YANG Data Model for Segment RoutingOrange Business Servicestephane.litkowski@orange.comHuaweiyingzhen.qu@huawei.comIndividualpushpasis.ietf@gmail.comIndividualjefftant.ietf@gmail.comSPRING Working Group
This document defines a YANG data model (, ) for segment routing () configuration and operation.
This YANG model is intended to be used on network elements to configure or operate segment routing.
This document defines also generic containers that SHOULD be reused by IGP protocol modules to support segment routing.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
in .
This document defines a YANG data model for segment routing configuration and operation.
This document does not define the IGP extensions to support segment routing but defines generic
groupings that SHOULD be reused by IGP extension modules. The reason of this design choice is to not require
implementations to support all IGP extensions. For example, an implementation may support IS-IS extension but not OSPF.
A simplified graphical representation of the data model is
presented in .The meaning of the symbols in these diagrams is as follows:
Brackets "[" and "]" enclose list keys.Curly braces "{" and "}" contain names of optional features that
make the corresponding node conditional.Abbreviations before data node names: "rw" means configuration
(read-write), and "ro" state data (read-only).Symbols after data node names: "?" means an optional node and "*"
denotes a "list" or "leaf-list".Parentheses enclose choice and case nodes, and case nodes are
also marked with a colon (":").Ellipsis ("...") stands for contents of subtrees that are not
shown.As the module definition is just starting, it is expected that there will be changes
as the module matures.
This module augments the "/rt:routing:" with a segment-routing container.
This container defines all the configuration parameters related to segment-routing.
The segment-routing configuration is split in global configuration and interface configuration.
The global configuration includes :
segment-routing transport type : The underlying transport type
for segment routing. The version of the model limits the transport
type to an MPLS dataplane. The transport-type is only defined once
for a particular routing-instance and is agnostic to the
control plane used. Only a single transport-type is supported
in this version of the model. bindings : Defines prefix to SID mappings. The operator can control advertisement of Prefix-SID independently
for IPv4 and IPv6. Two types of mappings are available :
Mapping-server : maps non local prefixes to a segment ID. Configuration of bindings does not
automatically allow advertisement of those
bindings. Advertisement must be controlled by each
routing-protocol instance (see ). Multiple mapping policies
may be defined.Connected prefixes : maps connected prefixes to a segment ID. Advertisement of the mapping
will be done by IGP when enabled for segment routing (see ). The SID value can be expressed as an index (default), or an absolute
value. The "last-hop-behavior" configuration dictates the PHP behavior:
"explicit-null", "php", or "non-php".SRGB (Segment Routing Global Block): Defines a list of label
blocks represented by a pair of lower-bound/upper-bound labels.
The SRGB is also agnostic to the control plane used. So all
routing-protocol instance will have to advertise the same SRGB.SRLB (Segment Routing Local Block): Defines a list of label
blocks represented by a pair of lower-bound/upper-bound labels, reserved for lcoal SIDs.
Support of segment-routing extensions for a particular IGP control plane is done by augmenting routing-protocol configuration with segment-routing extensions.
This augmentation SHOULD be part of separate YANG modules in order to not create any dependency for implementations to support all protocol extensions.
This module defines groupings that SHOULD be used by IGP segment routing modules.
The "controlplane-cfg" grouping defines the generic global configuration for the IGP.The "enabled" leaf enables segment-routing extensions for the
routing-protocol instance.The "bindings" container controls the routing-protocol instance's
advertisement of local bindings and the processing of received
bindings.The interface configuration is part of the "igp-interface-cfg" grouping and includes Adjacency SID properties.
This section is a first proposal on how to use S-bit in Adj-SID to create bundles.
Authors would like to trigger discussion based on this first proposal.
In case of parallel IP links between routers, an additional Adjacency
SID may be advertised representing more than one adjacency (i.e.,
a bundle of adjacencies). The "advertise-adj-group-sid" configuration
controls whether or not an additional adjacency SID is advertised.
The "advertise-adj-group-sid" would be a list of "group-id".
The "group-id" will permit to identify interfaces that must
be bundled together.
In the figure above, R1 and R2 are interconnected by four links. A routing protocol adjacency is established on each link.
Operator would like to create segment-routing Adj-SID that represent some bundles of links. We can imagine two different bundles : L1/L2 and L2/L3.
To achieve this behavior, the service provider will configure a "group-id" X for both interfaces L1 and L2 and a "group-id" Y for both interfaces L3 and L3.
