Diameter Maintenance and Extensions (DIME) M. Jones
Internet-Draft
Intended status: Standards Track M. Liebsch
Expires: September 10, 2020
L. Morand
March 9, 2020
Diameter Group Signaling
draft-ietf-dime-group-signaling-13.txt
Abstract
In large network deployments, a single Diameter node can support over
a million concurrent Diameter sessions. Recent use cases have
revealed the need for Diameter nodes to apply the same operation to a
large group of Diameter sessions concurrently. The Diameter base
protocol commands operate on a single session so these use cases
could result in many thousands of command exchanges to enforce the
same operation on each session in the group. In order to reduce
signaling, it would be desirable to enable bulk operations on all (or
part of) the sessions managed by a Diameter node using a single or a
few command exchanges. This document specifies the Diameter protocol
extensions to achieve this signaling optimization.
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 https://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 September 10, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Building and Modifying Session Groups . . . . . . . . . . 4
3.2. Issuing Group Commands . . . . . . . . . . . . . . . . . 4
3.3. Permission Considerations . . . . . . . . . . . . . . . . 5
4. Protocol Description . . . . . . . . . . . . . . . . . . . . 6
4.1. Session Grouping Capability Discovery . . . . . . . . . . 6
4.1.1. Implicit Capability Discovery . . . . . . . . . . . . 6
4.1.2. Explicit Capability Discovery . . . . . . . . . . . . 7
4.2. Session Grouping . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Group assignment at session initiation . . . . . . . 8
4.2.2. Removing a session from a session group . . . . . . . 10
4.2.3. Mid-session group assignment modifications . . . . . 12
4.3. Deleting a Session Group . . . . . . . . . . . . . . . . 13
4.4. Performing Group Operations . . . . . . . . . . . . . . . 13
4.4.1. Sending Group Commands . . . . . . . . . . . . . . . 13
4.4.2. Receiving Group Commands . . . . . . . . . . . . . . 14
4.4.3. Error Handling for Group Commands . . . . . . . . . . 14
4.4.4. Single-Session Fallback . . . . . . . . . . . . . . . 15
5. Operation with Proxy Agents . . . . . . . . . . . . . . . . . 15
6. Commands Formatting . . . . . . . . . . . . . . . . . . . . . 16
6.1. Formatting Example: Group Re-Auth-Request . . . . . . . . 16
7. Attribute-Value-Pairs (AVP) . . . . . . . . . . . . . . . . . 17
7.1. Session-Group-Info AVP . . . . . . . . . . . . . . . . . 17
7.2. Session-Group-Control-Vector AVP . . . . . . . . . . . . 18
7.3. Session-Group-Id AVP . . . . . . . . . . . . . . . . . . 18
7.4. Group-Response-Action AVP . . . . . . . . . . . . . . . . 19
7.5. Session-Group-Capability-Vector AVP . . . . . . . . . . . 19
8. Result-Code AVP Values . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. AVP Codes . . . . . . . . . . . . . . . . . . . . . . . . 20
9.2. New Registries . . . . . . . . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
12. Normative References . . . . . . . . . . . . . . . . . . . . 21
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Appendix A. Session Management -- Exemplary Session State
Machine . . . . . . . . . . . . . . . . . . . . . . 22
A.1. Use of groups for the Authorization Session State Machine 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
In large network deployments, a single Diameter node can support over
a million concurrent Diameter sessions. Recent use cases have
revealed the need for Diameter nodes to apply the same operation to a
large group of Diameter sessions concurrently. For example, a policy
decision point may need to modify the authorized quality of service
for all active users having the same type of subscription. The
Diameter base protocol commands operate on a single session so these
use cases could result in many thousands of command exchanges to
enforce the same operation on each session in the group. In order to
reduce signaling, it would be desirable to enable bulk operations on
all (or part of) the sessions managed by a Diameter node using a
single or a few command exchanges.
This document describes mechanisms for grouping Diameter sessions and
applying Diameter commands, such as performing re-authentication, re-
authorization, termination and abortion of sessions to a group of
sessions. This document does not define a new Diameter application.
Instead it defines mechanisms, commands and AVPs that may be used by
any Diameter application that requires management of groups of
sessions.
These mechanisms take the following design goals and features into
account:
o Minimal impact to existing applications
o Extension of existing commands' Command Code Format (CCF) with
optional AVPs to enable grouping and group operations
o Fallback to single session operation
o Implicit discovery of capability to support grouping and group
operations in case no external mechanism is available to discover a
Diameter peer's capability to support session grouping and session
group operations
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses terminology defined in [RFC6733].
3. Protocol Overview
3.1. Building and Modifying Session Groups
Client and Server can assign a new Diameter session to a group, e.g.,
in case the subscription profile of the associated user has similar
characteristics as the profile of other users whose Diameter session
has been assigned to one or multiple groups. A single command can be
issued and applied to all sessions associated with such group(s),
e.g., to adjust common profile or policy settings.
The assignment of a Diameter session to a group can be changed during
an ongoing session (mid-session). For example, if a user's
subscription profile changes mid-session, a Diameter server may
remove a session from an existing group and assign this session to a
different group that is more appropriate for the new subscription
profile.
