifies the protocol as it makes it easier to maintain shared state.
o Similar to SNMP, COPS-PR requires applications to be useful since
it is also designed as a programmatic interface between management applications and devices.
- As of the time of the meeting, there are no standardized PIB
modules.
- Compared to SNMP, there is not yet enough experience to understand
the strong and weak aspects of the protocol in operational environments.
- COPS-PR does not support easy retrieval and playback of
configurations. The reasons are similar as for SNMP.
- The COPS-PR view of the world is data-centric, similar to SNMP's
view of the world. A mapping from the data-centric view to a task-oriented view and vice versa, has similar complexities as with SNMP.
CIM / MOF / UML / PCIM
The development of the Common Information Model (CIM) [CIM] started in the DMTF in the mid 1990s. The development follows a top-down approach where core classes are defined first and later extended to model specific services. The DMTF and the IETF jointly developed policy extensions of the CIM, known as PCIM RFC3060.
+ The CIM technology generally follows principles of object-
orientation with full support of methods on data objects, which is not available in SNMP or COPS-PR.
+ The MOF format allows representation of instances in a common
format. No such common format exists for SNMP or COPS-PR. It is of course possible to store instances in the form of BER encoded ASN.1 sequences, but this is generally not suitable for human readability.
+ There is support for a query facility which allows the locating of
CIM objects. However, the query language itself is not yet specified as part of the CIM standards. Implementations currently use proprietary query languages, such as the Windows Management Instrumentation Query Language (WQL).
+ The information modeling work in CIM is done by using Unified
Modeling Language (UML) as a graphical notation. This attracts people with a computer science background who have learned to use UML as part of their education.
o The main practical use of CIM schemas today seems to be the
definition of data structures used internally by management systems.
- The CIM schemas have rather complex interrelationships that must
be understood before one can reasonably extend the set of existing schemas.
- Interoperability between CIM implementations seems to be
problematic compared to the number of interoperable SNMP implementations available today.
- So far, CIM schemas have seen limited implementation and usage as
an interface between management systems and network devices.
CLI / TELNET / SSH
Most devices have a builtin command line interface (CLI) for configuration and troubleshooting purposes. Network access to the CLI has traditionally been through the TELNET protocol, while the SSH protocol is gaining momentum to address security issues associated with TELNET. In the following, only CLIs that actually parse and execute commands are considered. (Menu-oriented interfaces are difficult for automation and thus not relevant here.)
+ Command line interfaces are generally task-oriented, which make
them easier to use for human operators.
+ A saved sequence of textual commands can easily be replayed.
Simple substitutions can be made with arbitrary text processing tools.
+ It is usually necessary to learn at least parts of the command
line interface of new devices in order to create the initial configuration. Once people have learned (parts of) the command line interface, it is natural for them to use the same interface and abstractions for automating configuration changes.
+ A command line interface does not require any special purpose
applications (telnet and ssh are readily available on most systems today).
+ Most command line interfaces provide context sensitive help that
reduces the learning curve.
- Some command line interfaces lack a common data model. It is very
well possible that the same command on different devices, even from the same vendor, behaves differently.
- The command line interface is primarily targeted to humans which
can adapt to minor syntax and format changes easily. Using command line interfaces as a programmatic interface is troublesome because of parsing complexities.
- Command line interfaces often lack proper version control for the
syntax and the semantics. It is therefore time consuming and error prone to maintain programs or scripts that interface with different versions of a command line interface.
- Since command line interfaces are proprietary, they can not be
used efficiently to automate processes in an environment with a heterogenous set of devices.
- The access control facilities, if present at all, are often ad-hoc
and sometimes insufficient.
HTTP / HTML
Many devices have an embedded web server which can be used to configure the device and to obtain status information. The commonly used protocol is HTTP, and information is rendered in HTML. Some devices also expect that clients have facilities such as Java or Java Script.
+ Embedded web servers for configuration are end-user friendly and
solution oriented.
+ Embedded web servers are suitable for configuring consumer devices
by inexperienced users.
+ Web server configuration is widely deployed, especially in boxes
targeted to the consumer market.
+ There is no need for specialized applications to use embedded web
servers since web browsers are commonly available today.
- Embedded web servers are management application hostile. Parsing
HTML pages to extract useful information is extremely painful.
- Replay of configuration is often problematic, either because the
web pages rely on some active content or because different versions of the same device use different ways to interact with the user.
