I2RS WG D. Migault
Internet-Draft J. Halpern
Intended status: Informational Ericsson
Expires: September 8, 2017 S. Hares
Huawei
March 7, 2017
I2RS Environment Security Requirements
draft-ietf-i2rs-security-environment-reqs-03
Abstract
This document provides environment security requirements for the I2RS
architecture. Environment security requirements are independent of
the protocol used for I2RS. The security environment requirements
are the good security practices to be used during implementation and
deployment of the code related to the new interface to routing system
(I2RS) so that I2RS implementations can be securely deployed and
operated.
Environmental security requirements do not specify the I2RS protocol
seecurity requirements. This is done in another document (draft-
ietf-i2rs-protocol-security-requirements).
Status of This Memo
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on September 8, 2017.
Copyright Notice
Copyright (c) 2017 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 and Acronyms . . . . . . . . . . . . . . . . . . 4
2.1. Requirements notation . . . . . . . . . . . . . . . . . . 4
3. I2RS Plane Isolation . . . . . . . . . . . . . . . . . . . . 4
3.1. I2RS Plane and Management plane . . . . . . . . . . . . . 5
3.1.1. Deadlocks . . . . . . . . . . . . . . . . . . . . . . 6
3.1.2. Data Store leaking . . . . . . . . . . . . . . . . . 7
3.2. I2RS Plane and Forwarding Plane . . . . . . . . . . . . . 10
3.3. I2RS Plane and Control Plane . . . . . . . . . . . . . . 11
3.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 11
4. I2RS Access Control for Routing System Resources . . . . . . 14
4.1. I2RS Access Control Architecture . . . . . . . . . . . . 14
4.1.1. access control Enforcement Scope . . . . . . . . . . 17
4.1.2. Notification Requirements . . . . . . . . . . . . . . 17
4.1.3. Trust . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1.4. Sharing access control Information . . . . . . . . . 18
4.1.5. Sharing Access Control in Groups of I2RS Clients and
Agents . . . . . . . . . . . . . . . . . . . . . . . 20
4.1.6. Managing Access Control Policy . . . . . . . . . . . 22
4.2. I2RS Agent Access Control Policies . . . . . . . . . . . 23
4.2.1. I2RS Agent Access Control . . . . . . . . . . . . . . 23
4.2.2. I2RS Client Access Control Policies . . . . . . . . . 24
4.2.3. Application and Access Control Policies . . . . . . . 25
5. I2RS Application Isolation . . . . . . . . . . . . . . . . . 26
5.1. Robustness Toward Programmability . . . . . . . . . . . . 26
5.2. Application Isolation . . . . . . . . . . . . . . . . . . 27
5.2.1. DoS . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.2.2. Application Logic Control . . . . . . . . . . . . . . 29
6. Security Considerations . . . . . . . . . . . . . . . . . . . 29
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1. Normative References . . . . . . . . . . . . . . . . . . 30
9.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
This document provides environment security requirements for the I2RS
architecture. Environment security requirements are independent of
the protocol used for I2RS. The I2RS protocol security requirements
[I-D.ietf-i2rs-protocol-security-requirements] define the security
for the communication between I2RS client and agent. The security
environment requirements are good security practices to be used
during implementation and deployment of the I2RS protocol so that
I2RS protocol implementations can be securely deployed and operated.
These environment security requirements address the security
considerations described in the I2RS Architecture [RFC7921] required
to provide a stable and secure environment in which the dynamic
programmatic interface to the routing system (I2RS) should operates.
Even though the I2RS protocol is mostly concerned with the interface
between the I2RS client and the I2RS agent, the environmental
security requirements must consider the entire I2RS architecture and
specify where security functions may be hosted and what criteria
should be met in order to address any new attack vectors exposed by
deploying this architecture. Environment security for I2RS has to be
considered the complete I2RS architecture and not only on the
protocol interface.
This document is structured as follows:
o Section 2 describes the terminology used in this document,
o Section 3 describes how the I2RS plane can be securely isolated
from the management plane, control plane and forwarding plane.
The subsequent sections of the document focuses on the security
within the I2RS plane.
o Section 4 analyzes how the I2RS access control policies can be
deployed throughout the I2RS plane in order to limit access to the
routing system resources to authorized components with the
authorized privileges. This analysis examines how providing a
robust communication system between the components aids the access
control.
o Section 5 details how I2RS keeps applications isolated from
another and without affecting the I2RS components. Applications
may be independent, with different scopes, owned by different
tenants. In addition, the applications may modify the routing
system in an automatic way.
Motivations are described before the requirements are given.
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The reader is expected to be familiar with the I2RS problem statement
[RFC7920], I2RS architecture, [RFC7921], traceability requirements
[RFC7922], I2RS Pub/Sub requirements [RFC7923], I2RS ephemeral state
requirements [I-D.ietf-i2rs-ephemeral-state], I2RS protocol security
requirements [I-D.ietf-i2rs-protocol-security-requirements].
2. Terminology and Acronyms
- Environment Security Requirements : Security requirements
specifying how the environment a protocol operates in needs to
be secure. These requirements do not specify the protocol
security requirements.
- I2RS plane: The environment the I2RS process is running on. It
includes the applications, the I2RS client and the I2RS agent.
- I2RS user: The user of the I2RS client software or system.
- I2RS access control policies: The policies controlling access of
the routing resources by applications. These policies are
divided into policies applied by the I2RS client regarding
applications and policies applied by the I2RS agent regarding
I2RS clients.
- I2RS client access control policies: The access control policies
processed by the I2RS client.
- I2RS agent access control policies: The access control policies
processed by the I2RS agent.
2.1. Requirements notation
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].
