| Network Working Group | A. Clemm |
| Internet-Draft | Huawei |
| Intended status: Standards Track | J. Medved |
| Expires: June 16, 2018 | Cisco |
| R. Varga | |
| Pantheon Technologies SRO | |
| N. Bahadur | |
| Bracket Computing | |
| H. Ananthakrishnan | |
| Packet Design | |
| X. Liu | |
| Jabil | |
| December 13, 2017 |
A Data Model for Network Topologies
draft-ietf-i2rs-yang-network-topo-19.txt
This document defines an abstract (generic) YANG data model for network/service topologies and inventories. The data model serves as a base model which is augmented with technology-specific details in other, more specific topology and inventory data models.
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This document introduces an abstract (base) YANG [RFC7950] data model [RFC3444] 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 (i.e. network stacks of networks that are layered on top of each other) and to maintain 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.
While 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 to augment network inventory information 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 [RFC1195] and OSPF [RFC2328], traffic engineering (TE) data [RFC3209], 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 does 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.yang", 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 and topology specific attributes. Network hierarchy (stack) allows any given network to have one or more "supporting networks". The relationship of the base network data model, the inventory data models and the topology data models is shown in the following figure (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 :
'''''''''''' '''''''''''' '''''''''''' ''''''''''''
Figure 1: The network data model structure
The network-topology YANG module introduced in this document, entitled "ietf-network-topology.yang", 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-network.yang 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 to capture relationships between topologies, as well as dependencies between nodes and termination points across topologies. An example of a topology stack is shown in the following figure.
+---------------------------------------+
/ _[X1]_ "Service" /
/ _/ : \_ /
/ _/ : \_ /
/ _/ : \_ /
/ / : \ /
/ [X2]__________________[X3] /
+---------:--------------:------:-------+
: : :
+----:--------------:----:--------------+
/ : : : "L3" /
/ : : : /
/ : : : /
/ [Y1]_____________[Y2] /
/ * * * /
/ * * * /
+--------------*-------------*--*-------+
* * *
+--------*----------*----*--------------+
/ [Z1]_______________[Z1] "Optical" /
/ \_ * _/ /
/ \_ * _/ /
/ \_ * _/ /
/ \ * / /
/ [Z] /
+---------------------------------------+
Figure 2: Topology hierarchy (stack) example
The figure shows three topology levels. At 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. The figure shows two Service Functions (X1 and X3) mapping onto a single L3 network element (Y2); this could happen, for example, if two service functions reside in the same VM (or server) and share the same set of network interfaces. The figure shows a single "L3" network element (Y2) mapped onto multiple "Optical" network elements (Z and Z1). 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 the following figure.
VPN1 VPN2
+---------------------+ +---------------------+
/ [Y5]... / / [Z5]______[Z3] /
/ / \ : / / : \_ / : /
/ / \ : / / : \_ / : /
/ / \ : / / : \ / : /
/ [Y4]____[Y1] : / / : [Z2] : /
+------:-------:---:--+ +---:---------:-----:-+
: : : : : :
: : : : : :
: +-------:---:-----:------------:-----:-----+
: / [X1]__:___:___________[X2] : /
:/ / \_ : : _____/ / : /
: / \_ : _____/ / : /
/: / \: / / : /
/ : / [X5] / : /
/ : / __/ \__ / : /
/ : / ___/ \__ / : /
/ : / ___/ \ / : /
/ [X4]__________________[X3]..: /
+------------------------------------------+
L3 Topology
Figure 3: Topology hierarchy (stack) example
The figure 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 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 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 that the data model can be applied to are described in [I-D.draft-ietf-i2rs-usecase-reqs-summary].
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 but 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 to layer a network that is configured on top of one 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 [I-D.draft-ietf-netmod-revised-datastores], defined as requirement Ephemeral-REQ-03 in [RFC8242]. This allows network topology data that is written, i.e. configured by a client and not system controlled, to refer to a 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 data store, then 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Datastore: 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 adopted from [I-D.draft-ietf-netmod-revised-datastores])
Data subtree: An instantiated data node and the data nodes that are hierarchically contained within it.
