Internet Engineering Task Force S. Amante
Internet-Draft Level 3 Communications, Inc.
Intended status: Informational J. Medved
Expires: April 5, 2013 Cisco Systems, Inc.
T. Nadeau
Juniper Networks
October 2, 2012
Topology API Use Cases
draft-amante-irs-topology-use-cases-00
Abstract
This document describes use cases for gathering routing, forwarding
and policy information, (hereafter referred to as topology
information), about the network and reflecting changes to the
topology back into the network and related systems. It describes
several applications that need to view or change the topology of the
underlying physical or logical network. This document further
demonstrates a need for a "Topology Manager" and related functions
that collects topology data from network elements and other data
sources, coalesces the collected data into a coherent view of the
overall network topology, and normalizes the network topology view
for use by clients -- namely, applications that consume or want to
change topology information.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Statistics Collection . . . . . . . . . . . . . . . . . . 5
1.2. Inventory Collection . . . . . . . . . . . . . . . . . . . 5
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Orchestration, Collection & Presentation Framework . . . . . . 7
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Topology Manager . . . . . . . . . . . . . . . . . . . . . 8
3.3. Policy Manager . . . . . . . . . . . . . . . . . . . . . . 10
3.4. Orchestration Manager . . . . . . . . . . . . . . . . . . 11
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Virtualized Views of the Network . . . . . . . . . . . . . 12
4.1.1. Capacity Planning and Traffic Engineering . . . . . . 12
4.1.2. Services Provisioning . . . . . . . . . . . . . . . . 15
4.1.3. Rapid IP Renumbering, AS Migration . . . . . . . . . . 15
4.1.4. Troubleshooting & Monitoring . . . . . . . . . . . . . 17
4.2. Path Computation Element (PCE) . . . . . . . . . . . . . . 17
4.3. ALTO Server . . . . . . . . . . . . . . . . . . . . . . . 18
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
In today's networks, a variety of applications, such as Traffic
Engineering, Capacity Planning, Security Auditing or Services
Provisioning (for example, Virtual Private Networks), have a common
need to acquire and consume network topology information.
Unfortunately, all of these applications are (typically) vertically
integrated: each uses its own proprietary normalized view of the
network and proprietary data collectors, interpreters and adapters,
which speak a variety of protocols, (SNMP, CLI, SQL, etc.) directly
to network elements and to back-office systems. While some of the
topological information can be distributed using routing protocols,
unfortunately it is not desirable for some of these applications to
understand or participate in routing protocols.
This approach is incredibly inefficient for several reasons. First,
developers must write duplicate 'network discovery' functions, which
then become challenging to maintain over time, particularly as/when
new equipment are first introduced to the network. Second, since
there is no common "vocabulary" to describe various components in the
network, such as physical links, logical links, or IP prefixes, each
application has its own data model. To solve this, some solutions
have distributed this information in the normalized form of routing
distribution. However, this information still does not contain
"inactive" topological information, thus not containing information
considered to be part of a network's inventory.
These limitations lead to applications being unable to easily
exchange information with each other. For example, applications
cannot share changes with each other that are (to be) applied to the
physical and/or logical network, such as installation of new physical
links, or deployment of security ACL's. Each application must
frequently poll network elements and other data sources to ensure
that it has a consistent representation of the network so that it can
carry out its particular domain-specific tasks. In other cases,
applications that cannot speak routing protocols must use proprietary
CLI or other management interfaces which represent the topological
information in non-standard formats or worse, semantic models.
Overall, the software architecture described above at best results in
incredibly inefficient use of both software developer resources and
network resources, and at worst, it results in some applications
simply not having access to this information.
Figure 1 is an illustration of how individual applications collect
data from the underlying network. Applications retrieve inventory,
network topology, state and statistics information by communicating
directly with underlying Network Elements as well as with
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intermediary proxies of the information. In addition, applications
transmit changes required of a Network Element's configuration and/or
state directly to individual Network Elements, (most commonly using
CLI or Netconf). It is important to note that the "data models" or
semantics of this information contained within Network Elements are
largely proprietary with respect to most configuration and state
information, hence why a proprietary CLI is often the only choice to
reflect changes in a NE's configuration or state. This remains the
case even when standards-based mechanisms such as Netconf are used
which provide a standard syntax model, but still often lack due to
the proprietary semantics associated with the internal representation
of the information.
