Network Working Group J. Medved
Internet-Draft Cisco
Intended status: Experimental N. Bahadur
Expires: April 24, 2014 Juniper Networks
A. Clemm
Cisco
H. Ananthakrishnan
Juniper Networks
October 21, 2013
An Information Model for Network Topologies
draft-medved-i2rs-topology-im-01.txt
Abstract
This document defines the information model for network topologies.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 4
3. Network Topology Model Overview . . . . . . . . . . . . . . . 4
4. Network Topology Information Model . . . . . . . . . . . . . 5
4.1. Base Model: the Network-Topology Component . . . . . . . 6
4.2. Layer 3 Unicast Topology (IGP) Extensions . . . . . . . . 9
4.2.1. The L3-Unicast-Topology Component . . . . . . . . . . 9
4.2.2. The OSPF-Topology Component . . . . . . . . . . . . . 11
4.2.3. The IS-IS-Topology Component . . . . . . . . . . . . 12
4.2.4. The TED (Traffic Engineering Data) Component . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 15
1. Introduction
This document introduces an information model for network topologies.
The model allows applications to have a holistic view of an entire
network. [I-D.amante-i2rs-topology-use-cases] describes an entity -
the Topology Manager - that would create a cohesive, abstracted model
of the network and expose it to applications via northbound API.
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The information model can be related to a corresponding data model,
for example, a data model defined in YANG [RFC6020], defining the
actual data that is exchanged across specific interfaces. On the
relationship between information and data models, please refer to
[RFC3444].
In order to capture information that is specific to different network
topology types, this document defines an abstract (basic) topology
model that can be extended and adapted. As a result, the information
model is generic in nature and can be applied to many network
topologies. Applications can operate on any topology at a generic
level where specifics of particular topology types are not required,
and at a topology-specific level when those specifics come into play.
Specific topology types that are covered in this document include
Layer 3 Unicast IGP, IS-IS, and OSPF. We also define the information
model for traffic engineering (TE) data. Adaptations and extensions
to other types of topologies (such as Layer 2 topology or OpenFlow
topology) are possible, using similar model patterns to the ones that
are illustrated.
This revision of the document focuses on the "live" topology
information model ([I-D.amante-i2rs-topology-use-cases],
Section 3.2). The "inventory" and "statistics collection"
information models will be addressed separately.
The information model contains several components:
Network-Topology contains a generic network topology model. It
defines a network topology at its most general level of
abstraction. It models aspects such as nodes and edges that
constitute a topology graph, as well as termination points
contained in the nodes that actually terminate edges of the graph.
A network can contain multiple topologies, for example topologies
at different network layers or overlay topologies. The model
therefore allows to show relationships between topologies, as well
as dependencies between nodes and termination points across
topologies.
L3-Unicast-IGP-Topology applies the general network topology model
to Layer 3 Unicast IGP topologies. It extends the general
topology with information specific to Layer 3 Unicast IGP. In
doing so, it also illustrates the extension patterns associated
with extending respectively extending the general topology model
to meet the needs of a specific topology.
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OSPF-Topology Module "ospf-topology" defines a topology model for
OSPF, building on and extending the Layer 3 Unicast IGP topology
model. It serves as an example of how the general topology model
can be refined across multiple levels.
IS-IS-Topology defines a topology model for IS-IS, again building on
and extending the Layer 3 Unicast IGP topology model.
TED defines information kept in the Traffic Engineering Database
(TED) that is leveraged by IS-IS and OSPF topologies.
2. Definitions and Acronyms
Data model: An abstract model of a conceptual domain that is intended
for implementors and contains enough specifics to result in
interoperable implementations and data representations
Datastore: A conceptual store of instantiated management information,
with individual data items represented by data nodes which are
arranged in hierarchical manner.
IGP: Interior Gateway Protocol
Information Model: An abstract model of a conceptual domain,
independent of a specific implementations or data representation
IS-IS: Intermediate System to Intermediate System protocol
LSP: Label Switched Path
OSPF: Open Shortest Path First, a link state routing protocol
RBNF: Routing Backus-Naur Form
URI: Uniform Resource Identifier
SRLG: Shared Risk Link Group
TED: Traffic Engineering Database
3. Network Topology Model Overview
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This section provides an overview of the network topology model. We
start with the structure of the foundational model that represents a
generic topology. Subsequently, an overview of selected specific
topologies is given - Layer 3 Unicast IGP, OSPF, and IS-IS,
respectively. Throughout the document, selected design choices are
explained and the pattern that should be applied to extend the model
to new types of topologies is presented.