IGP: Interior Gateway Protocol
IS-IS: Intermediate System to Intermediate System protocol
OSPF: Open Shortest Path First, a link state routing protocol
URI: Uniform Resource Identifier
The abstract (base) network data model is defined in the ietf-network.yang module. Its structure is shown in the following figure. The notation syntax follows [I-D.draft-ietf-netmod-yang-tree-diagrams].
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
Figure 4: The structure of the abstract (base) network data model
The data model contains a container with a list of networks. Each network is captured in its own list entry, distinguished via a network-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 module 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. insert them below "network-types" by ways of 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 empty type. 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-types" another presence container "l3-unicast-igp-network", which in turn would contain a presence container "ospf-network". Actual examples of this pattern can be found in [I-D.draft-ietf-i2rs-yang-l3-topology].
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 it is contained in. In cases where the same entity takes part in multiple networks, or at multiple layers of a networking stack, the same 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 that it a is part of. To represent that the same entity or same 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, respectively the (entities) nodes in that network, can then be referred to as underlay network and 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 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 allows also 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. In one way, network data is configured by client applications, for example in case of overlay networks that are configured by an SDN Controller application. In another way, it is automatically controlled by the system, in 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 [I-D.draft-ietf-netmod-revised-datastores] is used to account for those possibilities. Specifically, for each network, the origin of its data is indicated per the "origin" metadata annotation - "intended" for data that was configured by a client application, "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-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-network-topology.yang" module. It builds on the network data model defined in the "ietf-network.yang" 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 following figure. The notation syntax follows [I-D.draft-ietf-netmod-yang-tree-diagrams].
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? -> ../../../nw:node[nw:node-id=current()/+
| ../source-node]/termination-point/tp-id
+--rw destination
| +--rw dest-node? -> ../../../nw:node/node-id
| +--rw dest-tp? -> ../../../nw:node[nw:node-id=current()/+
| ../dest-node]/termination-point/tp-id
+--rw supporting-link* [network-ref link-ref]
+--rw network-ref -> ../../../nw:supporting-network/+
| network-ref
+--rw link-ref -> /nw:networks/network+
[nw:network-id=current()/../network-ref]/+
link/link-id
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 -> /nw:networks/network[nw:network-id=+
current()/../network-ref]/node+
[nw:node-id=current()/../node-ref]/+
termination-point/tp-id
Figure 5: The structure of the abstract (base) network topology data model
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 in an underlay topology (which are terminated by the corresponding underlay termination points). 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: for the new network type, a new YANG module is introduced. In this module, a number of augmentations are defined against the network and network-topology YANG modules.
We start with augmentations against the ietf-network.yang module. First, a new network type needs to be defined. For this, a presence container that represents the new network type is defined. It is inserted by means of augmentation below the network-types container. Subsequently, data nodes for any network-type specific node parameters 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 ietf-network-topology.yang. Data nodes are defined both for link parameters, as well as termination point parameters, that are specific to the new network type. Those data nodes are inserted by way of 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 further 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 "sub-type" augmenting the module of a network "super-type".
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 are used to refer to specific nodes, be it in management operations or in specifications of constraints, can remain relatively compact. Of course, this means there is no separate structure in instance information that separates elements of different lists from one another. Such structure is semantically not required, although it might enhance human readability in some cases.
To minimize assumptions of 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 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 that.
Where additional specifics about mappings between upper and lower layers are required, those 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 which introduces a leaf of type ifref that references the corresponding interface [RFC7223]. 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 [RFC7950].
A dangling leafref of a configured object leaves the corresponding instance in a state in which it lacks referential integrity, rendering it in effect inoperational. Any corresponding object instance is therefore removed from the operational state datastore until the situation has been resolved, i.e. until either the supporting object is added to the operational state datastore, or until the instance is reconfigured to refer to another object that is actually reflected in the operational state datastore. It does 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/tps refer to nodes in the underlay are actually in existence, i.e. nodes which are reflected in the operational state datastore. Configuration requests in which supporting nodes/links/tps 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/tp 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 [I-D.draft-ietf-netconf-yang-push].
