Segment Routing based Virtual Transport Network (VTN) for Enhanced VPN
draft-ietf-spring-sr-for-enhanced-vpn-04
| Document | Type | Active Internet-Draft (spring WG) | |
|---|---|---|---|
| Authors | Jie Dong , Stewart Bryant , Takuya Miyasaka , Yongqing Zhu , Fengwei Qin , Zhenqiang Li , Francois Clad | ||
| Last updated | 2022-10-11 | ||
| Replaces | draft-dong-spring-sr-for-enhanced-vpn | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | WG state | WG Document | |
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| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-ietf-spring-sr-for-enhanced-vpn-04
SPRING Working Group J. Dong
Internet-Draft Huawei Technologies
Intended status: Informational S. Bryant
Expires: 14 April 2023 University of Surrey
T. Miyasaka
KDDI Corporation
Y. Zhu
China Telecom
F. Qin
Z. Li
China Mobile
F. Clad
Cisco Systems
11 October 2022
Segment Routing based Virtual Transport Network (VTN) for Enhanced VPN
draft-ietf-spring-sr-for-enhanced-vpn-04
Abstract
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 topological or service based
instructions. A segment can further be associated with a set of
network resources used for executing the instruction. Such a segment
is called resource-aware segment.
A Virtual Transport Network (VTN) is a virtual underlay network which
has a network topology and a set of network resources allocated from
the physical underlay network.
Resource-aware Segment Identifiers (SIDs) may be used to build SR
paths with a set of reserved network resources. In addition, a group
of resource-aware SIDs may be used to build SR based virtual underlay
networks, which have customized network topology and resource
attributes required by one or a group of customers and/or services.
Such virtual networks are the SR instantiations of VTNs.
This document describes a suggested way to use resource-aware SIDs to
build SR based VTNs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 14 April 2023.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Resource-Aware SIDs for VTN . . . . . . . . . . . . . . . . . 3
2.1. SR-MPLS based VTN . . . . . . . . . . . . . . . . . . . . 4
2.2. SRv6 based VTN . . . . . . . . . . . . . . . . . . . . . 4
2.3. VTN Identification . . . . . . . . . . . . . . . . . . . 5
2.4. Scalability Considerations . . . . . . . . . . . . . . . 5
3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. VTN Topology and Resource Planning . . . . . . . . . . . 6
3.2. VTN Network Resource and SID Allocation . . . . . . . . . 7
3.3. Construction of SR based VTNs . . . . . . . . . . . . . . 9
3.4. Mapping Services to SR based VTN . . . . . . . . . . . . 12
3.5. VTN Visibility to Customers . . . . . . . . . . . . . . . 12
4. Characteristics of SR based VTNs . . . . . . . . . . . . . . 12
5. Service Assurance of VTNs . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
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10.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Segment Routing (SR) [RFC8402] specifies a mechanism to steer packets
through an ordered list of segments. A segment is referred to by its
Segment Identifier (SID). With SR, explicit source routing can be
achieved without introducing per-path state into the network.
[I-D.ietf-spring-resource-aware-segments] extends SR by associating
SIDs with network resource attributes (e.g., bandwidth, processing or
storage resources). These resource-aware SIDs retain their original
functionality, with the additional semantics of identifying the set
of network resources available for the packet processing action.
Multiple resource-aware SIDs may be allocated on a network segment,
each associated with a set of network resources assigned to meet the
requirements of one or a group of customers and/or services.
A Virtual Transport Network (VTN) is a virtual underlay network which
has a network topology and a set of network resources allocated from
the physical underlay network.
Once allocated, Resource-aware SIDs can be used to build SR paths
with a set of reserved network resources. In addition, a group of
resource-aware SIDs may be used to build SR based virtual networks,
which have customized network topology and resource attributes
required by one or a group of customers and/or services. Such
virtual networks are the SR instantiations of VTNs as defined in
[I-D.ietf-teas-enhanced-vpn], and can be used to enable the enhanced
VPN (VPN+) services.
This document describes a suggested way to use resource-aware SIDs to
build SR based VTNs. Although the procedure is illustrated using SR-
MPLS, this mechanism is applicable to both SR over MPLS data plane
(SR-MPLS) [RFC8660] and SR over IPv6 data plane (SRv6) [RFC8986].