In the case of mobile users, the user's session may get transferred
mid-session to a new Diameter client during handover and assigned to
a different group, which is maintained at the new Diameter client.
A session group, which has sessions assigned, can be deleted, e.g.,
due to a change in multiple users' subscription profile so that the
group's assigned sessions do not share certain characteristics
anymore. Deletion of such group requires subsequent individual
treatment of each of the assigned sessions. A node may decide to
assign some of these sessions to any other existing or new group.
3.2. Issuing Group Commands
Changes in the network condition may result in the Diameter server's
decision to close all sessions in a given group. As example, the
server issues a single Session Termination Request (STR) command,
including the identifier of the group of sessions which are to be
terminated. The Diameter client treats the STR as group command and
initiates the termination of all sessions associated with the
identified group. Subsequently, the client confirms the successful
termination of these sessions to the server by sending a single
Session Termination Answer (STA) command, which includes the
identifier of the group.
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3.3. Permission Considerations
Permission considerations in the context of this draft apply to the
permission of Diameter nodes to build new session groups, to assign/
remove a session to/from a session group and to delete an existing
session group.
This specification follows the most flexible model where both, a
Diameter client and a Diameter server can create a new group and
assign a new identifier to that session group. When a client or a
server decides to create a new session group, e.g., to group all
sessions which share certain characteristics, this node builds a
session group identifier according to the rules described in
Section 7.3 and becomes the owner of the group. This specification
does not restrict the permission to add or remove a session to/from a
session group to the group owner. Either the client and the server
can assign a session to a group. However, a session can be removed
from a session group and/or moved to another session group only by
the node that has assigned this session to the session group. A
session group is deleted and its identifier released after the last
session has been removed from this session group. The owner of a
session group can delete a session group and its group identifier
mid-session, resulting in individual treatment of the sessions which
have been previously assigned to the deleted group. A session group
must only be deleted by the Diameter node that created it.
Diameter applications with implicit support for session groups MAY
define a more constrained permission model. For example, a more
constrained model could require that a client must not remove a
session from a group which is owned by the server. Details about
enforcing a more constraint permission model are out of scope of this
specification.
The following table depicts the permission considerations as per the
present specification:
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+-------------------------------------------------+--------+--------+
| Operation | Server | Client |
+-------------------------------------------------+--------+--------+
| Create a new Session Group (Diameter node | X | X |
| becomes the group owner) | | |
+-------------------------------------------------+--------+--------+
| Assign a Session to an owned Session Group | X | X |
+-------------------------------------------------+--------+--------+
| Assign a Session to a non-owned Session Group | X | X |
+-------------------------------------------------+--------+--------+
| Remove a Session from an owned Session Group | X | X |
+-------------------------------------------------+-----------------+
| Remove a Session from a non-owned Session Group | X | X |
+-------------------------------------------------+--------+--------+
| Remove a Session from a Session Group where the | X | X |
| Diameter node created the assignment | | |
+-------------------------------------------------+--------+--------+
| Remove a Session from a Session Group where the | | |
| Diameter node did not create the assignment | | |
+-------------------------------------------------+--------+--------+
| Overrule a different Diameter node's | | |
| group assignment *) | | |
+-------------------------------------------------+--------+--------+
| Delete a Session Group which is owned by the | X | X |
| Diameter node | | |
+-------------------------------------------------+--------+--------+
| Delete a Session Group which is not owned by | | |
| the Diameter node | | |
+-------------------------------------------------+--------+--------+
Default Permission as per this Specification
4. Protocol Description
4.1. Session Grouping Capability Discovery
Diameter nodes SHOULD NOT perform group operations with peer nodes
unless the node has advertised support for session grouping and group
operations.
4.1.1. Implicit Capability Discovery
Newly defined Diameter applications may natively support Diameter
session grouping and group operations. Such applications provide
intrinsic discovery for the support of session grouping capability
using the assigned Application Id advertised during the capability
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exchange phase two Diameter peers establish a transport connection
(see Section 5.3 of [RFC6733]).
System- and deployment-specific means, as well as out-of-band
mechanisms for capability discovery can be used to announce nodes'
support for session grouping and session group operations. In such
case, the optional Session-Group-Capability-Vector AVP, as described
in Section 4.1.2 can be omitted in Diameter messages being exchanged
between nodes.
4.1.2. Explicit Capability Discovery
If no other mechanism for capability discovery is deployed to enable
Diameter nodes to learn about nodes' capability to support session
grouping and group commands for a given application, a Diameter node
SHOULD append the Session-Group-Capability-Vector AVP to any Diameter
application messages exchanged with the other Diameter nodes to
announce its capability to support session grouping and session group
operations for the advertised application. Implementations following
the specification as per this document MUST set the
BASE_SESSION_GROUP_CAPABILITY flag of the Session-Group-Capability-
Vector AVP.
When a Diameter node receives at least one Session-Group-Capability-
Vector AVP from a node with the BASE_SESSION_GROUP_CAPABILITY flag
set, the receiving Diameter node discovers the supported session
grouping capability of the sending Diameter node for the advertised
application and MUST cache this information for the lifetime of the
routing table entry associated with the peer identity/Application Id
pair (see Section 2.7 of [RFC6733]).