3. I2RS Plane Isolation
Isolating the I2RS plane from other network planes (the management,
forwarding plane, and control planes) is fundamental to the security
of the I2RS environment. Clearly differentiating the I2RS components
from the rest of the network device does the following:
1. protects the I2RS components from vulnerabilities in other parts
of the network,
2. protects other systems vital to the health of the network from
vulnerabilities in the I2RS plane.
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Separating the I2RS plane from other network control and forwarding
planes is similar to the best common practice of placing software
into software containers within modules with clear interfaces to
exterior modules. In a similar way, although the I2RS plane cannot
be completely isolated from other planes, it can be carefully
designed so the interactions between the I2RS plane and other planes
can be identified and controlled. The following is a brief
description of how the I2RS plane positions itself in regard to the
other planes.
3.1. I2RS Plane and Management plane
The purpose of the I2RS plane is to provide a standard programmatic
interface of the routing system resources to network oriented
applications. Routing protocols often run in a control plane and
provide entries for the forwarding plane as shown in figure 1. The
I2RS plane which contains the I2RS applications, the I2RS client, the
north bound interface between the I2RS client and I2RS applications,
the I2RS protocol, the I2RS agent, and south bound API (SB API) to
the routing system. The communication interfaces in the I2RS plane
are shown on the the left hand side of the figure 1.
The management plane contains the mangement application the
management client, the north bound API between the management client
and management application, the mangement server, the management
protocol (E.g. RESTCONF) between mangement client and management
server, and the south bound API between the management server and the
control plane. The communication interfaces associated with the
management plane are shown on the right hand side of figure 2.
The I2RS plane and the management plane both interact with control
plane on which the routing systems operate. [RFC7921] describes
several of these interaction points such as the local configuration,
the static system state, routing, and signaling. A routing resource
may be accessed by I2RS plane, the mangement plane, or routing
protocol(s) which creates the potential for overlapping access. The
southbound APIs can limit the scope of the management plane's and the
I2RS plane's interaction with the routing resources.
Security focus:
Implementers need to carefully examine the southbound APIs from the
I2RS Plane and the management plane to determine if these APIs
overlap or conflict during use. If these APIs overlap or conflict,
these interactions can provide errors which are not traceable or
provide a risk for security intrusions between the two planes.
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APIs that interact with the
I2RS Plane and Management Plane
I2RS applications Mangement applications
|| NB API NB API ||
|| ||
I2RS plane management plane
|| control plane configuration||
|| datastore datastore ||
|| ||
||SB API SB API ||
---------------------------------------
| Routing System with protocols |<protocols>
| control plane |
| (applied datastore) |
+-------------------------------------+
| forwarding plane |
+-------------------------------------+
| system |
+-------------------------------------+
Figure 1 - North Bound (NB) APIs and
South Bound (SB) APIs
The north bound interface may also be a source of conflicting
interactions between the I2RS plane and the management plane. It is
important that conflicting interactions do not provide a deadlock
situation or allow a vulnerability due to data store leaking.
3.1.1. Deadlocks
How can a deadlock occur?
The I2RS applications and the management applications may both
interact with the Routing System. For example, I2RS applications may
set ephemeral state for an BGP routing process allowing a peer to
temporarily increase the maximum number of prefix it will accept. At
the same time, a management plane process may change a BGP Peer's
configuration for the maximum number of prefixes to decrease the
maximum number of prefixes. [RFC7921] suggests that implementations
SHOULD provide operator configurable knobs that will determine which
functions (I2RS or configuration management) has precedence in the
routing system, and that events should signal an I2RS agent if the
I2RS ephemeral state is overwritten. This is an example of policy
that prevents a deadlock situation for both the I2RS application and
the mangement application.
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It is important that implementations include both policy knobs for
resolving the deadlocks between the the I2RS plane and the management
plane, and event signaling which reports deadlocks occuring within a
system supporting I2RS.
3.1.2. Data Store leaking
A vulnerability can occur if there is leakage between the I2RS
ephemeral control plane data store and the management plane's
configuration datastore. [I-D.ietf-netmod-revised-datastores]
describes a datastore architecture with control plane datastores
(such as the I2RS protocol's ephemeral datastore) being logically
different than the the configuration data store. The mixture of the
I2RS ephemeral configuration and management configuration is done by
the routing system code (specific to an implementation). The routing
system code resolves any conflict between I2RS control plane
configuration and the management plane configuration, and then
installs the state in the routing system. Implementation policy
determines which configuration state should be installed.
The applied datastore provides information on what is installed in
each part of a system - including the routing system. The
operational state data store provides both the applied data store
information and additional operational state from the control plane
protocols and control plane datastore.
Since it is the routing system code which mixing the configuration
from the I2RS control plane datastore and the management datastore to
create applied datastore for the routing system, this code must take
care to prevent:
o the I2RS system "infecting" the management system configuration
datastore with information from the I2RS control plane data store,
o the management system "infecting" the I2RS system data with data
not specifically imported by I2RS data models,
o the management system indirectly "infecting" the I2RS system by
propagating improper information from one system to another via
I2RS.
In this circumstance, we define "infecting" as inteferring with and
leading into a incoherent state. Planned interactions such as
interactions denoted in in two cooperating Yang data modules is not
incoherent state.
For example, BGP configuration and BGP I2RS ephemeral state
configuration could have a defined interaction. The I2RS plane may
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legitimately update a routing resource configured by the management
plane, or the reverse (the management plane updates a resource the
I2RS plane has configured) if the interactions are defined by Yang
modules or local policy. Infecting, is when the implementation is
updated by two processes resulting in an incoherent state. Indirect
"infecting", we define as as changes made by the I2RS plane that
cause changes in routing protocols which add state unexpected by the
management plane or the reverse (the mangement plane adding changes
in routing protocols the I2RS plane does not expect).
