Internet DRAFT - draft-ietf-dime-realm-based-redirect
draft-ietf-dime-realm-based-redirect
Internet Engineering Task Force T. Tsou
Internet-Draft Huawei Technologies (USA)
Updates: 6733 (if approved) R. Hao
Intended status: Standards Track Comcast Cable
Expires: April 04, 2014 T. Taylor, Ed.
Huawei Technologies
October 01, 2013
Realm-Based Redirection In Diameter
draft-ietf-dime-realm-based-redirect-13
Abstract
The Diameter protocol includes a capability for message redirection,
controlled by an application-independent "redirect agent". In some
circumstances, an operator may wish to redirect messages to an
alternate domain without specifying individual hosts. This document
specifies an application-specific mechanism by which a Diameter
server or proxy (node) can perform such a redirection when S-NAPTR is
not used for dynamic peer discovery. A node performing this new
function is referred to as a "Realm-based Redirect Server".
This memo updates Sections 6.13 and 6.14 of RFC6733 with respect to
the usage of the Redirect-Host-Usage and Redirect-Max-Cache-Time
AVPs.
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
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This Internet-Draft will expire on April 04, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Support of Realm-Based Redirection Within
Applications . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Realm-Based Redirection . . . . . . . . . . . . . . . . . . . 4
3.1. Configuration of the Realm-based Redirect Server . . . . 5
3.2. Behaviour of Diameter Nodes . . . . . . . . . . . . . . . 5
3.2.1. Behaviour at the Realm-based Redirect Server . . . . 5
3.2.2. Proxy Behaviour . . . . . . . . . . . . . . . . . . . 6
3.2.3. Client Behaviour . . . . . . . . . . . . . . . . . . 6
3.3. The Redirect-Realm AVP . . . . . . . . . . . . . . . . . 7
3.4. DIAMETER_REALM_REDIRECT_INDICATION Protocol Error Code . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Diameter base protocol [RFC6733] specifies a basic redirection
service provided by redirect agent. The redirect indication returned
by the redirect agent is described in Section 6.1.8 and Sections
6.12-6.14 of [RFC6733], and provides to the message sender one or
more individual hosts as destination of the redirected message.
However, consider the case where an operator has offered a specific
service but no longer wishes to do so. The operator has arranged for
an alternative domain to provide the service. To aid in the
transition to the new arrangement, the original operator maintains a
redirect server to indicate to the message sender the alternative
domain to which redirect the request. However, the original operator
should be relieved from configuring in the redirect server a list of
hosts to contact in the alternative operator's domain, and should
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simply be able to provide redirect indications to the domain as a
whole.
1.1. Terminology
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].
Within this specification, the term "realm-based redirection" is used
to refer to a mode of operation where a realm rather than an
individual host is returned as redirect indication.
The term "Realm-based Redirect Server" denotes the Diameter node
(Diameter server or proxy) that returns the realm-based redirection.
The behaviour of the Realm-based Redirect Server itself is a slight
modification of the behaviour of a basic redirect agent as described
in Section 6.1.8 of [RFC6733].
This document uses a number of terms consistently with their usage in
[RFC6733]: "Diameter client", "Diameter node", Diameter peer",
"Diameter server", "proxy", "realm" or "domain", "redirect agent",
and "session" as defined in Section 1.2, and "application" as defined
implicitly by Sections 1.3.4, 2.3, and 2.4.
2. Support of Realm-Based Redirection Within Applications
The DNS-based dynamic peer discovery mechanism defined in the
Diameter base protocol [RFC6733] provides a simple mechanism for
realm-based redirection, using the S-NAPTR DDDS application
[RFC3958]. When S-NAPTR is used for peer discovery, redirection of
Diameter requests from the original realm to a new realm may be
performed by updating the existing NAPTR resource records for the
original realm as follows: the NAPTR RR for the desired
application(s) and supported application protocol(s) provided by the
new realm will have an empty FLAG field and the REPLACEMENT field
will contain the new realm to use for the next DNS lookup. The new
realm can be arbitrary; the restriction in [RFC6733] that the NAPTR
replacement field match the domain of the original query does not
apply for realm-based redirect purposes.
However, the use of DNS-based dynamic peer discovery is optional for
Diameter implementations. For deployments which do not make use of
S-NAPTR peer discovery, support of realm-based redirection needs to
be specified as part of functionality supported by a Diameter
application. In this way, support of the considered Diameter
application (discovered during capabilities exchange procedures as
defined in Diameter base protocol [RFC6733]) indicates implicit
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support of the realm-based redirection mechanism. A new application
specification can incorporate the mechanism specified here by making
it mandatory to implement for the application, and referencing this
specification normatively.
The result of making realm-based redirection an application-specific
behaviour is that it cannot be performed by a redirect agent as
defined in [RFC6733], but MUST be performed instead by an
application-aware Diameter node (Diameter server or proxy) (hereafter
called a "Realm-based Redirect Server").
