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203 lines
4.5 KiB
Plaintext
203 lines
4.5 KiB
Plaintext
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Network Working Group S.E. Hardcastle-Kille
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Requests for Comments 1275 University College London
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November 1991
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Replication Requirements to provide an Internet Directory using X.500
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Status of this Memo
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This memo provides information for the Internet community. It
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does not specify an Internet standard. Distribution of this memo
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is unlimited.
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Abstract
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This RFCconsiders certain deficiencies of the 1988 X.500
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standard, which need to be addressed before an effective open
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Internet Directory can be established using these protocols and
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services [CCI88]. The only areas considered are primary
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problems, to which solutions must be found before a pilot can be
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deployed. This RFCconcerns itself with deficiencies which can
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only be addressed by use of additional protocol or procedures for
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distributed operation.
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RFC 1275 Replication Requirements November 1991
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1 Distributed Operation Extensions
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The Internet Directory will operate DSAs over TCP/IP using RFC 1006
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[RC87], and DSAs over the an ISO Network Service. Distributed
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operation procedures should not require full connectivity.
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2 Knowledge Replication
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Knowledge information is critical to resolution of names, and
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performing searches. Knowledge information high up the tree needs to
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be widely available. Consider resolving a name below ``Country=US''.
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To do this, a DSA needs to have full knowledge at this point. Many
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DSAs need to be able to do this, in order to give reasonable response
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and availability. It would be an unacceptable bottleneck to force
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such resolution to a single or small number of DSAs. To replicate
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this knowledge widely, a systematic approach to replication is needed.
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3 Data Replication
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Searches are often made at the root and country level, and this is a
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vital service (e.g., an approximate match of an organisation name).
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Data needs to be collected in such a way that this sort of searching
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is reasonably efficient. The usual X.500 approach of subordinate
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references militates against this. At a node in the DIT, subordinate
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references to the entries below are held. These entries will be in
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many DSAs, each of which needs to be accessed in order to perform the
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single level search. It is suggested that replication of data is
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necessary to achieve this.
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The major requirement for this replication is high up the DIT, where
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information must be replicated between different implementations. At
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lower levels of the DIT, it is reasonable for DSAs to be of the same
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implementation and to use implementation specific techniques in order
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to achieve performance and availability.
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4 Alternate DSAs
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When a DSA Referral is returned, only the master DSA is indicated.
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This will lead to a single point of failure. It seems important to
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allow for additional references to slave copies, in order to get
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Hardcastle-Kille Page 1
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RFC 1275 Replication Requirements November 1991
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better availability. This needs to be solved in conjunction with the
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problem described in the previous section.
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5 Guidelines for use of Replication
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To be effective, the replication specification needs to provide
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guidelines for deployment in the pilot, in order to meet the desired
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service criteria.
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6 Some scaling targets
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Most techniques for replication have scaling limits. It is important
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that mechanisms used do not stress the limits of the mechanism. The
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order of magnitude envisioned in the pilot is 100 000 non-leaf entries
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and several million leaf entries.
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References
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[CCI88] The Directory --- overview of concepts, models and services,
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December 1988. CCITT X.500 Series Recommendations.
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[RC87] Marshall T. Rose and Dwight E. Cass. ISO Transport Services
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on top of the TCP. Request for Comments 1006, Northrop
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Corporation Technology Center, May 1987.
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7 Security Considerations
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Security considerations are not discussed in this memo.
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8 Author's Address
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Steve Hardcastle-Kille
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Department of Computer Science
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University College London
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Gower Street
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WC1E 6BT
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England
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Hardcastle-Kille Page 2
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RFC 1275 Replication Requirements November 1991
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Phone: +44-71-380-7294
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EMail: S.Kille@CS.UCL.AC.UK
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Hardcastle-Kille Page 3
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