Prevention for Data Store Leakage
The primary protection in this space is going to need to be
validation rules on:
o the data being sent/received by the I2RS agent (including
notification of changes that the I2RS agent sends the I2RS
client),
o any data transferred between management datastores (configuration
or operational state) and I2RS ephemeral control plane data
stores;
o data transferred between I2RS Agent and Routing system,
o data transferred between a management server and the I2RS routing
system,
o data transfered between I2RS agent and system (e.g. interfaces
ephemeral configuration),
o data transferred between management server and the system (e.g.
interface configuration).
The next few paragraphs will provide some ideas on how this might be
implemented. These suggest implementation policy should resolve what
is not resolved in the YANG Data module definitions.
The Network Access Control Module (NACM) has been define to control
access to the configuration datastore via the management protocol
across a network. A similar network access control module could be
defined for the I2RS-NACM (per [I-D.ietf-netconf-rfc6536bis].
Figure 2 shows how the I2RS-NACM could be created to support parallel
features with the management protocol (E.g. NETCONF) NACM.
I2RS implementations may also need to define an access modules which
control access to the routing system (Routing Access Control Module
(RACM)) by policy. The I2RS-RACM would control how the I2RS agent
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access the routing system through the SB API interface. In parallel,
the management system would have a RACM to control the SB API
interface (see figure 2). I2RS agent and the management server may
want to read/write system information interfaces or other system
functions. In order to prevent leakage between the I2RS system and
the management system, there needs to be system access control module
(SACM) that protects the jointly held data.
I2RS- || (I2RS Mgt protocol ||
NACM || Protocol) (E.g. NETCONF)|| NACM
------- ----------
I2RS ||I2RS Agent Mgt server||
SACM || I2RS Control-DS config DS || SACM
-----|| (RACM) (RACM) ||=======||
| ||SB API SB API || ||
| +-----------------------------------+ ||
| | Routing System with protocols | ||
| | control plane | ||
| | (applied datastore) | ||
| | (operational state) | ||
| +--------------||-------------------+ ||
| | forwarding plane | ||
| +--------------||-------------------+ ||
---| system |======||
+-----------------------------------+
*Mgt = management
DS = Datastore
Control-DS = Control plane protocol data store
NACM = Network Access Control Module
RACM = Routing System Access Control Module
figure 2
The I2RS clients and the I2RS agents also need a set of policy which
defines what can be received from the network or sent to the network.
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I2RS applications Mangement applications
|| NB API MB API ||
|| (APP NAC policy) (APP NAC policy)||
|| I2RS client mgt client ||
|| (NAC policy) (NAC policy)||
|| ||
I2RS protocol mgt protocol
(NETCONF/RESTCONF)
figure 3
3.2. I2RS Plane and Forwarding Plane
Applications hosted by the I2RS client belong to the I2RS plane. It
is difficult to constrained these applications to the I2RS plane, or
even to limit their scope within the I2RS plane. Applications using
I2RS may also interact with components outside the I2RS plane. For
example an application may use an management client to configure the
network and monitored events via an I2RS agent as figure 4 shows.
+--------------------------------------+
| Application |
+--------------------------------------+
|| NB API NB API ||
|| I2RS client mgt client ||
|| ||
I2RS protocol mgt protocol
(NETCONF/RESTCONF)
figure 4
Applications may also communicate with multiple I2RS clients in order
to have a broader view of the current and potential states of the
network and the I2RS plane itself. These varied remote communication
relationships between applications using the I2RS protocol to change
the forwarding plane make it possible for an individual application
to be an effective attack vector against the operation of the
network, a router's I2RS plane, the forwarding plane of the routing
system, and other planes (management and control planes).
Prevention measures:
Systems should consider the following prevention errors:
application validation - There is little the I2RS plane can do to
validate applications with which it interacts. The I2RS client
passes the I2RS agent an opaque identifier for the application so
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that an application's actions can be traced back to the
application.
Validation against common misconfigurations or errors - One way of
securing the interfaces between application, the I2RS plane, and
the forwarding plane is to limit the information accepted and to
limit the rate information is accepted between these three
software planes. Another method is to performing rudimentary
checks on the results of any updates to the forwarding plane.
3.3. I2RS Plane and Control Plane
The network control plane consists of the processes and protocols
that discover topology, advertise reachability, and determine the
shortest path between any location on the network and any
destination. I2RS client configures, monitors or receives events via
the I2RS agent's interaction with the routing system including the
process that handling the control plane signaling protocols (BGP,
ISIS, OSPF, etc.), route information databases (RIBs), and interface
databases. In some situation to manage an network outage or to
control traffic, the I2RS protocol may modify information in the
route database or the configuration of routing process. While this
is not a part of normal processing, such action allows the network
operator to bypass temporary outages or DoS attacks.
This capability to modify the routing process information carries
with it the risk that the I2RS agent may alter the normal properties
of the routing protocols which provide normal loop free routing in
the control plane. For example, information configured by the I2RS
agent into routing process or RIBs could cause forwarding problems or
routing loops. As a second example, state which is inserted or
deleted from routing processes (control traffic, counters, etc.)
could cause the routing protocols to fail to converge or loop).
Prevention measures:
The I2RS implementation can provide internal checks that after a
routing system protocol changes that it is still operating correctly.
These checks would be specific to the routing protocol the I2RS Agent
would change. For example, if a BGP maximum prefix limit for a BGP
peer is lowered then the BGP peer should not allow the number
prefixes received from that peer to exceed this number.
3.4. Requirements
To isolate I2RS transactions from other planes, it is required that:
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SEC-ENV-REQ 1: Application-to-routing system resources
communications should use an isolated communication
channel. Various level of isolation can be
considered. The highest level of isolation may be
provided by using a physically isolated network.
Alternatives may also consider logical isolation
(e.g. using vLAN). In a virtual environment that
shares a common infrastructure, encryption may also
be used as a way to enforce isolation. Encryption
can be added by using a secure transport required by
the I2RS protocol security
[I-D.ietf-i2rs-protocol-security-requirements], and
sending the non-confidential I2RS data (designed for
a non-secure transport) over a secure transport.
