A YANG Data Model
for Network TopologiesHuawei USA - Futurewei Technologies Inc.Santa ClaraCAUnited States of Americaludwig@clemm.org, alexander.clemm@huawei.comCiscojmedved@cisco.comPantheon Technologies SROrobert.varga@pantheon.techBracket Computingnitin_bahadur@yahoo.comPacket Designhari@packetdesign.comJabilxufeng.liu.ietf@gmail.comtopologyThis document defines an abstract (generic, or base) YANG data model
for network/service topologies and inventories. The data model serves as
a base model that is augmented with technology-specific details in
other, more specific topology and inventory data models.This document introduces an abstract (base) YANG data model to represent
networks and topologies. The data model is divided into two parts:
The first part of the data model defines a network data model that
enables the definition of network hierarchies, or network stacks (i.e.,
networks that are layered on top of each other) and maintenance of an
inventory of nodes contained in a network. The second part of the data
model augments the basic network data model with information to describe
topology information. Specifically, it adds the concepts of "links" and
"termination points" to describe how nodes in a network are
connected to each other. Moreover, the data model introduces vertical
layering relationships between networks that can be augmented to cover
both network inventories and network/service topologies.Although it would be possible to combine both parts into a single
data model, the separation facilitates integration of network topology
and network inventory data models, because it allows network
inventory information to be augmented separately, and without concern
for topology, into the network data model.The data model can be augmented to describe the specifics of
particular types of networks and topologies. For example, an augmenting
data model can provide network node information with attributes that are
specific to a particular network type. Examples of augmenting models
include data models for Layer 2 network topologies; Layer 3 network
topologies such as unicast IGP, IS-IS ,
and OSPF ; traffic engineering (TE) data ; or any of the variety of transport and service
topologies. Information specific to particular network types will be
captured in separate, technology-specific data models.The basic data models introduced in this document are generic in
nature and can be applied to many network and service topologies and
inventories. The data models allow applications to operate on an
inventory or topology of any network at a generic level, where the
specifics of particular inventory/topology types are not required. At
the same time, where data specific to a network type comes into
play and the data model is augmented, the instantiated data still
adheres to the same structure and is represented in a consistent
fashion. This also facilitates the representation of network hierarchies
and dependencies between different network components and network
types.The abstract (base) network YANG module introduced in this document,
entitled "ietf-network" (), contains a
list of abstract network nodes and defines the concept of
"network hierarchy" (network stack). The abstract network node can be
augmented in inventory and topology data models with
inventory-specific and topology-specific attributes. The network
hierarchy (stack) allows any given network to have one or more
"supporting networks". The relationship between the base network data
model, the inventory data models, and the topology data models is shown
in (dotted lines in the figure
denote possible augmentations to models defined in this document).
+------------------------+
| |
| Abstract Network Model |
| |
+------------------------+
|
+-------+-------+
| |
V V
+------------+ ..............
| Abstract | : Inventory :
| Topology | : Model(s) :
| Model | : :
+------------+ ''''''''''''''
|
+-------------+-------------+-------------+
| | | |
V V V V
............ ............ ............ ............
: L1 : : L2 : : L3 : : Service :
: Topology : : Topology : : Topology : : Topology :
: Model : : Model : : Model : : Model :
'''''''''''' '''''''''''' '''''''''''' ''''''''''''
The network-topology YANG module introduced in this document,
entitled "ietf-network-topology"
(), defines a generic topology
data model at its most general level of abstraction. The module defines a
topology graph and components from which it is composed: nodes, edges,
and termination points. Nodes (from the "ietf&nbhy;network" module)
represent graph vertices and links represent graph edges. Nodes also
contain termination points that anchor the links. A network can contain
multiple topologies -- for example, topologies at different layers and
overlay topologies. The data model therefore allows relationships between
topologies, as well as dependencies between nodes and termination points
across topologies, to be captured. An example of a topology stack is
shown in .
+---------------------------------------+
/ _[X1]_ "Service" /
/ _/ : \_ /
/ _/ : \_ /
/ _/ : \_ /
/ / : \ /
/ [X2]__________________[X3] /
+---------:--------------:------:-------+
: : :
+----:--------------:----:--------------+
/ : : : "L3" /
/ : : : /
/ : : : /
/ [Y1]_____________[Y2] /
/ * * * /
/ * * * /
+--------------*-------------*--*-------+
* * *
+--------*----------*----*--------------+
/ [Z1]_______________[Z2] "Optical" /
/ \_ * _/ /
/ \_ * _/ /
/ \_ * _/ /
/ \ * / /
/ [Z] /
+---------------------------------------+
shows three topology levels.
At the top, the "Service" topology shows relationships between service
entities, such as service functions in a service chain. The "L3"
topology shows network elements at Layer 3 (IP), and the "Optical"
topology shows network elements at Layer 1. Service functions in the
"Service" topology are mapped onto network elements in the "L3"
topology, which in turn are mapped onto network elements in the
"Optical" topology. Two service functions (X1 and X3) are mapped onto a
single L3 network element (Y2); this could happen, for example, if
two service functions reside in the same Virtual Machine (VM)
(or server) and share the same set of network interfaces. A single
"L3" network element (Y2) is mapped onto two "Optical" network elements
(Z2 and Z). This could happen, for example, if a single IP router
attaches to multiple Reconfigurable Optical Add/Drop Multiplexers
(ROADMs) in the optical domain.Another example of a service topology stack is shown in
.
VPN1 VPN2
+---------------------+ +---------------------+
/ [Y5]... / / [Z5]______[Z3] /
/ / \ : / / : \_ / : /
/ / \ : / / : \_ / : /
/ / \ : / / : \ / : /
/ [Y4]____[Y1] : / / : [Z2] : /
+------:-------:---:--+ +---:---------:-----:-+
: : : : : :
: : : : : :
: +-------:---:-----:------------:-----:-----+
: / [X1]__:___:___________[X2] : /
:/ / \_ : : _____/ / : /
: / \_ : _____/ / : /
/: / \: / / : /
/ : / [X5] / : /
/ : / __/ \__ / : /
/ : / ___/ \__ / : /
/ : / ___/ \ / : /
/ [X4]__________________[X3]..: /
+------------------------------------------+
L3 Topology
shows two VPN service
topologies (VPN1 and VPN2) instantiated over a common L3 topology. Each
VPN service topology is mapped onto a subset of nodes from the common L3
topology.There are multiple applications for such a data model. For example,
within the context of Interface to the Routing System (I2RS), nodes
within the network can use the data model to capture their understanding
of the overall network topology and expose it to a network controller. A
network controller can then use the instantiated topology data to
compare and reconcile its own view of the network topology with that of
the network elements that it controls. Alternatively, nodes within the
network could propagate this understanding to compare and reconcile this
understanding either among themselves or with the help of a controller.
Beyond the network element and the immediate context of I2RS itself, a
network controller might even use the data model to represent its view
of the topology that it controls and expose it to applications north of
itself. Further use cases where the data model can be applied are
described in .
