7 Network Working Group S.E. Hardcastle-Kille
8 Requests for Comments 1275 University College London
18 Replication Requirements to provide an Internet Directory using X.500
30 This memo provides information for the Internet community. It
31 does not specify an Internet standard. Distribution of this memo
35 This RFCconsiders certain deficiencies of the 1988 X.500
36 standard, which need to be addressed before an effective open
37 Internet Directory can be established using these protocols and
38 services [CCI88]. The only areas considered are primary
39 problems, to which solutions must be found before a pilot can be
40 deployed. This RFCconcerns itself with deficiencies which can
41 only be addressed by use of additional protocol or procedures for
42 distributed operation.
47 RFC 1275 Replication Requirements November 1991
50 1 Distributed Operation Extensions
52 The Internet Directory will operate DSAs over TCP/IP using RFC 1006
53 [RC87], and DSAs over the an ISO Network Service. Distributed
54 operation procedures should not require full connectivity.
57 2 Knowledge Replication
59 Knowledge information is critical to resolution of names, and
60 performing searches. Knowledge information high up the tree needs to
61 be widely available. Consider resolving a name below ``Country=US''.
62 To do this, a DSA needs to have full knowledge at this point. Many
63 DSAs need to be able to do this, in order to give reasonable response
64 and availability. It would be an unacceptable bottleneck to force
65 such resolution to a single or small number of DSAs. To replicate
66 this knowledge widely, a systematic approach to replication is needed.
71 Searches are often made at the root and country level, and this is a
72 vital service (e.g., an approximate match of an organisation name).
73 Data needs to be collected in such a way that this sort of searching
74 is reasonably efficient. The usual X.500 approach of subordinate
75 references militates against this. At a node in the DIT, subordinate
76 references to the entries below are held. These entries will be in
77 many DSAs, each of which needs to be accessed in order to perform the
78 single level search. It is suggested that replication of data is
79 necessary to achieve this.
81 The major requirement for this replication is high up the DIT, where
82 information must be replicated between different implementations. At
83 lower levels of the DIT, it is reasonable for DSAs to be of the same
84 implementation and to use implementation specific techniques in order
85 to achieve performance and availability.
90 When a DSA Referral is returned, only the master DSA is indicated.
91 This will lead to a single point of failure. It seems important to
92 allow for additional references to slave copies, in order to get
95 Hardcastle-Kille Page 1
100 RFC 1275 Replication Requirements November 1991
103 better availability. This needs to be solved in conjunction with the
104 problem described in the previous section.
107 5 Guidelines for use of Replication
109 To be effective, the replication specification needs to provide
110 guidelines for deployment in the pilot, in order to meet the desired
114 6 Some scaling targets
116 Most techniques for replication have scaling limits. It is important
117 that mechanisms used do not stress the limits of the mechanism. The
118 order of magnitude envisioned in the pilot is 100 000 non-leaf entries
119 and several million leaf entries.
124 [CCI88] The Directory --- overview of concepts, models and services,
125 December 1988. CCITT X.500 Series Recommendations.
127 [RC87] Marshall T. Rose and Dwight E. Cass. ISO Transport Services
128 on top of the TCP. Request for Comments 1006, Northrop
129 Corporation Technology Center, May 1987.
132 7 Security Considerations
134 Security considerations are not discussed in this memo.
139 Steve Hardcastle-Kille
140 Department of Computer Science
141 University College London
148 Hardcastle-Kille Page 2
153 RFC 1275 Replication Requirements November 1991
156 Phone: +44-71-380-7294
158 EMail: S.Kille@CS.UCL.AC.UK
201 Hardcastle-Kille Page 3