+---------------+
+----------------+ |
| Applications |-+
+----------------+
^ ^ ^
SQL, RPC, ReST # | * SQL, RPC, ReST ...
######################## | ************************
# | *
+------------+ | +------------+
| Statistics | | | Inventory |
| Collection | | | Collection |
+------------+ | +------------+
^ | NETCONF, SNMP, ^
| | CLI, TL1, ... |
+-------------------------+-------------------------+
| | |
V V V
+----------------+ +----------------+ +----------------+
| Network Element| | Network Element| | Network Element|
| +------------+ |<-LLDP->| +------------+ |<-LMP->| +------------+ |
| | Data Model | | | | Data Model | | | | Data Model | |
| +------------+ | | +------------+ | | +------------+ |
+----------------+ +----------------+ +----------------+
Figure 1: Applications getting topology data
Figure 1 shows how current management interfaces such as NETCONF,
SNMP, CLI, etc. are used to transmit or receive information to/from
various Network Elements. The figure also shows that protocols such
as LLDP and LMP participate in topology discovery, specifically to
discover adjacent network elements.
The following sections describe the "Statistics Collection" and
"Inventory Collection" functions.
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1.1. Statistics Collection
In Figure 1, "Statistics Collection" is a dedicated infrastructure
that collects statistics from Network Elements. It periodically
polls Network Elements (for example, every 5-minutes) for octets
transferred per interface, per LSP, etc. Collected statistics are
stored and collated, (for example, to provide hourly, daily, weekly
95th-percentile figures), within the statistics data warehouse.
Applications typically query the statistics data warehouse rather
than poll Network Elements directly to get the appropriate set of
link utilization figures for their analysis.
1.2. Inventory Collection
"Inventory Collection" is a network function responsible for
collecting network element component and state (i.e.: interface up/
down, SFP/XFP optics inserted into physical port, etc.) information
directly from network elements, as well as storing inventory
information about physical network assets that are not retrievable
from network elements, (hereafter referred to as a inventory asset
database). Inventory Collection from network elements commonly use
SNMP and CLI to acquire inventory information. The information
housed in the Inventory Manager is retrieved by applications using a
variety of protocols: SQL, RPC, etc. Inventory information,
retrieved from Network Elements, is updated in the Inventory
Collection system on a periodic basis to reflect changes in the
physical and/or logical network assets. The polling interval to
retrieve updated information is varied depending on scaling
constraints of the Inventory Collection systems and expected
intervals at which changes to the physical and/or logical assets are
expected to occur.
Examples of changes in network inventory that need be learned by the
Inventory Collection function are as follows:
o Discovery of new Network Elements. These elements may or may not
be actively used in the network (i.e.: provisioned but not yet
activated).
o Insertion or removal of line cards or other modules, i.e.: optics
modules, during service or equipment provisioning.
o Changes made to a specific Network Element through a management
interface by a field technician.
o Indication of an NE's physical location and associated cable run
list, at the time of installation.
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o Insertion of removal of cables that result in dynamic discovery of
a new or lost adjacent neighbor, etc.
1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]
2. Terminology
The following briefly defines some of the terminology used within
this document.
Inventory Manager: Describes a function of collecting network
element inventory and state information directly from network
elements, and potentially associated offline inventory databases,
via standards-based data models. Components contained in this
super set might be visible or invisible to a specific network
layer, i.e.: a physical link is visible within the IGP, however
the Layer-2 switch through which the physical link traverses is
unknown to the Layer-3 IGP. .
Policy Manager: Describes a function of attaching metadata to
network components/attributes. Such metadata is likely to include
security, routing, L2 VLAN ID, IP numbering, etc. policies that
enable the Topology Manager to: a) assemble a normalized view of
the network for clients to access; b) allow clients (or, upper-
layer applications) read-only vs. read-write access to various
network layers and/or network components, etc. The Policy Manager
function may be a sub-component of the Topology Manager or it may
be a standalone. This will be determined as the work with IRS
evolves.