The data model makes use of groupings, instead of simply defining data nodes "in-line". 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 tradeoff for this 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 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. While this may appear as a limitation, it does keep the data model simple, generic, and allows it to very easily be subjected to applications that make use of graph algorithms. Bi-directional connections can be represented through pairs of unidirectional links. Multipoint networks can be represented through pseudo-nodes (similar to IS-IS, for example). By introducing hierarchies of nodes, with nodes at one level mapping onto a set of other nodes at another level, and 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, 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 link-to-links mapping is known, and the termination points of each link are known, termination point mapping information 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 does provide for 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 which contains a data node for each of its network types. A network can encompass several types of network simultaneously, hence a container is used instead of a case construct, with each network type in turn represented by a dedicated presence container itself. The reason for not simply using an empty leaf, or even simpler, do away even with the network container and just use a leaf-list of network-type instead, is to be able to represent "class hierarchies" of network types, with one network type refining the other. Network-type specific containers are to be defined in the network-specific modules, augmenting the network-types container.
One common requirement concerns the ability to represent 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 it is contained in. 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 the following figure. It depicts three networks with two nodes each. A physical network P 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 underlay. X1 has both Y1 and D1 as underlay nodes, while Y1 has D1 as underlay node. Likewise, X2 has both Y2 and D2 as underlay nodes, while Y2 has D2 as underlay node. The fact that X1 and Y1 are both instantiated on the same physical node D1 can be easily derived.
+---------------------+
/ [X1]____[X2] / X(Service Overlay)
+----:--:----:--------+
..: :..: :
........: ....: : :....
+-----:-------------:--+ : :...
/ [Y1]____[Y2]....: / :.. :
+------|-------|-------+ :.. :...
Y(L3) | +---------------------:-----+ :
| +----:----|-:----------+
+------------------------/---[D1] [D2] /
+----------------------+
P (Physical network)
Figure 6: Topology hierarchy example - multiple underlays
In the case of a physical network, nodes represent physical devices and termination points 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 ("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 is discovered about a network; the topology is considered a property of the network that is reflected in the data model. That said, certain types of topology need to also be configurable by an application, such as in the case of overlay topologies.
The YANG data model for network topology designates all data as "config true". The distinction between data that is actually configured and data that is in effect, including data that is discovered about the network, is provided through the datastores introduced as part of the Network Management Datastore Architecture, NMDA [I-D.draft-ietf-netmod-revised-datastores]. Network topology data that is discovered is automatically populated as part of the operational state datastore, <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, it is also instantiated as part of the operational state datastore, i.e. <operational>.
Configured network topology will in general 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 non-existing 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 [RFC7952] annotation defined in [I-D.draft-ietf-netmod-revised-datastores]. 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. An alternative would define them as strings.
The case for strings is that they will be easier to implement. The reason for choosing URIs is that the topology/node/tp exists in a larger context, hence it is useful to be able to correlate identifiers across systems. While strings, being the universal data type, are easier for human beings, they also muddle things. What typically happens is that strings have some structure which 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, more complex system.
The data model makes use of data types that have been defined in [RFC6991].
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 e.g. data model "ietf-routing" [RFC8022].
The data model obeys the requirements for the ephemeral state found in the document [RFC8242]. 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.
<CODE BEGINS> file "ietf-network@2017-12-13.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";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/i2rs/>
WG List: <mailto:i2rs@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Jan Medved
<mailto:jmedved@cisco.com>
Editor: Robert Varga
<mailto:robert.varga@pantheon.tech>
Editor: Nitin Bahadur
<mailto:nitin_bahadur@yahoo.com>
Editor: Hariharan Ananthakrishnan
<mailto:hari@packetdesign.com>
Editor: Xufeng Liu
<mailto:Xufeng_Liu@jabil.com>";
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) 2017 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of
draft-ietf-i2rs-yang-network-topo-19;
see the RFC itself for full legal notices.
