Internet DRAFT - draft-fossati-core-fp-link-format-attribute
draft-fossati-core-fp-link-format-attribute
Internet Engineering Task Force T. Fossati
Internet-Draft KoanLogic
Intended status: Standards Track S. Loreto
Expires: January 10, 2013 Ericsson
July 9, 2012
Resource Discovery through Proxies
draft-fossati-core-fp-link-format-attribute-00
Abstract
The aim of this draft is to open a discussion on how to make it
possible to advertise the fact that a given resource hosted by a
server can only be reached through a specific CoAP Proxy.
This memo proposes the definition of the "fp" (forward proxy) CoAP
link format attribute, that can be used to inform CoAP endpoints that
a given resource can be reached by passing through the advertising
Proxy.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 10, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Fossati & Loreto Expires January 10, 2013 [Page 1]
Internet-Draft Resource Discovery through Proxies July 2012
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Proxied Discovery Scenario . . . . . . . . . . . . . . . . . . 3
3. The fp Link Format Attribute . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
4.1. fp Attribute . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Fossati & Loreto Expires January 10, 2013 [Page 2]
Internet-Draft Resource Discovery through Proxies July 2012
1. Introduction
The discovery mechanism described in [I-D.ietf-core-link-format]
assumes cheap and pervasive multicast. However as discussed in
[I-D.shelby-core-resource-directory] direct discovery of resources is
not always practical due to limitations in the underlying radio link
(see Section 1 of [I-D.ietf-6lowpan-nd]), the absence of a multicast
routing protocol to bridge through different links, sleeping nodes,
disperse networks.
The Resource Directory (RD) provides a first solution hosting
descriptions of resources held on other servers and allowing lookups
to be performed for those resources. The current solution however
does not address the scenario where the URI (of the resource of
interest) is associated to a CoAP origin server that can only be
accessed through a CoAP proxies either for topological and/or
security reasons or because it is a sleepy origin server.
Given their topological role, CoAP Proxies (Section 5.7 of
[I-D.ietf-core-coap]) can be used effectively to address the above
mentioned scenarios. However, in order to achieve this capability,
the fact that a given resource is made available through a proxy must
be made explicit to consuming endpoints, so that they can use the
Proxy-Uri Option to dereference the final target.
This memo defines the "fp" (forward proxy) CoAP link format
attribute, that can be used to inform CoAP endpoints that a given
resource can be reached by passing through the advertising Proxy.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Proxied Discovery Scenario
Consider the scenario depicted in Figure 1. Two separate CoAP links
are proxied by P. Node A hosts resource /res of type "x", and P knows
it -- either through explicit or implicit mechanism (e.g. previous
discovery on the local link, or a co-located RD, etc.)
Fossati & Loreto Expires January 10, 2013 [Page 3]
Internet-Draft Resource Discovery through Proxies July 2012
| |
</res>;rt="x" (A)---+ |
| |
+---(P)---+
| |
| +---(B)
| |
Figure 1
We would like to allow B to discover that A hosts a resource with
type "x" even if A can't be directly reached by B.
P may in principle let this information filter from one link to the
other, but given the mechanisms currently defined for the discovery
via /.well-known/core (Section 2.1 of [I-D.ietf-core-link-format]),
there is no way for a consuming node to ascertain that an advertised
link is to be accessed through a given forward Proxy or by a direct
route.
We may choose to use the anchor parameter in the link and define a
new relation name to express the "proxied by" relation, but this may
actually have zero chance to succeed because of the freedom left to a
consuming node to actually ignore anchored links (Section 2.3 of
[I-D.ietf-core-link-format]).
3. The fp Link Format Attribute
The proposed solution, instead, envisages a new link format
attribute, "fp" that is added by the Proxy to the original set of
attributes of the linked resource to inform the requesting endpoint
that the advertised (absolute) URI must be requested to the
advertising Proxy using the Proxy-URI Option, as illustrated in
Figure 2. The "fp" link format attribute MAY be set to the Proxy IP
address.
When advertised on a link different from the one on which it resides,
the original resource link SHALL be transformed by the Proxy into an
absolute URI that can be used as-is in a Proxy-Uri Option by the
requesting node.
Fossati & Loreto Expires January 10, 2013 [Page 4]
Internet-Draft Resource Discovery through Proxies July 2012
P B
| |
|<-----' Uri-Path: .well-known
| GET | Uri-Path: core
| | Uri-Query: rt=x
| |
`----->| Content-Type: link-format
| 2.05 | payload: <coap://A/res>;rt="x";fp="proxy IP address"
Figure 2
Note that in case the "fp" attribute is present, the URI-Reference in
the link-value [RFC5988] MUST always be a URI and not a relative-ref
[RFC3986].
The forwarding path to /res is now set up, and B can reach it through
P using the Proxy-Uri Options as follows:
A P B
| | |
| |<-----' Proxy-Uri: coap://A/res
| | GET |
|<-----' | Uri-Path: res
| GET | |
| | |
`----->| |
| 2.05 | |
| `----->|
| | 2.05 |
4. IANA Considerations
4.1. fp Attribute
This section defines a new Web Linking [RFC5988] attribute for use
with [I-D.ietf-core-link-format]. The "fp" (forward proxy) CoAP link
format attribute, that can be used by Proxy nodes to inform CoAP
endpoints that a given resource can be reached by passing through the
advertising Proxy.
5. Security Considerations
The mechanism specified in this document shares the same security
concerns as the discovery process described in
[I-D.ietf-core-link-format].
Fossati & Loreto Expires January 10, 2013 [Page 5]
Internet-Draft Resource Discovery through Proxies July 2012
Especially critical to the CoAP network consistency, is the fact that
in NoSec mode a malicious attacker could poison the response of a
query to the /.well-known/core in order to re-route traffic.
6. References
6.1. Normative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-10 (work in progress), June 2012.
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-13 (work in progress),
May 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
6.2. Informative References
[I-D.ietf-6lowpan-nd]
Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low Power and Lossy Networks
(6LoWPAN)", draft-ietf-6lowpan-nd-18 (work in progress),
October 2011.
[I-D.shelby-core-resource-directory]
Krco, S. and Z. Shelby, "CoRE Resource Directory",
draft-shelby-core-resource-directory-02 (work in
progress), October 2011.
Fossati & Loreto Expires January 10, 2013 [Page 6]
Internet-Draft Resource Discovery through Proxies July 2012
Authors' Addresses
Thomas Fossati
KoanLogic
Via di Sabbiuno, 11/5
Bologna 40100
Italy
Email: tho@koanlogic.com
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: salvatore.loreto@ericsson.com
Fossati & Loreto Expires January 10, 2013 [Page 7]