SEC-ENV-REQ 2: The interface used by the routing element to receive
I2RS transactions via the I2RS protocol (e.g. the IP
address) SHOULD be a dedicated physical or logical
interface. As previously, mentioned a dedicated
physical interface may contribute to a higher
isolation. Isolation may also be achieved by using a
dedicated IP address or a dedicated port.
SEC-ENV-REQ 3: An I2RS agent SHOULD have specific permissions for
interaction with each routing element and access to
the routing element should governed by policy
specific to the I2RS agent's interfaces (network,
routing system, system, or cross-datastore).
Explanation:
When the I2RS agent performs an action on a routing element, the
action is performed in a process (or processes) associated with a
routing process. For example, in a typical UNIX system, the user is
designated with a user id (uid) and belongs to groups designated by
group ids (gid). If such a user id (uid) and group id (gid) is the
identifier for the routing processes peforming routing tasks in the
control plane, then the I2RS Agent process would communicate with
these routing processes. It is important that the I2RS agent has its
own unique identifier and the routing processes have their own
identifier so that access control can uniquely filter data between
I2RS Agent and routing processes.
The specific policy the the I2RS agent uses to filter data from the
network or from different processes on a system (routing, system or
cross-datastore) should be specific to the I2RS agent. For example,
the network access filter policy that the I2RS agent uses should be
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uniquely identifiable from the configuration datastore updated by a
management protocol.
SEC-ENV-REQ 4: I2RS plane should be informed when a routing system
resource is modified by a user outside the I2RS plane
access. Notifications from the control plane SHOULD
not to flood the I2RS plane, and rate limiting (or
summarization) is expected to be applied. These
routing system notification MAY translated to the
appropriate I2RS agent notifications, and passed to
various I2RS clients via notification relays.
Explanation:
This requirements is also described in section 7.6 of [RFC7921] for
the I2RS client, and this section extends it to the entire I2RS plane
(I2RS agent, client, and application).
A routing system resource may be accessed by the management plane or
control plane protocols so a change to a routing system resource may
remain unnoticed unless and until the routing system resource
notifies the I2RS plane by notifying the I2RS agent. Such
notification is expected to trigger synchronization of the I2RS
resource state between the I2RS agent and I2RS client - signalled by
the I2RS agent sending a notification to an I2RS client.
The updated resource should be available in the operational state if
there is a yang module referencing that operational state, but this
is not always the case. In the cases, where operational state is not
updated, the I2RS SB (southbound) API should include the ability to
send a notification.
SEC-ENV-REQ 5: I2RS plane should define an "I2RS plane overwrite
policy". Such policy defines how an I2RS is able to
update and overwrite a resource set by a user outside
the I2RS plane. Such hierarchy has been described in
section 6.3 and 7.8 of [RFC7921]
Explanation:
A key part of the I2RS architecture is notification regarding routing
system changes across the I2RS plane (I2RS client to/from I2RS
agent). The security environment requirements above (SEC-ENV-REQ-03
to SEC-ENV-REQ-05) provide the assurance that the I2RS plane and the
routing systems the I2RS plane attaches to remains untouched by the
other planes or the I2RS plane is notificed of such changes.
Section 6.3 of [RFC7921] describes how the I2RS agent within the I2RS
plane interacts with forwarding plane's local configuration, and
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provides the example of an overwrite policy between the I2RS plane
and local configuration (instantiated in 2 Policy Knobs) that
operators may wish to set. The prompt notification of any outside
overwrite is key to the architecture and proper interworking of the
I2RS Plane.
4. I2RS Access Control for Routing System Resources
This section provides recommendations on how I2RS access control
policies associated to the routing system resources. These policies
only apply within the I2RS plane. More especially, the policies are
associated to the applications, I2RS clients and I2RS agents, with
their associated identity and roles.
The I2RS deployment of I2RS applications, I2RS clients, and I2RS
agents can be located locally in a closed environment or distributed
over open networks. The normal case for routing system management is
over an open environment. Even in a closed environment access
control policies should be carefully defined to be able to, in the
future to carefully extend the I2RS plane to remote applications or
remote I2RS clients.
[I-D.ietf-i2rs-protocol-security-requirements] defines the security
requirements of the I2RS protocol between the I2RS client and the
I2RS agent over a secure transport. This section focuses on I2RS
access control architecture (section 4.1), access control policies of
the I2RS agent (section 4.2), the I2RS client (section 4.3), and the
application (section 4.4).
4.1. I2RS Access Control Architecture
Overview:
Applications access to routing system resource via numerous
intermediaries nodes. The application communicates with an I2RS
client. In some cases, the I2RS client is only associated to a
single application attached to one or more agents (case a and case b
in figure 4 below). In other cases, the I2RS client may be connected
to two applications (case c in figure 4 below), or the I2RS may act
as a broker (agent/client device shown in case d in the figure 4
below). The I2RS client broker approach provides scalability to the
I2RS architecture as it avoids that each application be registered to
the I2RS agent. Similarly, the I2RS access control should be able to
scale numerous applications.
The goal of the security environment requirements in this section are
to control the interactions between the applications and the I2RS
client, and the interactions between the I2RS client and the I2RS
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agent. The key challenge is that the I2RS architecture puts the I2RS
Client in control of the stream of communication (application to I2RS
client and I2RS client to the I2RS agent). The I2RS agent must trust
the I2RS client's actions without having an ability to verify the
I2RS client's actions.