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
revision 2017-12-13 {
description
"Initial revision.
NOTE TO RFC EDITOR:
(1) Please replace the following reference
to draft-ietf-i2rs-yang-network-topo-19 with
RFC number when published (i.e. RFC xxxx).
(2) Please replace the date in the revision statement with the
date of publication when published. ";
reference
"draft-ietf-i2rs-yang-network-topo-19";
}
typedef node-id {
type inet:uri;
description
"Identifier for a node. The precise structure of the node-id
will be up to the implementation. Some implementations MAY
for example, 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 an 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 they are
contained in.";
}
uses network-ref;
}
container networks {
description
"Serves as 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
network-topology data model), as well as 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
"Identifies a node uniquely within the containing
network.";
}
list supporting-node {
key "network-ref node-ref";
description
"Represents another node, in an underlay network, that
this node is supported by. 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 that the
underlay node is part of.";
}
leaf node-ref {
type leafref {
path "/nw:networks/nw:network/nw:node/nw:node-id";
require-instance false;
}
description
"References the underlay node itself.";
}
}
}
}
}
}
<CODE ENDS>
NOTE TO RFC EDITOR: Please change the date in the file name after the CODE BEGINS statement to the date of publication when published.
<CODE BEGINS> file "ietf-network-topology@2017-12-13.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";
}
import ietf-network {
prefix nw;
reference
"draft-ietf-i2rs-yang-network-topo-19
NOTE TO RFC EDITOR:
(1) Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).
(2) Please replace the date in the revision statement with the
date of publication when published.";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/i2rs/>
WG List: <mailto:i2rs@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Jan Medved
<mailto:jmedved@cisco.com>
Editor: Robert Varga
<mailto:robert.varga@pantheon.tech>
Editor: Nitin Bahadur
<mailto:nitin_bahadur@yahoo.com>
Editor: Hariharan Ananthakrishnan
<mailto:hari@packetdesign.com>
Editor: Xufeng Liu
<mailto:Xufeng_Liu@jabil.com>";
description
"This module defines a common base model for 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) 2017 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of
draft-ietf-i2rs-yang-network-topo-19;
see the RFC itself for full legal notices.
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
revision 2017-12-13 {
description
"Initial revision.
NOTE TO RFC EDITOR: Please replace the following reference
to draft-ietf-i2rs-yang-network-topo-19 with
RFC number when published (i.e. RFC xxxx).";
reference
"draft-ietf-i2rs-yang-network-topo-19";
}
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 that the link is a part
of.";
}
typedef tp-id {
type inet:uri;
description
"An identifier for termination points (TPs) 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. While 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 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 references a termination point
in a specific node. While 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 same topology.";
}
leaf source-tp {
type leafref {
path "../../../nw:node[nw:node-id=current()/../"+
"source-node]/termination-point/tp-id";
require-instance false;
}
description
"Termination point within source node that 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
"Termination point within destination node that
terminates the link.";
}
}
list supporting-link {
key "network-ref link-ref";
description
"Identifies the link, or links, that this link
is dependent on.";
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 which 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
"Augment termination points which 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 that
the termination point is dependent on, or maps onto.
Those termination points will themselves be contained
in a supporting node.
This dependency information can be inferred from
the dependencies between links. For this reason,
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, must be in a
different topology";
}
}
}
}
}
<CODE ENDS>
NOTE TO RFC EDITOR: Please change the date in the file name after the CODE BEGINS statement to the date of publication when published.
This document registers the following namespace URIs in the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-network
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
URI:urn:ietf:params:xml:ns:yang:ietf-network-topology
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-network-state
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
URI:urn:ietf:params:xml:ns:yang:ietf-network-topology-state
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document registers the following YANG modules in the "YANG Module Names" registry [RFC6020]:
NOTE TO THE RFC EDITOR: In the list below, please replace references to "draft-ietf-i2rs-yang-network-topo-19 (RFC form)" with RFC number when published (i.e. RFC xxxx).