Topology Manager: Network components (inventory, etc.) are retrieved
from the Inventory Manager and synthesized with information from
the Policy Manager into cohesive, normalized views of network
layers. The Topology Manager exposes normalized views of the
network via standards-based data models to Clients, or higher-
layer applications, to act upon in a read-only and/or read-write
fashion. The Topology Manager may also push information back into
the Inventory Manager and/or Network Elements to execute changes
to the network's behavior, configuration or state.
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Orchestration Manager: Describes a function of stitching together
resources (i.e.: compute, storage) and/or services with the
network or vice-versa. The Orchestration Manager relies on the
capabilities provided by the other "Managers" listed above in
order to realize a complete service.
Normalized Topology Data Model: A data model that is constructed and
represented using an open, standards-based model that is
consistent between implementations.
Data Model Abstraction: The notion that one is able to represent the
same set of elements in a data model at different levels of
"focus" in order to limit the amount of information exchanged in
order to convey this information.
Multi-Layer Topology: Topology is commonly referred to using the OSI
protocol layering model. For example, Layer 3 represents routed
topologies that typically use IPv4 or IPv6 addresses. It is
envisioned that, eventually, multiple layers of the network may be
represented in a single, normalized view of the network to certain
applications, (i.e.: Capacity Planning, Traffic Engineering, etc.)
Network Element (NE): refers to a network device that typically is
addressable (but not always), and hosts. It is sometimes referred
to as Nodes.
Links: Every NE contains at least 1 link. These are used to connect
the NE to other NEs in the network. Links may be in a variety of
states including up, down, administratively down, internally
testing, or dormant. Links are often synonymous with network
ports on NEs.
3. Orchestration, Collection & Presentation Framework
3.1. Overview
Section 1 demonstrates the need for a network function that would
provide a common, standard-based topology view to applications. Such
topology collection/management/presentation function would be a part
wider framework, that would also include policy management and
orchestration. The framework is shown in Figure 2.
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+---------------+
+----------------+ |
| Applications |-+
+----------------+
Websockets, ReST, XMPP, ... ^ Websockets, ReST, XMPP, ...
+-------------------------+-------------------------+
| | |
+------------+ +-------------------------+ +-------------+
| Policy |<----| Topology Manager |---->|Orchestration|
| Manager | | +---------------------+ | | Manager |
+------------+ | | Topology Data Model | | +-------------+
| +---------------------+ |
+-------------------------+
^ ^ ^
Websockets, ReST, XMPP # | * Websockets, ReST, XMPP
######################## | ************************
# | *
+------------+ | +------------+
| Statistics | | | Inventory |
| Collection | | | Collection |
+------------+ | +------------+
^ | IRS, NETCONF, SNMP, ^
| | TL1 ... |
+-------------------------+-------------------------+
| | |
V V V
+----------------+ +----------------+ +----------------+
| Network Element| | Network Element| | Network Element|
| +------------+ |<-LLDP->| +------------+ |<-LMP->| +------------+ |
| | Data Model | | | | Data Model | | | | Data Model | |
| +------------+ | | +------------+ | | +------------+ |
+----------------+ +----------------+ +----------------+
Figure 2: Topology Manager
The following sections describe in detail the Topology Manager,
Policy Manager and Orchestration Manager functions.
3.2. Topology Manager
The Topology Manager is responsible for retrieving topological
information from the network via a variety of sources. The first
most obvious source is the "live" IGP or an equivalent mechanism.
"Live" IGP provides information about links that are components of
the active topology, in other words links that are present in the
Link State Database (LSDB) and are eligible for forwarding. The
second source of topology information is the Inventory Collection
system, which provides information for network components not visible
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within the IGP's LSDB, (i.e.: links or nodes, or properties of those
links or nodes, at lower layers of the network).
The Topology Manager would synthesize retrieved information into
cohesive, abstracted views of the network using a standards-based,
normalized topology data model. The Topology Manager can then expose
these data models to Clients, or higher-layer applications using a
northbound interface, which would be a protocol/API commonly used by
higher-layer applications to retrieve and update information.
Examples of such protocols are ReST, Websockets, or XMPP. Topology
Manager's clients would be able to act upon the information in a
read-only and/or read-write fashion, (based on policies defined
within the Policy Manager).
Clients may request changes to the network topology by publishing
changes within data models and sending those to the Topology Manager.
