BGP SPF for Virtual Transport Network
(VTN)
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 Virtual Transport Network (VTN) is a virtual underlay network which
consists of a customized network topology and a set of network resource
allocated from the physical network. In a network, multiple VTNs can be
created to meet different service requirements, and services may be
mapped to the same or different VTNs.
In networks where BGP Shortest Path First (SPF) is used to distribute
the link-state information among network nodes, the information of VTNs
needs to be distributed along with the basic network information. This
document specifies the BGP SPF mechanisms with necessary extensions to
distribute the VTN information and perform VTN-specific path
computaton.
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.
describes the
use of resource-aware segments to build SR based
VTNs. The SIDs of each VTN and the associated topology and resource
attributes need to be distributed using the control plane. specifies the IGP mechanism and
extensions to build a set of SR based VTNs. further specifies the
BGP-LS mechanisms and extensions to advertise the VTN information in
each domain and the VTN information on the inter-domain links to the
network controller, so that the controller could use the collected
information to build the inter-domain SR VTNs.
In networks where BGP SPF is used to distribute the link-state
information among network nodes, the VTN information needs to be
distributed along with the basic network link state and TE information.
And comparing with the Internal Gateway Protocols (IGPs), BGP SPF may
have some advantage in supporting a relatively large number of VTNs.
This document specifies the BGP SPF mechanisms with necessary extensions
to advertise the information of VTNs. 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 RFC 2119 RFC 8174 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 VTN 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. A VTN is associated with
a Multi-Topology ID (MT-ID) and/or an Algorithm ID which are used to
define the VTN topology and path computation constraints. In some
cases, each VTN may be associated with a separate MT-ID or a Flex-Algo
ID. When the amount of VTNs in a network is large, as described in
, multiple
VTNs 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 VTNs, 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. While the mechanism in this
document is based on 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
describes the usage with Segment Routing data plane. To build SR based
VTN, the SR-MPLS and SRv6 TLVs as defined in and are reused for BGP SPF.
The VTN 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:
Virtual Transport Network Definition (VTND) TLV: This is used
to advertise the association between the VTN and the topology ID
and/or algorithm ID. It can be carried in BGP-LS attribute
associated with a Node NLRI.
VTN ID TLV: This is used to describe the identifiers of one or
more VTNs a link belongs to. 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.
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.
VTN-specific prefix-SID TLV: This is used to advertise the
prefix-SID and its associated VTN. It can be carried in BGP-LS
attribute which is associated with a Prefix NLRI.
VTN-specific Adj-SID TLV: This is used to advertise the adj-SID
and its associated VTN. It can be carried in BGP-LS attribute of
the associated Link NLRI.
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 VTN is associated with a unique
MT-ID, The BGP-LS mechanisms used to distribute the VTN topology and
resource information to the network controller are described in . Such mechanism can be reused
for the distribution of VTN information with BGP SPF.
In network scenarios where each VTN is associated with a unique
Flex-Algo ID, The BGP-LS mechanisms used to distribute the VTN
topology and resource information to the network controller are
described in . Such
mechanism can be reused for the distribution of VTN information with
BGP SPF.
In network scenarios where multiple VTNs are associated with the
same <topology, algorithm> tuple, while each VTN has different
resource attributes, the BGP-LS mechanisms which can be used to
distribute the VTN topology and resource information to the network
controller are described in . Such mechanism can be
reused for the distribution of VTN 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 NLRI for shortest path
computation. With the introduction of VTN, the same mechanism is used
for the shortest path computation of each VTN. The path computation for
a VTN is based on the topology attributes and the constraints specified
with the MT-ID and/or Algorithm ID associated with the VTN. When
multiple VTNs are associated with the same topology, the result of the
shortest path computation based on that topology could be shared by
these VTNs.
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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