The network topology model is defined by the following components,
whose relationship is roughly depicted in the figure below.
+-----------------------+
| Network-Topology |
+-----------+-----------+
^
/|\
| "extends"
+-----------^-------------+
| L3-Unicast-Topology |
+--+-------------------+--+
^ ^
/|\ /|\
| "extends" | "extends"
+--------^-------+ +-------^-------+ +--------+
| OSPF-Topology | | ISIS-Topology | | TED |
+--------^-------+ +-------^-------+ +----v---+
: : :
:...................:.................:
Figure 1: Overall model structure
The Network-Topology component defines the basic network topology
model. The L3-Unicast-Topology module extends this model with
additional definitions needed to represent Layer 3 Unicast IGP
topologies. This component in turn is extended by OSPF-Topology and
ISIS-Topology components providing additional definitions for OSPF
and IS-IS topologies, respectively. The TED component, used by both
OSPF-Topology and ISIS-Topology components, contains a set of
auxiliary definitions related to traffic engineering.
4. Network Topology Information Model
This section specifies the network topology information model in
Routing Backus-Naur Form (RBNF, [RFC5511]). It also provides
diagrams of the main entities that the information model is comprised
of.
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4.1. Base Model: the Network-Topology Component
The following diagram contains an informal graphical depiction of the
main elements of the information model:
+----------------+
| topology |<...
+----------------+ :
* * : :
| | :...:
| |
+--------+ +--------+
...>| node |<.......| link |<...
: +--------+<.......+--------+ :
: : * : : : :
:..... | : : :...:
| : :
+--------+<...........: :
| TP |<.............:
+--------+
Roughly speaking, the basic information model works as follows: A
topology contains nodes and links. Each node in turn contains
termination points. A link connects two nodes (a source and a
destination), terminating on each at a termination point. Nodes can
map onto and be supported by other nodes, while links can map onto
and be supported by other links. Topologies can map onto other,
underlay topologies.
The information model for the Network-Topology component is more
formally shown in the following diagram.
<network-topology> ::= (<topology>...)
<topology> ::= <TOPOLOGY_IDENTIFIER>
(<node>
(<link>...)
[<topology-type>]
[<underlay-topologies>]
[<topology-extension>]
<topology-type> ::= (<IGP> [<igp-topology-type>]) |
(<BGP> [<bgp-topology-type>])
<igp-topology-type> ::= <OSPF> | <ISIS>
<bgp-topology-type> ::= <>
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<underlay-topologies> ::= (<TOPOLOGY_IDENTIFIER>...)
<topology-extension> ::= <igp-topology-extension> |
<bgp-topology-extension> |
...
<node> ::= <NODE_IDENTIFIER>
(<termination-point>...)
[<supporting-nodes>]
[<node-extension>]
<termination-point> ::= <TERMINATION_POINT_IDENTIFIER>
[<supporting-termination-points>]
[<termination-point-extension>]
<supporting-termination-points> ::=
(<TERMINATION_POINT_IDENTIFIER>...)
<termination-point-extension> ::=
<igp-termination-point-extension> |
<bgp-termination-point-extension>
...
<supporting-nodes> ::= (<NODE_IDENTIFIER>...)
<node-extension> ::= <igp-node-extension> |
<bgp-node-extension> |
...
<link> ::= <LINK_IDENTIFIER>
<source>
<destination>
[<supporting-links>]
[<link-extension> ]
<source> ::= <termination-point-reference>
<destination> ::= <termination-point-reference>
<termination-point-reference> ::= <NODE_IDENTIFIER>
<TERMINATION_POINT_IDENTIFIER>
<supporting-links> ::= (<LINK_IDENTIFIER>...)
<link-extension> ::= <igp-link-extension> |
<bgp-link-extension> |
...