The Topology Manager internally validates the requested changes
against various constraints and, if the changes are permitted, the
Topology Manager updates associated Managers (Policy or Inventory
Managers), communicates those changes to the individual network
elements and, finally, verifies that those configurations were
properly received and executed by the network elements.
It is envisioned that the Topology Manager will ultimately contain
topology information for multiple layers of the network: Transport,
Ethernet and IP/MPLS as well as multiple (IGP) areas and/or multiple
Autonomous Systems (ASes). This allows the Topology Manager to
stitch together a holistic view of several layers of the network,
which is an important requirement, particularly for upper-layer
Traffic Engineering, Capacity Planning and Provisioning Clients
(applications) used to design, augment and optimize IP/MPLS networks
that require knowledge of underlying Shared Risk Link Groups (SRLG)
within the Transport and/or Ethernet layers of the network.
The Topology Manager must have the ability to discover and
communicate with network elements who are not only active and visible
within the Link State Database (LSDB) of an active IGP, but also
network elements who are active, but invisible to a LSDB (e.g.: L2
Ethernet switches, ROADM's, etc.) that are part of the underlying
Transport network. This requirement will influence the choice of
protocols needed by the Topology Manager to communicate to/from
network elements at the various network layers.
It is also important to recognize that the Topology Manager will be
gleaning not only (relatively) static inventory information from the
Inventory Manager, i.e.: what linecards, interface types, etc. are
actively inserted into network elements, but also dynamic inventory
information, as well. With respect to the latter, network elements
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are expected to rely on various Link Layer Discovery Protocols (i.e.:
LLDP, LMP, etc.) that will aid in automatically identifying an
adjacent node, port, etc. at the far-side of a link. This
information is then pushed to or pulled by the Topology Manager in
order for it to have an accurate representation of the physical
topology of the network.
3.3. Policy Manager
The Policy Manager is the function used to enforce and program
policies applicable to network component/attribute data. Policy
enforcement is a network-wide function that can be consumed by
various network elements and services including the Inventory
Manager, Topology Manager or other network elements. Such policies
are likely to encompass the following.
o Logical Identifier Numbering Policies
* Correlation of IP prefix to link based on type of link (P-P,
P-PE, PE-CE, etc.)
* Correlation of IP Prefix to IGP Area
* Layer-2 VLAN ID assignments, etc.
o Routing Configuration Policies
* OSPF Area or IS-IS Net-ID to Node (Type) Correlation
* BGP routing policies, i.e.: nodes designated for injection of
aggregate routes, max-prefix policies, AFI/SAFI to node
correlation, etc.
o Security Policies
* Access Control Lists
* Rate-limiting
o Network Component/Attribute Data Access Policies. Client's
(upper-layer application) read-only or read-write access to
Network Components/Attributes contained in the "Inventory Manager"
as well as Policies contained within the "Policy Manager" itself.
The Policy Manager function may be a sub-component of the Topology or
Orchestration Manager or it may be a standalone. This will be
determined as the work with IRS evolves.
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3.4. Orchestration Manager
The Orchestration Manager provides the ability to stitch together
resources (i.e.: compute, storage) and/or services with the network
or vice-versa. Examples of 'generic' services may include the
following:
o Application-specific Load Balancing
o Application-specific Network (Bandwidth) Optimization
o Application or End-User specific Class-of-Service
o Application or End-User specific Network Access Control
The above services could then enable coupling of resources with the
network to realize the following:
o Network Optimization: Creation and Migration of Virtual Machines
(VM's) so they are adjacent to storage in the same DataCenter.
o Network Access Control: Coupling of available (generic) compute
nodes within the appropriate point of the data-path to perform
firewall, NAT, etc. functions on data traffic.
The Orchestration Manager is expected to exchange data models with
the Topology Manager, Policy Manager and Inventory Manager functions.
In addition, the Orchestration Manager is expected to support publish
and subscribe capabilities to those functions, as well as to Clients,
to enable scalability with respect to event notifications.
The Orchestration Manager may receive requests from Clients
(applications) for immediate access to specific network resources.
However, Clients may request to schedule future appointments to
reserve appropriate network resources when, for example, a special
event is scheduled to start and end.