An application can specify that realm-based redirection operates only
on complete sessions beginning with the initial message, or on every
message within the application, even if earlier messages of the same
session were not redirected. This distinction matters only when
realm-based redirection is first initiated. In the former case,
existing sessions will not be disrupted by the deployment of realm-
based redirection. In the latter case, existing sessions will be
disrupted if they are stateful.
3. Realm-Based Redirection
This section specifies an extension of the Diameter base protocol
[RFC6733] to achieve realm-based redirection. The elements of this
solution are:
o a new result code, DIAMETER_REALM_REDIRECT_INDICATION (3xxx TBD1);
o a new attribute-value pair (AVP), Redirect-Realm (code TBD2); and
o associated behaviour at Diameter nodes implementing this
specification.
This behaviour includes the optional use of the Redirect-Host-Usage
and Redirect-Max-Cache-Time AVPs. In this document, these AVPs apply
to the peer discovered by a node acting on the redirect server's
response, an extension to their normal usage as described in Sections
6.13 and 6.14 of [RFC6733].
Section 3.2.2 and Section 3.2.3 describe how a proxy or client may
update its routing table for the application and initial realm, as a
result of selecting a peer in the new realm after realm-based
redirection. Note that as a result, the proxy or client will
automatically route subsequent requests for that application to the
new realm (with the possible exception of requests within sessions
already established with the initial realm) until the cached routing
entry expires. This should be borne in mind if the rerouting is
intended to be temporary.
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3.1. Configuration of the Realm-based Redirect Server
A Diameter node (Diameter server or proxy) acting as Realm-based
Redirect Server MUST be configured as follows to execute realm-based
redirection:
o configured with an application that incorporates realm-based
redirection;
o the Local Action field of the routing table described in
Section 2.7 of [RFC6733] is set to LOCAL;
o an application-specific field is set to indicate that the required
local action is to perform realm-based redirection;
o an associated application-specific field is configured with the
identities of one or more realms to which the request should be
redirected.
3.2. Behaviour of Diameter Nodes
3.2.1. Behaviour at the Realm-based Redirect Server
As mentioned in Section 2, an application can specify that realm-
based redirection operates only on complete sessions beginning with
the initial message (i.e., to prevent disruption of established
sessions), or on every message within the application, even if
earlier messages of the same session were not redirected.
If a Realm-based Redirect Server configured as described in
Section 3.1 receives a request to which realm-based redirection
applies, the Realm-based Redirect Server MUST reply with an answer
message with the 'E' bit set, while maintaining the Hop-by-Hop
Identifier in the header. The Realm-based Redirect Server MUST
include the Result-Code AVP set to
DIAMETER_REALM_REDIRECT_INDICATION. The Realm-based Redirect Server
MUST also include the alternate realm identifier(s) with which it has
been configured, each in a separate Redirect-Realm AVP instance.
The Realm-based Redirect Server MAY include a copy of the Redirect-
Host-Usage AVP, which SHOULD be set to REALM_AND_APPLICATION. If
this AVP is added, the Redirect-Max-Cache-Time AVP MUST also be
included. Note that these AVPs apply to the peer discovered by a
node acting on the Realm-based Redirect Server's response, as
described in the next section. This is an extension of their normal
usage as described by Sections 6.13 and 6.14 of [RFC6733].
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Realm-based redirection MAY be applied even if a Destination-Host
AVP is present in the request, depending on the operator-based
policy.
3.2.2. Proxy Behaviour
A proxy conforming to this specification that receives an answer
message with the Result-Code AVP set to
DIAMETER_REALM_REDIRECT_INDICATION MUST attempt to reroute the
original request to a server in a realm identified by a Redirect-
Realm AVP instance in the answer message, and if it fails MUST
forward the indication toward the client. To reroute the request, it
MUST take the following actions:
1. Select a specific realm from amongst those identified in
instances of the Redirect-Realm AVP in the answer message.
2. If successful, locate and establish a route to a peer in the
realm given by the Redirect-Realm AVP, using normal discovery
procedures as described in Section 5.2 of [RFC6733].
3. If again successful:
a. update its cache of routing entries for the realm and
application to which the original request was directed,
taking into account the Redirect-Host-Usage and Redirect-Max-
Cache-Time AVPs, if present in the answer.
b. Remove the Destination-Host (if present) and Destination-
Realm AVPs from the original request and add a new
Destination-Realm AVP containing the realm selected in the
initial step.
c. Forward the modified request.
4. If either of the preceding steps 2-3 fail and additional realms
have been identified in the original answer, select another
instance of the Redirect-Realm AVP in that answer and repeat
steps 2-3 for the realm that it identifies.