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The elements of the Network-Topology information model are as
follows:
o A network can contain multiple topologies. Each topology is
captured in its own list element, distinguished via a topology-id.
o A topology has a certain type, such as OSPF or IS-IS. A topology
can even have multiple types simultaneously. The type, or types,
are captured in the list of "topology-type" components.
o A topology can in turn be part of a hierarchy of topologies,
building on top of other topologies. Any such topologies are
captured in list "underlay-topology".
o Furthermore, a topology contains nodes and links, each captured in
their own list.
o A node has a node-id. This distinguishes the node from other
nodes in the list. In addition, a node has a list of termination
points, used to terminate links. An examples of a termination
point might be a physical or logical port or, more generally, an
interface. Also, a node can in turn map onto other nodes in an
underlay topology. This is captured in list "supporting-node".
o A link is identified by a link-id, uniquely identifying the link
within the topology. Links are point-to-point and unidirectional.
Accordingly, a link contains a source and a destination. Both
source and destination reference a corresponding node, as well as
a termination point on that node. Analogous to a node, a link can
in turn map onto other links an underlay topology. This is
captured in list "supporting-link".
o The topology, node, link and termination-point elements can be
extended with topology-specific components (topology-extensions,
node-extension, link-extension and termination-point-extension
respectively). This document defines extensions for the L3
unicast topology.
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The topology model includes links that are point-to-point and
unidirectional. It does not directly support multipoint and
bidirectional links. While this may appear as a limitation, it does
keep the model simple, generic, and allows it to very easily be
subjected applications that make use of graph algorithms. Bi-
directional connections can be represented through pairs of
unidirectional links. By introducing hierarchies of nodes, with
nodes at one level mapping onto a set of other nodes at another
level, and the introducing new links for nodes at that level,
topologies with connections representing non-point-to-point
communication patterns can be represented.
To minimize assumptions of what a topology might actually represent,
mappings between topologies, nodes, links, and termination points are
kept strictly generic. For example, no assumptions are made whether
a termination point actually refers to an interface, or whether a
node refers to a specific "system" or device; the model at this
generic level makes no provisions for that. Any greater specifics
about mappings between upper and lower layers can be captured in
extending modules.
Links are terminated by a single termination point, not sets of
termination points. Connections involving multihoming or link
aggregation schemes need to be modeled using multiple point-to-point
links, then define a link at a higher layer that is supported by
those individual links.
In a hierarchy of topologies, there are nodes mapping to nodes, links
mapping to links, and termination points mapping to termination
points. Some of this information is redundant. Specifically, with
the link-to-links mapping known, and the termination points of each
link known, maintaining separate termination point mapping
information is not needed but can be derived via transitive closure.
4.2. Layer 3 Unicast Topology (IGP) Extensions
4.2.1. The L3-Unicast-Topology Component
In order to represent a general Layer 3 Unicast IGP topology, the
basic network topology model needs to be extended. The corresponding
extensions are introduced in a component, whose structure is
informally depicted in the following diagram.
+----------------+
| topology |....
+----------------+ :
* * ^ ^ :
| | /|\ :....:
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...... | | +------------------+
: : | | ...... |
: +:-------+ +-------:+ : +-------^--------+
:..>| node |<...| link |<..: | l3 unicast-IGP |
+--------+<...+--------+ | topology |
^ ^ +----------------+
/|\ /|\ ^ ^
| | /|\ /|\
| | | |
+----^---+ +---^----+ +-----^--+ +--^-----+
+------+ | l3 IGP | | l3 IGP | | OSPF | | IS-IS |
|prefix|---*| node | | link | | topo | | topo |
+------| +--------+ +--------+ +--------+ +--------+
^ ^ ^ ^
/|\ /|\ /|\ /|\
+-------+ | | +----------+
| | | |
+----^---+ +-----^--+ +--^-----+ +----^---+
| OSPF | | IS-IS | | OSPF | | IS-IS |
| node | | node | | link | | link |
+--------+ +--------+ +--------+ +--------+
Roughly speaking, layer 3 IGP topology refines the generic topology,
and layer 3 IGP nodes, IGP links, and IGP termination points (not
depicted) refine the generic nodes, links, and termination points.