In this data model, a network is categorized as either system controlled
or not. If a network is system controlled, then it is automatically
populated by the server and represents dynamically learned information
that can be read from the operational state datastore. The data model
can also be used to create or modify network topologies that might be
associated with an inventory model or with an overlay network. Such a
network is not system controlled; rather, it is configured by a client.
The data model allows a network to refer to a supporting network,
supporting nodes, supporting links, etc. The data model also allows the
layering of a network that is configured on top of a network that is
system controlled. This permits the configuration of overlay networks on
top of networks that are discovered. Specifically, this data model is
structured to support being implemented as part of the ephemeral
datastore , the requirements for which are
defined in Section 3 of . This allows
network topology data that is written, i.e., configured by a client and
not system controlled, to refer to dynamically learned data that is
controlled by the system, not configured by a client. A simple use case
might involve creating an overlay network that is supported by the
dynamically discovered IP-routed network topology. When an
implementation places written data for this data model in the ephemeral
datastore, such a network MAY refer to another network that is system
controlled.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
"NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document
are to be interpreted as described in BCP 14
when,
and only when, they appear in all capitals, as shown here.A conceptual place to store and access
information. A datastore might be implemented, for example, using
files, a database, flash memory locations, or combinations thereof.
A datastore maps to an instantiated YANG data tree (definition
from ).An instantiated data node and the data nodes
that are hierarchically contained within it.Interior Gateway Protocol.Intermediate System to Intermediate System.Open Shortest Path First (a link-state routing
protocol).Software-Defined Networking.Uniform Resource Identifier.Virtual Machine.The abstract (base) network data model is defined in the
"ietf&nbhy;network" module. Its structure is shown in
. The notation syntax
follows the syntax used in .
module: ietf-network
+--rw networks
+--rw network* [network-id]
+--rw network-id network-id
+--rw network-types
+--rw supporting-network* [network-ref]
| +--rw network-ref -> /networks/network/network-id
+--rw node* [node-id]
+--rw node-id node-id
+--rw supporting-node* [network-ref node-ref]
+--rw network-ref
| -> ../../../supporting-network/network-ref
+--rw node-ref -> /networks/network/node/node-id
The data model contains a container with a list of networks.
Each network is captured in its own list entry, distinguished
via a network&nbhy;id.A network has a certain type, such as L2, L3, OSPF, or IS-IS. A
network can even have multiple types simultaneously. The type or
types are captured underneath the container "network-types". In this
model, it serves merely as an augmentation target; network-specific
modules will later introduce new data nodes to represent
new network types below this target, i.e., will insert them below
"network&nbhy;types" via YANG augmentation.When a network is of a certain type, it will contain a
corresponding data node. Network types SHOULD always be represented
using presence containers, not leafs of type "empty". This allows
the representation of hierarchies of network subtypes within the
instance information. For example, an instance of an OSPF network
(which, at the same time, is a Layer 3 unicast IGP network) would
contain underneath "network&nbhy;types" another presence container
"l3&nbhy;unicast&nbhy;igp&nbhy;network", which in turn would contain
a presence container "ospf&nbhy;network". Actual examples of this
pattern can be found in .
A network can in turn be part of a hierarchy of networks, building
on top of other networks. Any such networks are captured in the list
"supporting-network". A supporting network is, in effect, an underlay
network.Furthermore, a network contains an inventory of nodes that are part
of the network. The nodes of a network are captured in their own list.
Each node is identified relative to its containing network by a
node-id.It should be noted that a node does not exist independently of a
network; instead, it is a part of the network that contains it.
In cases where the same device or entity takes part in multiple
networks, or at multiple layers of a networking stack, the same device
or entity will be represented by multiple nodes, one for each network.
In other words, the node represents an abstraction of the device for
the particular network of which it is a part. To indicate that the
same entity or device is part of multiple topologies or networks, it is
possible to create one "physical" network with a list of nodes for each
of the devices or entities. This (physical) network -- the nodes
(entities) in that network -- can then be referred to as an underlay
network and as nodes from the other (logical) networks and nodes,
respectively. Note that the data model allows for the definition of
more than one underlay network (and node), allowing for simultaneous
representation of layered network topologies and service topologies,
and their physical instantiation.Similar to a network, a node can be supported by other nodes and
map onto one or more other nodes in an underlay network. This is
captured in the list "supporting-node". The resulting hierarchy of
nodes also allows for the representation of device stacks, where a
node at one level is supported by a set of nodes at an underlying
level. For example:a "router" node might be supported by a node representing
a route processor and separate nodes for various line cards and
service modules,a virtual router might be supported or hosted on a physical
device represented by a separate node,and so on.Network data of a network at a particular layer can come into being
in one of two ways: (1) the network data is configured by client
applications -- for example, in the case of overlay networks that are
configured by an SDN Controller application, or (2) the network
data is automatically controlled by the system, in the case of networks
that can be discovered. It is possible for a configured (overlay)
network to refer to a (discovered) underlay network.The revised datastore architecture
is used to account for those possibilities. Specifically, for each
network, the origin of its data is indicated per the "origin" metadata
annotation (as defined in
) -- "intended" for data that was
configured by a client application and "learned" for data that is
discovered. Network data that is discovered is automatically populated
as part of the operational state datastore. Network data that is
configured is part of the configuration and intended datastores,
respectively. Configured network data that is actually in effect is, in
addition, reflected in the operational state datastore. Data in the
operational state datastore will always have complete referential
integrity. Should a configured data item (such as a node) have a
dangling reference that refers to a non&nbhy;existing data item (such
as a supporting node), the configured data item will automatically be
removed from the operational state datastore and thus only appear in
the intended datastore. It will be up to the client application (such
as an SDN Controller) to resolve the situation and ensure that the
reference to the supporting resources is configured properly.
The abstract (base) network topology data model is defined in the
"ietf&nbhy;network&nbhy;topology" module. It builds on the
network data model defined in the "ietf&nbhy;network" module,
augmenting it with links (defining how nodes are connected) and
termination points (which anchor the links and are contained in
nodes). The structure of the network topology module is shown in
. The notation syntax
follows the syntax used in .
module: ietf-network-topology
augment /nw:networks/nw:network:
+--rw link* [link-id]
+--rw link-id link-id
+--rw source
| +--rw source-node? -> ../../../nw:node/node-id
| +--rw source-tp? leafref
+--rw destination
| +--rw dest-node? -> ../../../nw:node/node-id
| +--rw dest-tp? leafref
+--rw supporting-link* [network-ref link-ref]
+--rw network-ref
| -> ../../../nw:supporting-network/network-ref
+--rw link-ref leafref
augment /nw:networks/nw:network/nw:node:
+--rw termination-point* [tp-id]
+--rw tp-id tp-id
+--rw supporting-termination-point*
[network-ref node-ref tp-ref]
+--rw network-ref
| -> ../../../nw:supporting-node/network-ref
+--rw node-ref
| -> ../../../nw:supporting-node/node-ref
+--rw tp-ref leafref
A node has a list of termination points that are used to terminate
links. An example of a termination point might be a physical or
logical port or, more generally, an interface.Like a node, a termination point can in turn be supported by an
underlying termination point, contained in the supporting node of the
underlay network.A link is identified by a link-id that uniquely identifies the link
within a given 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. Similar to a node, a link can map
onto one or more links (which are terminated by the corresponding
underlay termination points) in an underlay topology. This is captured
in the list "supporting-link".In order to derive a data model for a specific type of network, the
base data model can be extended. This can be done roughly as follows:
a new YANG module for the new network type is introduced. In this
module, a number of augmentations are defined against the
"ietf&nbhy;network" and "ietf&nbhy;network&nbhy;topology" modules.We start with augmentations against the "ietf&nbhy;network"
module. First, a new network type needs to be defined; this is done
by defining a presence container that represents the new network type.
