BGP SPF for Network Resource
Partitions
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
jie.dong@huawei.com
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
lizhenbin@huawei.com
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
rainsword.wang@huawei.com
LSVR Working Group
A VTN is a virtual underlay network which has customized network
topology and a set of dedicated or shared network resources. Network
Resource Partition (NRP) refers to a set of network resources that are
available to carry traffic and meet the SLOs and SLEs. Multiple NRPs can
be created in a network to provide different Virtual Transport Networks
(VTN) to meet the requirements of different services or different
service groups. In the context of network slicing, a VTN can be
instantiated as a Network Resource Partition (NRP).
As the number of NRP increases, there can be scalability concerns
about using Interial Gateway Protocols (IGP) to distribute the NRP
information in the network. In networks where BGP Shortest Path First
(SPF) can used as the underlay routing mechanism to distribute the
link-state information among network nodes, the information of NRPs
needs to be distributed along with the basic network information. This
document specifies the BGP SPF mechanisms with necessary extensions to
distribute the NRP information and perform NRP-specific path
computation.
The concept of Virtual Transport Network (VTN) is introduced in . A VTN is a virtual underlay
network which has customized network topology and a set of dedicated or
shared network resources. In a network, different VTNs may be created to
meet different service requirements, and services can be mapped to the
same or different VTNs.
introduces the
concept Network Resource Partition (NRP) as a set of network resources
that are available to carry traffic and meet the SLOs and SLEs. In the
context of network slicing, an NRP can be used to instantiate a VTN for
one or a group of IETF network slice services.
describes the
use of resource-aware segments to build SR based
NRPs. The SIDs of each NRP and the associated topology and resource
attributes need to be distributed using the control plane. specifies the IGP mechanism and
extensions to build a relatively large number of SR based NRPs. further specifies the
BGP-LS mechanisms and extensions to advertise the NRP information within
each domain and the NRP information on the inter-domain links to the
network controller, so that the controller could use the collected
information to obtain the view of the inter-domain SR NRPs .
As the number of NRP increases, there can be scalability concerns
about using IGP to distribute the NRP information in the network. In
networks where BGP SPF is used to distribute the link-state information
among network nodes, the NRP information needs to be distributed along
with the basic network link state and TE information. Comparing with the
Internal Gateway Protocols (IGPs), BGP SPF may have some advantage in
supporting a relatively large number of NRPs. This document specifies
the BGP SPF mechanisms with necessary extensions to advertise the
information of NRPs. The proposed mechanism is applicable to segment
routing with MPLS data plane (SR-MPLS), segment routing with IPv6 data
plane (SRv6), and native IPv6 data plane.
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
BCP14 when, and only
when, they appear in all capitals, as shown here.
As described in , the NLRI
and TLVs of BGP-LS can be reused by BGP SPF, this section describes
the TLVs which are defined in BGP-LS and can be reused in BGP SPF for
the distribution of NRP related information.
According to , a virtual
transport network (VTN) has a customized network topology and a set of
dedicated or shared network resources. Thus a VTN can be defined as
the combination of a set of network attributes, including the topology
attribute and the network resource attribute. As the instantiation of
VTN, an NRP is associated with a Multi-Topology ID (MT-ID) and/or an
Algorithm ID which are used to define the NRP topology and path
computation constraints. In some cases, each NRP can be associated
with a separate MT-ID or a Flex-Algo ID. When the amount of NRPs in a
network is large, as described in , multiple NRPs may be
associated with the same topology and/or algorithm, so that the amount
of topology-specific path computation can be shared by a group of
NRPs, this could help to reduce the computation overhead in the
control plane.
does not cover the usage of
Multi-Topology or Flex-Algo with BGP SPF. This document proposes to
use Multi-Topology
or Flex-Algo with BGP
SPF for topology and/or algorithm -specific link-state information
distribution and path computation. For this purpose, the
Multi-topology TLV as defined in , the SR Algorithm TLV as defined
, and the Flex-Algo Definition TLV as defined
in are reused for BGP
SPF.
does not explicitly describe
the usage with Segment Routing data plane. To build SR based NRPs, the
SR-MPLS and SRv6 TLVs as defined in and are reused for BGP SPF.