In addition, layer 3 IGP nodes can contain prefixes. The pattern
recurses with OSPF and IS-IS topologies, which are in turn derived
from the corresponding layer 3 IGP entities.
A more formal depiction in RBNF format follows below:
<igp-topology-extension> ::= <TOPOLOGY_NAME>
[(<FLAGS>...)]
[(<ospf-topology> | <isis-topology>)]
<igp-node-extension> ::= <NODE_NAME>
(<router-id>...)
[(<prefix>...)]
[(<FLAGS>...)]
[(<isis-node> | <ospf-node>)]
<router-id> ::= <IPV4><IPV4_ADDRESS> | <NUMBER>
<ip-address> ::= (<IPV4><IPV4_ADDRESS>) | (<IPV6><IPV6_ADDRESS>)
<prefix> ::= <ip-route>
<METRIC>
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(<FLAGS>...)
[(<ospf-prefix> | <isis-prefix>)]
<ip-route> ::= <ip-address>
<PREFIX_LENGTH>
<igp-link-extension> ::= <LINK_NAME>
<METRIC>
[(<FLAGS>...)]
[ (<isis-link> |<ospf-link>) ]
<igp-termination-point-extension> ::= (<ip-address>...) | <NUMBER>
The model extends the original network-topology model as follows:
o Additional topology attributes are introduced. This allows to
introduce additional flags in extending modules that are
associated with specific IGP topologies, without needing to revise
this component.
o Additional node attributes are introduced. New attributes include
router-id, a set of flags, as well a list of prefixes. Each
prefix in turn includes an ip prefix, a metric and a prefix-
specific set of flags. The prefix is also extensible to any OSPF/
ISIS specific attributes.
o Links are extended as well with a set of parameters, allowing to
associate a link with an IGP name, another set of flags, and a
link metric.
4.2.2. The OSPF-Topology Component
OSPF is the next type of topology represented in the model. OSPF
represents a particular type of Layer 3 Unicast IGP. Accordingly,
the Layer 3 Unicast IGP topology model needs to be extended. The
corresponding extensions are introduced in a separate component
"ospf-topology", whose structure is depicted in the following
diagram. For the most part, this module extends the IGP topology
info model.
<ospf-topology> ::= <AREA_IDENTIFIER>
<ospf-node> ::= <ospf-router-type>
[<DR_INTERFACE_IDENTIFIER>]
[(<MUTLI_TOPOLOGY_IDENTIFIER>...)]
[<ospf-node-capabilities>]
[<ted-node>]
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<ospf-router-type> ::= <ABR> | <ASBR> | <INTERNAL> | <PSEUDONODE>
<ospf-node-capabilities> ::= <>
<ospf-link> ::= [<MULTI_TOPOLOGY_IDENTIFIER>]
[<ted-link>]
<ospf-prefix> ::= [<forwarding-address>]
<forwarding-address> ::= <IPV4><IPV4_ADDRESS>
The module extends the IGP topology component as follows:
o Additional topology attributes are introduced, which extend the
igp-topology-extension of the L3 Unicast topology component. The
attributes include an OSPF area-id identifying the area.
o OSPF node extends IGP node extension with additional OSPF
attributes. New attributes include router-type,
DR_INTERFACE_IDENTIFIER for pseudonodes, list of multi-topology-
ids, OSPF node capabilities and traffic engineering attributes.
o Links are extended with multi-topology-id and traffic engineering
link attributes.
o IGP prefixes are extended with OSPF specific forwarding address.
4.2.3. The IS-IS-Topology Component
IS-IS is another type of Layer 3 Unicast IGP. Like OSPF topology,
IS-IS topology is defined in a separate component, "isis-topology",
which extends IGP topology.
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<isis-topology> ::= <NET_IDENTIFIER>
<isis-node> ::= <isis-router-type> <iso>
(<NET_IDENTIFIER>...)
[(<MULTI_TOPOLOGY_IDENTIFIER>...)]