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a) I2RS application-client pair talking
to one I2RS agent
+-----------+ +---------+ +-------+
| I2RS |=====| I2RS |======| I2RS |
|application| | client 1| | agent |
+-----------+ +---------+ +-------+
b) I2RS application client pair talking to
two i2RS agents
+--------+
+-------------+ +---------+ | I2RS |
| I2RS |===| I2RS |=====| agent 1|
|application 1| | client 1| +--------+
| | | | +--------+
| | | |=====| I2RS |
+-------------+ +---------+ | agent 2|
+--------+
c) two applications talk to 1 client
+--------+
+-------------+ +--------+ | I2RS |
| I2RS |===|I2RS |=====| agent 1|
|application 1| |client 1| +--------+
+-------------+ | | +--------+
+-------------+ | |=====| I2RS |
| I2RS | | | | agent 2|
|application 2|===| | +--------+
+-------------+ +--------+
d) I2RS Broker (agent/client
+--------+
+-------------+ +--------+ | I2RS |
| I2RS |==|I2RS |=====|agent 3/|
|application 1| |client 1| ==|client 3+----+
+-------------+ +--------+ | +--+-----+ |
| | |
+-------------+ +--------+ | +-------+ +--|----+
| I2RS | |I2RS |===| |I2RS | |I2RS |
|application 2|==|client 2| |agent 1| |agent 2|
+-------------+ +--------+ +-------+ +-------+
figure 4
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4.1.1. access control Enforcement Scope
SEC-ENV-REQ 6: I2RS access control should be performed through the
whole I2RS plane. It should not be enforced by the
I2RS agent only within the routing element. Instead,
the I2RS client should enforce the I2RS client access
control against applications and the I2RS agent
should enforce the I2RS agent access control against
the I2RS clients. The mechanisms for the I2RS client
access control are not in scope of the I2RS
architecture [RFC7921], which exclusively focuses on
the I2RS agent access control provided by the I2RS
protocol.
Explanation:
This architecture results in a layered and hierarchical or multi-
party I2RS access control. An application will be able to access a
routing system resource only if both the I2RS client is granted
access by the I2RS agent and the application is granted access by the
I2RS client.
4.1.2. Notification Requirements
SEC-ENV-REQ 7: When an access request to a routing resource is
refused by one party (the I2RS client or the I2RS
agent), the requester (e.g the application) as well
as all intermediaries should indicate the reason the
access has not been granted, and which entity
rejected the request.
Explanation:
In case the I2RS client access control or the I2RS agent access
control does not grant access to a routing system resource, the
application should be able to determine whether its request has been
rejected by the I2RS client or the I2RS agent as well as the reason
that caused the reject.
SEC-REQ-07 indicates the I2RS agent may reject the request because
the I2RS client is not an authorized I2RS client or lacks the
privileges to perform the requested transaction (read, write, start
notifications or logging). The I2RS client should be notified of the
reason the I2RS agent rejected the transaction due to a lack of
authorization or priviledges, and the I2RS client should return a
message to the application indicating the I2RS agent reject the
transacation with an indication of this reason. Similarly, if the
I2RS client does not grant the access to the application, the I2RS
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client should also inform the application. An example of an error
message could be, "Read failure: you do not have the read
permission", "Write failure: you do not have write permission", or
"Write failure: resource accessed by someone else".
This requirement has been written in a generic manner as it concerns
the following interactions:
o interactions between the application and the I2RS client,
o interactions between the I2RS client and the I2RS agent at a
content level (Protocol security requirements are described by
[I-D.ietf-i2rs-protocol-security-requirements]), and
o interactions between the I2RS agent and the I2RS routing system
(forwarding plane, control plane, and routing plane).
4.1.3. Trust
SEC-ENV-REQ 8: In order to provide coherent access control policies
enforced by multiple parties (e.g. the I2RS client or
the I2RS agent), theses parties should trust each
others, and communication between them should also be
trusted (e.g. TLS) in order to reduce additional
vector of attacks.
SEC-ENV-REQ 9: I2RS client or I2RS agent SHOULD also be able to
refuse a communication with an application or an I2RS
client when the communication channel does not
fulfill enough security requirements.
Explanation:
The participants in the I2RS Plane (I2RS client, I2RS agent, and I2RS
application) exchange critical information, and to be effective the
communication should be trusted and free from security attacks.
The I2RS client or the I2RS agent should be able to reject messages
over a communication channel that can be easily hijacked, like a
clear text UDP channel.
4.1.4. Sharing access control Information
For the I2RS client:
SEC-ENV-REQ 10: The I2RS client MAY request information on its I2RS
access control subset policies from the I2RS agent or
cache requests that have been rejected by the I2RS
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agent to limit forwarding unnecessary queries to the
I2RS agent.
SEC-ENV-REQ 11: The I2RS client MAY support receiving notifications
when its I2RS access control subset policies have
been updated by the I2RS agent.
Similarly, for the applications:
SEC-ENV-REQ 12: The applications MAY request information on its I2RS
access control subset policies in order to limit
forwarding unnecessary queries to the I2RS client.
SEC-ENV-REQ 13: The applications MAY subscribe to a service that
provides notification when its I2RS access control
subset policies have been updated.
For both the application and the client:
SEC-ENV-REQ 14: The I2RS access control should explicitly specify
accesses that are granted. More specifically,
anything not explicitly granted should be denied
(default rule).
Explanation:
In order to limit the number of access requests that result in an
error, each application or I2RS client can retrieve the I2RS access
control policies that applies to it. This subset of rules is
designated as the "Individual I2RS access control policies". As
these policies are subject to changes, a dynamic synchronization
mechanism should be provided. However, such mechanism may be
implemented with different level of completeness and dynamicity of
the individual I2RS access control policies. One example, may be
caching transaction requests that have been rejected.
I2RS access control should be appropriately be balanced between the
I2RS client and the I2RS agent. It remains relatively easy to avoid
the complete disclosure of the access control policies of the I2RS
agent. Relative disclosure of access control policies may allow the
leaking confidential information in case of misconfiguration. It is
important to balance the level of trust of the I2RS client and the
necessity of distributing the enforcement of the access control
policies.