The new network type is inserted, by means of augmentation, below the
network&nbhy;types container. Subsequently, data nodes for any node
parameters that are specific to a network type are defined and
augmented into the node list. The new data nodes can be defined as
conditional ("when") on the presence of the corresponding network type
in the containing network. In cases where there are any requirements or
restrictions in terms of network hierarchies, such as when a network of
a new network type requires a specific type of underlay network,
it is possible to define corresponding constraints as well and augment
the supporting-network list accordingly. However, care should be taken
to avoid excessive definitions of constraints.Subsequently, augmentations are defined against the
"ietf&nbhy;network&nbhy;topology" module. Data nodes are defined
for link parameters, as well as termination point parameters, that are
specific to the new network type. Those data nodes are inserted via
augmentation into the link and termination-point lists, respectively.
Again, data nodes can be defined as conditional on the presence of the
corresponding network type in the containing network, by adding a
corresponding "when" statement.It is possible, but not required, to group data nodes for a given
network type under a dedicated container. Doing so introduces
additional structure but lengthens data node path names.In cases where a hierarchy of network types is defined,
augmentations can in turn be applied against augmenting modules, with
the module of a network whose type is more specific augmenting the
module of a network whose type is more general.Rather than maintaining lists in separate containers, the data model
is kept relatively flat in terms of its containment structure. Lists
of nodes, links, termination points, and supporting nodes;
supporting links; and supporting termination points are not kept in
separate containers. Therefore, path identifiers that are used to refer
to specific nodes -- in management operations or in specifications
of constraints -- can remain relatively compact. Of course, this means
that there is no separate structure in instance information that
separates elements of different lists from one another. Such a
structure is semantically not required, but it might provide
enhanced "human readability" in some cases.To minimize assumptions regarding what a particular entity might
actually represent, mappings between networks, nodes, links, and
termination points are kept strictly generic. For example, no
assumptions are made regarding whether a termination point actually
refers to an interface or whether a node refers to a specific "system"
or device; the data model at this generic level makes no provisions
for these.Where additional specifics about mappings between upper and lower
layers are required, the information can be captured in augmenting
modules. For example, to express that a termination point in a
particular network type maps to an interface, an augmenting module can
introduce an augmentation to the termination point. The
augmentation introduces a leaf of type "interface&nbhy;ref". That
leaf references the corresponding interface . Similarly, if a node maps to a particular device or
network element, an augmenting module can augment the node data with a
leaf that references the network element.It is possible for links at one level of a hierarchy to map to
multiple links at another level of the hierarchy. For example, a VPN
topology might model VPN tunnels as links. Where a VPN tunnel maps
to a path that is composed of a chain of several links, the link
will contain a list of those supporting links. Likewise, it is
possible for a link at one level of a hierarchy to aggregate a
bundle of links at another level of the hierarchy.It is possible for a network to undergo churn even as other networks
are layered on top of it. When a supporting node, link, or
termination point is deleted, the supporting leafrefs in the overlay
will be left dangling. To allow for this possibility, the data model
makes use of the "require-instance" construct of YANG 1.1
.
A dangling leafref of a configured object leaves the corresponding
instance in a state in which it lacks referential integrity,
effectively rendering it nonoperational. Any corresponding object
instance is therefore removed from the operational state datastore
until the situation has been resolved, i.e., until either (1) the
supporting object is added to the operational state datastore or
(2) the instance is reconfigured to refer to another object that
is actually reflected in the operational state datastore. It will
remain part of the intended datastore.
It is the responsibility of the application maintaining the overlay
to deal with the possibility of churn in the underlay network.
When a server receives a request to configure an overlay network,
it SHOULD validate whether supporting nodes / links /
termination points refer to nodes in the underlay that actually exist,
i.e., verify that the nodes are reflected in the operational state
datastore. Configuration requests in which supporting nodes / links /
termination points refer to objects currently not in existence SHOULD
be rejected. It is the responsibility of the application to update
the overlay when a supporting node / link / termination point is
deleted at a later point in time. For this purpose, an application
might subscribe to updates when changes to the underlay occur --
for example, using mechanisms defined in .
The data model makes use of groupings instead of simply defining
data nodes "inline". This makes it easier to include the
corresponding data nodes in notifications, which then do not need to
respecify each data node that is to be included. The trade&nbhy;off
is that it makes the specification of constraints more complex,
because constraints involving data nodes outside the grouping need
to be specified in conjunction with a "uses" statement where the
grouping is applied. This also means that constraints and
XML Path Language (XPath) statements need to be specified in such a way
that they navigate "down" first and select entire sets of nodes, as
opposed to being able to simply specify them against individual data
nodes.The topology data model includes links that are point-to-point
and unidirectional. It does not directly support multipoint and
bidirectional links. Although this may appear as a limitation,
the decision to do so keeps the data model simple and generic, and it
allows it to be very easily subjected to applications that make use of
graph algorithms. Bidirectional connections can be represented through
pairs of unidirectional links. Multipoint networks can be represented
through pseudonodes (similar to IS&nbhy;IS, for example). By introducing
hierarchies of nodes with nodes at one level mapping onto a set of
other nodes at another level and by introducing new links for nodes
at that level, topologies with connections representing
non-point-to-point communication patterns can be represented.Links are terminated by a single termination point, not sets of
termination points. Connections involving multihoming or link
aggregation schemes need to be represented using multiple
point-to-point links and then defining a link at a higher layer
that is supported by those individual links.In a hierarchy of networks, there are nodes mapping to nodes,
links mapping to links, and termination points mapping to
termination points. Some of this information is redundant.
