Network Working Group M. Tuexen
INTERNET DRAFT Siemens AG
Q. Xie
Motorola
R. Stewart
M. Shore
Cisco
L. Ong
Point Reyes Networks
J. Loughney
M. Stillman
Nokia
Expires October 2, 2001 April 2, 2001
Requirements for Reliable Server Pooling
<draft-ietf-rserpool-reqts-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026].
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Abstract
The goal is to develop an architecture and protocols for the management
and operation of server pools supporting highly reliable applications,
and for client access mechanisms to a server pool.
This document defines a basic set requirements for reliable server
pooling.
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1. Introduction
1.1. Overview
The Internet is always on. Many users expect services to be always
available; many business depend upon connectivity 24 hours a day, 7 days
a week, 365 days a year. In order to fulfill this, many proprietary
solutions and operating system dependent solutions have been developed
to provide highly reliable and highly available servers.
This document defines requirements for reliable server pooling.
Highly available services also put the same high reliability
requirements upon the transport layer protocol beneath RSerPool - it
must provide strong survivability in the face of network component
failures.
Supporting real time applications is another main focus of RSerPool
which leads to requirements on the processing time needed.
Scalability is another important requirement.
RSerPool introduces new security vulnerabilities into existing
applications, both in the pool formation and pool member selection
process and in the failover process. Therefore, during the protocol
development process it will be necessary to catalogue the threats to
RSerPool and identify appropriate responses to those threats.
1.2. Terminology
This document uses the following terms:
Operation scope:
The part of the network visible to pool users by a specific
instance of the reliable server pooling protocols.
Pool (or server pool):
A collection of servers providing the same application
functionality.
Pool handle (or pool name):
A logical pointer to a pool. Each server pool will be
identifiable in the operation scope of the system by a unique
pool handle or "name".
Pool element:
A server entity having registered to a pool.
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Pool user:
A server pool user.
Pool element handle (or endpoint handle):
A logical pointer to a particular pool element in a pool,
consisting of the name of the pool and a destination transport
address of the pool element.
Name space:
A cohesive structure of pool names and relations that may be
queried by an internal or external agent.
Name server:
Entity which the responsible for managing and maintaining the
name space within the RSerPool operation scope.
1.3. Abbreviations
PE: Pool element
PU: Pool user
SCTP: Stream Control Transmission Protocol
TCP: Transmission Control Protocol
2. Requirements
2.1. Communication Model
The general architecture should be based on a peer to peer model.
However, the binding should be based on a client server model.
2.2. Processing Power
It should be possible to use the protocol stack in small devices, like
handheld wireless devices. The solution must scale to devices with a
differing range of processing power.
2.3. Transport Protocol
The protocols used for the pool handling should not cause network
congestion. This means that it should not generate heavy traffic, even
in case of failures, and has to use flow control and congestion
avoidance algorithms which are interoperable with currently deployed
techniques, especially the flow control of TCP [RFC793] and SCTP
[RFC2960]. Therefore, for large pools, only a subset of all possible
IP-addresses are returned by the name servers.
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The architecture should not rely on multicast capabilities of the
underlying layer. Nevertheless, it can make use of it if multicast
capabilities are available.
Network failures have to be handled and concealed from the application
layer as much as possible by the transport protocol. This means that the
underlying transport protocol must provide a strong network failure
handling capability on top of an acknowledged error-free non-duplicated
data delivery service. The failure of a network element must be handled
by the transport protocol in a way that the timing requirements are
still fulfilled.
2.4. Support of RSerPool Unaware Clients
Furthermore, it is expected that there will be a transition phase with
some systems supporting the RSerPool architecture and some are not. To
make this transition as seamless as possible it should be possible for
hosts not supporting this architecture to use also the new pooling
services via some mechanism.
2.5. Registering and Deregistering
Another important requirement is that servers should be able to register
to (become PEs) and deregister from a server pool transparently without
an interruption in service. This means that after a PE has
deregistered, it will continue to serve PUs, which started the
connection before the deregistration of the PE. No PE will establish a
new connection with the deregistered PE, because other PE of the server
pool will be used.
Servers should be able to register in multiple server pools which may
belong to different namespaces.
2.6. Server Selection
The RSerPool mechanisms must be able to support different server
selection mechanisms. These are called server pool policies.
Examples of server pool policies are:
- Round Robin
- Least used
- Most used
The set of supported policies must be extensible in the sense that new
policies can be added as required.
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There must be a way for the client to provide information to the name
server about the pool elements.
The name servers should be extensible using a plug-in architecture.