Finally, the Orchestration Manager should have the flexibility to
determine what network layer(s) may be able to satisfy a given
Client's request, based on constraints received from the Client as
well as those constraints learned from the Policy and/or Topology
Manager functions. This could allow the Orchestration Manager to,
for example, satisfy a given service request for a given Client using
the optical network (via OTN service) if there is insufficient IP/
MPLS capacity at the specific moment the Client's request is
received.
The operational model is shown in the following figure.
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TBD.
Figure 3: Overall Reference Model
4. Use Cases
4.1. Virtualized Views of the Network
4.1.1. Capacity Planning and Traffic Engineering
When performing Traffic Engineering and/or Capacity Planning of an
IP/MPLS network, it is important to account for SRLG's that exist
within the underlying physical, optical and Ethernet networks.
Currently, it's quite common to create and/or take "snapshots", at
infrequent intervals, that comprise the inventory data of the
underlying physical and optical layer networks. This inventory data
then needs to be massaged or normalized to conform to the data import
requirements of sometimes separate Traffic Engineering and/or
Capacity Planning tools. This process is error-prone and
inefficient, particularly as the underlying network inventory
information changes due to introduction of, for example, new network
element makes or models, linecards, capabilities, etc. at the optical
and/or Ethernet layers of the underlying network.
This is inefficient with respect to the time and expense consumed by
software developer, Capacity Planning and Traffic Engineering
resources to normalize and sanity check underlying network inventory
information, before it can be consumed by IP/MPLS Capacity Planning
and Traffic Engineering applications. Due to this inefficiency, the
underlying physical network inventory information, (containing SRLG
and corresponding critical network asset information), used by the
IP/MPLS Capacity Planning and TE applications is not updated
frequently, thus exposing the network to, at minimum, inefficient
utilization and, at worst, critical impairments.
An Inventory Manager function is required that will, first, extract
inventory information from network elements -- and potentially
associated offline inventory databases to acquire physical cross-
connects and other information that is not available directly from
network elements -- at the physical, optical, Ethernet and IP/MPLS
layers of the network via standards-based data models. Data models
and associated vocabulary will be required to represent not only
components inside or directly connected to network elements, but also
to represent components of a physical layer path (i.e.: cross-connect
panels, etc.) The aforementioned inventory will comprise the
complete set of inactive and active network components.
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A Statistics Collection Function is also required. As stated above,
it will collect utilization statistics from Network Elements, archive
and aggregate them in a statistics data warehouse. Summaries of
these figures then need to be exposed in normalized data models to
the Topology Manager so it can easily acquire historical link and LSP
utilization figures that can be used to, for example, build trended
utilization models to forecast expected changes to the physical
and/or logical network components to accommodate network growth.
The Topology Manager function may then augment the Inventory Manager
information by communicating directly with Network Elements to reveal
the IGP-based view of the active topology of the network. This will
allow the Topology Manager to include dynamic information from the
IGP, such as Available Bandwidth, Reserved Bandwidth, etc. Traffic
Engineering (TE) attributes associated with links, contained with the
Traffic Engineering Database (TED) on Network Elements.
It is important to recognize that extracting topology information
from the network solely via an IGP, (such as IS-IS TE or OSPF TE), is
inadequate for this use case. First, IGP's only expose the active
components (e.g. vertices of the SPF tree) of the IP network;
unfortunately, they are not aware of "hidden" or inactive interfaces
within IP/MPLS network elements, (e.g.: unused linecards or unused
ports), or components that reside at a lower layer than IP/MPLS, e.g.
Ethernet switches, Optical transport systems, etc. This occurs
frequently during the course of maintenance, augment and optimization
activities on the network. Second, IGP's only convey SRLG
information that have been first applied within the router's
configurations, either manually or programatically. As mentioned
previously, this SRLG information in the IP/MPLS network is subject
to being infrequently updated and, as a result, may inadequately
account for critical, underlying network fate sharing properties that
are necessary to properly design resilient circuits and/or paths
through the network.