Specifically, if the mapping of a link to one or more other links is
known and the termination points of each link are known, the mapping
information for the termination points can be derived via transitive
closure and does not have to be explicitly configured. Nonetheless, in
order to not constrain applications regarding which mappings they want
to configure and which should be derived, the data model provides the
option to configure this information explicitly. The data model
includes integrity constraints to allow for validating for
consistency.A network's network types are represented using a container that
contains a data node for each of its network types. A network can
encompass several types of networks simultaneously; hence, a container
is used instead of a case construct, with each network type in turn
represented by a dedicated presence container. The reason for not
simply using an empty leaf, or (even more simply) even doing away
with the network container and just using a leaf&nbhy;list of
"network&nbhy;type" instead, is to be able to represent
"class hierarchies" of network types, with one network type
"refining" the other. Containers specific to a network type are to be
defined in the network-specific modules, augmenting the network-types
container.One common requirement concerns the ability to indicate that the
same device can be part of multiple networks and topologies. However,
the data model defines a node as relative to the network that
contains it. The same node cannot be part of multiple topologies.
In many cases, a node will be the abstraction of a particular device in
a network. To reflect that the same device is part of multiple
topologies, the following approach might be chosen: a new type of
network to represent a "physical" (or "device") network is introduced,
with nodes representing devices. This network forms an underlay network
for logical networks above it, with nodes of the logical network
mapping onto nodes in the physical network.This scenario is depicted in .
This figure depicts three networks with two nodes each. A physical
network ("P" in the figure) consists of an inventory of two nodes (D1
and D2), each representing a device. A second network, X, has a third
network, Y, as its underlay. Both X and Y also have the physical
network (P) as their underlay. X1 has both Y1 and D1 as underlay
nodes, while Y1 has D1 as its underlay node. Likewise, X2 has both Y2
and D2 as underlay nodes, while Y2 has D2 as its underlay node. The
fact that X1 and Y1 are both instantiated on the same physical node
(D1) can be easily seen.
+---------------------+
/ [X1]____[X2] / X(Service Overlay)
+----:--:----:--------+
..: :..: :
........: ....: : :....
+-----:-------------:--+ : :...
/ [Y1]____[Y2]....: / :.. :
+------|-------|-------+ :.. :...
Y(L3) | +---------------------:-----+ :
| +----:----|-:----------+
+------------------------/---[D1] [D2] /
+----------------------+
P (Physical Network)
In the case of a physical network, nodes represent physical
devices and termination points represent physical ports. It should be
noted that it is also possible to augment the data model for a physical
network type, defining augmentations that have nodes reference
system information and termination points reference physical
interfaces, in order to provide a bridge between network and device
models.YANG requires data nodes to be designated as either configuration
data ("config true") or operational data ("config false"), but not both,
yet it is important to have all network information, including
vertical cross-network dependencies, captured in one coherent data
model. In most cases, network topology information about a network is
discovered; the topology is considered a property of the network that
is reflected in the data model. That said, certain types of topologies
need to also be configurable by an application, e.g., in the case of
overlay topologies.
The YANG data model for network topologies designates all data as
"config true". The distinction between data that is actually
configured and data that is in effect, including network data
that is discovered, is provided through the datastores
introduced as part of the Network Management Datastore Architecture
(NMDA) . Network topology data that is
discovered is automatically populated as part of the operational state
datastore, i.e., <operational>. It is "system
controlled". Network topology that is configured is instantiated as
part of a configuration datastore, e.g., <intended>. Only when
it has actually taken effect will it also be instantiated as part of
the operational state datastore, i.e., <operational>.
In general, a configured network topology will refer to an underlay
topology and include layering information, such as the supporting
node(s) underlying a node, supporting link(s) underlying a link, and
supporting termination point(s) underlying a termination point.
The supporting objects must be instantiated in the operational state
datastore in order for the dependent overlay object to be reflected in
the operational state datastore. Should a configured data item
(such as a node) have a dangling reference that refers to a
nonexistent data item (such as a supporting node), the configured
data item will automatically be removed from <operational> and
show up only in <intended>. It will be up to the client
application to resolve the situation and ensure that the reference to
the supporting resources is configured properly.
For each network, the origin of its data is indicated per the
"origin" metadata annotation defined in
. In general, the origin of discovered network
data is "learned"; the origin of configured network data is "intended".
The current data model defines identifiers of nodes, networks, links,
and termination points as URIs. Alternatively, they could have been
defined as strings.
The case for strings is that they will be easier to implement.
The reason for choosing URIs is that the topology / node /
termination point exists in a larger context; hence, it is useful to be
able to correlate identifiers across systems. Although strings -- being
the universal data type -- are easier for human beings, they also muddle
things. What typically happens is that strings have some structure that
is magically assigned, and the knowledge of this structure has to be
communicated to each system working with the data. A URI makes the
structure explicit and also attaches additional semantics: the URI,
unlike a free-form string, can be fed into a URI resolver, which can
point to additional resources associated with the URI. This property is
important when the topology data is integrated into a larger and
more complex system.
The data model makes use of data types that have been defined in .
This is a protocol-independent YANG data model with topology information.
It is separate from, and not linked with, data models that are used to
configure routing protocols or routing information. This includes,
for example, the "ietf-routing" YANG module .
The data model obeys the requirements for the ephemeral state
as specified in . For ephemeral topology data that
is system controlled, the process tasked with maintaining topology
information will load information from the routing process (such as OSPF)
into the operational state datastore without relying on a configuration
datastore.
file "ietf-network@2018-02-26.yang"
module ietf-network {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-network";
prefix nw;
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web:
WG List:
Editor: Alexander Clemm
Editor: Jan Medved
Editor: Robert Varga
Editor: Nitin Bahadur
Editor: Hariharan Ananthakrishnan
Editor: Xufeng Liu
";
description
"This module defines a common base data model for a collection
of nodes in a network. Node definitions are further used
in network topologies and inventories.
Copyright (c) 2018 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8345;
see the RFC itself for full legal notices.";
revision 2018-02-26 {
description
"Initial revision.";
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
typedef node-id {
type inet:uri;
description
"Identifier for a node. The precise structure of the node-id
will be up to the implementation. For example, some
implementations MAY pick a URI that includes the network-id
as part of the path. The identifier SHOULD be chosen
such that the same node in a real network topology will
always be identified through the same identifier, even if
the data model is instantiated in separate datastores. An
implementation MAY choose to capture semantics in the
identifier -- for example, to indicate the type of node.";
}
typedef network-id {
type inet:uri;
description
"Identifier for a network. The precise structure of the
network-id will be up to the implementation. The identifier
SHOULD be chosen such that the same network will always be
identified through the same identifier, even if the data model
is instantiated in separate datastores. An implementation MAY
choose to capture semantics in the identifier -- for example,
to indicate the type of network.";
}
grouping network-ref {
description
"Contains the information necessary to reference a network --
for example, an underlay network.";
leaf network-ref {
type leafref {
path "/nw:networks/nw:network/nw:network-id";
require-instance false;
}
description
"Used to reference a network -- for example, an underlay
network.";
}
}
grouping node-ref {
description
"Contains the information necessary to reference a node.";
leaf node-ref {
type leafref {
path "/nw:networks/nw:network[nw:network-id=current()/../"+
"network-ref]/nw:node/nw:node-id";
require-instance false;
}
description
"Used to reference a node.