I2RS access control should not solely rely only on the I2RS client or
the I2RS agent as illustrated below:
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- 1) I2RS clients are dedicated to a single application: In this
case, it is likely that I2RS access control is enforced only by
the I2RS agent, as the I2RS client is likely to accept all
access request of the application. It is recommended that even
in this case, I2RS client access control is not based on an
"Allow anything from application" policy, but instead the I2RS
client specifies accesses that are enabled. In addition, the
I2RS client may sync its associated I2RS access control
policies with the I2RS agent to limit the number of refused
access requests being sent to the I2RS agent. The I2RS client
is expected to balance benefits and problems with synchronizing
its access control policies with the I2RS agent to proxy
request validation versus simply passing the access request to
the I2RS agent.
- 2) A single I2RS client connects to multiple applications or
acts as a broker for many applications:
In this case the I2RS agent has a single I2RS client
attached, so the I2RS client could end being configured to
enforce access control policies instead of the I2RS Agent.
In this circumstance, it is possible that the I2RS agent may
grant an I2RS client with high priviledges and blindly trust
the I2RS client without enforcing access control policies on
what the I2RS client can do. Such a situation must be
avoided as it could be used by malicious applications for a
priviledge escalation by compromising the I2RS client
causing the I2RS client to perform some action on behalf of
the application that it normally does not have the
priviledges to perform. In order to mitigate such attack,
the I2RS client that connects to multiple applications or
operates as a broker is expected to host application with an
equivalent level of privileges.
4.1.5. Sharing Access Control in Groups of I2RS Clients and Agents
Overview:
To distribute the I2RS access control policies between I2RS clients
and I2RS agents, I2RS access control policies can also be distributed
within a set of I2RS clients or a set of I2RS agents.
Requirements:
SEC-ENV-REQ 15: I2RS clients should be distributed and act as brokers
for applications that share roughly similar
permissions.
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SEC-ENV-REQ 16: I2RS agents should be avoided granting extra
privileges to their authorized I2RS client. I2RS
agent should be shared by I2RS client with roughly
similar permissions. More explicitly, an I2RS agent
shared between I2RS clients that are only provided
read access to the routing system resources does not
need to perform any write access, so the I2RS client
should not be provided these accesses.
SEC-ENV-REQ 17: I2RS client and I2RS agent should be able to trace
[RFC7922] the various transaction they perform as
well as suspicious activities. These logs should be
collected regularly and analyzed by functions that
may be out of the I2RS plane.
Explanation:
This restriction for distributed I2RS clients to act as brokers only
for applications with roughly the same priviledges avoids the I2RS
client extra priviledges compared to hosted applications, and
discourages applications from perform privilege escalation within an
I2RS client. For example, suppose an I2RS client requires write
access to the resources. It is not recommended to grant the I2RS
agent the write access in order to satisfy a unique I2RS client.
Instead, the I2RS client that requires write access should be
connected to a I2RS agent that is already shared by I2RS client that
requires a write access.
Access control policies enforcement should be monitored in order to
detect violation of the policies or detect an attack. Access control
policies enforcement may not be performed by the I2RS client or the
I2RS agent as violation may require a more global view of the I2RS
access control policies. As a result, consistency check and
mitigation may instead be performed by the management plane.
However, I2RS clients and I2RS agents play a central role.
The I2RS agent can trace transactions that an I2RS client requests it
to perform, and to link this to the application via the secondary
opaque identifier to the application. This information is placed in
a tracing log which is retrieved by management processes. If a
particular application is granted a level of priviledges it should
not have, then this tracing mechanism may detect this security
intrusion after the instrusion has occurred.
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4.1.6. Managing Access Control Policy
Access control policies should be implemented so that the policies
remain manageable in short and longer term deployments of the I2RS
protocol and the I2RS plane.
Requirements:
SEC-ENV-REQ 18: access control should be managed in an automated way,
that is granting or revoking an application should
not involve manual configuration over the I2RS plane
(I2RS client, I2RS agent, and application).
Explanation:
Granting or configuring an application with new policy should not
require manual configuration of I2RS clients, I2RS agents, or other
applications.
SEC-ENV-REQ 19: Access control should be scalable when the number of
application grows as well as when the number of I2RS
client increases.
Explanation:
A typical implementation of a local I2RS client access control
policies may result in creating manually a system user associated to
each application. Such an approach is likely not to scale when the
number of applications increases into the hundreds.
SEC-ENV-REQ 20: Access control should be dynamically managed and
easily updated.
Explanation:
Although the numberof I2RS clients is expected to be lower than the
number of application, as I2RS agent provide access to the routing
resource, it is of primary importance that an access can be granted
or revoke in an efficient way.
SEC-ENV-REQ 21: I2RS clients and I2RS agents should be uniquely
identified in the network to enable centralized
management of the I2RS access control policies.
Explanation:
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Centralized management of the access control policies of an I2RS
plane with network that hosts several I2RS applications, clients and
agents requires that each devices can be identified.
4.2. I2RS Agent Access Control Policies
Overview:
The I2RS agent access control restricts the routing system resource
access to authorized identities - possible access policies may be
none, read or write. The initiator of an access request to a routing
resource is always an application. However, it remains challenging
for the I2RS agent to establish its access control policies based on
the application that initiates the request.
First, when an I2RS client acts as a broker, the I2RS agent may not
be able to authenticate the application. In that sense, the I2RS
agent relies on the capability of the I2RS client to authenticate the
applications and apply the appropriated I2RS client access control.
Second, an I2RS agent may not uniquely identify a piece of software
implementing an I2RS client. In fact, an I2RS client may be provided
multiple identities which can be associated to different roles or
privileges. The I2RS client is left responsible for using them
appropriately according to the application.
