RFC 2755 (rfc2755) - Page 2 of 12
Security Negotiation for WebNFS
Alternative Format: Original Text Document
RFC 2755 Security Negotiation for WebNFS January 2000
1. Introduction
The MOUNT protocol is used by an NFS client to obtain the necessary
filehandle for data access. MOUNT versions 1 and 2 [RFC 1094] return
NFS version 2 filehandles, whereas MOUNT version 3 [RFC 1813] returns
NFS version 3 filehandles.
Among the existing versions of the MOUNT protocol, only the MOUNT v3
provides an RPC procedure (MOUNTPROC3_MNT) which facilitates security
negotiation between an NFS v3 client and an NSF v3 server. When this
RPC procedure succeeds (MNT3_OK) the server returns to the client an
array of security mechanisms it supports for the specified pathname,
in addition to an NFS v3 filehandle.
A security mechanism referred to in this document is a generalized
security flavor which can be an RPC authentication flavor [RFC 1831]
or a security flavor referred to in the RPCSEC_GSS protocol
[RFC 2203]. A security mechanism is represented as a four-octet
integer.
No RPC procedures are available for security negotiation in versions
1 or 2 of the MOUNT protocol.
The NFS mount command provides a "sec=" option for an NFS client to
specify the desired security mechanism to use for NFS transactions.
If this mount option is not specified, the default action is to use
the default security mechanism over NFS v2 mounts, or to negotiate a
security mechanism via the MOUNTPROC3_MNT procedure of MOUNT v3 and
use it over NFS v3 mounts. In the latter, the client picks the first
security mechanism in the array returned from the server that is also
supported on the client.
As specified in RFC 2054, a WebNFS client first assumes that the
server supports WebNFS and uses the publsc filehandle as the initial
filehandle for data access, eliminating the need for the MOUNT
protocol. The WebNFS client falls back to MOUNT if the server does
not support WebNFS.
Since a WebNFS client does not use MOUNT initially, the
MOUNTPROC3_MNT procedure of MOUNT v3 is not available for security
negotiation until the WebNFS client falls back to MOUNT. A viable
protocol needs to be devised for the WebNFS client to negotiate
security mechanisms with the server in the absence of the
MOUNTPROC3_MNT procedure.
Chiu, et al. Informational