Nodes are identified relative to the network that
contains them.";
}
uses network-ref;
}
container networks {
description
"Serves as a top-level container for a list of networks.";
list network {
key "network-id";
description
"Describes a network.
A network typically contains an inventory of nodes,
topological information (augmented through the
network-topology data model), and layering information.";
leaf network-id {
type network-id;
description
"Identifies a network.";
}
container network-types {
description
"Serves as an augmentation target.
The network type is indicated through corresponding
presence containers augmented into this container.";
}
list supporting-network {
key "network-ref";
description
"An underlay network, used to represent layered network
topologies.";
leaf network-ref {
type leafref {
path "/nw:networks/nw:network/nw:network-id";
require-instance false;
}
description
"References the underlay network.";
}
}
list node {
key "node-id";
description
"The inventory of nodes of this network.";
leaf node-id {
type node-id;
description
"Uniquely identifies a node within the containing
network.";
}
list supporting-node {
key "network-ref node-ref";
description
"Represents another node that is in an underlay network
and that supports this node. Used to represent layering
structure.";
leaf network-ref {
type leafref {
path "../../../nw:supporting-network/nw:network-ref";
require-instance false;
}
description
"References the underlay network of which the
underlay node is a part.";
}
leaf node-ref {
type leafref {
path "/nw:networks/nw:network/nw:node/nw:node-id";
require-instance false;
}
description
"References the underlay node itself.";
}
}
}
}
}
}
]]> file "ietf-network-topology@2018-02-26.yang"
module ietf-network-topology {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-network-topology";
prefix nt;
import ietf-inet-types {
prefix inet;
reference
"RFC 6991: Common YANG Data Types";
}
import ietf-network {
prefix nw;
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web:
WG List:
Editor: Alexander Clemm
Editor: Jan Medved
Editor: Robert Varga
Editor: Nitin Bahadur
Editor: Hariharan Ananthakrishnan
Editor: Xufeng Liu
";
description
"This module defines a common base model for a network topology,
augmenting the base network data model with links to connect
nodes, as well as termination points to terminate links
on nodes.
Copyright (c) 2018 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8345;
see the RFC itself for full legal notices.";
revision 2018-02-26 {
description
"Initial revision.";
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
typedef link-id {
type inet:uri;
description
"An identifier for a link in a topology. The precise
structure of the link-id will be up to the implementation.
The identifier SHOULD be chosen such that the same link in a
real network topology will always be identified through the
same identifier, even if the data model is instantiated in
separate datastores. An implementation MAY choose to capture
semantics in the identifier -- for example, to indicate the
type of link and/or the type of topology of which the link is
a part.";
}
typedef tp-id {
type inet:uri;
description
"An identifier for termination points on a node. The precise
structure of the tp-id will be up to the implementation.
The identifier SHOULD be chosen such that the same termination
point in a real network topology will always be identified
through the same identifier, even if the data model is
instantiated in separate datastores. An implementation MAY
choose to capture semantics in the identifier -- for example,
to indicate the type of termination point and/or the type of
node that contains the termination point.";
}
grouping link-ref {
description
"This grouping can be used to reference a link in a specific
network. Although it is not used in this module, it is
defined here for the convenience of augmenting modules.";
leaf link-ref {
type leafref {
path "/nw:networks/nw:network[nw:network-id=current()/../"+
"network-ref]/nt:link/nt:link-id";
require-instance false;
}
description
"A type for an absolute reference to a link instance.
(This type should not be used for relative references.
In such a case, a relative path should be used instead.)";
}
uses nw:network-ref;
}
grouping tp-ref {
description
"This grouping can be used to reference a termination point
in a specific node. Although it is not used in this module,
it is defined here for the convenience of augmenting
modules.";
leaf tp-ref {
type leafref {
path "/nw:networks/nw:network[nw:network-id=current()/../"+
"network-ref]/nw:node[nw:node-id=current()/../"+
"node-ref]/nt:termination-point/nt:tp-id";
require-instance false;
}
description
"A type for an absolute reference to a termination point.
(This type should not be used for relative references.
In such a case, a relative path should be used instead.)";
}
uses nw:node-ref;
}
augment "/nw:networks/nw:network" {
description
"Add links to the network data model.";
list link {
key "link-id";
description
"A network link connects a local (source) node and
a remote (destination) node via a set of the respective
node's termination points. It is possible to have several
links between the same source and destination nodes.
Likewise, a link could potentially be re-homed between
termination points. Therefore, in order to ensure that we
would always know to distinguish between links, every link
is identified by a dedicated link identifier. Note that a
link models a point-to-point link, not a multipoint link.";
leaf link-id {
type link-id;
description
"The identifier of a link in the topology.
A link is specific to a topology to which it belongs.";
}
container source {
description
"This container holds the logical source of a particular
link.";
leaf source-node {
type leafref {
path "../../../nw:node/nw:node-id";
require-instance false;
}
description
"Source node identifier. Must be in the same topology.";
}
leaf source-tp {
type leafref {
path "../../../nw:node[nw:node-id=current()/../"+
"source-node]/termination-point/tp-id";
require-instance false;
}
description
"This termination point is located within the source node
and terminates the link.";
}
}
container destination {
description
"This container holds the logical destination of a
particular link.";
leaf dest-node {
type leafref {
path "../../../nw:node/nw:node-id";
require-instance false;
}
description
"Destination node identifier. Must be in the same
network.";
}
leaf dest-tp {
type leafref {
path "../../../nw:node[nw:node-id=current()/../"+
"dest-node]/termination-point/tp-id";
require-instance false;
}
description
"This termination point is located within the
destination node and terminates the link.";
}
}
list supporting-link {
key "network-ref link-ref";
description
"Identifies the link or links on which this link depends.";
leaf network-ref {
type leafref {
path "../../../nw:supporting-network/nw:network-ref";
require-instance false;
}
description
"This leaf identifies in which underlay topology
the supporting link is present.";
}
leaf link-ref {
type leafref {
path "/nw:networks/nw:network[nw:network-id=current()/"+
"../network-ref]/link/link-id";
require-instance false;
}
description
"This leaf identifies a link that is a part
of this link's underlay. Reference loops in which
a link identifies itself as its underlay, either
directly or transitively, are not allowed.";
}
}
}
}
augment "/nw:networks/nw:network/nw:node" {
description
"Augments termination points that terminate links.
Termination points can ultimately be mapped to interfaces.";
list termination-point {
key "tp-id";
description
"A termination point can terminate a link.
Depending on the type of topology, a termination point
could, for example, refer to a port or an interface.";
leaf tp-id {
type tp-id;
description
"Termination point identifier.";
}
list supporting-termination-point {
key "network-ref node-ref tp-ref";
description
"This list identifies any termination points on which a
given termination point depends or onto which it maps.
Those termination points will themselves be contained
in a supporting node. This dependency information can be
inferred from the dependencies between links. Therefore,
this item is not separately configurable. Hence, no
corresponding constraint needs to be articulated.