- The access control facilities, if present at all, are often ad-hoc
and sometimes insufficient.
XML
In the late 1990's, some vendors started to use the Extensible Markup Language (XML) [XML] for describing device configurations and for protocols that can be used to retrieve and manipulate XML formatted configurations.
+ XML is a machine readable format which is easy to process and
there are many good off the shelf tools available.
+ XML allows the description of structured data of almost arbitrary
complexity.
+ The basic syntax rules behind XML are relatively easy to learn.
+ XML provides a document-oriented view of configuration data
(similar to many proprietary configuration file formats).
+ XML has a robust schema language XSD [XSD] for which many good off
the shelf tools exist.
o XML alone is just syntax. XML schemas must be carefully designed
to make XML truly useful as a data exchange format.
- XML is rather verbose. This either increases the bandwidth
required to move management information around (which is an issue in e.g., wireless or asymmetric cable networks) or it requires that the systems involved have the processing power to do on the fly compression/decompression.
- There is a lack of commonly accepted standardized management
specific XML schemas.
Operator Requirements
During the breakout session, the operators were asked to identify needs that have not been sufficiently addressed. The results produced during the breakout session were later discussed and resulted in the following list of operator requirements.
1. Ease of use is a key requirement for any network management
technology from the operators point of view.
2. It is necessary to make a clear distinction between configuration
data, data that describes operational state and statistics. Some devices make it very hard to determine which parameters were administratively configured and which were obtained via other mechanisms such as routing protocols.
3. It is required to be able to fetch separately configuration data,
operational state data, and statistics from devices, and to be able to compare these between devices.
4. It is necessary to enable operators to concentrate on the
configuration of the network as a whole rather than individual devices.
5. Support for configuration transactions across a number of devices
would significantly simplify network configuration management.
6. Given configuration A and configuration B, it should be possible
to generate the operations necessary to get from A to B with minimal state changes and effects on network and systems. It is important to minimize the impact caused by configuration changes.
7. A mechanism to dump and restore configurations is a primitive
operation needed by operators. Standards for pulling and pushing configurations from/to devices are desirable.
8. It must be easy to do consistency checks of configurations over
time and between the ends of a link in order to determine the changes between two configurations and whether those configurations are consistent.
9. Network wide configurations are typically stored in central
master databases and transformed into formats that can be pushed to devices, either by generating sequences of CLI commands or complete configuration files that are pushed to devices. There is no common database schema for network configuration, although the models used by various operators are probably very similar. It is desirable to extract, document, and standardize the common parts of these network wide configuration database schemas.
10. It is highly desirable that text processing tools such as diff,
and version management tools such as RCS or CVS, can be used to process configurations, which implies that devices should not arbitrarily reorder data such as access control lists.
11. The granularity of access control needed on management interfaces
needs to match operational needs. Typical requirements are a role-based access control model and the principle of least privilege, where a user can be given only the minimum access necessary to perform a required task.
12. It must be possible to do consistency checks of access control
lists across devices.
13. It is important to distinguish between the distribution of
configurations and the activation of a certain configuration. Devices should be able to hold multiple configurations.
14. SNMP access control is data-oriented, while CLI access control is
usually command (task) oriented. Depending on the management function, sometimes data-oriented or task-oriented access control makes more sense. As such, it is a requirement to support both data-oriented and task-oriented access control.
So far, there is no published document that clearly defines the requirements of the operators.
SNMP Framework Discussions
During the discussions, many properties of the SNMP framework were identified.
1. It is usually not possible to retrieve complete device
configurations via SNMP so that they can be compared with previous configurations or checked for consistency across devices. There is usually only incomplete coverage of device features via the SNMP interface, and there is a lack of differentiation between configuration data and operational state data for many features.
2. The quality of SNMP instrumentations is sometimes disappointing.
SNMP access sometimes crashes systems or returns wrong data.
3. MIB modules and their implementations are not available in a
timely manner (sometimes MIB modules lag years behind) which forces users to use the CLI.
4. Operators view current SNMP programming/scripting interfaces as
being too low-level and thus too time consuming and inconvenient for practical use.
5. Lexicographic ordering is sometimes artificial with regard to
internal data structures and causes either significant runtime overhead, or increases implementation costs or implementation delay or both.
6. Poor performance for bulk data transfers. The typical examples
are routing tables.
7. Poor performance on query operations that were not anticipated
during the MIB design. A typical example is the following query: Which outgoing interface is being used for a specific destination address?