In this use case, the Inventory Manager will need to be capable of
using a variety of existing protocols such as: NETCONF, CLI, SNMP,
TL1, etc. depending on the capabilities of the network elements. The
Topology Manager will need to be capable of communicating via an IGP
from a (set of) Network Elements. It is important to consider that
to acquire topology information from Network Elements will require
read-only access to the IGP. However, the end result of the
computations performed by the Capacity Planning Client may require
changes to various IGP attributes, (e.g.: IGP metrics, TE link-
colors, etc.) These may be applied directly by devising a new
capability to either: a) inject information into the IGP that
overrides the same information injected by the originating Network
Element; or, b) allowing the Topology and/or Inventory Manager the
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ability to write changes to the Network Element's configuration in
order to have it adjust the appropriate IGP attribute(s) and re-flood
them throughout the IGP. It would be desirable to have a single
mechanism (data model or protocol) that allows the Topology Manager
to read and write IGP attributes.
Once the Topology Manager function has assembled a normalized view of
the topology and synthesized associated metadata with each component
of the topology (link type, link properties, statistics, intra-layer
relationships, etc.), it can then expose this information via its
northbound API to Clients. In this use case that means Capacity
Planning and Traffic Engineering applications, which are not required
to know innate details of individual network elements, but do require
generalized information about the node and links that comprise the
network, e.g.: links used to interconnect nodes, SRLG information
(from the underlying network), utilization rates of each link over
some period of time, etc. In this case, it is important that any
Client that understands both the web services API and the normalized
data model can communicate with the Topology Manager in order to
understand the network topology information that was provided by
network elements from potentially different vendors, all of which
likely represent that topology information internally using different
models. If the Client had gone directly to the network elements
themselves, it would have to translate and then normalize these
different representations for itself. However, in this case, the
Topology Manager has done that for it.
When this information is consumed by the Traffic Engineering
application, it may run a variety of CSPF algorithms the result of
which is likely a list of RSVP LSP's that need to be
(re-)established, or torn down, in the network to globally optimize
the packing efficiency of physical links throughout the network. The
end result of the Traffic Engineering application is "pushing" out to
the Topology Manager, via a standard data model to be defined here, a
list of RSVP LSP's and their associated characteristics, (i.e.: head
and tail-end LSR's, bandwidth, priority, preemption, etc.). The
Topology Manager then would consume this information and carry out
those instructions by speaking directly to network elements, perhaps
via PCEP Extensions for Stateful PCE [I-D.ietf-pce-stateful-pce],
which in turn initiates RSVP signaling through the network to
establish the LSP's.
After this information is consumed by the Capacity Planning
application, it may run a variety of algorithms the result of which
is a list of new inventory that is required to be purchased (or,
redeployed) as well as associated work orders for field technicians
to augment the network for expected growth. It would be ideal if
this information was also "pushed" back into the Topology and, in
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turn, Inventory Manager as "inactive" links and/or nodes, so that as
new equipment is installed it can be automatically correlated with
original design and work order packages associated with that augment.
4.1.2. Services Provisioning
Beyond Capacity Planning and Traffic Engineering applications, having
a normalized view of just the IP/MPLS layer of the network is still
very important for other mission critical applications such as
Security Auditing and IP/MPLS Services Provisioning, (e.g.: L2VPN,
L3VPN, etc.). With respect to the latter, these types of
applications should not need a detailed understanding of, for
example, SRLG information, assuming that the underlying MPLS Tunnel
LSP's are known to account for the resiliency requirements of all
services that ride over them. Nonetheless, for both types of
applications it is critical that they have a common and up-to-date
normalized view of the IP/MPLS network in order to easily instantiate
new services at the appropriate places in the network, in the case of
VPN services, or validate that ACL's are configured properly to
protect associated routing, signaling and management protocols on the
network, with respect to Security Auditing.
For this use case, what is most commonly needed by a VPN Service
Provisioning application is as follows. First, Service PE's need to
be identified in all markets/cities where the customer has identified
they want service. Next, does their exist one, or more, Servies PE's
in each city with connectivity to the access network(s), e.g.: SONET/
TDM, used to deliver the PE-CE tail circuits to the Service's PE.
Finally, does the Services PE have available capacity on both the
PE-CE access interface and its uplinks to terminate the tail circuit?
If this were to be generalized, this would be considered an Resource
Selection function. Namely, the VPN Provisioning application would
iteratively query the Topology Manager to narrow down the scope of
resources to the set of Services PE's with the appropriate uplink
bandwidth and access circuit capability plus capacity to realize the
requested VPN service. Once the VPN Provisioning application has a
candidate list of resources it then requests the Topology Manager to
go about configuring the Services PE's and associated access circuits
to realize the customer's VPN service.