2. Resource-Aware SIDs for VTN
As defined in [I-D.ietf-teas-enhanced-vpn], a VTN is a virtual
underlay network which has a specific network topology and a subset
of network resources allocated from the physical network.
When SR is used as the data plane of VTNs in the network, it is
necessary to compute and instantiate the SR paths with the topology
and/or algorithm constraints of the VTN, and steer the traffic to
only use the set of network resources allocated to the VTN.
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Based on the resource-aware segments defined in
[I-D.ietf-spring-resource-aware-segments], a group of resource-aware
SIDs can be allocated to represent the network segments of a VTN.
These resource-aware SIDs are associated with the group of network
resources allocated to the VTN on network nodes and links which
participate in the VTN. These resource-aware SIDs can also identify
the network topological or functional instructions associated with
the VTN.
The resource-aware SIDs may be allocated either by a centralized
network controller or by network nodes. The control plane mechanisms
for advertising the resource-aware SIDs for VTNs can be based on
[RFC4915], [RFC5120] and [I-D.ietf-lsr-flex-algo] with necessary
extensions. This is further described in section 3.3.
2.1. SR-MPLS based VTN
This section describes a mechanism of allocating resource-aware SIDs
to SR-MPLS based VTNs.
For an IGP link, multiple adj-SIDs are allocated, each of which is
associated with a VTN that the link participates in, and represents
those link resources that are allocated to the VTN. For an IGP node,
multiple prefix-SIDs are allocated, each of which is associated with
a VTN which the node participates in, and identifies the sets of
network resources allocated to the VTN on network nodes which
participate in the VTN. These set of resources will be used to
process packets which have the resource-aware SIDs as the active
segment.
In the case of multi-domain VTNs, on an inter-domain link, multiple
BGP peering SIDs [RFC9086] are allocated, each of which is associated
with a VTN which spans multiple domains, and represents a subset of
resources allocated on the inter-domain link.
2.2. SRv6 based VTN
This section describes a mechanism of allocating resource-aware SRv6
Locators and SIDs to SRv6 based VTNs.
An SRv6 Locator is allocated on each network node for each VTN in
which the node participates. This Locator (the VTN-specific Locator)
identifies the set of network resources allocated to the VTN on the
network nodes which participate in the VTN. The SRv6 SIDs associated
with a VTN are allocated from the SID space using the VTN-specific
Locator as the prefix. These SRv6 SIDs can be used to represent VTN-
specific SRv6 functions, and can identify the set of resources used
by network nodes to process packets.
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2.3. VTN Identification
In a simple case, each VTN can be mapped to a unique topology or
algorithm. Then the VTNs can be distinguished by the topology ID or
algorithm ID in the control plane, and the resource-aware SIDs
associated with a VTN can be identified using the <topology,
algorithm> tuple as described in [RFC8402]. In this case, the number
of VTNs supported in a network relies on the number of topologies or
algorithms supported.
In a more complicated case, multiple VTNs may be mapped to the same
<topology, algorithm> tuple, while each is allocated a separate set
of network resources. Then a new VTN identifier (VTN-ID) in the
control plane is needed to identify the VTN. The resource-aware SIDs
associated with different VTNs can be distinguished using VTN-IDs in
the control plane.
In the data plane, the resource-aware SIDs are used to identify the
VTN, and are also used to determine the forwarding instructions and
the set of network resources used for the packet processing action.
2.4. Scalability Considerations
Since multiple VTNs can be created in a network, and each VTN is
allocated a group of resource-aware SIDs, the mechanism of SR based
VTNs increases the number of SIDs and SRv6 Locators needed in a
network. There may be some concern, especially about the SR-MPLS
prefix-SIDs, which are allocated from the Segment Routing Global
Block (SRGB), that the SRGB will be used up. The amount of network
state will also increase accordingly. However, based on the SR
paradigm, resource-aware SIDs and the associated network state are
allocated and maintained per VTN, thus per-path network state is
avoided in the SR network. In the control plane, the amount of
information to be distributed for different VTNs may also become a
concern for the IGP protocols. The scalability of resource-aware SID
based VTNs are further analysed in [I-D.ietf-teas-nrp-scalability].