The corresponding information is simply provided by the
implementing system.";
leaf network-ref {
type leafref {
path "../../../nw:supporting-node/nw:network-ref";
require-instance false;
}
description
"This leaf identifies in which topology the
supporting termination point is present.";
}
leaf node-ref {
type leafref {
path "../../../nw:supporting-node/nw:node-ref";
require-instance false;
}
description
"This leaf identifies in which node the supporting
termination point is present.";
}
leaf tp-ref {
type leafref {
path "/nw:networks/nw:network[nw:network-id=current()/"+
"../network-ref]/nw:node[nw:node-id=current()/../"+
"node-ref]/termination-point/tp-id";
require-instance false;
}
description
"Reference to the underlay node (the underlay node must
be in a different topology).";
}
}
}
}
}
]]>
This document registers the following namespace URIs in the "IETF XML
Registry" :
This document registers the following YANG modules in the "YANG
Module Names" registry :
The YANG modules specified in this document define a schema for data
that is designed to be accessed via network management protocols such
as NETCONF or RESTCONF .
The lowest NETCONF layer is the secure transport layer, and the
mandatory-to-implement secure transport is Secure Shell (SSH)
. The lowest RESTCONF layer is HTTPS, and the
mandatory-to-implement secure transport is TLS .
The NETCONF access control model provides the
means to restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.
The network topology and inventory created by these modules reveal
information about the structure of networks that could be very helpful
to an attacker. As a privacy consideration, although there is no
personally identifiable information defined in these modules, it is
possible that some node identifiers may be associated with devices that
are in turn associated with specific users.
The YANG modules define information that can be configurable in certain
instances -- for example, in the case of overlay topologies that can be
created by client applications. In such cases, a malicious client could
introduce topologies that are undesired. Specifically, a malicious
client could attempt to remove or add a node, a link, or a termination
point by creating or deleting corresponding elements in node, link, or
termination point lists, respectively. In the case of a topology that
is learned, the server will automatically prohibit such misconfiguration
attempts. In the case of a topology that is configured, i.e., whose origin
is "intended", the undesired configuration could become effective and be
reflected in the operational state datastore, leading to disruption of
services provided via this topology. For example, the topology could
be "cut" or could be configured in a suboptimal way, leading to
increased consumption of resources in the underlay network due to the
routing and bandwidth utilization inefficiencies that would result.
Likewise, it could lead to degradation of service levels as well as
possible disruption of service. For those reasons, it is important that
the NETCONF access control model be vigorously applied to prevent topology
misconfiguration by unauthorized clients.
There are a number of data nodes defined in these YANG modules that are
writable/creatable/deletable (i.e., config true, which is the
default). These data nodes may be considered sensitive or vulnerable
in some network environments. Write operations (e.g., edit-config) to
these data nodes without proper protection can have a negative effect
on network operations. These are the subtrees and data nodes and
their sensitivity/vulnerability:In the "ietf-network" module:network: A malicious client could attempt to remove or add a network
in an effort to remove an overlay topology or to create an unauthorized
overlay.supporting network: A malicious client could attempt to disrupt the
logical structure of the model, resulting in a lack of overall data
integrity and making it more difficult to, for example, troubleshoot
problems rooted in the layering of network topologies.node: A malicious client could attempt to remove or add a node from
the network -- for example, in order to sabotage the topology of a
network overlay.supporting node: A malicious client could attempt to change the
supporting node in order to sabotage the layering of an overlay.In the "ietf-network-topology" module:link: A malicious client could attempt to remove a link from a
topology, add a new link, manipulate the way the link is layered
over supporting links, or modify the source or destination of the link.
In each case, the structure of the topology would be sabotaged, and
this scenario could, for example, result in an overlay topology that is
less than optimal.
termination point: A malicious client could attempt to remove
termination points from a node, add "phantom" termination points to a
node, or change the layering dependencies of termination points, again in
an effort to sabotage the integrity of a topology and potentially disrupt
orderly operations of an overlay.Network Configuration Access Control ModelNetwork Management Datastore Architecture (NMDA)A YANG Data Model for Interface ManagementSummary of I2RS Use Case RequirementsYANG Datastore SubscriptionA YANG Data Model for Layer 3 TopologiesYANG Tree Diagrams
In its simplest form, topology is learned by a network element
(e.g., a router) through its participation in peering protocols
(IS-IS, BGP, etc.). This learned topology can then be
exported (e.g., to a Network Management System) for external
utilization. Typically, any network element in a domain can be queried
for its topology and be expected to return the same result.
In a slightly more complex form, the network element may be a
controller. It could be a network element with satellite or
subtended devices hanging off of it, or it could be a controller
in the more classical sense -- that is, a special device designated to
orchestrate the activities of a number of other devices (e.g., an
Optical Controller). In this case, the controller device is logically a
singleton and must be queried distinctly.
It is worth noting that controllers can be built on top of
other controllers to establish a topology incorporating all
of the domains within an entire network.
In all of the cases above, the topology learned by the network
element is considered to be operational state data. That is, the
data is accumulated purely by the network element's interactions with
other systems and is subject to change dynamically without input or
consent.
Consider a scenario where an Optical Controller presents its
topology, in abstract TE terms, to a client packet controller.
This customized topology (which gets merged into the client's native
topology) contains sufficient information for the path-computing
client to select paths across the optical domain according to its
policies. If the client determines (at any given point in time) that
this imported topology does not cater exactly to its requirements,
it may decide to request modifications to the topology. Such
customization requests may include the addition or deletion of
topological elements or the modification of attributes
associated with existing topological elements. From the
perspective of the Optical Controller, these requests translate
into configuration changes to the exported abstract topology.
In certain scenarios, the topology learned by a controller
needs to be augmented with additional attributes before running
a computation algorithm on it. Consider the case where a
path-computation application on the controller needs to take the
geographic coordinates of the nodes into account while computing
paths on the learned topology. If the learned topology does not
contain these coordinates, then these additional attributes must be
configured on the corresponding topological elements.
In this scenario, an SDN Controller (for example, Open Daylight)
maintains a view of the topology of the network that it controls
based on information that it discovers from the network. In
addition, it provides an application in which it configures and
maintains an overlay topology.
The SDN Controller thus maintains two roles:
It is a client to the network.It is a server to its own northbound applications and clients,
e.g., an Operations Support System (OSS).
In other words, one system's client (or controller, in this case)
may be another system's server (or managed system).
In this scenario, the SDN Controller maintains a consolidated data
model of multiple layers of topology. This includes the lower layers
of the network topology, built from information that is discovered
from the network. It also includes upper layers of topology overlay,
configurable by the controller's client, i.e., the OSS. To the OSS,
the lower topology layers constitute "read-only" information. The
upper topology layers need to be read-writable.
The YANG modules defined in this document are designed to be used in
conjunction with implementations that support the Network Management
Datastore Architecture (NMDA) as defined in .