8. The SNMP credentials and key management are considered complex,
especially since they do not integrate well with other existing credential and key management systems.
9. The SMI language is hard to deal with and not very practical.
10. MIB modules are often over-engineered in the sense that they
contain lots of variables that operators do not look at.
11. SNMP traps are used to track state changes but often syslog
messages are considered more useful since they usually contain more information to describe the problem. SNMP traps usually require subsequent get operations to figure out what the trap really means.
12. Device manufacturers find SNMP instrumentations inherently
difficult to implement, especially with complex table indexing schemes and table interrelationships.
13. MIB modules often lack a description of how the various objects
can be used to achieve certain management functions. (MIB modules can often be characterized as a list of ingredients without a recipe.)
14. The lack of structured types and various RPC interactions
(methods) make MIB modules much more complex to design and implement.
15. The lack of query and aggregation capabilities (reduction of
data) causes efficiency and scalability problems.
16. The SNMP protocol was simplified in terms of the number of
protocol operations and resource requirements on managed devices. It was not simplified in terms of usability by network operators or instrumentation implementors.
17. There is a semantic mismatch between the low-level data-oriented
abstraction level of MIB modules and the task-oriented abstraction level desired by network operators. Bridging the gap with tools is in principle possible, but in general it is expensive as it requires some serious development and programming efforts.
18. SNMP seems to work reasonably well for small devices which have a
limited number of managed objects and where end-user management applications are shipped by the vendor. For more complex devices, SNMP becomes too expensive and too hard to use.
19. There is a disincentive for vendors to implement SNMP equivalent
MIB modules for all their CLI commands because they do not see a valued proposition. This undermines the value of third party standard SNMP solutions.
20. Rapid feature development is in general not compatible with the
standardization of the configuration interface.
Consolidated Observations
1. Programmatic interfaces have to provide full coverage otherwise
they will not be used by network operators since they have to revert to CLIs anyway.
2. Operators perceive that equipment vendors do not implement MIB
modules in a timely manner. Neither read-only nor read-write MIB modules are available on time today.
3. The attendees perceive that right now it is too hard to implement
useful MIB modules within network equipment.
4. Because of the previous items, SNMP is not widely used today for
network device configuration, although there are notable exceptions.
5. It is necessary to clearly distinguish between configuration data
and operational data.
6. It would be nice to have a single data definition language for
all programmatic interfaces (in case there happen to be multiple programmatic interfaces).
7. In general, there is a lack of input from the enterprise network
space. Those enterprises who provided input tend to operate their networks like network operators.
8. It is required to be able to dump and reload a device
configuration in a textual format in a standard manner across multiple vendors and device types.
9. It is desirable to have a mechanism to distribute configurations
to devices under transactional constraints.
10. Eliminating SNMP altogether is not an option.
11. Robust access control is needed. In addition, it is desirable to
be able to enable/disable individual MIB modules actually implemented on a device.
12. Textual configuration files should be able to contain
international characters. Human-readable strings should utilize the least-bad internationalized character set and encoding, which this year almost certainly means UTF-8. Protocol elements should be in case insensitive ASCII.
13. The deployed tools for event/alarm correlation, root cause
analysis and logging are not sufficient.
14. There is a need to support a human interface and a programmatic
interface.
15. The internal method routines for both interfaces should be the
same to ensure that data exchanged between these two interfaces is always consistent.
16. The implementation costs have to be low on devices.
17. The implementation costs have to be low on managers.
18. The specification costs for data models have to be low.
19. Standardization costs for data models have to be low.
20. There should be a single data modeling language with a human
friendly syntax.
21. The data modeling language must support compound data types.
22. There is a need for data aggregation capabilities on the devices.
23. There should be a common data interchange format for instance
data that allows easy post-processing and analysis.
24. There is a need for a common data exchange format with single and
multi-system transactions (which implies rollback across devices in error situations).
25. There is a need to reduce the semantic mismatch between current
data models and the primitives used by operators.
26. It should be possible to perform operations on selected subsets
of management data.
27. It is necessary to discover the capabilities of devices.
28. There is a need for a secure transport, authentication, identity,
and access control which integrates well with existing key and credential management infrastructure.
29. It must be possible to define task oriented views and access
control rules.
30. The complete configuration of a device should be doable with a
single protocol.
31. A configuration protocol must be efficient and reliable and it
must scale in the number of transactions and devices.
32. Devices must be able to support minimally interruptive
configuration deltas.
