One document matched: draft-ietf-find-cip-trans-01.txt-19606.txt
Differences from 01.txt-00.txt
FIND Working Group J. Allen
Internet Draft WebTV
<draft-ietf-find-cip-trans-01.txt> Paul J. Leach
Expires October 99 Microsoft
Roland Hedberg
Catalogix
CIP Transport Protocols
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its wroking groups. Note that
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as reference material or to cite them other than as "work in
progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
Distribution of this document is unlimited. Please send comments
to the FIND working group at <find@bunyip.com>. Discussions of
the working group are archived at
<URL: ftp://ftp.bunyip.com/pub/mailing-lists/find>.
Abstract
This document specifies three protocols for transporting CIP
requests, responses and index objects, utilizing TCP, mail,
and HTTP. The objects themselves are defined in [CIP-MIME] and the
overall CIP architecture is defined in [CIP-ARCH].
1. Protocol
In this section, the actual protocol for transmitting CIP index
objects and maintaining the mesh is presented. While companion
documents ([CIP-ARCH] and [CIP-MIME]) describe the concepts
involved and the formats of the CIP MIME objects, this document is
the authoritative definition of the message formats and transfer
mechanisms of CIP used over TCP, HTTP and mail.
1.1 Philosophy
The philosophy of the CIP protocol design is one of building-block
design. Instead of relying on bulky protocol definition tools, or
ad-hoc text encodings, CIP draws on existing, well understood
Internet technologies like MIME, RFC-822, Whois++, FTP, and SMTP.
Hopefully this will serve to ease implementation and consensus
building. It should also stand as an example of a simple way to
leverage existing Internet technologies to easily implement new
application-level services.
1.2 Conventions
The key words "MUST" and "MAY" in this document are to be
interpreted as described in "Key words for use in RFCs to Indicate
Requirement Levels" [KEYWORDS].
Formal syntax is defined using ABNF [ABNF].
In examples octets sent by the sender-CIP are preceded by ">>> "
and those sent by the receiver-CIP by "<<< ".
2 MIME message exchange mechanisms
CIP relies on interchange of standard MIME messages for all
requests and replies. These messages are passed over a bidirectional,
reliable transport system. This document defines transport over
reliable network streams (via TCP), via HTTP, and via the Internet
mail infrastructure.
The CIP server which initiates the connection (conventionally
referred to as a client) will be referred to below as the sender-CIP.
The CIP server which accepts a sender-CIP's incoming connection and
responds to the sender-CIP's requests is called a receiver-CIP.
2.1 The Stream Transport
CIP messages are transmitted over bi-directional TCP connections via
a simple text protocol. The transaction can take place over any TCP
port, as specified by the mesh configuration. There is no "well
known port" for CIP transactions. All configuration information in
the system must include both a hostname and a port.
All sender-CIP actions (including requests, connection initiation,
and connection finalization) are acknowledged by the receiver-CIP
with a response code. See section 2.1.1 for the format of these
codes, a list of the responses a CIP server may generate, and the
expected sender-CIP action for each.
In order to maintain backwards compatibility with existing Whois++
servers, CIPv3 sender-CIPs MUST first verify that the newer protocol
is supported. They do this by sending the following illegal Whois++
system command: "# CIP-Version: 3<cr><lf>". On existing Whois++
servers implementing version 1 and 2 of CIP, this results in a
500-series response code, and the server terminates the connection.
If the server implements CIPv3, it MUST instead respond with
response code 300. Future versions of CIP can be correctly
negotiated using this technique with a different string (i.e.
"CIP-Version: 4"). An example of this short interchange is given
below.
Note: If a sender-CIP can safely assume that the server implements
CIPv3, it may choose to send the "# CIP-Version: 3" string and
immediately follow it with the CIPv3 request. This optimization,
useful only in known homogeneous CIPv3 meshes, avoids waiting for
the roundtrip inherent in the negotiation.
Once a sender-CIP has successfully verified that the server supports
CIPv3 requests, it can send the request, formatted as a MIME message
with Mime-Version and Content-Type headers (only), using the network
standard line ending: "<cr><lf>".