These plug-ins would provide a more refined server selection by the name
servers using additional information provided by clients as hints.
For some applications it is important that a client repeatedly connects
to the same server in a pool if it is possible, i. e., if that server is
still alive. This feature should be supported through the use of pool
element handles.
2.7. Timing Requirements
A server pool can consist of a large number (up to 500) of pool
elements. This upper limit is important since the system will be used
for real time applications. So handling of name resolution has to be
fast.
Another consequence of the real time requirement is the supervision of
the pool elements. The name resolution should not result in a pool
element which is not operational.
2.8. Failover Support
The RSerPool architecture must be able to detect server failure quickly
and be able to perform failover without service interruption.
2.9. Robustness
The solution must allow itself to be implemented and deployed in such a
way that there is no single point of failure in the system.
2.10. Naming
Server pools are identified by pool handles. These pool handles are only
valid inside the operation scope. Interoperability between different
namespaces has to be provided by other mechanisms.
2.11. Scalability
The RSerPool architecture should not require a limitation on the number
of server pools or on the number of pool users.
2.12. Security Requirements
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2.12.1. General
- The scaling characteristics of the security architecture
should be compatible with those given previously.
- The security architecture should support hosts having a wide
range of processing powers.
2.12.2. Name Space Services
- It must not be possible for an attacker to falsely register as
a pool element with the name server either by masquerading as
another pool element or by registering in violation of local
authorization policy.
- It must not be possible for an attacker to deregister a server
which has successfully registered with the name server.
- It must not be possible for an attacker to spoof the response
to a query to the name server
- It must be possible to prohibit unauthorized queries to the
name server.
- It must be possible to protect the privacy of queries to the
name server and responses to those queries from the name
server.
- Communication among name servers must be afforded the same
protections as communication between clients and name servers.
2.12.3. Security State
The security context of an application is a subset of the overall
context, and context or state sharing is explicitly out-of-scope for
RSerPool. Because RSerPool does introduce new security vulnerabilities
to existing applications application designers employing RSerPool should
be aware of problems inherent in failing over secured connections.
Security services necessarily retain some state and this state may have
to be moved or re-established. Examples of this state include
authentication or retained ciphertext for ciphers operating in cipher
block chaining (CBC) or cipher feedback (CFB) mode. These problems must
be addressed by the application or by future work on RSerPool.
3. Acknowledgements
The authors would like to thank Bernard Aboba, Matt Holdrege,
Christopher Ross, Werner Vogels and many others for their invaluable
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comments and suggestions.
4. References
[RFC793] J. B. Postel, "Transmission Control Protocol", RFC 793,
September 1981.
[RFC959] J. B. Postel, J. Reynolds, "File Transfer Protocol (FTP)",
RFC 959, October 1985.
[RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3",
RFC 2026, October 1996.
[RFC2608] E. Guttman et al., "Service Location Protocol, Version 2",
RFC 2608, June 1999.
[RFC2719] L. Ong et al., "Framework Architecture for Signaling
Transport", RFC 2719, October 1999.
[RFC2960] R. R. Stewart et al., "Stream Control Transmission
Protocol", RFC 2960, November 2000.
5. Authors' Addresses
Michael Tuexen Tel.: +49 89 722 47210
Siemens AG e-mail: Michael.Tuexen@icn.siemens.de
ICN WN CS SE 51
D-81359 Munich
Germany
Qiaobing Xie Tel.: +1 847 632 3028
Motorola, Inc. e-mail: qxie1@email.mot.com
1501 W. Shure Drive, #2309
Arlington Heights, Il 60004
USA
Randall Stewart Tel.: +1 815 477 2127
Cisco Systems, Inc. e-mail: rrs@cisco.com
24 Burning Bush Trail
Crystal Lake, Il 60012
USA
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Melinda Shore Tel.: +1 607 272 7512
Cisco Systems, Inc. e-mail: mshore@cisco.com
809 Hayts Rd
Ithaca, NY 14850
USA
Lyndon Ong Tel.: +1 408 321 8237
Point Reyes Networks e-mail: long@pointreyesnet.com
1991 Concourse Drive
San Jose, CA
USA
John Loughney Tel.:
Nokia Research Center e-mail: john.loughney@nokia.com
PO Box 407
FIN-00045 Nokia Group
Finland
Maureen Stillman Tel.: +1 607 273 0724 62
Nokia e-mail: maureen.stillman@nokia.com
127 W. State Street
Ithaca, NY 14850
USA
This Internet Draft expires October 2, 2001.
Tuexen et al. [Page 8]
