Network Working Group A. Atlas
Internet-Draft Juniper Networks
Intended status: Informational S. Hares
Expires: March 15, 2013 Huawei Technologies
J. Halpern
Ericsson
September 11, 2012
A Policy Framework for the Interface to the Routing System
draft-atlas-irs-policy-framework-00
Abstract
A key aspect of the Interface to the Routing System (IRS) is what
mechanisms it includes to carry policy information and to enable
policy control. This applies both in the protocol itself and in the
sub-interfaces associated with the different components of the
routing system. Similarly, the data-models associated with the sub-
interfaces must be capable of expressing the appropriate granularity
for access and authorization-related policy. This document describes
the policy framework for IRS.
Status of this Memo
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This Internet-Draft will expire on March 15, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. General IRS Policy . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Policy between commissioner and agent . . . . . . . . . . 6
3.1.1. Identity . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.2. Security Role . . . . . . . . . . . . . . . . . . . . 6
3.1.3. Security Model . . . . . . . . . . . . . . . . . . . . 7
3.1.4. Scope and Influence . . . . . . . . . . . . . . . . . 7
3.1.5. Resources . . . . . . . . . . . . . . . . . . . . . . 8
3.1.6. Connectivity . . . . . . . . . . . . . . . . . . . . . 9
3.1.7. Priority . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.8. Precedence . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Policy between Agent and Local System . . . . . . . . . . 12
3.2.1. Local Configuration . . . . . . . . . . . . . . . . . 13
3.2.2. Removal of IRS-installed State . . . . . . . . . . . . 14
3.2.3. On Reboot . . . . . . . . . . . . . . . . . . . . . . 14
4. Policy in a Sub-Interface . . . . . . . . . . . . . . . . . . 15
4.1. Resource Reservation and Three-Phase Commit . . . . . . . 15
4.2. Defining IRS Behavior Based on Implicit and Explicit
Policy . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.1. Example of Implicit Policy . . . . . . . . . . . . . . 16
4.2.2. Passing Explicit Policy . . . . . . . . . . . . . . . 17
4.2.2.1. Explicit policy on Data Forwarding, Resources,
and Policy passing . . . . . . . . . . . . . . . . 17
4.2.2.2. Example of Explicit Policy . . . . . . . . . . . . 17
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Informative References . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The Interface to the Routing System (IRS) provides read and write
access to the information and state that enable the routing
components of routing elements. The IRS is introduced and described
in [I-D.atlas-irs-problem-statement] and [I-D.ward-irs-framework].
Policy helps provide filters and control on the level of access to
information and state that is enabled by individual protocol
interactions. A clear view of the policy features desirable at the
IRS is important to shape the architecture and requirements for the
protocols and sub-interfaces of the IRS. Policy can be explicitly
defined or implicitly assumed in a system, and can be enforced by
that system's rules and behavior. Since IRS provides sub-interfaces
to routing sub-systems that already have policy defined (implicitly
or explicitly), it is important to consider the existing policy
mechanisms and how an IRS sub-interface should interact with them.
IRS policy has four different aspects that need to be considered.
1. Policy related to the IRS protocol interactions between different
systems.
2. Policy related to the interaction between the IRS Agent and the
local system to which the IRS Agent is providing an interface.
3. Sub-interface policy to support scope and influence restrictions
and to preserve necessary policy associated with the related
routing sub-system.
4. Policy that can be installed or read via a sub-interface's data-
model that is associated with the related routing sub-system.
2. Terminology
The following memorable terminology is used in this document.
agent or IRS Agent: An IRS Agent provides the supported IRS sub-
interfaces to the local system's routing sub-systems. The IRS
Agent understands the IRS protocol and can be contacted by
commissioners.
commissioner: A commissioner speaks the IRS protocol to communicate
with IRS Agents and uses the IRS sub-interfaces to accomplish a
task as instructed by the commissioner's local application. A
commissioner can be seen as the part of an application that
supports IRS and could be a software library.