Name: ietf-network
Namespace: urn:ietf:params:xml:ns:yang:ietf-network
Prefix: nw
Reference: draft-ietf-i2rs-yang-network-topo-19.txt (RFC form)
Name: ietf-network-topology
Namespace: urn:ietf:params:xml:ns:yang:ietf-network-topology
Prefix: nt
Reference: draft-ietf-i2rs-yang-network-topo-19.txt (RFC form)
Name: ietf-network-state
Namespace: urn:ietf:params:xml:ns:yang:ietf-network-state
Prefix: nw-s
Reference: draft-ietf-i2rs-yang-network-topo-19.txt (RFC form)
Name: ietf-network-topology-state
Namespace: urn:ietf:params:xml:ns:yang:ietf-network-topology-state
Prefix: nt-s
Reference: draft-ietf-i2rs-yang-network-topo-19.txt (RFC form)
The YANG modules defined in this document are designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC5246].
The NETCONF access control model [RFC6536] 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 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, a termination point, by creating or deleting corresponding elements in the node, link, and 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 might be disrupted. For example, the topology could be "cut" or be configured in a suboptimal way, leading to increased consumption of resources in the underlay network due to resulting routing and bandwidth utilization inefficiencies. Likewise, it could lead to degradation of service levels as well as possibly disruption of service. For those reasons, it is important that the NETCONF access control model is vigorously applied to prevent topology misconfiguration by unauthorized clients.
Specifically, there are a number of data nodes defined in these YANG module 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:
These are the subtrees and data nodes and their sensitivity/vulnerability in the ietf-network-topology module:
The data model presented in this paper was contributed to by more people than can be listed on the author list. Additional contributors include:
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, and Xian Zhang.
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 expected to return the same result.
In a slightly more complex form, the network element may be a controller, either by nature of it having satellite or subtended devices hanging off of it, or in the more classical sense, such as 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 controllers to establish a topology incorporating of all 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 Transport Controller presents its topology in abstract TE Terms to a Client Packet Controller. This Customized Topology (that 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 exactly cater to its requirements, it may decide to request modifications to the topology. Such customization requests may include addition or deletion of topological elements or 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:
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) defined in [I-D.draft-ietf-netmod-revised-datastores]. In order to allow implementations to use the data model even in cases when NMDA is not supported, in the following two companion modules are defined that represent the operational state of networks and network topologies. The modules, ietf-network-state and ietf-network-topology-state, mirror modules ietf-network and ietf-network-topology defined earlier in this document. However, all data nodes are non-configurable. They represent state that comes into being by either learning topology information from the network, or by applying configuration from the mirrored modules.
The companion modules, ietf-network-state and ietf-network-topology-state, are redundant and SHOULD NOT be supported by implementations that support NMDA. It is for this reason that the definitions are defined in an appendix.
As the structure of both modules mirrors that of their underlying modules, the YANG tree is not depicted separately.
<CODE BEGINS> file "ietf-network-state@2017-12-13.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
"draft-ietf-i2rs-yang-network-topo-19
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/i2rs/>
WG List: <mailto:i2rs@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Jan Medved
<mailto:jmedved@cisco.com>
Editor: Robert Varga
<mailto:robert.varga@pantheon.tech>
Editor: Nitin Bahadur
<mailto:nitin_bahadur@yahoo.com>
Editor: Hariharan Ananthakrishnan
<mailto:hari@packetdesign.com>
Editor: Xufeng Liu
<mailto:Xufeng_Liu@jabil.com>";
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 is either learned and automatically populated,
or information that results from applying configured netwok
information 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) 2017 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of
draft-ietf-i2rs-yang-network-topo-19;
see the RFC itself for full legal notices.
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
revision 2017-12-13 {
description
"Initial revision.
NOTE TO RFC EDITOR:
(1) Please replace the following reference
to draft-ietf-i2rs-yang-network-topo-19 with
RFC number when published (i.e. RFC xxxx).