3.2.3. Client Behaviour
A client conforming to this specification MUST be prepared to receive
either an answer message containing a Result-Code AVP set to
DIAMETER_REALM_REDIRECT_INDICATION, or, as the result of proxy
action, some other result from a realm differing from the one to
which it sent the original request. In the case where it receives
DIAMETER_REALM_REDIRECT_INDICATION, the client SHOULD follow the same
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steps prescribed in the previous section for a proxy, in order both
to update its routing table and to obtain service for the original
request.
3.3. The Redirect-Realm AVP
The Redirect-Realm AVP (code TBD2) is of type DiameterIdentity. It
specifies a realm to which a node receiving a redirect indication
containing the result code value DIAMETER_REALM_REDIRECT_INDICATION
and the Redirect-Realm AVP SHOULD route the original request.
3.4. DIAMETER_REALM_REDIRECT_INDICATION Protocol Error Code
The DIAMETER_REALM_REDIRECT_INDICATION (3xxx TBD1) Protocol error
code indicates that a server has determined that the request within
an application supporting realm-based redirection could not be
satisfied locally and the initiator of the request SHOULD direct the
request directly to a peer within a realm that has been identified in
the response. When set, the Redirect-Realm AVP MUST be present.
4. Security Considerations
The general recommendations given in the section 13 of the Diameter
base protocol [RFC6733] apply. Specific security recommendations
related to the realm-based redirection defined in this document are
described below.
Realm-based redirection implies a change of the business
relationships between organizations. Before redirecting a request
towards a realm different from the initial realm, the client or proxy
MUST ensure that the authorization checks have been performed at each
connection along the path toward the realm identified in the realm-
based redirect indication. Details on Diameter authorization path
set-up are given in section 2.9 of [RFC6733]. Section 13 of
[RFC6733] provides recommendations on how to authenticate and secure
each peer-to-peer connection (using on TLS, DTLS or IPsec) along the
way, thus permitting the necessary hop-by-hop authorization checks.
Although it is assumed that the administrative domains are secure, a
compromised Diameter node acting as Realm-Based Redirect Server would
be able to redirect a large number of Diameter requests towards a
victim domain which would then be flooded with undesired Diameter
requests. Such an attack is nevertheless discouraged by the use of
secure Diameter peer-to-peer connections and authorization checks,
since these would enable a potential victim domain to discover from
where an attack is coming. That in itself, however, does not prevent
such a DoS attack.
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Because realm-based redirection defined in this document implies that
the Destination-Realm AVP in a client-initiated request can be
changed by a Diameter proxy in the path between the client and the
server, any cryptographic algorithm that would use the Destination-
Realm AVP as input to the calculation performed by the client and the
server would be broken by this form of redirection. Application
specifications that would rely on such cryptographic algorithm SHOULD
NOT incorporate this realm-based redirection.
5. IANA Considerations
This specification adds a new AVP code [TBD2] Redirect-Realm in the
AVP Code registry under Authentication, Authorization, and Accounting
(AAA) Parameters.
This specification allocates a new Result-Code value
DIAMETER_REALM_REDIRECT_INDICATION (3xxx TBD1) in the Result-Code AVP
Values (code 268) - Protocol Errors registry under Authentication,
Authorization, and Accounting (AAA) Parameters.
6. Acknowledgements
Glen Zorn, Sebastien Decugis, Wolfgang Steigerwald, Mark Jones,
Victor Fajardo, Jouni Korhonen, Avi Lior, and Lionel Morand
contributed comments that helped to shape this document. As
shepherd, Lionel contributed a second set of comments that added
polish to the document before it was submitted to the IESG. Benoit
Claise picked up additional points which were quickly resolved with
Lionel's help. During IETF Last Call Review, Enrico Marocco picked
up some important editorial corrections. Stefan Winter contributed
text on the use of S-NAPTR as an alternative method of realm-based
redirection already specified in [RFC6733]. Derek Atkins performed a
review on behalf of the Security Directorate. Lionel noted one more
correction.
Finally, this document benefited from comments and discussion raised
by IESG members Stewart Bryant, Stephen Farrell, Barry Leiba, Pete
Resnick, Jaari Arkko, and Sean Turner during IESG review.
The authors are very grateful to Lionel Morand for his active role as
document shepherd. At each stage, he worked to summarize and resolve
comments, making the editor's role easy. Thank you.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012.
7.2. Informative References
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
Authors' Addresses
Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 408 330 4424
Email: Tina.Tsou.Zouting@huawei.com
URI: http://tinatsou.weebly.com/contact.html
Ruibing Hao
Comcast Cable
One Comcast Center
Philadelphia, PA 19103
USA
Phone: +1 215 286 3991(O)
Email: Ruibing_Hao@cable.comcast.com
Tom Taylor (editor)
Huawei Technologies
Ottawa
Canada
Email: tom.taylor.stds@gmail.com
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