4.2. Session Grouping
This specification does not limit the number of session groups to
which a single session is assigned. It is left to the implementation
of an application to determine such limitations. If an application
facilitates a session to belong to multiple session groups, the
application MUST maintain consistency of associated application
session states for these multiple session groups.
Either Diameter node (client or server) can initiate the assignment
of a session to a single or multiple session groups. Modification of
a group by removing or adding a single or multiple user sessions can
be initiated and performed mid-session by either Diameter node
responsible for the session assignment to this group. Diameter AAA
applications typically assign client and server roles to the Diameter
nodes, which are referred to as relevant Diameter nodes to utilize
session grouping and issue group commands. Section 5 describes
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particularities about session grouping and performing group commands
when relay agents or proxies are deployed.
Diameter nodes, which are group-aware, MUST store and maintain an
entry about the group assignment together with a session's state. A
list of all known session groups is locally maintained on each node,
each group pointing to individual sessions being assigned to the
group. A Diameter node MUST also keep a record about sessions, which
have been assigned to a session group by itself.
4.2.1. Group assignment at session initiation
To assign a session to a group at session initiation, a Diameter
client sends a service specific request, e.g., NASREQ AA-Request
[RFC7155], containing one or more session group identifiers. Each of
these groups MUST be identified by a unique Session-Group-Id
contained in a separate Session-Group-Info AVP as specified in
Section 7.
The client may choose one or multiple session groups from a list of
existing session groups. Alternatively, the client may decide to
create a new group to which the session is assigned and identify
itself in the <DiameterIdentity> portion of the Session-Group-Id AVP
as per Section 7.3. For all assignments of a session to an active
session group made by the client or the server, the
SESSION_GROUP_STATUS_IND flag in the Session-Group-Info AVP, which
identifies the session group, MUST be set. A set
SESSION_GROUP_STATUS_IND flag indicates that the identified session
group has just been created or is still active.
The client MUST set the SESSION_GROUP_ALLOCATION_ACTION flag of the
Session-Group-Control-Vector AVP in each appended Session-Group-Info
AVP to indicate that the session contained in the request should be
assigned to the identified session group.
The client may also indicate in the request that the server is
responsible for the assignment of the session in one or multiple
sessions owned by the server. In such a case, the client MUST
include the Session-Group-Info AVP in the request including the
Session-Group-Control-Vector AVP with the
SESSION_GROUP_ALLOCATION_ACTION flag set but no Session-Group-Id AVP.
If the Diameter server receives a command request from a Diameter
client and the command includes at least one Session-Group-Info AVP
having the SESSION_GROUP_ALLOCATION_ACTION flag in the Session-Group-
Control-Vector AVP set, the server can accept or reject the request
for group assignment. Reasons for rejection may be e.g., lack of
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resources for managing additional groups. When rejected, the session
MUST NOT be assigned to any session group.
If the Diameter server accepts the client's request for a group
assignment, the server MUST assign the new session to each of the one
or multiple identified session groups when present in the Session-
Group-Info AVP. If one or multiple identified session groups are not
already stored by the server, the server MUST store the newly
identified group(s) to its local list of known session groups. When
sending the response to the client, e.g., a service-specific auth
response as per NASREQ AA-Answer [RFC7155], the server MUST include
all Session-Group-Info AVPs as received in the client's request.
In addition to the one or multiple session groups identified in the
client's request, the server may decide to assign the new session to
one or multiple additional groups. In such a case, the server MUST
add to the response the additional Session-Group-Info AVPs, each
identifying a session group to which the new session is assigned by
the server. Each of the Session-Group-Info AVP added by the server
MUST have the SESSION_GROUP_ALLOCATION_ACTION flag set in the
Session-Group-Control-Vector AVP set.
If the Diameter server rejects the client's request for a group
assignment, the server sends the response to the client, e.g., a
service-specific auth response as per NASREQ AA-Answer [RFC7155], and
MUST include all Session-Group-Info AVPs as received in the client's
request (if any) while clearing the SESSION_GROUP_ALLOCATION_ACTION
flag of the Session-Group-Control-Vector AVP. The server MAY accept
the client's request for the identified session but refuse the
session's assignment to any session group. The server sends the
response to the client indicating success in the result code. In
such case the session is treated as single session without assignment
to any session group by the Diameter nodes.
If the assignment of the session to one or some of the multiple
identified session groups fails, the session group assignment is
treated as failure. In such case the session is treated as single
session without assignment to any session group by the Diameter
nodes. The server sends the response to the client and MAY include
those Session-Group-Info AVPs for which the group assignment failed.
The SESSION_GROUP_ALLOCATION_ACTION flag of included Session-Group-
Info AVPs MUST be cleared.
If the Diameter server receives a command request from a Diameter
client and the command includes a Session-Group-Info AVP which does
not include a Session-Group-Id AVP, the server MAY decide to assign
the session to one or multiple session groups. For each session
group, to which the server assigns the new session, the server
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includes a Session-Group-Info AVP with the Session-Group-Id AVP
identifying a session group in the response sent to the client. Each
of the Session-Group-Info AVPs included by the server MUST have the
SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-Control-
Vector AVP set.