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scope: The set of information which the particular IRS entity
(agent or commissioner) is authorized to read. This access
includes the permission to see the existence of data and the
ability to retrieve the value of that data. In the context of an
interaction between a commissioner and an agent, the effective
scope is restricted to the intersection of the scopes of the two
entities.
influence: The set of field values which the particular IRS entity
(agent or commissioner) is authorized to install. This access can
restrict what fields can be modified or created, and what specific
value sets and ranges can be installed. In the context of an
interaction between a commissioner and an agent, the effective
influence is restricted to the intersection of the influences of
the two entities.
resources: A resource is an IRS-specific use of memory, storage, or
execution that a commissioner may consume due to its IRS
operations. The amount of each such resource that a commissioner
may consume in the context of a particular agent can be
constrained. Examples of such resources could include: the number
of installed operations, number of operations that haven't reached
their start-time, etc. These are not protocol-specific resources
or network-specific resources.
role or security role: A security role specifies the scope,
influence, resources, precedence values, etc. that a commissioner
or agent has.
identity: A commissioner is associated with exactly one specific
identity. State installed by a particular identity is owned by
that identity; state ownership can not be transferred. It is
possible for multiple communication channels to use the same
identity; in that case, the assumption is that the associated
commissioner is coordinating such communication. Similarly, an
agent is associated with a specific identity.
3. General IRS Policy
IRS needs its own implicit and explicit policy. This section
articulates some of the those key concepts and policy decisions. The
IRS policy applies to interactions between the agent and
commissioners and between the agent and the local system.
The agent's externally perceivable behavior and associated policy is
a key aspect of IRS that must be described. The commissioner's
behavior and functionality is specifically out-of-scope except where
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it needs to be described with respect to the agent's behavior and the
IRS protocol.
*********************** ***********************
* Application A * * Application B *
* * * *
* +----------------+ * * +----------------+ *
* | Commissioner A | * * | Commissioner B | *
* +----------------+ * * +----------------+ *
******* ^ ************* ***** ^ ****** ^ ******
| | |
| -----------------------| |
| | |
******* v ***** v ********* ************** v ********
* +----------------+ * * +----------------+ *
* | Agent 1 | * * | Agent 2 | *
* +----------------+ * * +----------------+ *
* ^ ^ * * ^ ^ *
* | | * * | | *
* v v * * v v *
* *********** ********** * * *********** ********* *
* * Routing * * Local * * * * Routing * * Local * *
* *********** * Config * * * *********** * Config* *
* ********** * * ********* *
* * * *
* Routing Element 1 * * Routing Element 2 *
*************************** *************************
Figure 1: Architecture of commissioners and agents
As can be seen in Figure 1, a commissioner can communicate with
multiple agents. The application associated with a commissioner may
have multiple tasks it is accomplishing (separate functions, short-
term versus longer-term, etc) and each such task may involve a set of
agents which may or may not differ.
As can also be seen in Figure 1, an IRS Agent may communicate with
multiple commissioners. Each commissioner may send the agent a
variety of install operations. The set of install operations
received by an agent may overlap and conflict. No simple protocol or
policy mechanisms by an agent can completely avoid indirect
interactions between different install operations. The functional
partitioning between the different commissioners must be done to
avoid undesirable indirect interactions.
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3.1. Policy between commissioner and agent
Multiple commissioners can communicate with the same agent. The
agent must have policies to manage the resulting complexity.
Implicit policy includes the assumptions about communication between
the commissioner and agent. Explicit policy includes mechanisms to
arbitrate between different commissioners, between operations of the
same commissioner, and to manage state owned by an commissioner
inside the agent.
3.1.1. Identity
By definition, a commissioner is associated with exactly one
identity. An agent will store data that is owned by a particular
commissioner, based upon that commissioner's identity. Since a
commissioner can communicate via multiple transport channels and no
channel needs to be active for the agent to have associated state,
the commissioner's identity is used to identify the ownership of the
data stored by the agent.
Similarly, by definition, an agent is associated with exactly one
identity. An commissioner may also store local state associated with
a particular agent. The agent's identity can be used to identify
ownership of the data stored by the commissioner.