4.1.3. Rapid IP Renumbering, AS Migration
A variety of reasons exist for the "rapid renumbering" of IPv4/IPv6
prefixes and ASN's in an IP/MPLS network. Perhaps the most common
reason is as a result of mergers, acquisitions or divestitures of
companies, organizations or divisions.
Inside the network of an Enterprise or Service Provider, there
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already exist protocols such as DHCP or SLAAC to support rapid
renumbering of hosts, (i.e.: servers, laptops, tablets, etc.). These
are outside the scope of this document. However, there still exists
a critical need to quickly renumber network infrastructure, namely:
router interfaces, management interfaces, etc. in order to: a) avoid
overlapping RFC 1918 addresses in previously separate domains; b)
allow for (better) aggregation of IP prefixes within areas/domains of
an IGP; c) allow for more efficient utilization of globally unique
IPv4 addresses, which are in limited supply; d) realize business
synergies of combining two different AS'es into one, etc.
The set of IPv4 and IPv6 prefixes that have been configured on point-
to-point, LAN, Loopback, Tunnel, Management, PE-CE and other
interfaces would be gathered from all network elements by the
Inventory Manager function. Similarly, the set of ASN's that have
been configured on individual NE's, as the global BGP Autonomous
System Number, and the PE-CE interfaces is also acquired from the
Inventory Manager. Afterward, an "inventory" report of the total
number, based on type, of IPv4/IPv6 prefixes could be quickly
assembled to understand how much address space is required to
accommodate the existing network, but also future growth plans.
Next, a new IP prefix and ASN would be assigned to the overall
network. An operator may then decide to manually carve up the IP
prefix into sub-prefixes that are assigned to various functions or
interface types in the network, i.e.: all Loopback interface
addresses are assigned from a specific GUA IPv4/IPv6 prefix. Other
rules may be crafted by the operator so that, for example, GUA IPv4/
IPv6 prefixes for interfaces within each IGP area are assigned out of
contiguous address space so that they may be (easily) summarized
within the IGP configuration. Finally, the set of ASN's, IP
prefixes, rules and/or policies governing how their are to be
assigned are encoded in a data model/schema an sent to a Topology
Manager (TM). The Topology Manager is then responsible for
communicating changes to the Inventory Manager and/or Network
Elements in a proper sequence, or order of operations, so as to not
lose network connectivity from the Topology Manager to the network
elements.
This function could be extended further whereby the Orchestration
Manager would be used in order to automatically create a list of IP
addresses and their associated DNS names, which would then be
"pushed" to Authoritative DNS servers so that interface names would
get updated in DNS automatically. In addition, the Orchestration
Manager function could notify a "Infrastructure Security" application
that IP prefixes on the network has changed so that it then updates
ACL's used to, for example, protect IP/MPLS routing and signaling
protocols used on the network.
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4.1.4. Troubleshooting & Monitoring
Once the Topology Manager has a normalized view of several layers of
the network, it's then possible to more easily expose a richer set of
data to network operators when performing diagnosis, troubleshooting
and repairs on the network. Specifically, there is a need to
(rapidly) assemble a current, accurate and comprehensive network
diagram of a L2VPN or L3VPN service for a particular customer when
either: a) attempting to diagnose a service fault/error; or, b)
attempting to augment the customer's existing service. Information
that may be assembled into a comprehensive picture could include
physical and logical components related specifically to that
customer's service, i.e.: VLAN's or channels used by the PE-CE access
circuits, CoS policies, historical PE-CE circuit utilization, etc.
The Topology Manager would assemble this information, on behalf of
each of the network elements and other data sources in and associated
with the network, and could present this information in a vendor-
independent data model to applications to be displayed allowing the
operator (or, potentially, the customer through a SP's Web portal) to
visualize the information.
4.2. Path Computation Element (PCE)
As described in [RFC4655] a PCE can be used to compute MPLS-TE paths
within a "domain" (such as an IGP area) or across multiple domains
(such as a multi-area AS, or multiple ASes).
o Within a single area, the PCE offers enhanced computational power
that may not be available on individual routers, sophisticated
policy control and algorithms, and coordination of computation
across the whole area.
o If a router wants to compute a MPLS-TE path across IGP areas its
own TED lacks visibility of the complete topology. That means
that the router cannot determine the end-to-end path, and cannot
even select the right exit router (Area Border Router - ABR) for
an optimal path. This is an issue for large-scale networks that
need to segment their core networks into distinct areas, but which
still want to take advantage of MPLS-TE.
