Abstract: | This specification defines a protocol for using server-to-server connections in a bidirectional way such that stanzas are sent and received on the same TCP connection. |
Authors: | Philipp Hancke, Dave Cridland |
Copyright: | © 1999 - 2011 XMPP Standards Foundation. SEE LEGAL NOTICES. |
Status: | Deferred |
Type: | Standards Track |
Version: | 0.1 |
Last Updated: | 2010-10-04 |
WARNING: Consideration of this document has been Deferred by the XMPP Standards Foundation. Implementation of the protocol described herein is not recommended.
1. Introduction
2. Protocol
2.1. Stream Feature
2.2. Negotiation
3. Examples
4. Security Considerations
5. XMPP Registrar Considerations
5.1. Protocol Namespaces
5.2. Stream Features
6. IANA Considerations
Appendices
A: Document Information
B: Author Information
C: Legal Notices
D: Relation to XMPP
E: Discussion Venue
F: Requirements Conformance
G: Notes
H: Revision History
XMPP Core [1] restricts server-to-server communication in such a way that a server has to use on TCP connection for XML stanzas sent from the server to the peer and another TCP connection (initiated by the peer) for stanzas from the peer to the server, for a total of two TCP connections. RFC 6120 [2] allows two servers to send stanzas in a bidirectional way, but does not define methods for explicitly signalling the usage thereof. This is accomplished in this specification.
If a server supports bidirectional server-to-server streams, it should inform the connecting entity when returning stream features during the stream negotiation process (both before and after TLS negotiation). This is done by including a <bidi/> element qualified by the 'urn:xmpp:features:bidi' namespace.
<stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> <bidi xmlns='urn:xmpp:features:bidi'/> </stream:features>
If the initiating entity chooses to use TLS, STARTTLS negotiation MUST be completed before enabling bidirectionality.
To enable bidirectional communication, the connecting server sends a <bidi/> element qualified by the 'urn:xmpp:bidi' namespace. This SHOULD be done before either SASL negotiation or Server Dialback [3].
C: <bidi xmlns='urn:xmpp:bidi'/>
Note: Since there is no reply to the request, it is possible to pipeline it.
After enabling bidirectionality, the connecting server continues to authenticate via SASL or requests to send stanzas for a domain pair with Server Dialback. The receiving server MUST NOT send stanzas to the peer before it has authenticated via SASL, or the peer's identity has been verified via Server Dialback. Note that the receiving server MUST NOT attempt to verify a dialback key on the same connection where the corresponding request was issued.
Also note that the receiving server MUST only send stanzas for which it has been authenticated - in the case of TLS/SASL based authentication, this is the value of the stream's 'to' attribute, whereas in the case of Server Dialback [4] this is the value of the 'to' attribute on any <db:result> element.
Finally, once bidirectionality is enabled, the receiving server MAY initiate Server Dialback [5] authentications for other domains it hosts to any domain authenticated to be hosted by the connecting server.
This section shows two complete examples of bidirectional streams, the first example uses SASL EXTERNAL, the second uses Server Dialback.
C: <stream:stream xmlns:stream='http://etherx.jabber.org/streams' xmlns='jabber:server' xmlns:db='jabber:server:dialback' to='montague.lit' from='capulet.lit' xml:lang='en' version='1.0'> S: <stream:stream xmlns='jabber:server' xmlns:db='jabber:server:dialback' xmlns:stream='http://etherx.jabber.org/streams' xml:lang='en' id='65b30434afd7646699d077f7affcb2c120c48e18' from='montague.lit' to='capulet.lit' version='1.0'> S: <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> <bidi xmlns='urn:xmpp:bidi'/> </stream:features> C: <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> S: <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> C: <stream:stream xmlns:stream='http://etherx.jabber.org/streams' xmlns='jabber:server' xmlns:db='jabber:server:dialback' to='montague.lit' from='capulet.lit' xml:lang='en' version='1.0'> S: <stream:stream xmlns='jabber:server' xmlns:db='jabber:server:dialback' xmlns:stream='http://etherx.jabber.org/streams' xml:lang='en' id='b5cd769b1dc292c6f6557fe76cabc4d112333f9a' from='montague.lit' to='capulet.lit' version='1.0'> S: <stream:features> <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'> <mechanism>EXTERNAL<mechanism> </mechanisms> <bidi xmlns='urn:xmpp:bidi'/> </stream:features> C: <bidi xmlns='urn:xmpp:bidi'/> <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='EXTERNAL'> Y2FwdWxldC5saXQ=</auth> S: <success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/> C: <stream:stream xmlns:stream='http://etherx.jabber.org/streams' xmlns='jabber:server' xmlns:db='jabber:server:dialback' to='montague.lit' from='capulet.lit' xml:lang='en' version='1.0'> S: <stream:stream xmlns='jabber:server' xmlns:db='jabber:server:dialback' xmlns:stream='http://etherx.jabber.org/streams' xml:lang='en' id='b5cd769b1dc292c6f6557fe76cabc4d112333f9a' from='montague.lit' to='capulet.lit' version='1.0'> S: <stream:features/> <!-- At this point, S is allowed to send C stanzas from capulet.lit since that is the value of 'to' in the stream open sent by C above. --> C: <iq from='juliet@capulet.lit/balcony' to='montague.lit' type='get' id='8dfc70af'><query xmlns='urn:xmpp:ping'/></iq> S: <iq from='montague.lit' to='juliet@capulet.lit/balcony' type='result' id='8dfc70af'><query xmlns='urn:xmpp:ping'/></iq>
C: <stream:stream xmlns:stream='http://etherx.jabber.org/streams' xmlns='jabber:server' xmlns:db='jabber:server:dialback' to='montague.lit' from='capulet.lit' xml:lang='en' version='1.0'> S: <stream:stream xmlns='jabber:server' xmlns:db='jabber:server:dialback' xmlns:stream='http://etherx.jabber.org/streams' xml:lang='en' id='65b30434afd7646699d077f7affcb2c120c48e18' from='montague.lit' to='capulet.lit' version='1.0'> S: <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> <bidi xmlns='urn:xmpp:bidi'/> </stream:features> C: <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> S: <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> C: <stream:stream xmlns:stream='http://etherx.jabber.org/streams' xmlns='jabber:server' xmlns:db='jabber:server:dialback' to='montague.lit' from='capulet.lit' xml:lang='en' version='1.0'> S: <stream:stream xmlns='jabber:server' xmlns:db='jabber:server:dialback' xmlns:stream='http://etherx.jabber.org/streams' xml:lang='en' id='b5cd769b1dc292c6f6557fe76cabc4d112333f9a' from='montague.lit' to='capulet.lit' version='1.0'> S: <stream:features> <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/> <bidi xmlns='urn:xmpp:bidi'/> </stream:features> <example caption="Stream Setup before TLS"><![CDATA[ C: <bidi xmlns='urn:xmpp:bidi'/> <db:result from='capulet.lit' to='montague.lit'> e3f5cf21f12749ef2cf59269bc0118f35bc46b26</db:result> <!-- At this point S may send from capulet.lit. --> S: <db:result from='montague.lit' to='capulet.lit' type='valid'/> C: <iq from='juliet@capulet.lit/balcony' to='montague.lit' type='get' id='8dfc70af'><query xmlns='urn:xmpp:ping'/></iq> S: <iq from='montague.lit' to='juliet@capulet.lit/balcony' type='result' id='8dfc70af'><query xmlns='urn:xmpp:ping'/></iq> S: <db:result from='conference.montague.lit' to='capulet.lit'> 1bac3ef56fed987cfe098c9785c654a5476ed765</db:result> <!-- The above is also legal - S attempts to authenticate as a different domain as well, presumably a MUC domain --> C: <db:result from='capulet.lit' to='conference.montague.lit' type='valid'/> <!-- Now S can send as conference.m.l as well as C sending to that domain. -->
This specification introduces no security considerations above and beyond those discussed in RFC 3920.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].
Series: XEP
Number: 0288
Publisher: XMPP Standards Foundation
Status:
Deferred
Type:
Standards Track
Version: 0.1
Last Updated: 2010-10-04
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0178, XEP-0220
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Source Control:
HTML
This document in other formats:
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JabberID:
fippo@ve.symlynx.com
Email:
dave.cridland@isode.com
JabberID:
dave.cridland@isode.com
The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.
2. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.
3. XEP-0220: Server Dialback <http://xmpp.org/extensions/xep-0220.html>.
4. XEP-0220: Server Dialback <http://xmpp.org/extensions/xep-0220.html>.
5. XEP-0220: Server Dialback <http://xmpp.org/extensions/xep-0220.html>.
6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Initial published version.
(psa)belated run-over pre-publication
Added notes on authentication
(dwd)initial version
(ph)END