33. A solution must support function call semantics (methods) to
implement functions, such as a longest prefix match on a routing table.
Recommendations
1. The workshop recommends that the IETF stop forcing working groups
to provide writable MIB modules. It should be the decision of the working group whether they want to provide writable objects or not.
2. The workshop recommends that a group be formed to investigate why
current MIB modules do not contain all the objects needed by operators to monitor their networks.
3. The workshop recommends that a group be formed to investigate why
the current SNMP protocol does not satisfy all the monitoring requirements of operators.
4. The workshop recommends, with strong consensus from both protocol
developers and operators, that the IETF focus resources on the standardization of configuration management mechanisms.
5. The workshop recommends, with strong consensus from the operators
and rough consensus from the protocol developers, that the IETF/IRTF should spend resources on the development and standardization of XML-based device configuration and management technologies (such as common XML configuration schemas, exchange protocols and so on).
6. The workshop recommends, with strong consensus from the operators
and rough consensus from the protocol developers, that the IETF/IRTF should not spend resources on developing HTML-based or HTTP-based methods for configuration management.
7. The workshop recommends, with rough consensus from the operators
and strong consensus from the protocol developers, that the IETF should continue to spend resources on the evolution of the SMI/SPPI data definition languages as being done in the SMIng working group.
8. The workshop recommends, with split consensus from the operators
and rough consensus from the protocol developers, that the IETF should spend resources on fixing the MIB development and standardization process.
The workshop also discussed the following items and achieved rough consensus, but did not make a recommendation.
1. The workshop had split consensus from the operators and rough
consensus from the protocol developers, that the IETF should not focus resources on CIM extensions.
2. The workshop had rough consensus from the protocol developers
that the IETF should not spend resources on COPS-PR development. So far, the operators have only very limited experience with COPS-PR. In general, however, they felt that further development of COPS-PR might be a waste of resources as they assume that COPS-PR does not really address their requirements.
3. The workshop had rough consensus from the protocol developers
that the IETF should not spend resources on SPPI PIB definitions. The operators had rough consensus that they do not care about SPPI PIBs.
Security Considerations
This document is a report of an IAB Network Management workshop. As such, it does not have any direct security implications for the Internet.
Acknowledgments
The editor would like to thank Dave Durham, Simon Leinen and John Schnizlein for taking detailed minutes during the workshop.
Normative References
RFC3410 Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[CIM] Distributed Management Task Force, "Common Information
Model (CIM) Specification Version 2.2", DSP 0004, June
1999.
RFC3060 Moore, B., Ellesson, E., Strassner, J. and A. Westerinen,
"Policy Core Information Model -- Version 1
Specification", RFC 3060, February 2001.
RFC2748 Durham, D., Boyle, J., Cohen, R., Herzog, S., Rajan, R.
and A. Sastry, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
RFC3084 Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie,
K., Herzog, S., Reichmeyer, F., Yavatkar, R. and A. Smith,
"COPS Usage for Policy Provisioning (COPS-PR)", RFC 3084,
March 2001.
[XML] Bray, T., Paoli, J. and C. Sperberg-McQueen, "Extensible
Markup Language (XML) 1.0", W3C Recommendation, February
1998.
Informative References
RFC2863 McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, June 2000.
[XSD] David, D., "XML Schema Part 0: Primer", W3C
Recommendation, May 2001.
Appendix - Participants
Ran Atkinson Extreme Networks Rob Austein InterNetShare Andy Bierman Cisco Systems Steve Bellovin AT&T Randy Bush AT&T Leslie Daigle VeriSign David Durham Intel Vijay Gill Wes Hardaker Network Associates Laboratories Ed Kern Simon Leinen Switch Ken Lindahl University of California Berkeley David Partain Ericsson Andrew Partan UUnet/Verio/MFN Vern Paxson ICIR Aiko Pras Univeristy of Twente Randy Presuhn BMC Software Juergen Schoenwaelder University of Osnabrueck John Schnizlein Cisco Systems Mike St. Johns Ruediger Volk Deutsche Telekom Steve Waldbusser Margaret Wassermann Windriver Glen Waters Nortel Networks Bert Wijnen Lucent
Author's Address
Comments should be submitted to the <[email protected]> mailing list.
Juergen Schoenwaelder International University Bremen P.O. Box 750 561 28725 Bremen Germany
Phone: +49 421 200 3587 EMail: [email protected]
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