The NRP extensions to BGP-LS as defined in applies to BGP SPF as
well. This section lists the TLVs which are reused by BGP SPF, the
detailed format of the TLVs are described in .
The BGP-LS Attribute TLVs which are defined in and reused with
BGP-LS-SPF SAFI are listed as below:
NRP Definition (NRPD) TLV: This is used to advertise the
association between the NRP and the topology ID and/or algorithm
ID. It can be carried in BGP-LS attribute associated with a Node
NLRI.
NRP IDs TLV: This is used to describe the identifiers of one or
more NRPs which are associated with a specific set of network
resources. It can be carried in BGP-LS attribute which is
associated with a Link NLRI, or it could be carried as a sub-TLV
in the L2 Bundle Member Attribute TLV or the NRP-specific TE
attribute TLV.
Link Attribute Flags TLV: This is used to specify the
characteristics of a link, its functionality is similar to the
IS-IS Link Attribute sub-TLV defined in .
It can be carried in BGP-LS attribute which is associated with a
Link NLRI, or it could be carried as a sub-TLV in the L2 Bundle
Member Attribute TLV.
NRP-specific prefix-SID TLV: This is used to advertise the
prefix-SID and its associated NRP. It can be carried in BGP-LS
attribute which is associated with a Prefix NLRI.
NRP-specific Adj-SID TLV: This is used to advertise the adj-SID
and its associated NRP. It can be carried in BGP-LS attribute of
the associated Link NLRI.
NRP Locator-block sub-TLV: This is used to advertise the SRv6
locator block and its associated NRP. It can be carried in the
SRv6 Locator TLV of the associated Prefix NLRI.
NRP ID Sub-TLV. This is used to advertise the relationship
between SRv6 End.X SIDs and its associated NRP.
Further BGP-LS TLVs may be defined in , their usage with BGP
SPF will be specified in a future version of this document.
In network scenarios where each NRP is associated with a unique
MT-ID, The BGP-LS mechanisms used to distribute the NRP topology and
resource information to the network controller are described in . Such mechanism can be reused
for the distribution of NRP information with BGP SPF.
In network scenarios where each NRP is associated with a unique
Flex-Algo ID, The BGP-LS mechanisms used to distribute the NRP
topology and resource information to the network controller are
described in . Such
mechanism can be reused for the distribution of NRP information with
BGP SPF.
In network scenarios where multiple NRPs are associated with the
same <topology, algorithm> tuple, while each NRP has different
resource attributes, the BGP-LS mechanisms which can be used to
distribute the NRP topology and resource information to the network
controller are described in . Such mechanism can be
reused for the distribution of NRP information with BGP SPF.
The Sequence Number TLV as defined in MUST be carried in the BGP-LS
attribute associated with the BGP-LS-SPF NLRI. If the Sequence-Number
TLV is not received then the corresponding Link NLRI is considered as
malformed and MUST be handled as 'Treat-as-withdraw'. An
implementation MAY log an error for further analysis.
describes the mechanisms of
using the BGP-LS-SPF Node, Link, and Prefix NLRIs for shortest path
computation. With the introduction of NRP, the same mechanism is used
for the shortest path computation of each NRP. The path computation for
a NRP is based on the topology attributes and the constraints specified
with the MT-ID and/or Algorithm ID associated with the NRP. When
multiple NRPs are associated with the same <topology, algorithm>
tuple, the result of the shortest path computation based on that
<topology, algorithm> could be shared by these NRPs.
This document introduces no additional security vulnerabilities to
BGP SPF.
The mechanism proposed in this document is subject to the same
vulnerabilities as any other protocol that relies on BGP SPF.
This document request no IANA actions.
Key words for use in RFCs to Indicate Requirement
Levels
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. This document specifies
an Internet Best Current Practices for the Internet Community, and
requests discussion and suggestions for improvements.
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