The details of what constitutes an identity can be dependent upon the
specifics of the IRS protocol and selected security mechanisms.
However, there are some critical considerations for identity that do
impose constraints.
An identity is not tied to a single communication channel. A
commissioner may use multiple IP addresses; an identity should not be
tied to a specific IP address. If the commissioner or agent is
associated with a system that may be mobile, that should be
considered in its identification. Finally, the syntax and semantics
for identifiers used for a commissioner and for an agent may be
different.
3.1.2. Security Role
In the context of an agent, each commissioner will have a security
role. The commissioner's identity and associated security role will
have to be verified via an acceptable security mechanism. A variety
of such mechanisms are anticipated to meet different security and
operational objectives. Example mechanisms might include a role
assertion from the commissioner to the agent that the agent can
cryptographically verify or having the agent to use an already
trusted protocol to verify the commissioner's security role and
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identity.
An agent must know the scope, influence, and resources associated
with each particular security role. This information may vary across
different agents even in the same network or it may be consistent
across different agents in the same network. The latter can be
enforced by having a commissioner that is authorized to influence the
meta-data model of security roles on the relevant set of agents.
A security role also defines what precedence values (See
Section 3.1.8) a commissioner can use.
3.1.3. Security Model
As described above, roles identify the scope, influence, and
resources allowed to an IRS Commissioner. The policy model therefore
needs to include these roles. The question of the bindings of
identities to roles, and the selection of identities are protocol
specific matters outside the scope of this document.
The policy model for roles needs to address two dimensions. It needs
to create the roles themselves. This should allow for use of
techniques like inheritance, presumably with some rules on how role
definitions can augment or restrict the inherited definitions.
The security model also needs to define, by reference to the policy
model itself, the scope and influence of the role. The question of
defining the resources of a role is for further study. The role
definition needs to indicate what types and instances of data can be
observed and what information about those instances entities with
that role can observe. The security model also needs to define which
data items can be modified, and what modifications (ranges, specified
values, or other assertions that must be met) are permitted.
3.1.4. Scope and Influence
Scope and influence are specified as part of a security role. A
security role may be defined and managed in an external repository,
centralized within an administration. The security role definitions
must be accessible to an agent.
In the context of an interaction between a commissioner and an agent,
the effective scope or influence is restricted to the intersection of
the scopes or influence of the two entities.
What information a particular commissioner is authorized to read is
known as the commissioner's scope. A scope includes the ability to
see that particular data exists and to read the same data. The scope
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can have its constraints specified in terms of specific portions of
data models.
Similarly, what information a commissioner can install may be
contrained. This is known as its influence. The influence is
specific in both the parts of the data models and in the set and
range of data that can be installed. For example, a commissioner
might be able to write static routes in the RIB data-model for
prefixes in 10.0/16.
While the commissioner's behavior and functionality is specifically
out-of-scope, it is useful to describe the same scope and influence
concepts for an agent operating in the context of a commissioner.
An agent's scope is the set of data that the agent can read or have
access to. An agent would generally learn such data because the
commissioner has sent that data to the agent in an operation.
An agent's influence is the set and range of data that the agent is
allowed to provide to the commissioner and that will be accepted by
the commissioner. For instance, commissioner B may accept next-hop
change notifications for prefix 10.0/16 from agent 1 but not from
agent 2.
3.1.5. Resources
When a commissioner sends operations to an agent, those operations
can consume resources. Therefore, it is important that the agent
have policy to limit the resources available to a particular
commissioner. This is based on the commissioner's identity and
security role. Such resource policy specifications need to be
provided in a data-model that can be modified by appropriately
authorized commissioners or local configuration.
Examples of such resource constraints include:
Number of installed operations owned,
Number of operations that haven't reached their start-time, and
Number of event notifications registered for.
As discussed in Section 3.1.7, a commissioner can specify priorities
for the operations it sends.
If compute resources are considered, it is not the intent to try and
determine the computation associated with particular operations.
Instead, the constraint could be on amount of compute-time given to a
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commissioner every pre-defined period. This can provide a mechanism
for fair sharing of compute resources between commissioners.