[<ted-node>]
<iso> ::= <ISO_SYSTEM_ID> <ISO_PSEUDONODE_ID>
<isis-router-type> ::= <LEVEL_2> | <LEVEL_1> | <LEVEL_2_1>
<isis-link> ::= [<MULTI_TOPOLOGY_IDENTIFIER>]
[<ted-link>]
<isis-prefix> ::= <>
The module extends the IGP topology component as follows:
o Additional topology attributes are introduced, which extend the
igp-topology-attributes of the L3 Unicast topology component. The
attributes include an ISIS NET-id identifying the area.
o ISIS node extends IGP node with the following ISIS attributes
router-type, iso-system-id to identify the router, list of multi-
topology-id, list of NET ids and traffic engineering attributes.
o Links are extended with multi-topology-id and traffic engineering
link attributes.
4.2.4. The TED (Traffic Engineering Data) Component
Traffic Engineering Data is required both by OSPF and IS-IS, which
are defined in separate components. Information shared by both is
defined in another component, "TED". This component defines a set of
groupings with auxiliary information required and shared by those
other components.
<ted-node> ::= <te-router-id>
<local-address>
<pcc-capabilities>
<te-router-id> ::= [<IPV4><IPV4_ADDRESS>]
[<IPV6><IPV6_ADDRESS>]
<local-address> ::= [((<IPV4><IPV4_ADDRESS>)...)] |
[((<IPV6><IPV6_ADDRESS><PREFIX_OPTION>)...)]
<pcc-capabilities> ::= <>
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<ted-link> ::= <COLOR>
<MAX_LINK_BANDWIDTH>
<MAX_RESV_LINK_BANDWIDTH>
(<UNRESERVED_BANDWIDTH>...)
<TE_DEFAULT_METRIC>
[<srlg-attributes>]
<srlg-attributes> ::= ( <interface-switching-capabilities>...)
(<SRLG_VALUE>...)
<LINK_PROTECTION_TYPE>
<interface-switching-capabilities> ::= <switching-capabilities>
<ENCODING>
(<MAX_LSP_BANDWIDTH>...)
[<packet-switch-capable>]
[<tdm-capable>]
<packet-switch-capable> ::= <MINIMUM_LSP_BANDWIDTH>
<INTERFACE_MTU>
<time-division-switch-capable> ::= <MINIMUM_LSP_BANDWIDTH>
<INDICATION>
<switching-capabilities> ::= <>
This module details traffic-engineering node and link attributes:
o TED node attributes include te-router-id for IPv4 and IPv6, local
IPv4 and IPv6 addresses and path computation client capabilities.
o TED link attributes comprise COLOR, MAX_LINK_BANDWIDTH,
MAX_RESV_LINK_BANDWIDTH, a list of UNRESERVED_BANDWIDTH and
TE_DEFAULT_METRIC. They also include SRLG attributes which
contains interface switching capabilities, a list of SRLG_VALUE
and LINK_PROTECTION_TYPE. The interface switching capabilities in
turn contains switching capability, ENCODING, MAX_LSP_BANDWIDTH
and interface switching specific attributes.
5. Security Considerations
TBD
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6. Contributors
The model presented in this paper was contributed to by more people
than can be listed on the author list. Additional contributors
include:
o Ken Gray, Juniper Networks
o Tom Nadeau, Juniper Networks
o Aleksandr Zhdankin, Cisco
o Tony Tkacik, Cisco
o Robert Varga, Pantheon Technologies
7. Acknowledgements
We wish to acknowledge the helpful contributions, comments, and
suggestions that were received from many people. We'd also like to
thank the people that contributed to the topology information model
during the I2RS Interim meeting in April 2013 - Shane Amante, Andy
Bierman, Ed Crabbe, Adrian Farrel, and Joel Halpern.
8. References
8.1. Normative References
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
8.2. Informative References
[I-D.amante-i2rs-topology-use-cases]
Medved, J., Previdi, S., Lopez, V., and S. Amante,
"Topology API Use Cases", draft-amante-i2rs-topology-use-
cases-01 (work in progress), October 2013.
[RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
Information Models and Data Models", RFC 3444, January
2003.
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Authors' Addresses
Jan Medved
Cisco
EMail: jmedved@cisco.com
Nitin Bahadur
Juniper Networks
EMail: nitinb@juniper.net>
Alexander Clemm
Cisco
EMail: alex@cisco.com
Hariharan Ananthakrishnan
Juniper Networks
EMail: hanantha@juniper.net
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