If the Diameter server receives a command request from a Diameter
client and the command does not contain any Session-Group-Info AVP,
the server MUST NOT assign the new session to any session group but
treat the request as for a single session. The server MUST NOT
return any Session-Group-Info AVP in the command response.
If the Diameter client receives a response to its previously issued
request from the server and the response includes at least one
Session-Group-Info AVP having the SESSION_GROUP_ALLOCATION_ACTION
flag of the associated Session-Group-Control-Vector AVP set, the
client MUST add the new session to all session groups as identified
in the one or multiple Session-Group-Info AVPs. If the Diameter
client fails to add the session to one or more session groups as
identified in the one or multiple Session-Group-info AVPs, the client
MUST terminate the session. The client MAY send a subsequent request
for session initiation to the server without requesting the
assignment of the session to a session group
If the Diameter client receives a response to its previously issued
request from the server and the one or more Session-Group-Info AVPs
have the SESSION_GROUP_ALLOCATION_ACTION flag of the associated
Session-Group-Control-Vector AVP cleared, the client MUST terminate
the assignment of the session to the one or multiple groups. If the
response from the server indicates success in the result code but
solely the assignment of the session to a session group has been
rejected by the server, the client treats the session as single
session without group assignment.
A Diameter client, which sent a request for session initiation to a
Diameter server and appended a single or multiple Session-Group-Id
AVPs but cannot find any Session-Group-Info AVP in the associated
response from the Diameter server proceeds as if the request was
processed for a single session. The Diameter client MUST NOT retry
to request group assignment for this session, but MAY try to request
group assignment for other new sessions.
4.2.2. Removing a session from a session group
When a Diameter client decides to remove a session from a particular
session group, the client sends a service-specific re-authorization
request to the server and adds one Session-Group-Info AVP to the
request for each session group, from which the client wants to remove
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the session. The session, which is to be removed from a group, is
identified in the Session-Id AVP of the command request. The
SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-Control-
Vector AVP in each Session-Group-Info AVP MUST be cleared to indicate
removal of the session from the session group identified in the
associated Session-Group-id AVP.
When a Diameter client decides to remove a session from all session
groups, to which the session has been previously assigned, the client
sends a service-specific re-authorization request to the server and
adds a single Session-Group-Info AVP to the request which has the
SESSION_GROUP_ALLOCATION_ACTION flag cleared and the Session-Group-Id
AVP omitted. The session, which is to be removed from all groups, to
which the session has been previously assigned, is identified in the
Session-Id AVP of the command request.
If the Diameter server receives a request from the client which has
at least one Session-Group-Info AVP appended with the
SESSION_GROUP_ALLOCATION_ACTION flag cleared, the server MUST remove
the session from the session group identified in the associated
Session-Group-Id AVP. If the request includes at least one Session-
Group-info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag cleared
and no Session-Id AVP present, the server MUST remove the session
from all session groups to which the session has been previously
assigned. The server MUST include in its response to the requesting
client all Session-Group-Id AVPs as received in the request.
When the Diameter server decides to remove a session from one or
multiple particular session groups or from all session groups to
which the session has been assigned beforehand, the server sends a
Re-Authorization Request (RAR) or a service-specific server-initiated
request to the client, indicating the session in the Session-Id AVP
of the request. The client sends a Re-Authorization Answer (RAA) or
a service-specific answer to respond to the server's request. The
client subsequently sends service-specific re-authorization request
containing one or multiple Session-Group-Info AVPs, each indicating a
session group, to which the session had been previously assigned. To
indicate removal of the indicated session from one or multiple
session groups, the server sends a service-specific auth response to
the client, containing a list of Session-Group-Info AVPs with the
SESSION_GROUP_ALLOCATION_ACTION flag cleared and the Session-Group-Id
AVP identifying the session group, from which the session should be
removed. The server MAY include to the service-specific auth
response a list of Session-Group-Info AVPs with the
SESSION_GROUP_ALLOCATION_ACTION flag set and the Session-Group-Id AVP
identifying session groups to which the session remains subscribed.
If the server decides to remove the identified session from all
session groups, to which the session has been previously assigned,
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the server includes in the service-specific auth response at least
one Session-Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION
flag cleared and Session-Group-Id AVP absent.
4.2.3. Mid-session group assignment modifications
Either Diameter node (client or server) can modify the group
membership of an active Diameter session according to the specified
permission considerations.
To update an assigned group mid-session, a Diameter client sends a
service-specific re-authorization request to the server, containing
one or multiple Session-Group-Info AVPs with the
SESSION_GROUP_ALLOCATION_ACTION flag set and the Session-Group-Id AVP
present, identifying the session group to which the session should be
assigned. With the same message, the client may send one or multiple
Session-Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag
cleared and the Session-Group-Id AVP identifying the session group
from which the identified session is to be removed. To remove the
session from all previously assigned session groups, the client
includes at least one Session-Group-Info AVP with the
SESSION_GROUP_ALLOCATION_ACTION flag cleared and no Session-Group-Id
AVP present. When the server received the service-specific re-
authorization request, it MUST update its locally maintained view of
the session groups for the identified session according to the
appended Session-Group-Info AVPs. The server sends a service-
specific auth response to the client containing one or multiple
Session-Group-Info AVPs with the SESSION_GROUP_ALLOCATION_ACTION flag
set and the Session-Group-Id AVP identifying the new session group to
which the identified session has been assigned.