3.1.6. Connectivity
A commissioner does not need to maintain an active communication
channel with an agent. Therefore, an agent may need to open a
communication channel to the commissioner to communicate previously
requested information. The lack of an active communication channel
does not imply that the associated commissioner is non-functional.
When communication is required, the agent or commissioner can open a
new communication channel.
State held by an agent that is owned by a commissioner should not be
removed or cleaned up when a commissioner is no longer communicating
- even if the agent cannot successfully open a new communication
channel to the commissioner.
3.1.7. Priority
The motivating example for priority is when a single commissioner is
sending operations to accomplish multiple tasks. For example, one
task might be long-term and another task might deal with unexpected
requests that are more important. In this case, the commissioner may
wish to provide a hint to the relevant agents as to which operations
should be done first.
Communication from a commissioner can come across multiple channels,
so simply specifying that operations be done in order is not
sufficient. Additionally, all operations may not be immediately
carried out, due to varying start-times or other constraints. With
these factors and this motivating example, it is useful to introduce
the concept of prioritization for operations sent from the same
commissioner.
By introducing the concept of priority for operations, a commissioner
can accomplish multiple uncorrelated tasks that affect the same agent
with the specified prioritization.
A default priority can be specified for each particular communication
channel. In addition, an IRS operation can specify a priority to use
instead. Priorities between operations from different commissioners
need not be compared.
The priority can be used by an agent to determine which operation
from a commissioner to execute next.
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3.1.8. Precedence
A mechanism is needed for the agent to determine what state to
install when there are overlapping install operations. An install
operation may overlap with locally-installed configuration state or
with a previous install operation that was requested by a
commissioner. The mechanism to resolve this is termed "precedence".
No simple mechanism can fully handle indirect interactions;
considering such interactions is out-of-scope. Indirect interactions
must be considered when different commissioners are given their
tasks.
A critical aspect of precedence-based decisions is that preference is
only given based on arrival time of the install operation when
multiple commissioners use the same precedence value.
Each install operation has a precedence associated with it. This
precedence may come from the default associated with the
commissioner, with the specific communication channel, or with the
specific operation. The range of possible precedence values that can
be used is known based on the commissioner's security role. The
determination of the precedence associated with any operation is a
policy decision at the agent, but may utilize any or all of the
information described above.
When an install operation is executed, the agent first determines if
there is overlapping existing IRS-installed state. If not, the agent
must determine if it overlaps existing local-configuration state.
Local-configuration state will also have a precedence associated with
it so that the agent can make an appropriate decision.
A commissioner can specify whether an install operation should be
store-if-not-best. This allows a commissioner to determine what
happens when an install operation doesn't win the precedence
comparison. If store-if-not-best is specified, then the install
operation succeeds and the associated installed state is stored but
not actively installed by the agent. If store-if-not-best is not
specified, then the install operation will fail.
The store-if-not-best flag is stored with the installed operation's
precedence. If the agent determines that an installed operation must
be preempted, then the agent consults the store-if-not-best flag. If
store-if-not-best is specified, then the agent stores the preempted
operation and does not notify the associated commissioner. If store-
if-not-best is not specified, then the agent notifies the associated
commisioner of the preemption and removes the previously installed
state.
