XMPP as defined in &rfc3920; does not support direct client-to-client interactions, since it requires authentication with a server: an XMPP client is allowed access to the network only once it has authenticated with a server, and the server must not grant access if authentication fails for any reason. If an unauthenticated client attempts to communicate directly with another client, such communication will fail because all XMPP communications are sent through one or more servers and a client cannot inject messages onto the network without first authenticating with a server.
-However, it is possible to establish an XMPP-like communications system on a local (or even wide-area) network using the principles of zero-configuration networking. In this situation, the clients obviate the XMPP requirement for authentication with a server by relying on zero-configuration networking to establish serverless communication using the _presence._tcp DNS SRV service type. Once discovery has been completed, the clients are then able to exchange messages and other structured data using the XMPP &MESSAGE; and &IQ; stanzas.
-Serverless messaging is restricted to a local network (or ad-hoc wide-area network) because of how zero-configuration networking works. It is impossible for clients that communicate via this serverless mode to insert messages into an XMPP network, which is why this kind of "mesh" is most accurately referred to as an XMPP-like system that exists outside the context of existing XMPP networks (though see the Security Considerations regarding the ability to "forward" messages from a serverless mesh to an XMPP network or vice-versa).
+However, it is possible to establish an XMPP-like communication system on a local (or even wide-area) network using the principles of zero-configuration networking. In this situation, the clients obviate the XMPP requirement for authentication with a server by relying on zero-configuration networking to establish serverless communication using the _presence._tcp DNS SRV service type. Once discovery has been completed, the clients are able to negotiate an XML stream between themselves (as generalized in &xep0246;) and then exchange messages and other structured data using the XMPP &MESSAGE; and &IQ; stanzas.
+Serverless messaging is typically restricted to a local network (or ad-hoc wide-area network) because of how zero-configuration networking works. It is impossible for clients that communicate via this serverless mode to insert messages into an XMPP network, which is why this kind of "mesh" is most accurately referred to as an XMPP-like system that exists outside the context of existing XMPP networks (though see the Security Considerations regarding the ability to "forward" messages from a serverless mesh to an XMPP network or vice-versa).
Such a "mesh" can be quite valuable in certain circumstances. For instance, participants in a trade show or conference, users of the same wifi hotspot, or employees on the same local area network can communicate without the need for a pre-configured server. For this reason, support for serverless messaging has been a feature of Apple's iChat client when operating in Bonjour (formerly Rendezvous) mode for many years. Because it is desirable for other Jabber/XMPP clients to support such functionality, this document describes how to use zero-configuration networking as the basis for serverless communication, mainly for use on local links (although the protocol can also be used on ad-hoc wide-area networks).
In order to discover other users, a client sends an mDNS request for PTR records that match "_presence._tcp.local.". The client then receives replies from all machines that advertise support for serverless messaging.
In order to discover other users, a client sends an mDNS request for PTR records that match "_presence._tcp.local.". The client then receives replies from all machines that advertise support for serverless messaging.
Devices that use serverless messaging may have multiple network interfaces. As a result, it is possible to discover the same entity multiple times. Even if a client discovers the same presence name on multiple network interfaces, it MUST show only one entity in the serverless roster. In addition, because local IP addresses can be dynamically re-assigned, the client SHOULD NOT store the IP address to be used for communications when it discovers that address in the initial DNS lookup phase; instead, it SHOULD delay sending the Multicast DNS query until the client is ready to communicate with the other entity.
+Devices that use serverless messaging may have multiple network interfaces. As a result, it is possible to discover the same entity multiple times. Even if a client discovers the same presence name on multiple network interfaces, it MUST show only one entity in the serverless roster. In addition, because local IP addresses can be dynamically re-assigned, the client SHOULD NOT store the IP address to be used for communication when it discovers that address in the initial DNS lookup phase; instead, it SHOULD delay sending the Multicast DNS query until the client is ready to communicate with the other entity.
If an entity has an associated icon (e.g., a user avatar or photo), its client SHOULD publish the raw binary data for that image via a DNS NULL record of the following form:
@@ -431,7 +431,7 @@ _presence._tcp.local. IN NULL raw-binary-data-hereXMPP networks use TLS (&rfc2246;) for channel encryption, SASL (&rfc4422;) for authentication, and the Domain Name System (&rfc1034;) for weak validation of server hostnames; these technologies help to ensure the identity of sending entities and to encrypt XML streams. By contrast, zero-configuration networking uses dynamic discovery and asserted machine names as the basis of sender identity. Therefore, serverless messaging does not result in authenticated identities in the same way that XMPP itself does, nor does it provide for an encrypted channel between entities.
+XMPP networks use TLS (&rfc4346;) for channel encryption, SASL (&rfc4422;) for authentication, and the Domain Name System (&rfc1034;) for weak validation of server hostnames; these technologies help to ensure the identity of sending entities and to encrypt XML streams. By contrast, zero-configuration networking uses dynamic discovery and asserted machine names as the basis of sender identity. Therefore, serverless messaging does not result in authenticated identities in the same way that XMPP itself does, nor does it provide for an encrypted channel between entities.
There are two potential solutions to this problem:
It is RECOMMENDED to use one of these methods to secure communications between serverless entities. However, subject to client configuration and local service policies, two entities MAY accept an unauthenticated and unencrypted channel; but a client SHOULD warn the human user that the channel is unauthenticated and unencrypted.
Because of fundamental differences between a true XMPP network and a serverless client "mesh", entities communicating via serverless messagin MUST NOT attempt to inject serverless traffic onto an XMPP network and an XMPP server MUST reject communications until an entity is properly authenticated in accordance with the rules defined in RFC 3920. However, a client on a serverless mesh MAY forward traffic to an XMPP network after having properly authenticated on such a network (e.g., to forward a message received on a serverless client mesh to a contact on an XMPP network).
+Because of fundamental differences between a true XMPP network and a serverless client "mesh", entities communicating via serverless messaging MUST NOT attempt to inject serverless traffic onto an XMPP network and an XMPP server MUST reject communications until an entity is properly authenticated in accordance with the rules defined in RFC 3920. However, a client on a serverless mesh MAY forward traffic to an XMPP network after having properly authenticated on such a network (e.g., to forward a message received on a serverless client mesh to a contact on an XMPP network).
Because there is no mechanism for validating the information that is published in DNS TXT records, it is possible for clients to "poison" this information (e.g., by publishing email addresses or Jabber IDs that are controlled by or associated with other users).
@@ -591,7 +591,7 @@ _presence._tcp.local. IN NULL raw-binary-data-here