When a Diameter server enforces an update to the assigned groups mid-
session, it sends a Re-Authorization Request (RAR) message or a
service-specific request to the client identifying the session, for
which the session group lists are to be updated. The client responds
with a Re-Authorization Answer (RAA) message or a service-specific
answer. The client subsequently sends a service-specific re-
authorization request containing one or multiple Session-Group-Info
AVPs with the SESSION_GROUP_ALLOCATION_ACTION flag set and the
Session-Group-Id AVP identifying the session group to which the
session had been previously assigned. The server responds with a
service-specific auth response and includes one or multiple Session-
Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag set and
the Session-Group-Id AVP identifying the session group, to which the
identified session is to be assigned. With the same response
message, the server may send one or multiple Session-Group-Info AVPs
with the SESSION_GROUP_ALLOCATION_ACTION flag cleared and the
Session-Group-Id AVP identifying the session groups from which the
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identified session is to be removed. When server wants to remove the
session from all previously assigned session groups, it sends at
least one Session-Group-Info AVP with the response having the
SESSION_GROUP_ALLOCATION_ACTION flag cleared and no Session-Group-Id
AVP present.
4.3. Deleting a Session Group
To delete a session group and release the associated Session-Group-Id
value, the owner of a session group appends a single Session-Group-
Info AVP having the SESSION_GROUP_STATUS_IND flag cleared and the
Session-Group-Id AVP identifying the session group, which is to be
deleted. The SESSION_GROUP_ALLOCATION_ACTION flag of the associated
Session-Group-Control-Vector AVP MUST be cleared.
4.4. Performing Group Operations
4.4.1. Sending Group Commands
Either Diameter node (client or server) can request the recipient of
a request to process an associated command for all sessions assigned
to one or multiple groups by identifying these groups in the request.
The sender of the request appends for each group, to which the
command applies, a Session-Group-Info AVP including the Session-
Group-Id AVP to identify the associated session group. Both, the
SESSION_GROUP_ALLOCATION_ACTION flag as well as the
SESSION_GROUP_STATUS_IND flag MUST be set.
If the Command Code Format (CCF) of the request mandates a Session-Id
AVP, the Session-Id AVP MUST identify one of the single sessions
which is assigned to at least one of the groups being identified in
the appended Session-Group-Id AVPs.
The sender of the request MUST indicate to the receiver how multiple
resulting transactions associated with a group command are to be
treated by appending a single instance of a Group-Response-Action
AVP. For example, when a server sends a Re-Authorization Request
(RAR) or a service-specific server-initiated request to the client,
it indicates to the client to follow the request according to one of
three possible procedures. When the server sets the Group-Response-
Action AVP to ALL_GROUPS (1), the client sends a single RAR message
for all identified groups. When the server sets the Group-Response-
Action AVP to PER_GROUP (2), the client sends a single RAR message
for each identified group individually. When the server sets the
Group-Response-Action AVP to PER_SESSION (3), the client follows-up
with a single RAR message per impacted session. If a session is
included in more than one of the identified session groups, the
client sends only one RAR message for that session.
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If the sender sends a request including the Group-Response-Action AVP
set to ALL_GROUPS (1) or PER_GROUP (2), it has to expect some delay
before receiving the corresponding answer(s) as the answer(s) will
only be sent back when the request is processed for all the sessions
or all the session of a session group. If the process of the request
is delay-sensitive, the sender SHOULD NOT set the Group-Response-
Action AVP to ALL_GROUPS (1) or PER_GROUP (2). If the answer can be
sent before the complete process of the request for all the sessions
or if the request timeout timer is high enough, the sender MAY set
the Group-Response-Action AVP to ALL_GROUPS (1) or PER_GROUP (2).
If the sender wants the receiver of the request to process the
associated command solely for a single session, the sender does not
append any group identifier, but identifies the relevant session in
the Session-Id AVP.
4.4.2. Receiving Group Commands
A Diameter node receiving a request to process a command for a group
of sessions, identifies the relevant groups according to the appended
Session-Group-Id AVP in the Session-Group-Info AVP and processes the
group command according to the appended Group-Response-Action AVP .
If the received request identifies multiple groups in multiple
appended Session-Group-Id AVPs, the receiver SHOULD process the
associated command for each of these groups. If a session has been
assigned to more than one of the identified groups, the receiver MUST
process the associated command only once per session.
4.4.3. Error Handling for Group Commands
When a Diameter node receives a request to process a command for one
or more session groups and the result of processing the command is an
error that applies to all sessions in the identified groups, an
associated protocol error MUST be returned to the source of the
request. In such case, the sender of the request MUST fall back to
single-session processing and the session groups, which have been
identified in the group command, MUST be deleted according to the
procedure described in Section 4.3.
When a Diameter node receives a request to process a command for one
or more session groups and the result of processing the command
succeeds for some sessions identified in one or multiple session
groups, but fails for one or more sessions, the Result-Code AVP in
the response message SHOULD indicate DIAMETER_LIMITED_SUCCESS as per
Section 7.1.2 of [RFC6733].