(2) Please replace the date in the revision statement with the
date of the publication when published.";
reference
"draft-ietf-i2rs-yang-network-topo-19";
}
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 they are
contained in.";
}
uses network-ref;
}
container networks {
config false;
description
"Serves as 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
network-topology data model), as well as 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
"Identifies a node uniquely within the containing
network.";
}
list supporting-node {
key "network-ref node-ref";
description
"Represents another node, in an underlay network, that
this node is supported by. 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 that the
underlay node is part of.";
}
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.";
}
}
}
}
}
}
<CODE ENDS>
NOTE TO RFC EDITOR: Please change the date in the file name after the CODE BEGINS statement to the date of the publication when published.
<CODE BEGINS> file "ietf-network-topology-state@2017-12-13.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
"draft-ietf-i2rs-yang-network-topo-19
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
}
import ietf-network-topology {
prefix nt;
reference
"draft-ietf-i2rs-yang-network-topo-19
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/i2rs/>
WG List: <mailto:i2rs@ietf.org>
Editor: Alexander Clemm
<mailto:ludwig@clemm.org>
Editor: Jan Medved
<mailto:jmedved@cisco.com>
Editor: Robert Varga
<mailto:robert.varga@pantheon.tech>
Editor: Nitin Bahadur
<mailto:nitin_bahadur@yahoo.com>
Editor: Hariharan Ananthakrishnan
<mailto:hari@packetdesign.com>
Editor: Xufeng Liu
<mailto:Xufeng_Liu@jabil.com>";
description
"This module defines a common base data model for network
topology state, representing topology that is either learned,
or topology that 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) 2017 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
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of
draft-ietf-i2rs-yang-network-topo-19;
see the RFC itself for full legal notices.
NOTE TO RFC EDITOR: Please replace above reference to
draft-ietf-i2rs-yang-network-topo-19 with RFC
number when published (i.e. RFC xxxx).";
revision 2017-12-13 {
description
"Initial revision.
NOTE TO RFC EDITOR:
(1) Please replace the following reference
to draft-ietf-i2rs-yang-network-topo-19 with
RFC number when published (i.e. RFC xxxx).
(2) Please replace the date in the revision statement with the
date of publication when published.";
reference
"draft-ietf-i2rs-yang-network-topo-19";
}
grouping link-ref {
description
"References a link in a specific network. While 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 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. While
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 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
"Termination point within source node that 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
"Termination point within destination node that
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, that this link
is dependent on.";
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 which 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
"Augment termination points which 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 that
the termination point is dependent on, or maps onto.
Those termination points will themselves be contained
in a supporting node.
This dependency information can be inferred from
the dependencies between links. For this reason,
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, must be in a
different topology";
}
}
}
}
}
<CODE ENDS>
NOTE TO RFC EDITOR: Please change the date in the file name after the CODE BEGINS statement to the date of the publication when published.
This section contains an example of an instance data tree in JSON encoding [RFC7951]. The example instantiates ietf-network-topology (and ietf-network, which ietf-network-topology augments) for the topology that is depicted in the following diagram. 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.
+------------+ +------------+
| D1 | | D2 |
/-\ /-\ /-\ /-\
| | 1-0-1 | |---------------->| | 2-1-1 | |
| | 1-2-1 | |<----------------| | 2-0-1 | |
\-/ 1-3-1 \-/ \-/ 2-3-1 \-/
| /----\ | | /----\ |
+---| |---+ +---| |---+
\----/ \----/
A | A |
| | | |
| | | |
| | +------------+ | |
| | | D3 | | |
| | /-\ /-\ | |
| +----->| | 3-1-1 | |-------+ |
+---------| | 3-2-1 | |<---------+
\-/ \-/
| |
+------------+
Figure 7: A network topology example
The corresponding instance data tree is depicted below:
{
"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",
"destination": {
"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",
"destination": {
"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",
"destination": {
"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",
"destination": {
"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",
"destination": {
"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",
"destination": {
"source-node": "D3",
"source-tp": "3-2-1"
}
"destination": {
"dest-node": "D2",
"dest-tp": "2-3-1"
}
}
]
}
]
}
}
Figure 8: Instance data tree