Network Working Group                            S.E. Hardcastle-Kille
Requests for Comments 1275                   University College London
                                                         November 1991
Replication Requirements to provide an Internet Directory using X.500
Status of this Memo

This memo provides information for the Internet community. It

does not specify an Internet standard. Distribution of this memo

is unlimited.

Abstract

This RFCconsiders certain deficiencies of the 1988 X.500 standard, which need to be addressed before an effective open Internet Directory can be established using these protocols and services [CCI88]. The only areas considered are primary problems, to which solutions must be found before a pilot can be deployed. This RFCconcerns itself with deficiencies which can only be addressed by use of additional protocol or procedures for distributed operation.

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1 Distributed Operation Extensions

The Internet Directory will operate DSAs over TCP/IP using RFC 1006

[RC87], and DSAs over the an ISO Network Service. Distributed

operation procedures should not require full connectivity.

2 Knowledge Replication

Knowledge information is critical to resolution of names, and

performing searches. Knowledge information high up the tree needs to

be widely available. Consider resolving a name below ``Country=US''.

To do this, a DSA needs to have full knowledge at this point. Many

DSAs need to be able to do this, in order to give reasonable response

and availability. It would be an unacceptable bottleneck to force

such resolution to a single or small number of DSAs. To replicate

this knowledge widely, a systematic approach to replication is needed.

3 Data Replication

Searches are often made at the root and country level, and this is a

vital service (e.g., an approximate match of an organisation name).

Data needs to be collected in such a way that this sort of searching

is reasonably efficient. The usual X.500 approach of subordinate

references militates against this. At a node in the DIT, subordinate

references to the entries below are held. These entries will be in

many DSAs, each of which needs to be accessed in order to perform the

single level search. It is suggested that replication of data is

necessary to achieve this.

The major requirement for this replication is high up the DIT, where

information must be replicated between different implementations. At

lower levels of the DIT, it is reasonable for DSAs to be of the same

implementation and to use implementation specific techniques in order

to achieve performance and availability.

4 Alternate DSAs

When a DSA Referral is returned, only the master DSA is indicated.

This will lead to a single point of failure. It seems important to

allow for additional references to slave copies, in order to get

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better availability. This needs to be solved in conjunction with the

problem described in the previous section.

5 Guidelines for use of Replication

To be effective, the replication specification needs to provide

guidelines for deployment in the pilot, in order to meet the desired

service criteria.

6 Some scaling targets

Most techniques for replication have scaling limits. It is important

that mechanisms used do not stress the limits of the mechanism. The

order of magnitude envisioned in the pilot is 100 000 non-leaf entries

and several million leaf entries.

References

[CCI88] The Directory --- overview of concepts, models and services,

December 1988. CCITT X.500 Series Recommendations.

[RC87] Marshall T. Rose and Dwight E. Cass. ISO Transport Services

on top of the TCP. Request for Comments 1006, Northrop Corporation Technology Center, May 1987.

7 Security Considerations

Security considerations are not discussed in this memo.

8 Author's Address

Steve Hardcastle-Kille
Department of Computer Science
University College London
Gower Street
WC1E 6BT
England

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Phone: +44-71-380-7294

EMail: S.Kille@CS.UCL.AC.UK

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