Cip-Req = Req-Hdrs CRLF Req-Body
Req-Hdrs = *( Version-Hdr | Req-Cntnt-Hdr )
Req-Body = Body ; format of request body as in [CIP-MIME]
Body = Data CRLF "." CRLF
Data = ; data with CRLF "." CRLF replaced by
; CRLF ".." CRLF
Version-Hdr = "Mime-Version:" "1.0" CRLF
Req-Cntnt-Hdr = "Content-Type:" Req-Content CRLF
Req-Content = ; format is specified in [CIP-MIME]
Cip-Rsp = Rsp-Code CRLF [ Rsp-Hdrs CRLF Rsp-Body ]
[ Indx-Cntnt-Hdr CRLF Index-Body ]
Rsp-Code = DIGIT DIGIT DIGIT Comment
Comment = ; any chars except CR and LF
Rsp-Hdrs = *( Version-Hdr | Rsp-Cntnt-Hdr )
Rsp-Cntnt-Hdr = "Content-Type:" Rsp-Content CRLF
Rsp-Content = ; format is specified in [CIP-MIME]
Rsp-Body = Body ; format of response body as in [CIP-MIME]
Indx-Cntnt-Hdr = "Content-Type:" Indx-Obj-Type CRLF
Indx-Obj-Type = ; any registered index object's MIME-type
; the format is specified in [RFC2045]
Index-Body = Body ; format defined in each index
; specifications
CRLF = CR LF ; Internet standard newline
CR = %x0D ; carriage return
LF = %x0A ; linefeed
DIGIT = %x30-39
The message is terminated using SMTP-style message termination.
The data is sent octet-for-octet, except when the pattern
<cr><lf>1*["."]<cr><lf> is seen, in which case one more period
is added.
When the data is finished, the octet pattern "<cr><lf>.<cr><lf>" is
transmitted to the receiver-CIP.
On the receiver-CIP's side, the reverse transformation is applied,
and the message read consists of all bytes up to, but not including,
the terminating pattern.
In response to the request, the receiver-CIP sends a response code,
from either the 200, 400, or 500 series. The receiver-CIP then
processes the request and replies, if necessary, with a MIME message.
This reply is also delimited by an SMTP-style message terminator.
After responding with a response code, the receiver-CIP MUST prepare
to read another request message, resetting state to the point when
the sender-CIP has just verified the CIP version. If the sender-CIP
is finished making requests, it may close the connection. In
response the receiver-CIP MUST abort reading the message and prepare
for a new sender-CIP connection (resetting its state completely).
An example is given below. It is again worth reiterating that the
command format is defined in [CIP-MIME] whereas the message body is
defined in each index object definition. In this example the index
object definition in [CIP-TIO] will be used. Line endings are
explicitly shown in anglebrackets; newlines in this text are added
only for readability.
Comments occur in curly-brackets.
{ sender-CIP connects to receiver-CIP }
<<< % 220 Example CIP server ready<cr><lf>
>>> # CIP-Version: 3<cr><lf>
<<< % 300 CIPv3 OK!<cr><lf>
>>> Mime-Version: 1.0<cr><lf>
>>> Content-type: application/index.cmd.datachanged; type=
>>> x-tagged-index-1; dsi=1.2.752.17.5.10<cr><lf>
>>> <cr><lf>
>>> updatetype: incremental tagbased<cr><lf>
>>> thisupdate: 855938804<cr><lf>
>>> lastupdate: 855940000<cr><lf>
>>> .<cr><lf>
<<< % 200 Good MIME message received
>>> MIME-Version: 1.0<cr><lf>
>>> Content-Type: application/index.obj.tagged;
>>> dsi=1.2.752.17.5.10;
>>> base-uri="ldap://ldap.umu.se/dc=umu,dc=se"<cr><lf>
>>> <cr><lf>
>>> version: x-tagged-index-1<cr><lf>
>>> updatetype: incremental<cr><lf>
>>> lastupdate: 855940000<cr><lf>
>>> thisupdate: 855938804<cr><lf>
>>> BEGIN IO-schema<cr><lf>
>>> cn: TOKEN<cr><lf>
>>> sn: FULL<cr><lf>
>>> title: FULL<cr><lf>
>>> END IO-Schema<cr><lf>
>>> BEGIN Update Block<cr><lf>
>>> BEGIN Old<cr><lf>
>>> title: 3/testpilot<cr><lf>
>>> END Old<cr><lf>
>>> BEGIN New<cr><lf>
>>> title: 3/chiefpilot<cr><lf>
>>> END New<cr><lf>
>>> END Update Block<cr><lf>
>>> .<cr><lf>
<<< % 200 Good MIME message received
{ Sender-CIP shuts down socket for writing }
<<< % 222 Connection closing in response to sender-CIP shutdown
{ receiver-CIP closes its side, resets, and awaits a
new sender-CIP }
An example of an unsuccessful version negotiation looks like this:
{ sender-CIP connects to receiver-CIP }
<<< % 220 Whois++ server ready<cr><lf>
>>> # CIP-Version: 3<cr><lf>
<<< % 500 Syntax error<cr><lf>
{ server closes connection }
The sender-CIP may attempt to retry using version 1 or 2 protocol.
