RFC 2145 (rfc2145) - Page 2 of 7
Use and Interpretation of HTTP Version Numbers
Alternative Format: Original Text Document
RFC 2145 HTTP Version Numbers May 1997
TABLE OF CONTENTS
1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Robustness Principle . . . . . . . . . . . . . . . . . . 3
2 HTTP version numbers. . . . . . . . . . . . . . . . . . . . . . 3
2.1 Proxy behavior. . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Compatibility between minor versions of the same major
version. . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Which version number to send in a message. . . . . . . . 5
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4 References. . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Authors' addresses. . . . . . . . . . . . . . . . . . . . . . . 6
1 Introduction
HTTP request and response messages include an HTTP protocol version
number. According to section 3.1 of the HTTP/1.1 specification [2],
HTTP uses a "." numbering scheme to indicate
versions of the protocol. The protocol versioning policy is
intended to allow the sender to indicate the format of a message
and its capacity for understanding further HTTP communication,
rather than the features obtained via that communication. No
change is made to the version number for the addition of message
components which do not affect communication behavior or which
only add to extensible field values. The number is
incremented when the changes made to the protocol add features
which do not change the general message parsing algorithm, but
which may add to the message semantics and imply additional
capabilities of the sender. The number is incremented when
the format of a message within the protocol is changed.
The same language appears in the description of HTTP/1.0 [1].
Many readers of these documents have expressed some confusion about
the intended meaning of this policy. Also, some people who wrote
HTTP implementations before RFC 1945 [1] was issued were not aware of
the intentions behind the introduction of version numbers in
HTTP/1.0. This has led to debate and inconsistency regarding the use
and interpretation of HTTP version numbers, and has led to
interoperability problems in certain cases.
Mogul, et. al. Informational