In the case of limited success, the sessions, for which the
processing of the group command failed, MUST be identified using a
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Failed-AVP AVP as per Section 7.5 of [RFC6733]. The sender of the
request MUST fall back to single-session operation for each of the
identified sessions, for which the group command failed. In
addition, each of these sessions MUST be removed from all session
groups to which the group command applied. To remove sessions from a
session group, the Diameter client performs the procedure described
in Section 4.2.2.
4.4.4. Single-Session Fallback
Either Diameter node can fall back to single session operation by
ignoring and omitting the optional group session-specific AVPs.
Fallback to single-session operation is performed by processing the
Diameter command solely for the session identified in the mandatory
Session-Id AVP. In such case, the response to the group command MUST
NOT identify any group but identify solely the single session for
which the command has been processed.
5. Operation with Proxy Agents
In the case of a present stateful Proxy Agent between a Diameter
client and a Diameter server, the Proxy Agent MUST perform the same
mechanisms per this specification to advertise session grouping and
group operations capability towards the client and the server
respectively. The Proxy MUST update and maintain consistency of its
local session states as per the result of the group commands which
are operated between a Diameter client and a server. In such case,
the Proxy Agent MUST act as a Diameter server in front of the
Diameter client and MUST act as a Diameter client in front of the
Diameter server. Therefore, the client and server behavior described
in Section 4 applies respectively to the stateful Proxy Agent.
If a stateful Proxy Agent manipulates session groups, it MUST
maintain consistency of session groups between a client and a server.
This applies to a deployment where the Proxy Agent utilizes session
grouping and performs group operations with, for example, a Diameter
server, whereas the Diameter client is not aware of session groups.
In such case the Proxy Agent must reflect the states associated with
the session groups as individual session operations towards the
client and ensure the client has a consistent view of each session.
The same applies to a deployment where all nodes, the Diameter client
and server, as well as the Proxy Agent are group-aware but the Proxy
Agent manipulates groups, e.g., to adopt different administrative
policies that apply to the client's domain and the server's domain.
Stateless Proxy Agents do not maintain any session state (only
transaction state are maintained). Consequently, the notion of
session group is transparent for any stateless Proxy Agent present
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between a Diameter client and a Diameter server handling session
groups. Session group related AVPs being defined as optional AVP are
ignored by stateless Proxy Agents and should not be removed from the
Diameter commands. If they are removed by the Proxy Agent for any
reason, the Diameter client and Diameter server will discover the
absence the related session group AVPs and will fall back to single-
session processing, as described in Section 4.
6. Commands Formatting
This document does not specify new Diameter commands to enable group
operations, but relies on command extensibility capability provided
by the Diameter Base protocol. This section provides the guidelines
to extend the CCF of existing Diameter commands with optional AVPs to
enable the recipient of the command applying the command to all
sessions associated with the identified group(s).
6.1. Formatting Example: Group Re-Auth-Request
A request for re-authentication of one or more groups of users is
issued by appending one or multiple Session-Group-Id AVP(s), as well
as a single instance of a Group-Response-Action AVP to the Re-Auth-
Request (RAR). The one or multiple Session-Group-Id AVP(s) identify
the associated group(s) for which the group re-authentication has
been requested. The Group-Response-Action AVP identifies the
expected means to perform and respond to the group command. The
recipient of the group command initiates re-authentication for all
users associated with the identified group(s). Furthermore, the
sender of the group re-authentication request appends a Group-
Response-Action AVP to provide more information to the receiver of
the command about how to accomplish the group operation.
The value of the mandatory Session-Id AVP MUST identify a session
associated with a single user, which is assigned to at least one of
the groups being identified in the appended Session-Group-Id AVPs.
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<RAR> ::= < Diameter Header: 258, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Destination-Host }
{ Auth-Application-Id }
{ Re-Auth-Request-Type }
[ User-Name ]
[ Origin-State-Id ]
* [ Proxy-Info ]
* [ Route-Record ]
[ Session-Group-Capability-Vector ]
* [ Session-Group-Info ]
[ Group-Response-Action ]
* [ AVP ]
7. Attribute-Value-Pairs (AVP)
+--------------------+
| AVP Flag rules |
+----+---+------+----+
AVP | | |SHOULD|MUST|
Attribute Name Code Value Type |MUST|MAY| NOT | NOT|
+-------------------------------------------------+----+---+------+----+
|Session-Group-Info TBD1 Grouped | | P | | V |
|Session-Group-Control-Vector TBD2 Unsigned32 | | P | | V |
|Session-Group-Id TBD3 OctetString | | P | | V |
|Group-Response-Action TBD4 Unsigned32 | | P | | V |
|Session-Group-Capability-Vector TBD5 Unsigned32 | | P | | V |
+-------------------------------------------------+----+---+------+----+
AVPs for the Diameter Group Signaling
7.1. Session-Group-Info AVP
The Session-Group-Info AVP (AVP Code TBD1) is of type Grouped. It
contains the identifier of the session group as well as an indication
of the node responsible for session group identifier assignment.
Session-Group-Info ::= < AVP Header: TBD1 >
< Session-Group-Control-Vector >
[ Session-Group-Id ]
* [ AVP ]
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7.2. Session-Group-Control-Vector AVP
The Session-Group-Control-Vector AVP (AVP Code TBD2) is of type
Unsigned32 and contains a 32-bit flags field to control the group
assignment at session-group aware nodes.