Sender-CIP may cache results of this unsuccessful negotiation to
avoid later attempts.
2.1.1 Transport specific response codes
The following response codes are used with the stream transport:
Code Suggested description Sender-CIP action
text
200 MIME request received Expect no output, continue session
and processed (or close)
201 MIME request received Read a response, delimited by SMTP-
and processed, output style message delimiter.
follows
220 Initial server banner Continue with Whois++ interaction,
message or attempt CIP version negotiation.
222 Connection closing (in Done with transaction.
response to sender-CIP
close)
300 Requested CIP version Continue with CIP transaction, in
accepted the specified version.
400 Temporarily unable to Retry at a later time. May be used
process request to indicate that the server does not
currently have the resources
available to accept an index.
500 Bad MIME message format Retry with correctly formatted MIME
501 Unknown or missing Retry with correct CIP command
request in
application/index.cmd
502 Request is missing Retry with correct CIP attributes.
required CIP attributes
520 Aborting connection for Alert local administrator.
some unexpected reason
530 Request requires valid Sign the request, if possible, and
signature retry. Otherwise, report problem to
the administrator.
531 Request has invalid Report problem to the administrator.
signature
532 Cannot check signature Alert local administrator, who should
cooperate with remote administrator
tp diagnose and resolve the problem.
(Probably missing a public key.)
2.2 Internet mail infrastructure as transport
As an alternative to TCP streams, CIP transactions can take place
over the existing Internet mail infrastructure. There are two
motivations for this feature of CIP. First, it lowers the barriers
to entry for leaf servers. When the need for a full TCP
implementation is relaxed, leaf nodes (which, by definition, only
send index objects) can consist of as little as a database and an
indexing program (possibly written in a very high level language)
to participate in the mesh.
Second, it keeps with the philosophy of making use of existing
Internet technology. The MIME messages used for requests and
responses are, by definition of the MIME specification, suitable
for transport via the Internet mail infrastructure. With a few
simple rules, we open up an entirely different way to interact with
CIP servers which choose to implement this transport. See Protocol
Conformance, below, for details on what options server implementers
have about supporting the various transports.
The basic rhythm of request/response is maintained when using the
mail transport. The following sections clarify some special cases
which need to be considered for mail transport of CIP objects. In
general, all mail protocols and mail format specifications
(especially MIME Security Multiparts) can be used with the CIP mail
transport.
2.2.1 CIP-Version negotiation
Since no information on which CIP-version is in use is present in
the MIME message, this information has to be carried in the
mailheader. Therefor CIP requests sent using the mail transport
MUST include a CIP-version headerline, to be registered according
to [MHREG].
The format of this line is:
DIGIT = %x30-39
number = 1*DIGIT
cipversion = "CIP-Version:" <sp> number["." number]
2.2.2 Return path
When CIP transactions take place over a bidirectional stream, the
return path for errors and results is implicit. Using mail as a
transport introduces difficulties to the recipient, because it's
not always clear from the headers exactly where the reply should go,
though in practice there are some heuristics used by MUA's.
CIP solves this problem by fiat. CIP requests sent using the mail
transport MUST include a Reply-To header as specified by RFC-822.
