X.400 1988 to 1984 downgrading (RFC1328)
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2019-Feb-10
Internet Society Requests For Comment (RFCs)
This document considers issues of downgrading from X.400(1988) to X.400(1984) [MHS88a, MHS84]. Annexe B of X.419 specifies some downgrading rules [MHS88b], but these are not sufficient for provision of service in an environment containing both 1984 and 1988 components. This document defines a number of extensions to this annexe. [STANDARDS-TRACK]
Network Working Group S. Hardcastle-Kille Request for Comments: 1328 University College London May 1992
X.400 1988 to 1984 downgrading
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
This document considers issues of downgrading from X.400(1988) to X.400(1984) [MHS88a, MHS84]. Annexe B of X.419 specifies some downgrading rules [MHS88b], but these are not sufficient for provision of service in an environment containing both 1984 and 1988 components. This document defines a number of extensions to this annexe.
This specification is not tutorial. COSINE Study 8.2 by J.A.I. Craigie gives a useful overview [Cra88].
1. The need to Downgrade
It is expected that X.400(1988) systems will be extensively deployed, whilst there is still substantial use of X.400(1984). If 1988 features are to be used, it it important for there to be a clear approach to downgrading. This document specifies an approach to downgrading for the Internet and COSINE communities. As 1988 is a strict superset of 1984, the mapping is a one-way problem.
2. Avoiding Downgrading
Perhaps the most important consideration is to configure systems so as to minimise the need for downgrading. Use of 1984 systems to interconnect 1988 systems should be strenuously avoided.
In practice, many of the downgrading issues will be avoided. When a 1988 originator sends to a 1984 recipient, 1988 specific features will not be used as they will not work! For distribution lists with 1984 and 1988 recipients, messages will tend to be "lowest common denominator".
Hardcastle-Kille [Page 1]
RFC 1328 X.400 1988 to 1984 downgrading May 1992
In general there is a problem with O/R addresses which use 88 specific features. The X.419 downgrade approach will mean that addresses using these features cannot be specified from 84 systems. Worse, a message originating from such an address cannot be transferred into X.400(1984). This is unacceptable. Two approaches are defined. The first is a general purpose mechanism, which can be implemented by the gateway only. The second is a special purpose mechanism to optimise for a form of X.400(88) address which is expected to be used frequently (Common Name). The second approach requires cooperation from all X.400(88) UAs and MTAs which are involved in these interactions.
3.1 General Approach
The first approach is to use a DDA "X400-88". The DDA value is an std-or encoding of the address as defined in RFC 1327 [Kil92]. This will allow source routing through an appropriate gateway. This solution is general, and does not require co-operation. For example:
88: PD-ADDRESS=Empire State Building; PRMD=XX; ADMD=ZZ; C=US;
84: O=MHS-Relay; PRMD=UK.AC; C=GB; DD.X400-88=/PD-ADDRESS=Empir...