The following control flags are defined in this document:
SESSION_GROUP_ALLOCATION_ACTION (0x00000001)
This flag indicates the action to be performed for the identified
session. When this flag is set, it indicates that the identified
Diameter session is to be assigned to the session group as
identified by the Session-Group-Id AVP or the session's assignment
to the session group identified in the Session-Group-Id AVP is
still valid. When the flag is cleared, the identified Diameter
session is to be removed from at least one session group. When
the flag is cleared and the Session-Group-Info AVP identifies a
particular session group in the associated Session-Group-Id AVP,
the session is to be removed solely from the identified session
group. When the flag is cleared and the Session-Group-Info AVP
does not identify a particular session group (Session-Group-Id AVP
is absent), the identified Diameter session is to be removed from
all session groups, to which it has been previously assigned.
SESSION_GROUP_STATUS_IND (0x00000010)
This flag indicates the status of the session group identified in
the associated Session-Group-Id AVP. The flag is set when the
identified session group has just been created or is still active.
If the flag is cleared, the identified session group is deleted
and the associated Session-Group-Id is released. If the Session-
Group-Info AVP does not include a Session-Group-Id AVP, this flag
is meaningless and MUST be ignored by the receiver.
7.3. Session-Group-Id AVP
The Session-Group-Id AVP (AVP Code TBD3) is of type UTF8String and
identifies a group of Diameter sessions.
The Session-Group-Id MUST be globally unique. The default format of
the Session-Group-id MUST comply to the format recommended for a
Session-Id, as defined in the section 8.8 of the [RFC6733]. The
<DiameterIdentity> portion of the Session-Group-Id MUST identify the
Diameter node, which owns the session group.
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7.4. Group-Response-Action AVP
The Group-Response-Action AVP (AVP Code TBD4) is of type Unsigned32
and contains a 32-bit address space representing values indicating
how the node SHOULD issue follow up exchanges in response to a
command which impacts multiple sessions. The following values are
defined by this document:
ALL_GROUPS (1)
Follow up message exchanges associated with a group command should
be performed with a single message exchange for all impacted
groups.
PER_GROUP (2)
Follow up message exchanges associated with a group command should
be performed with a separate message exchange for each impacted
group.
PER_SESSION (3)
Follow up message exchanges associated with a group command should
be performed with a separate message exchange for each impacted
session.
7.5. Session-Group-Capability-Vector AVP
The Session-Group-Capability-Vector AVP (AVP Code TBD5) is of type
Unsigned32 and contains a 32-bit flags field to indicate capabilities
in the context of session-group assignment and group operations.
The following capabilities are defined in this document:
BASE_SESSION_GROUP_CAPABILITY (0x00000001)
This flag indicates the capability to support session grouping and
session group operations according to this specification.
8. Result-Code AVP Values
This document does not define new Result-Code [RFC6733] values for
existing applications, which are extended to support group commands.
Specification documents of new applications, which will have
intrinsic support for group commands, may specify new Result-Codes.
9. IANA Considerations
This section contains the namespaces that have either been created in
this specification or had their values assigned to existing
namespaces managed by IANA.
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9.1. AVP Codes
This specification requires IANA to register the following new AVPs
from the AVP Code namespace defined in [RFC6733].
o Session-Group-Info
o Session-Group-Control-Vector
o Session-Group-Id
o Group-Response-Action
o Session-Group-Capability-Vector
The AVPs are defined in Section 7.
9.2. New Registries
This specification requires IANA to create two registries:
o Session-Group-Control-Vector AVP registry for control bits with
two initial assignments, which are described in Section 7.2. The
future registration assignment policy is proposed to be
Specification Required.
o Session-Group-Capability-Vector AVP with one initial assignment,
which is described in Section 7.5. The future registration
assignment policy is proposed to be Standards Action.
The AVP names can be used as registry names.
10. Security Considerations
The security considerations of the Diameter protocol itself are
discussed in [RFC6733]. Use of the AVPs defined in this document
MUST take into consideration the security issues and requirements of
the Diameter base protocol. In particular, the Session-Group-Info
AVP (including the Session-group-Control-Vector and the Session-
Group-Id AVPs) should be considered as a security-sensitive AVPs in
the same manner than the Session-Id AVP in the Diameter base protocol
[RFC6733].
The management of session groups relies upon the existing trust
relationship between the Diameter client and the Diameter server
managing the groups of sessions. This document defines a mechanism
that allows a client or a server to act on multiple sessions at the
same time using only one command. if the Diameter client or server is
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compromised, an attacker could launch DoS attacks by terminating a
large number of sessions with a limited set of commands using the
session group management concept.
According to the Diameter base protocol [RFC6733], transport
connections between Diameter peers are protected by TLS/TCP, DTLS/
SCTP or alternative security mechanisms that are independent of
Diameter, such as IPsec. However, the lack of end-to-end security
features makes it difficult to establish trust in the session group
related information received from non-adjacent nodes. Any Diameter
agent in the message path can potentially modify the content of the
message and therefore the information sent by the Diameter client or
the server. There is ongoing work on the specification of end-to-end
security features for Diameter. Such features would enable the
establishment of trust relationship between non-adjacent nodes and
the security required for session group management would normally
rely on this end-to-end security. However, there is no assumption in
this document that such end-to-end security mechanism will be
available. It is only assumed that the solution defined on this
document relies on the security framework provided by the Diameter
based protocol.