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/----------\ NO |------------|
/ Overlap? \________\| Install as |
\ / /| IRS state |
\----------/ |------------|
|
| YES
V
/-----------------\ YES /------------\ YES |---------------|
/ New Precedence \_______\/ Old store-if \_____\| Store old IRS |
\ better than Old? / /\ -not-best? / /|---------------|
\-----------------/ \------------/ |
| | |
| | NO |
| V V
| |------------------| |-------------|
| | Send Preempt |___\| Install new |
| NO | Notification to | /| IRS state |
| | Old Commissioner | |-------------|
| |------------------|
V
/-------------\ YES /-----------\ NO /----------\ NO
/ New precedence\____\ / same \___\ / new store- \___
\ equal to old / / \ Commissioner/ / \if-best on? / |
\-------------/ \-----------/ \----------/ |
| NO |YES YES | V
| | | |--------------|
| | | | Send a reject|
| V | | to new |
| |-------------------| | | Commissioner |
| | Install new State | | |--------------|
| |-------------------| V
| |----------------|
V | Save new State |
/-------------\ NO |-------------------| |----------------|
/ New store-if \____\| Send Preempt |
\ -not-best? / /| Notification to |
\-------------/ | New Commissioner |
| | and forget new |
| | IRS state |
| Yes |-------------------|
V
|---------------------|
| store new IRS state |
|---------------------|
Figure 2: Precedence Decision-Making
If the overlapping new operation has a precedence that is better than
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the existing state, then the agent should preempt the existing state
and act according to the existing state's store-if-not-best flag. If
that store-if-not-best flag is set, the agent will store the old
state and install the new state. If the store-if-not-best flag is
clear, the agent will send a preemption notification to the Old IRS
Comissioner, install the new IRS state, and forget the old.
If the overlapping existing state has the same precedence and the
same commissioner associated, then the agent completes the install
operation; otherwise, the agent must reject or store the install
operation, based on the store-if-not-best flag.
If the new overlapping operation has a precedence that is worse than
the existing state, then the agent must reject or store the install
operation, based on the state of the new store-if-not-best flag. If
the store-if-not-best flag is set, then then the agent will store the
new IRS state. If the store-if-not-best flag is clear, then the the
IRS agent will send a preempt notification to the new commissioner
and forget the new IRS state.
This decision process is illustrated in Figure 2.
When an uninstall operation (e.g. remove) is done, the stored state
with the next best precedence should be selected and installed.
A consequence of the precedence policy mechanism is that a
commissioner must be able to handle its installed operations being
preempted at any time, either explicitly or simply by having the
active state changed. Such preemption can be minimized by
appropriate separation of tasks, with their associated install
operations, between the local systems of the commissioners and by
knowledgeable local system configuration.
3.2. Policy between Agent and Local System
It is critical to understand and clearly specify how IRS interacts
with local configuration. The key questions are:
1. What happens when Local Configuration overlaps with IRS installed
state?
2. What happens when IRS installed state is removed?
3. How is state recreated when a local system reboots?
A consequence of using IRS is that the local system's state may not
be synchronized with the local configuration. Since this is a change
in understood behavior, any discrepencies should be clearly visible
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to the operator with an associated explanation.
Logically, the local configuration is essentially modeled as a local
commissioner, with its own precedence, identity, and security role
and immediate permanent install operations. The key differences are
both that all relevant local configuration state need not be cached
by the agent and that reboot imposes the need to process local
configuration state before any other IRS-installed state.
3.2.1. Local Configuration
The local system's local configuration may have overlapping influence
with that of one or more commisssioners using an agent. Therefore,
explicit and implicit policy interactions must be specified. The
mechanism that IRS provides for deciding between overlapping install
operations is "precedence". This same mechanism can be used to
decide between local configuration and an IRS operation. Local
configuration can specify the precedence value to be used for the
local system.
A precedence value that causes the desired behavior can be specified
as follows. (MAX is the highest precedence given to a commissioner.
MIN is the lowest precedence given to a commissioner.)
MAX+1 Precedence: If the local configuration has a precedence
higher than that given to any commissioner, then state from the
local configuration will always be installed. If any IRS-
installed state is therefore preempted, the agent will notify the
associated commissioner.
MIN-1 Precedence: If the local configuration has a precedence
lower than that given to any commissioner, then IRS-installed
state will always override local configuration. That this
preemption has occurred should be reflected in how the local
system displays its state.
Other Precedence: The local configuration can have higher
precedence than that given to some commissioners, lower precedence
than that given to other commissioners, and equal precedence to
that given to other commissioners. Then some local configuration
state may be preempted by IRS-installed state while some IRS-
installed state can be preempted by local configuration.
Local-configuration wins all precedence ties.
Just as an agent must check to determine if an install operation
overlaps with existing installed state, the process of committing
local configuration must check to see if there is overlapping IRS-
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installed state.