This will result in R1 advertising an additional Adj-SID for each adjacency, for example a Adj-SID with S flag set and value of 400 will be added to L1 and L2.
A Adj-SID with S flag set and value of 500 will be added to L3 and L4. As L1/L2 and L3/L4 does not share the same "group-id", a different SID value will be allocated.
The "advertise-protection" defines how protection for an interface
is advertised. It does not control the activation or deactivation of
protection. If the "single" option is used, a single Adj-SID will be
advertised for the interface. If the interface is protected, the
B-Flag for the Adj-SID advertisement will be set. If the "dual"
option is used and if the interface is protected, two Adj-SIDs will
be advertised for the interface adjacencies. One Adj-SID will always
have the B-Flag set and the other will have the B-Flag clear. This
option is intended to be used in the case of traffic engineering
where a path must use either protected segments or non-protected
segments.
The operational states contains information reflecting the usage of
allocated SRGB labels.
It also includes a list of all global SIDs, their associated
bindings, and other information such as the source protocol and
algorithm.
The model defines the following notifications for segment-routing.
segment-routing-global-srgb-collision: Rasied when a control plan
advertised SRGB blocks have conflicts. segment-routing-global-sid-collision: Raised when a control plane
advertised index is already associated with another target (in
this version, the only defined targets are IPv4 and IPv6 prefixes). segment-routing-index-out-of-range: Raised when a control plane
advertised index fall outside the range of SRGBs configured for
the network device.TBD.Authors would like to thank Derek Yeung, Acee Lindem, Greg Hankins, Hannes Gredler, Uma Chunduri, Jeffrey Zhang, Shradda Hedge, Les Ginsberg for their contributions.TBD.Key words for use in RFCs to Indicate Requirement LevelsHarvard University1350 Mass. Ave.CambridgeMA 02138- +1 617 495 3864sob@harvard.edu
General
keyword
In many standards track documents several words are used to signify
the requirements in the specification. These words are often
capitalized. This document defines these words as they should be
interpreted in IETF documents. Authors who follow these guidelines
should incorporate this phrase near the beginning of their document:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.
Note that the force of these words is modified by the requirement
level of the document in which they are used.
YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS-TRACK]The YANG 1.1 Data Modeling Language YANG is a data modeling language used to model configuration data,
state data, Remote Procedure Calls, and notifications for network
management protocols. This document describes the syntax and
semantics of version 1.1 of the YANG language. YANG version 1.1 is a
maintenance release of the YANG language, addressing ambiguities and
defects in the original specification. There are a small number of
backward incompatibilities from YANG version 1. This document also
specifies the YANG mappings to the Network Configuration Protocol
(NETCONF). [STANDARDS-TRACK]Segment Routing Architecture Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through an ordered list of instructions, called
segments. A segment can represent any instruction, topological or
service-based. A segment can have a local semantic to an SR node or
global within an SR domain. SR allows to enforce a flow through any
topological path and service chain while maintaining per-flow state
only at the ingress node to the SR domain.
Segment Routing can be directly applied to the MPLS architecture with
no change on the forwarding plane. A segment is encoded as an MPLS
label. An ordered list of segments is encoded as a stack of labels.
The segment to process is on the top of the stack. Upon completion
of a segment, the related label is popped from the stack.
Segment Routing can be applied to the IPv6 architecture, with a new
type of routing header. A segment is encoded as an IPv6 address. An
ordered list of segments is encoded as an ordered list of IPv6
addresses in the routing header. The active segment is indicated by
the Destination Address of the packet. The next active segment is
indicated by a pointer in the new routing header.Signaling MSD (Maximum SID Depth) using IS-ISThis document proposes a way to expose Maximum SID Depth (MSD)
supported by a node at node and/or link level by an ISIS Router. In
a Segment Routing (SR) enabled network a centralized controller that
programs SR tunnels at the head-end node needs to know the MSD
information at node level and/or link level to push the label stack
of an appropriate depth. Signaling MSD (Maximum SID Depth) using OSPFThis document proposes a way to expose Maximum SID Depth (MSD)
supported by a node at node and/or link level by an OSPF Router. In
a Segment Routing (SR) enabled network a centralized controller that
programs SR tunnels at the head-end node needs to know the MSD
information at node level and/or link level to push the label stack
of an appropriate depth . Here the term OSPF means both OSPFv2 and
OSPFv3.