Third, each I2RS client may contact various I2RS agent with different
privileges and access control policies.
4.2.1. I2RS Agent Access Control
This section provides recommendations on the I2RS agent access
control policies to keep I2RS access control coherent within the I2RS
plane.
Requirements:
SEC-ENV-REQ 22: I2RS agent access control policies should be
primarily based on the I2RS clients as described in
[RFC7921].
SEC-ENV-REQ 23: I2RS agent access control policies MAY be based on
the application if the application identity has been
authenticated by the I2RS client and passed via the
secondary identity to the I2RS agent.
SEC-ENV-REQ 24: The I2RS agent should know which identity (E.g.
system user) performed the latest update of the
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routing resource. This is true for an identity
inside and outside the I2RS plane so the I2RS agent
can appropriately perform an update according to the
priorities associated to the requesting identity and
the identity that last updated the resource.
SEC-ENV-REQ 25: the I2RS agent should have a "I2RS agent overwrite
Policy" that indicates how identities can be
prioritized. This requirements is also described in
section 7.6 of [RFC7921]. Similar requirements exist
for components within the I2RS plane, but this is
within the scope of the I2RS protocol security
requirements
[I-D.ietf-i2rs-protocol-security-requirements].
Explanation:
If the I2RS application is authenticated to the I2RS client, and the
I2RS client is authenticated to the I2RS agent, and the I2RS client
uses the opaque secondary identifier to pass an authenticated
identifier to the I2RS agent, then this identifier may be used for
access control. However, caution should be taken when using this
chain of authentication since the secondary identifier is intended in
the I2RS protocol only to aid traceability.
From the environment perspective the I2RS agent MUST be aware when
the resource has been modified outside the I2RS plane by another
plane (management, control, or forwarding). The prioritization
between the different planes should set a deterministic policy that
allows the collision of two planes (I2RS plane and another plane) to
be resolved via an overwrite policy in the I2RS agent.
Similar requirements exist for knowledge about identities within the
I2RS plane which modify things in the routing system, but this is
within the scope of the I2RS protocol's requirements for ephemeral
state [I-D.ietf-i2rs-ephemeral-state] and security requirements
[I-D.ietf-i2rs-protocol-security-requirements].
4.2.2. I2RS Client Access Control Policies
Overview:
The I2RS client access control policies are responsible for
authenticating the application managing the privileges for the
applications, and enforcing access control to resources by the
applications.
Requirements:
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REQ 26: I2RS client should authenticate its applications. If the
I2RS client acts as a broker and supports multiple
applications, it should authenticate each application.
REQ 27: I2RS client should define access control policies associated
to each applications. An access to a routing resource by an
application should not be forwarded immediately and
transparently by the I2RS client based on the I2RS agent
access control policies. The I2RS client should first check
whether the application has sufficient privileges, and if so
send an access request to the I2RS agent.
Explanation:
If no authentication mechanisms have being provided between the I2RS
client and the application, then I2RS client must be dedicated to a
single application. By doing so, application authentication relies
on the I2RS authentication mechanisms between the I2RS client and the
I2RS agent.
If an I2RS client has multiple identities that are associated with
different privileges for accessing an I2RS agent(s), the I2RS client
access control policies should specify the I2RS client identity with
the access control policy.
4.2.3. Application and Access Control Policies
Overview
Applications do not enforce access control policies. Instead these
are enforced by the I2RS clients and the I2RS agents. This section
provides recommendations for applications in order to ease I2RS
access control by the I2RS client and the I2RS agent.
Requirements:
SEC-ENV-REQ 28: Applications SHOULD be uniquely identified by their
associated I2RS clients
Explanation:
Different application may use different methods (or multiple methods)
to communicate with its associated I2RS client, and each application
may not use the same form of an application identifier. However, the
I2RS client must obtain an identifier for each application. One
method for this identification can be a system user id.
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SEC-ENV-REQ 29: Each application SHOULD be associated to a restricted
number of I2RS client
Explanation:
The I2RS client provides access to resource on its behalf and this
access should only be granted for trusted applications, or
applications with an similar level of trust. This does not prevent
an I2RS client to host a large number of applications with the same
levels of trust.
SEC-ENV-REQ 30: An application SHOULD be provided means and methods
to contact their associated I2RS client.
Explanation:
It is obvious when an I2RS client belongs to the application as part
of a module or a library that the application can communicate with a
I2RS client. Similarly, if the application runs into a dedicated
system with a I2RS client, it is obvious which I2RS client the
application should contact. If the application connects to the I2RS
client remotely, the application needs some means to retrieve the
necessary information to contact its associated I2RS client (e.g. an
IP address or a FQDN).
5. I2RS Application Isolation
A key aspect of the I2RS architecture is the network oriented
application that uses the I2RS high bandwidth programmatic interface
to monitor or change one or more routing systems. I2RS applications
could be control by a single entity or serve various tenants of the
network. If multiple entities use an I2RS application to monitor or
change the network, security policies must preserve the isolation of
each entity's control and not let malicious entities controlling one
I2RS application interfere with other I2RS applications.
This section discusses both security aspects related to
programmability as well as application isolation in the I2RS
architecture.
5.1. Robustness Toward Programmability
Overview
I2RS provides a programmatic interface in and out of the Internet
routing system which provides the following advantages for security:
o the use of automation reduces configuration errors;
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o the programmatic interface enables fast network reconfiguration
and agility in adapting to network attacks; and
o monitoring facilities to detect a network attack, and
configuration changes which can help mitigate the network attack.
Programmability allows applications to flexible control which may
cause problems due to:
o applications which belong to different tenants with different
objectives,
o applications which lack coordination resulting in unstable routing
configurations such as oscillations between network
configurations, and creation of loops for example. For example,
one application may monitor a state and change to positive, and a
second application performs the reverse operation (turns it
negative). This fluctuation can cause a routing system to become
unstable.