Any mail received for processing by a CIP server implementing the
mail transport without a Reply-To header MUST be ignored, and a
message should be logged for the local administrator. The receiver
MUST not attempt to reply with an error to any address derived
from the incoming mail.
If there are no circumstances under which a response is to be sent
to a CIP request, the sender should include a Reply-To header with
the address "<>" in it.
Receivers MUST never attempt to send replies to that address, as
it is defined to be invalid (both here, and by the BNF grammar in
RFC-822). It should be noted that, in general, it is a bad idea to
turn off error reporting in this way. However, in the simplest case
of an index pushing program, this MAY be a desirable simplification.
2.3 HTTP transport
HTTP MAY also be used to transport CIP objects, since they are just
MIME objects. A transaction is performed by using the POST method to
send an application/index.cmd and returning an
application/index.response or an application/index.obj in the HTTP
reply. The URL that is the target of the post is a configuration
parameter of the CIP-sender to CIP-receiver relationship.
Example:
{ the client opens the connection and sends a POST }
>>> POST / HTTP/1.1<cr><lf>
>>> Host: cip.some.corp<cr><lf>
>>> Content-type: application/index.cmd.noop<cr><lf>
>>> Date: Thu, 6 Jun 1997 18:16:03 GMT<cr><lf>
>>> Content-Length: 2<cr><lf>
>>> Connection: close<cr><lf>
>>> <cr><lf>
{ the server processes the request }
<<< HTTP/1.1 204 No Content<cr><lf>
{ the server closes the connection }
In addition to leveraging the security capabilities that come with
HTTP, there are other HTTP features that MAY be useful in a CIP
context. A CIP client MAY use the Accept-Charset and Accept-Language
HTTP headers to express a desire to retrieve an index in a particular
character set or natural language. It MAY use the Accept-Encoding
header to (e.g.) indicate that it can handle compressed responses,
which the CIP server MAY send in conjunction with the Transfer-
Encoding header. It MAY use the If-Modified-Since header to prevent
wasted transmission of an index that has not changed since the last
poll. A CIP server can use the Retry-After header to request that
the client retry later when the server is less busy.
3. Security considerations
There are two levels at which the index information can be
protected; the first is by use of the technology available for
securing MIME [MIME-SEC] objects, and secondly by using the
technology available for securing the transport.
When it comes to transport the stream transport can be protected by
the use of TLS [TLS] . For HTTP the Security is handled by
using HTTP Basic Authentication [RFC 2068], HTTP Message Digest
Authentication [RFC2069] or SSL/TLS. Extra protection for the SMTP
exchange can be achieve by the use of Secure SMTP over TLS [SMTPTLS].
4. References
[RFC 2045] Freed, N., Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
November, 1996
[RFC 2068] Fielding, et.al., "Hypertext Transfer Protocol --
HTTP/1.1", January, 1997.
[RFC 2069] Franks, et. al., "An Extension to HTTP: Digest Access
Authentication", January, 1997.
[CIP-ARCH] Allen, J., Mealling, M, "The Common Indexing Protocol",
work in progress.
[CIP-MIME] Allen, J., Mealling, M., "MIME Object Definitions for the
Common Indexing Protocol", work in progress.
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[CIP-TIO] Hedberg, et.al. "A Tagged Index Object for use in the
Common Indexing Protocol", work in progress.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March 1997.
[MIME-SEC] Galvin, Murphy, Crocker, Freed, "Security Multiparts for
MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, Trusted
Information Systems, CyberCash, Innosoft International, October
1995.
[TLS] Dierks, T., Allen, C., "The TLS Protocol Version 1.0", RFC
2246, Certicom, January 1999.
[SMTPTLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over
TLS", RFC 2487, Internet Mail Consortium, January 1999.
[MHREG] Jacob, P., "Mail and Netnews Header Registration Procedure",
work in progress.
5. Authors' Addresses
Jeff R. Allen Paul J. Leach
246 Hawthorne St. Microsoft
Palo Alto, CA 94301 1 Microsoft Way
USA Redmond, WA 98052
EMail: jeff.allen@acm.org Email: paulle@microsoft.com
Roland Hedberg
Catalogix
Dalsveien 53
0775 Oslo
Norway
EMail: roland@catalogix.ac.se
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