In some cases, a Diameter Proxy agent can act on behalf of a client
or server. In such a case, the security requirements that normally
apply to a client (or a server) apply equally to the Proxy agent.
11. Acknowledgments
The authors of this document want to thank Ben Campbell and Eric
McMurry for their valuable comments to early versions of this draft.
Furthermore, authors thank Steve Donovan and Mark Bales for the
thorough review and comments on advanced versions of the WG document,
which helped a lot to improve this specification.
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<https://www.rfc-editor.org/info/rfc6733>.
[RFC7155] Zorn, G., Ed., "Diameter Network Access Server
Application", RFC 7155, DOI 10.17487/RFC7155, April 2014,
<https://www.rfc-editor.org/info/rfc7155>.
Appendix A. Session Management -- Exemplary Session State Machine
A.1. Use of groups for the Authorization Session State Machine
Section 8.1 in [RFC6733] defines a set of finite state machines,
representing the life cycle of Diameter sessions, and which must be
observed by all Diameter implementations that make use of the
authentication and/or authorization portion of a Diameter
application. This section defines, as example, additional state
transitions related to the processing of the group commands which may
impact multiple sessions.
The group membership is session state and therefore only those state
machines from [RFC6733] in which the server is maintaining session
state are relevant in this document. As in [RFC6733], the term
Service-Specific below refers to a message defined in a Diameter
application (e.g., Mobile IPv4, NASREQ).
The following state machine is observed by a client when state is
maintained on the server. State transitions which are unmodified
from [RFC6733] are not repeated here.
The Diameter group command in the following tables is differentiated
from a single-session related command by a preceding 'G' (Group). A
Group Re-Auth Request, which applies to one or multiple session
groups, has been exemplarily described in Section 6.1. Such Group
RAR command is denoted as 'GRAR' in the following table. The same
notation applies to other commands as per [RFC6733].
CLIENT, STATEFUL
State Event Action New State
---------------------------------------------------------------
Idle Client or Device Requests Send Pending
access service
specific
auth req
optionally
including
groups
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Open GASR received with Send GASA Discon
Group-Response-Action with
= ALL_GROUPS, Result-Code
session is assigned to = SUCCESS,
received group(s) and Send GSTR.
client will comply with
request to end the session
Open GASR received with Send GASA Discon
Group-Response-Action with
= PER_GROUPS, Result-Code
session is assigned to = SUCCESS,
received group(s) and Send GSTR
client will comply with per group
request to end the session
Open GASR received with Send GASA Discon
Group-Response-Action with
= PER_SESSION, Result-Code
session is assigned to = SUCCESS,
received group(s) and Send STR
client will comply with per session
request to end the session
Open GASR received, Send GASA Open
client will not comply with with
request to end all session Result-Code
in received group(s) != SUCCESS
Discon GSTA Received Discon. Idle
user/device
Open GRAR received with Send GRAA, Pending
Group-Response-Action Send
= ALL_GROUPS, service
session is assigned to specific
received group(s) and group
client will perform re-auth req
subsequent re-auth
Open GRAR received with Send GRAA, Pending
Group-Response-Action Send
= PER_GROUP, service
session is assigned to specific
received group(s) and group
client will perform re-auth req
subsequent re-auth per group
Open GRAR received with Send GRAA, Pending
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Group-Response-Action Send
= PER_SESSION, service
session is assigned to specific
received group(s) and re-auth req
client will perform per session
subsequent re-auth
Open GRAR received and client will Send GRAA Idle
not perform subsequent with
re-auth Result-Code
!= SUCCESS,
Discon.
user/device
Pending Successful service-specific Provide Open
group re-authorization answer service
received.
Pending Failed service-specific Discon. Idle
group re-authorization answer user/device
received.
The following state machine is observed by a server when it is
maintaining state for the session. State transitions which are
unmodified from [RFC6733] are not repeated here.
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SERVER, STATEFUL
State Event Action New State
---------------------------------------------------------------
Idle Service-specific authorization Send Open
request received, and user successful
is authorized service
specific
answer
optionally
including
groups
Open Server wants to terminate Send GASR Discon
group(s)
Discon GASA received Cleanup Idle
Any GSTR received Send GSTA, Idle
Cleanup
Open Server wants to reauth Send GRAR Pending
group(s)
Pending GRAA received with Result-Code Update Open
= SUCCESS session(s)
Pending GRAA received with Result-Code Cleanup Idle
!= SUCCESS session(s)
Open Service-specific group Send Open
re-authoization request successful
received and user is service
authorized specific
group
re-auth
answer
Open Service-specific group Send Idle
re-authorization request failed
received and user is service
not authorized specific
group
re-auth
answer,
cleanup
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Authors' Addresses
Mark Jones
Email: mark@azu.ca
Marco Liebsch
Email: marco.liebsch@neclab.eu
Lionel Morand
Email: lionel.morand@orange.com
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