What the process of committing local configuration is can vary by
local system. Well known examples are when a return is sent to the
CLI and when an explicit commit command is specified. How the proper
checks for interaction between the agent and local configuration are
done is a local system matter.
Similarly, when an agent checks to see if an install operation
overlaps with existing installed state, the agent must determine if
it overlaps with existing local configuration.
If the precedence associated with local configuration is changed,
then it is retroactive. All local configuration state stored by the
agent must be updated with the new precedence value and installation
decisions made for overlapping data. This change could be very
disruptive.
3.2.2. Removal of IRS-installed State
When a piece of local configuration is removed, the local system goes
back to the appropriate system default. However, when an operation
removes some IRS-installed state is removed, the correct behavior is
not to just go back to the system default. Instead, any stored state
must be considered - whether that comes from local configuration or
stored IRS install operations that didn't have the highest
precedence. If there is any stored state, then the highest
precedence of the options is selected and installed. That existing
overlapping state might come from the local -configuration.
If IRS's implicit policy were to just go to the system default, then
the local configuration and the local system state would not be
synchronized and there would be no remaining IRS-state to explain the
discrepency. Since IRS state can also be stored and not installed,
the same mechanism can be used for stored IRS install operations and
for local configuration.
3.2.3. On Reboot
When the local system reboots, only persistent IRS-installed state is
preserved by the agent. The implicit policy for IRS is that the
local configuration is read and installed first. After the local
system has its local configuration installed, the persistent IRS
install operations are executed to bring the system to the persistent
state.
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4. Policy in a Sub-Interface
It is critical to consider how policy influences a sub-interface when
defining the sub-interface and its associated data-model(s). There
are several different aspects to consider.
How are scope and influence policy specified in the data model?
What granularity levels are necessary for the particular sub-
interface?
How does the implicit policy in the associated routing sub-system
effect what IRS can be allowed to influence?
Are the implicit policies of the associated routing sub-system
captured in the semantic content of the information model, data
model, and description?
What explicit policy communicated in the associated routing sub-
system needs to be included in the data-model? What indirection
and abstractions are needed?
4.1. Resource Reservation and Three-Phase Commit
Some agents and sub-interfaces may offer the ability to reserve
resources required by operations before the operation start time.
There are two aspects to how to support this.
First, if the agent can do time-aware resource reservation, then an
install operation can specify "reserve-only" to prompt an
acknowledgement or failure as to the ability of the agent to confirm
the reservation. Then the commissioner can either send an operation
to commit the reservation, which causes the associated install
operation, or to remove the reservation. A "reserve-only" operation
will have its reservation expire at the end of its associated life-
time.
Second, part of a sub-interface's data-model may be to request a
reservation with a known start-time and duration. An example might
be reserving a specific bandwidth on a path for an LSP between two
devices. It is important to consider whether a particular sub-
interface should offer a time-based reservation service as part of
its data-model.
4.2. Defining IRS Behavior Based on Implicit and Explicit Policy
The semantics in a data-model must respect and describe the implicit
policy of the associated routing sub-system. This doesn't imply that
the data-model components should instantiate it or allow reading or
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writing.
Policy Routing systems must deal with the verification, reading and
installing of routes from sources such as EGP, IGP, and static
routes. Policy routing may also control forwarding and the
monitoring of data forwarding; and data resources. The explicit
policy examples are given for the routing framework. It is assumed
the reader can extend this framework to the data forwarding and data
resource arena.
4.2.1. Example of Implicit Policy
The ISIS protocol specification uses implicit policy to set
constraints on level 1 peers. Due to this fact, many ISIS
implementations only let one level 1 ISIS peer associate with one
Level 2 peer domain.
This policy is not encoded in any local configuration directly, but
is rather included as an implicit policy. When local configuration
policy is checked (prior to a configuration commit), this local
policy is checked. If the configuration input from a CLI is in
error, the input will be rejected, and the CLI will warn the user.
Similarily programmic interfaces for the local configuration cause
the implicit policy to be checked.