In order to allow implementations to use the data model even in cases
when NMDA is not supported, the following two companion modules --
"ietf&nbhy;network&nbhy;state" and
"ietf&nbhy;network&nbhy;topology&nbhy;state" -- are defined; they
represent the operational state of networks and network topologies,
respectively. These modules mirror the "ietf&nbhy;network" and
"ietf&nbhy;network&nbhy;topology" modules (defined
in Sections and
of this
document); however, in the case of these modules, all data nodes are
non&nbhy;configurable. They represent state that comes into being by
either (1) learning topology information from the network or
(2) applying configuration from the mirrored modules.
The "ietf-network-state" and "ietf-network-topology-state"
companion modules are redundant and SHOULD NOT be supported by
implementations that support NMDA; therefore, we define these modules
in Appendices and
(below)
instead of the main body of this document.
As the structure of both modules mirrors that of their underlying
modules, the YANG tree is not depicted separately. file "ietf-network-state@2018-02-26.yang"
module ietf-network-state {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-network-state";
prefix nw-s;
import ietf-network {
prefix nw;
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web:
WG List:
Editor: Alexander Clemm
Editor: Jan Medved
Editor: Robert Varga
Editor: Nitin Bahadur
Editor: Hariharan Ananthakrishnan
Editor: Xufeng Liu
";
description
"This module defines a common base data model for a collection
of nodes in a network. Node definitions are further used
in network topologies and inventories. It represents
information that either (1) is learned and automatically
populated or (2) results from applying network information
that has been configured per the 'ietf-network' data model,
mirroring the corresponding data nodes in this data model.
The data model mirrors 'ietf-network' but contains only
read-only state data. The data model is not needed when the
underlying implementation infrastructure supports the Network
Management Datastore Architecture (NMDA).
Copyright (c) 2018 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8345;
see the RFC itself for full legal notices.";
revision 2018-02-26 {
description
"Initial revision.";
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
grouping network-ref {
description
"Contains the information necessary to reference a network --
for example, an underlay network.";
leaf network-ref {
type leafref {
path "/nw-s:networks/nw-s:network/nw-s:network-id";
require-instance false;
}
description
"Used to reference a network -- for example, an underlay
network.";
}
}
grouping node-ref {
description
"Contains the information necessary to reference a node.";
leaf node-ref {
type leafref {
path "/nw-s:networks/nw-s:network[nw-s:network-id=current()"+
"/../network-ref]/nw-s:node/nw-s:node-id";
require-instance false;
}
description
"Used to reference a node.
Nodes are identified relative to the network that
contains them.";
}
uses network-ref;
}
container networks {
config false;
description
"Serves as a top-level container for a list of networks.";
list network {
key "network-id";
description
"Describes a network.
A network typically contains an inventory of nodes,
topological information (augmented through the
network-topology data model), and layering information.";
container network-types {
description
"Serves as an augmentation target.
The network type is indicated through corresponding
presence containers augmented into this container.";
}
leaf network-id {
type nw:network-id;
description
"Identifies a network.";
}
list supporting-network {
key "network-ref";
description
"An underlay network, used to represent layered network
topologies.";
leaf network-ref {
type leafref {
path "/nw-s:networks/nw-s:network/nw-s:network-id";
require-instance false;
}
description
"References the underlay network.";
}
}
list node {
key "node-id";
description
"The inventory of nodes of this network.";
leaf node-id {
type nw:node-id;
description
"Uniquely identifies a node within the containing
network.";
}
list supporting-node {
key "network-ref node-ref";
description
"Represents another node that is in an underlay network
and that supports this node. Used to represent layering
structure.";
leaf network-ref {
type leafref {
path "../../../nw-s:supporting-network/nw-s:network-ref";
require-instance false;
}
description
"References the underlay network of which the
underlay node is a part.";
}
leaf node-ref {
type leafref {
path "/nw-s:networks/nw-s:network/nw-s:node/nw-s:node-id";
require-instance false;
}
description
"References the underlay node itself.";
}
}
}
}
}
}
]]> file "ietf-network-topology-state@2018-02-26.yang"
module ietf-network-topology-state {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-network-topology-state";
prefix nt-s;
import ietf-network-state {
prefix nw-s;
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
import ietf-network-topology {
prefix nt;
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web:
WG List:
Editor: Alexander Clemm
Editor: Jan Medved
Editor: Robert Varga
Editor: Nitin Bahadur
Editor: Hariharan Ananthakrishnan
Editor: Xufeng Liu
";
description
"This module defines a common base data model for network
topology state, representing topology that either (1) is learned
or (2) results from applying topology that has been configured
per the 'ietf-network-topology' data model, mirroring the
corresponding data nodes in this data model. It augments the
base network state data model with links to connect nodes, as
well as termination points to terminate links on nodes.
The data model mirrors 'ietf-network-topology' but contains only
read-only state data. The data model is not needed when the
underlying implementation infrastructure supports the Network
Management Datastore Architecture (NMDA).
Copyright (c) 2018 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8345;
see the RFC itself for full legal notices.";
revision 2018-02-26 {
description
"Initial revision.";
reference
"RFC 8345: A YANG Data Model for Network Topologies";
}
grouping link-ref {
description
"References a link in a specific network. Although this
grouping is not used in this module, it is defined here for
the convenience of augmenting modules.";
leaf link-ref {
type leafref {
path "/nw-s:networks/nw-s:network[nw-s:network-id=current()"+
"/../network-ref]/nt-s:link/nt-s:link-id";
require-instance false;
}
description
"A type for an absolute reference to a link instance.
(This type should not be used for relative references.
In such a case, a relative path should be used instead.)";
}
uses nw-s:network-ref;
}
grouping tp-ref {
description
"References a termination point in a specific node. Although
this grouping is not used in this module, it is defined here
for the convenience of augmenting modules.";
leaf tp-ref {
type leafref {
path "/nw-s:networks/nw-s:network[nw-s:network-id=current()"+
"/../network-ref]/nw-s:node[nw-s:node-id=current()/../"+
"node-ref]/nt-s:termination-point/nt-s:tp-id";
require-instance false;
}
description
"A type for an absolute reference to a termination point.
(This type should not be used for relative references.
In such a case, a relative path should be used instead.)";
}
uses nw-s:node-ref;
}
augment "/nw-s:networks/nw-s:network" {
description
"Add links to the network data model.";
list link {
key "link-id";
description
"A network link connects a local (source) node and
a remote (destination) node via a set of the respective
node's termination points. It is possible to have several
links between the same source and destination nodes.