The I2RS plane requires data and application isolation to prevent
such situations to happen. However, to guarantee the network
stability constant monitoring and error detection are recommended to
be activated.
Requirement:
SEC-ENV-REQ 31: The I2RS agents should monitor constantly parts of
the system for which I2RS clients or applications
have provided requests. It should also be able to
detect any I2RS clients or applications causing
problems that may lead the routing system in an
unstable state.
Explanation:
Monitoring consists at least in logging events and receiving streams
of data. I2RS Plane implementations should monitor the I2RS
applications and I2RS clients for potential problems. The cause for
the I2RS clients or applications providing problematic requests can
be failures in the implementation code or malicious intent. ]
5.2. Application Isolation
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5.2.1. DoS
Overview:
Requirements for robustness to DoS attacks have been addressed in the
communication channel section [RFC7921]. This section focuses on
requirements for application isolation that help prevent DoS.
Requirements:
SEC-ENV-REQ 32: In order to prevent DoS, it is recommended the I2RS
agent controls the resources allocated to each I2RS
clients. I2RS client that acts as broker may not be
protected as efficiently against these attacks unless
the broker performs resource controls for the hosted
applications.
SEC-ENV-REQ 33: I2RS agent SHOULD make a response redirection unless
the redirection is previously validated and agreed by
the destination.
SEC-ENV-REQ 34: I2RS Appications should avoid the use of underlying
protocols that are not robust to reflection attacks.
Explanation:
The I2RS interface is used by application to interact with the
routing states. If the I2RS client is shared between multiple
applications, one application can use the I2RS client to perform DoS
or DDoS attacks on the I2RS agent(s) and through the I2RS agents
attacks on the network. DoS attack targeting the I2RS agent would
consist in providing requests that keep the I2RS agent busy for a
long time. These attacks on the I2RS agent may involve an
application (requesting through an I2RS Client) heavy computation by
the I2RS agent in order to block operations like disk access.
Some DoS attacks may attack the I2RS Client's reception of
notification and monitoring data stream over the network. Other DoS
attacks may focus on the application directly by performing
reflection attacks to reflect traffic. In such an attack could be
performed by first detecting an application is related to monitoring
the RIB or changing the RIB. Reflection-based DoS may be also attack
at various levels in the stack utilizing UDP at the service to
redirect data to a specific repository
I2RS implementation should consider how to protect I2RS against such
attacks.
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5.2.2. Application Logic Control
Overview
This section examines how application logic must be design to ensure
application isolation.
Requirements:
SEC-ENV-REQ 35: Application logic should remain opaque to external
listeners. Application logic may be partly hidden by
encrypting the communication between the I2RS client
and the I2RS agent. Additional ways to obfuscate the
communications may involve sending random messages of
various sizes. Such strategies have to be balanced
with network load. Note that I2RS client broker are
more likely to hide the application logic compared to
I2RS client associated to a single application.
Explanation:
Applications use the I2RS interface in order to update the routing
system. These updates may be driven by behavior on the forwarding
plane or any external behaviors. In this case, correlating
observation to the I2RS traffic may enable to derive the application
logic. Once the application logic has been derived, a malicious
application may generate traffic or any event in the network in order
to activate the alternate application.
6. Security Considerations
The whole document is about security requirements for the I2RS
environment. To protect personal privacy, any identifier (I2RS
application identifier, I2RS client identifier, or I2RS agent
identifier) should not contain personal identifiable information.
7. IANA Considerations
No IANA considerations for this requirements.
8. Acknowledgments
A number of people provided a significant amount of helping comments
and reviews. Among them the authors would like to thank Russ White,
Russ Housley, Thomas Nadeau, Juergen Schoenwaelder, Jeffrey Haas,
Alia Atlas, and Linda Dunbar.
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9. References
9.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7920] Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
Statement for the Interface to the Routing System",
RFC 7920, DOI 10.17487/RFC7920, June 2016,
<http://www.rfc-editor.org/info/rfc7920>.
[RFC7921] Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
Nadeau, "An Architecture for the Interface to the Routing
System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
<http://www.rfc-editor.org/info/rfc7921>.
[RFC7922] Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
the Routing System (I2RS) Traceability: Framework and
Information Model", RFC 7922, DOI 10.17487/RFC7922, June
2016, <http://www.rfc-editor.org/info/rfc7922>.
[RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
for Subscription to YANG Datastores", RFC 7923,
DOI 10.17487/RFC7923, June 2016,
<http://www.rfc-editor.org/info/rfc7923>.
[I-D.ietf-i2rs-protocol-security-requirements]
Hares, S., Migault, D., and J. Halpern, "I2RS Security
Related Requirements", draft-ietf-i2rs-protocol-security-
requirements-17 (work in progress), September 2016.
9.2. Informative References
[I-D.ietf-i2rs-ephemeral-state]
Haas, J. and S. Hares, "I2RS Ephemeral State
Requirements", draft-ietf-i2rs-ephemeral-state-23 (work in
progress), November 2016.
[I-D.ietf-netconf-rfc6536bis]
Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", draft-ietf-
netconf-rfc6536bis-00 (work in progress), January 2017.
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[I-D.ietf-netmod-revised-datastores]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "A Revised Conceptual Model for YANG
Datastores", draft-ietf-netmod-revised-datastores-00 (work
in progress), December 2016.
Authors' Addresses
Daniel Migault
Ericsson
8400 boulevard Decarie
Montreal, QC H4P 2N2
Canada
Phone: +1 514-452-2160
Email: daniel.migault@ericsson.com
Joel Halpern
Ericsson
Email: Joel.Halpern@ericsson.com
Susan Hares
Huawei
7453 Hickory Hill
Saline, MI 48176
USA
Email: shares@ndzh.com
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