IRS data models guide the commissioner in an interoperable
interaction with the reading and installation of data at a particular
agent. The IRS data models must contain both the implicit policy and
the explicit policy. Although an agent may not report the IRS
implicit policy in the protocol, the commissioner must know of the
existence of the implicit policy.
This knowledge allows the commissioner to know the implicit policy
interactions on different systems in a heterogeneous network. For
example, assume a situation where a commissioner is talking to two
agents - one on system A and one on system B. The routing process on
system A has has different implicit rules for the ISIS Level 1 peer
to Level 2 peer connection than the routing process on system B.
Routing process A is built to allow one level 1 ISIS peer associated
with 2 ISIS Level 2 peers. Routing process B upholds the standard
implicit policy that 1 level ISIS peer can only be associated with 1
ISIS Level 2 peer. The commissioner setting up the ISIS peering in a
network containing system A and system B must know that System A will
allow a level 1 peer to connect to 2 ISIS Level 2 peers. When the
commissioner's scope allows it to read data from system A and system
B, it should not flag the difference in ISIS level 1 peer connections
as a problem. Instead the commissioner will need to determine if the
use of the different configurations can cause a network problem.
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4.2.2. Passing Explicit Policy
Routing systems' explicit policy controls protocols, associates/
deassociates interfaces, route verification policy, route forwarding
policy, route aggregation policy, and route deaggregation policy.
All of this policy can be found in the detailed configuration
specification of a routing process. However, even via CLI, it is
rarely possible to configure all the possible options. Other
configuration mechanisms do not have public models for all the
private router configuration. The developers of a routing system
often have a complete policy model either in formal modeling
languages or informal language.
Explicit policy contained in an IRS data model is the detailed
configuration model at the deepest level that an gent can access.
This detailed configuration model may come from IETF Standards and/or
the vendor specific configurations. The public data models must
specify a vendor specific tree where the individual configuration is
plugged into.
4.2.2.1. Explicit policy on Data Forwarding, Resources, and Policy
passing
Forwarding policy has to do with the data flow may also be controlled
by an agent. If so, the explicit policy must be placed in a data
model along with the implicit policy.
Lastly, protocols have begun to pass explicit policy about passing
policy. Examples of this type of policy are BGP ORFs, BGP Flowspecs,
and ISIS policy passing. Commissioners must know the implicit policy
and explicit policy this policy impacts, and the precedence between
these policy. Due to the extensive use of BGP ORFs and the growing
use in BGP Flowspecs policy, early data models for BGP should
describe the implicit policy, explicit policy, policy precedence for
the BGP ORFS and BGP FlowSpecs, and how they interacts with other
BGP, route policy and preferences. This information should be placed
inside an IRS Data Model for an Agent supporting these features.
These explicit models for BGP policy are not trivial, but these
models exist today. Frequently, IRS data models may be simply a
casting of existing implicit policy and explicit policy into a common
standard form so that programmic interfaces may interact with a
routing element.
4.2.2.2. Example of Explicit Policy
There are two clear explicit policy pieces for ISIS. First is the
peer level. Second is the policy of the external routes to be
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redistributed into and out of ISIS.
5. Acknowledgements
The authors would like to thank Ross Callon, Adrian Farrel, David
Meyer, David Ward, Rex Fernando, Russ White, Bruno Risjman, and
Thomas Nadeau for their suggestions and review.
6. IANA Considerations
This document includes no request to IANA.
7. Security Considerations
This is empty boilerplate for now.
8. Informative References
[I-D.atlas-irs-problem-statement]
Atlas, A., Nadeau, T., and D. Ward, "Interface to the
Routing System Problem Statement",
draft-atlas-irs-problem-statement-00 (work in progress),
July 2012.
[I-D.ward-irs-framework]
Atlas, A., Nadeau, T., and D. Ward, "Interface to the
Routing System Framework", draft-ward-irs-framework-00
(work in progress), July 2012.
Authors' Addresses
Alia Atlas
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Email: akatlas@juniper.net
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Susan Hares
Huawei Technologies
Email: shares@ndzh.com
Joel Halpern
Ericsson
Email: Joel.Halpern@ericsson.com
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