Likewise, a link could potentially be re-homed between
termination points. Therefore, in order to ensure that we
would always know to distinguish between links, every link
is identified by a dedicated link identifier. Note that a
link models a point-to-point link, not a multipoint link.";
container source {
description
"This container holds the logical source of a particular
link.";
leaf source-node {
type leafref {
path "../../../nw-s:node/nw-s:node-id";
require-instance false;
}
description
"Source node identifier. Must be in the same topology.";
}
leaf source-tp {
type leafref {
path "../../../nw-s:node[nw-s:node-id=current()/../"+
"source-node]/termination-point/tp-id";
require-instance false;
}
description
"This termination point is located within the source node
and terminates the link.";
}
}
container destination {
description
"This container holds the logical destination of a
particular link.";
leaf dest-node {
type leafref {
path "../../../nw-s:node/nw-s:node-id";
require-instance false;
}
description
"Destination node identifier. Must be in the same
network.";
}
leaf dest-tp {
type leafref {
path "../../../nw-s:node[nw-s:node-id=current()/../"+
"dest-node]/termination-point/tp-id";
require-instance false;
}
description
"This termination point is located within the
destination node and terminates the link.";
}
}
leaf link-id {
type nt:link-id;
description
"The identifier of a link in the topology.
A link is specific to a topology to which it belongs.";
}
list supporting-link {
key "network-ref link-ref";
description
"Identifies the link or links on which this link depends.";
leaf network-ref {
type leafref {
path "../../../nw-s:supporting-network/nw-s:network-ref";
require-instance false;
}
description
"This leaf identifies in which underlay topology
the supporting link is present.";
}
leaf link-ref {
type leafref {
path "/nw-s:networks/nw-s:network[nw-s:network-id="+
"current()/../network-ref]/link/link-id";
require-instance false;
}
description
"This leaf identifies a link that is a part
of this link's underlay. Reference loops in which
a link identifies itself as its underlay, either
directly or transitively, are not allowed.";
}
}
}
}
augment "/nw-s:networks/nw-s:network/nw-s:node" {
description
"Augments termination points that terminate links.
Termination points can ultimately be mapped to interfaces.";
list termination-point {
key "tp-id";
description
"A termination point can terminate a link.
Depending on the type of topology, a termination point
could, for example, refer to a port or an interface.";
leaf tp-id {
type nt:tp-id;
description
"Termination point identifier.";
}
list supporting-termination-point {
key "network-ref node-ref tp-ref";
description
"This list identifies any termination points on which a
given termination point depends or onto which it maps.
Those termination points will themselves be contained
in a supporting node. This dependency information can be
inferred from the dependencies between links. Therefore,
this item is not separately configurable. Hence, no
corresponding constraint needs to be articulated.
The corresponding information is simply provided by the
implementing system.";
leaf network-ref {
type leafref {
path "../../../nw-s:supporting-node/nw-s:network-ref";
require-instance false;
}
description
"This leaf identifies in which topology the
supporting termination point is present.";
}
leaf node-ref {
type leafref {
path "../../../nw-s:supporting-node/nw-s:node-ref";
require-instance false;
}
description
"This leaf identifies in which node the supporting
termination point is present.";
}
leaf tp-ref {
type leafref {
path "/nw-s:networks/nw-s:network[nw-s:network-id="+
"current()/../network-ref]/nw-s:node[nw-s:node-id="+
"current()/../node-ref]/termination-point/tp-id";
require-instance false;
}
description
"Reference to the underlay node (the underlay node must
be in a different topology).";
}
}
}
}
}
]]> This section contains an example of an instance data tree in JSON
encoding . The example instantiates
"ietf-network-topology" (and "ietf-network", which "ietf-network-topology"
augments) for the topology depicted in .
There are three nodes: D1, D2, and D3. D1 has three termination points
(1-0-1, 1-2-1, and 1-3-1). D2 has three termination points as well
(2-1-1, 2-0-1, and 2-3-1). D3 has two termination points (3-1-1 and 3-2-1).
In addition, there are six links, two between each pair of nodes with one
going in each direction.
| | 2-1-1 | |
| | 1-2-1 | |<----------------| | 2-0-1 | |
\-/ 1-3-1 \-/ \-/ 2-3-1 \-/
| /----\ | | /----\ |
+---| |---+ +---| |---+
\----/ \----/
A | A |
| | | |
| | | |
| | +------------+ | |
| | | D3 | | |
| | /-\ /-\ | |
| +----->| | 3-1-1 | |-------+ |
+---------| | 3-2-1 | |<---------+
\-/ \-/
| |
+------------+ ]]>
The corresponding instance data tree is depicted in
:
{
"ietf-network:networks": {
"network": [
{
"network-types": {
},
"network-id": "otn-hc",
"node": [
{
"node-id": "D1",
"termination-point": [
{
"tp-id": "1-0-1"
},
{
"tp-id": "1-2-1"
},
{
"tp-id": "1-3-1"
}
]
},
{
"node-id": "D2",
"termination-point": [
{
"tp-id": "2-0-1"
},
{
"tp-id": "2-1-1"
},
{
"tp-id": "2-3-1"
}
]
},
{
"node-id": "D3",
"termination-point": [
{
"tp-id": "3-1-1"
},
{
"tp-id": "3-2-1"
}
]
}
],
"ietf-network-topology:link": [
{
"link-id": "D1,1-2-1,D2,2-1-1",
"source": {
"source-node": "D1",
"source-tp": "1-2-1"
}
"destination": {
"dest-node": "D2",
"dest-tp": "2-1-1"
}
},
{
"link-id": "D2,2-1-1,D1,1-2-1",
"source": {
"source-node": "D2",
"source-tp": "2-1-1"
}
"destination": {
"dest-node": "D1",
"dest-tp": "1-2-1"
}
},
{
"link-id": "D1,1-3-1,D3,3-1-1",
"source": {
"source-node": "D1",
"source-tp": "1-3-1"
}
"destination": {
"dest-node": "D3",
"dest-tp": "3-1-1"
}
},
{
"link-id": "D3,3-1-1,D1,1-3-1",
"source": {
"source-node": "D3",
"source-tp": "3-1-1"
}
"destination": {
"dest-node": "D1",
"dest-tp": "1-3-1"
}
},
{
"link-id": "D2,2-3-1,D3,3-2-1",
"source": {
"source-node": "D2",
"source-tp": "2-3-1"
}
"destination": {
"dest-node": "D3",
"dest-tp": "3-2-1"
}
},
{
"link-id": "D3,3-2-1,D2,2-3-1",
"source": {
"source-node": "D3",
"source-tp": "3-2-1"
}
"destination": {
"dest-node": "D2",
"dest-tp": "2-3-1"
}
}
]
}
]
}
}
We wish to acknowledge the helpful contributions, comments, and
suggestions that were received from Alia Atlas,
Andy Bierman, Martin Bjorklund, Igor Bryskin, Benoit Claise,
Susan Hares, Ladislav Lhotka, Carlos Pignataro,
Juergen Schoenwaelder, Robert Wilton, Qin Wu, and Xian Zhang.More people contributed to the data model presented in this paper
than can be listed in the "Authors' Addresses" section.
Additional contributors include:
Vishnu Pavan Beeram, JuniperKen Gray, CiscoTom Nadeau, BrocadeTony TkacikKent Watsen, JuniperAleksandr Zhdankin, Cisco