The PCE presents a computation server that may have visibility into
more than one IGP area or AS, or may cooperate with other PCEs to
perform distributed path computation. The PCE needs access to the
topology and the Traffic Engineering Database (TED) for the area(s)
it serves, but [RFC4655] does not describe how this is achieved.
Many implementations make the PCE a passive participant in the IGP so
that it can learn the latest state of the network, but this may be
sub-optimal when the network is subject to a high degree of churn, or
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when the PCE is responsible for multiple areas.
The following figure shows how a PCE can get its TED information
using a Topology Server.
+----------+
| ----- | TED synchronization via Topology API
| | TED |<-+----------------------------------+
| ----- | |
| | | |
| | | |
| v | |
| ----- | |
| | PCE | | |
| ----- | |
+----------+ |
^ |
| Request/ |
| Response |
v |
Service +----------+ Signaling +----------+ +----------+
Request | Head-End | Protocol | Adjacent | | Topology |
-------->| Node |<------------>| Node | | Manager |
+----------+ +----------+ +----------+
Figure 4: Topology use case: Path Computation Element
4.3. ALTO Server
An ALTO Server [RFC5693] is an entity that generates an abstracted
network topology and provides it to network-aware applications over a
web service based API. Example applications are p2p clients or
trackers, or CDNs. The abstracted network topology comes in the form
of two maps: a Network Map that specifies allocation of prefixes to
PIDs, and a Cost Map that specifies the cost between PIDs listed in
the Network Map. For more details, see [I-D.ietf-alto-protocol].
ALTO abstract network topologies can be auto-generated from the
physical topology of the underlying network. The generation would
typically be based on policies and rules set by the operator. Both
prefix and TE data are required: prefix data is required to generate
ALTO Network Maps, TE (topology) data is required to generate ALTO
Cost Maps. Prefix data is carried and originated in BGP, TE data is
originated and carried in an IGP. The mechanism defined in this
document provides a single interface through which an ALTO Server can
retrieve all the necessary prefix and network topology data from the
underlying network. Note an ALTO Server can use other mechanisms to
get network data, for example, peering with multiple IGP and BGP
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Speakers.
The following figure shows how an ALTO Server can get network
topology information from the underlying network using the Topology
API.
+--------+
| Client |<--+
+--------+ |
| ALTO +--------+ +----------+
+--------+ | Protocol | ALTO | Network Topology | Topology |
| Client |<--+------------| Server |<-----------------| Manager |
+--------+ | | | | |
| +--------+ +----------+
+--------+ |
| Client |<--+
+--------+
Figure 5: Topology use case: ALTO Server
5. Acknowledgements
The authors wish to thank Alia Atlas, Dave Ward, Hannes Gredler,
Stafano Previdi for their valuable contributions and feedback to this
draft.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
At the moment, the Use Cases covered in this document apply
specifically to a single Service Provider or Enterprise network.
Therefore, network administrations should take appropriate
precautions to ensure appropriate access controls exist so that only
internal applications and end-users have physical or logical access
to the Topology Manager. This should be similar to precautions that
are already taken by Network Administrators to secure their existing
Network Management, OSS and BSS systems.
As this work evolves, it will be important to determine the
appropriate granularity of access controls in terms of what
individuals or groups may have read and/or write access to various
types of information contained with the Topology Manager. It would
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be ideal, if these access control mechanisms were centralized within
the Topology Manager itself.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. 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.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-13 (work in progress),
September 2012.
[I-D.ietf-pce-stateful-pce]
Crabbe, E., Medved, J., Varga, R., and I. Minei, "PCEP
Extensions for Stateful PCE",
draft-ietf-pce-stateful-pce-01 (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.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
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Authors' Addresses
Shane Amante
Level 3 Communications, Inc.
1025 Eldorado Blvd
Broomfield, CO 80021
USA
Email: shane@level3.net
Jan Medved
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Email: jmedved@cisco.com
Thomas D. Nadeau
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: tnadeau@juniper.net
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