3. Procedures
This section describes possible procedures for creating SR based VTNs
and the corresponding forwarding tables and entries. The approaches
described in this section are not normative, but illustrate how the
VTN-specific Locator and VTN ID could be used to build and operate
VTNs in SR networks. Although it is illustrated using SR-MPLS, this
mechanism is applicable to both SR-MPLS and SRv6.
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Suppose a virtual network is requested by some customer or service.
One of the basic requirements is that the customer or service is
allocated with dedicated network resource, so that it does not
experience unexpected interference from other services in the same
network. Other possible requirements specified by the customer may
include the required topology, bandwidth, latency, reliability, etc.
According to the customer's requirements, a centralized network
controller calculates a subset of the underlay network topology to
support the service. With this topology, the set of network
resources required on each network element is also determined. The
subset of network topology and network resources are the two major
characteristics of a VTN. Depending on the service requirements, the
network topology and network resource of this VTN can be dedicated
for an individual customer or service, or can be shared by a group of
customers and/or services.
Based on the mechanisms described in section 2, a group of resource-
aware SIDs can be allocated for the VTN. With SR-MPLS, it is a group
of prefix-SIDs and adj-SIDs which are allocated to identify the
network nodes and links in the VTN, and also to identify the set of
network resources allocated on these network nodes and links for the
VTN. As the resource-aware SIDs can be allocated either by a
centralized network controller or by the network nodes, control plane
protocols such as IGP (e.g., IS-IS or OSPF) and BGP-LS can be used to
distribute the SIDs and the associated resource and topology
information of a VTN to other nodes in the same VTN and also to the
controller, so that both the network nodes and the controller can
generate the VTN-specific forwarding table or forwarding entries
based on the resource-aware SIDs of the VTN. The detailed control
plane mechanisms and possible extensions are described in the
accompanying documents [I-D.ietf-lsr-isis-sr-vtn-mt]
[I-D.ietf-idr-bgpls-sr-vtn-mt] [I-D.zhu-lsr-isis-sr-vtn-flexalgo]
[I-D.zhu-idr-bgpls-sr-vtn-flexalgo] [I-D.dong-lsr-sr-enhanced-vpn]
[I-D.dong-idr-bgpls-sr-enhanced-vpn] and are out of the scope of this
document.
3.1. VTN Topology and Resource Planning
A centralized network controller can be responsible for the planning
of a VTN to meet the received service request. The controller needs
to collect the information on network connectivity, network
resources, network performance and any other relevant network states
from the underlay network. This can be done using either IGP TE
extensions such as [RFC5305] [RFC3630] [RFC7471] [RFC8570], and/or
BGP-LS [RFC7752] [RFC8571], or any other form of control plane
signaling.
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Based on the information collected from the underlay network, the
controller obtains the underlay network topology and the information
about the allocated and available network resources. When a service
request is received, the controller determines the subset of the
network topology, and the set of resources needed on each network
segment (e.g., links and nodes) in the sub-topology to meet the
service requirements, whilst maintaining the needs of the existing
services that are using the same network. The subset of the network
topology and network resources will be used to constitute a VTN, and
will be used as the virtual underlay network of the requested
service.
3.2. VTN Network Resource and SID Allocation
According to the result of VTN planning, the network controller
instructs the set of network nodes involved to join a specific VTN
and allocate the required set of network resources for the VTN. This
may be done with Netconf/YANG [RFC6241] [RFC7950] or with any other
control or management plane mechanism with necessary extensions.
Thus, the controller not only allocates the resources to the newly
computed VTN, but also keeps track of the remaining available
resources in order to cope with subsequent VTN requests.
On each network node involved in the VTN, a set of network resources
(e.g., link bandwidth) is allocated to the VTN. Such set of network
resources can be dedicated for the processing of traffic in that VTN,
and cannot be used by traffic in other VTNs. Note it is also
possible that a group of VTNs may share a set of network resources on
some network segments. A group of resource-aware SIDs, such as
prefix-SIDs and adj-SIDs are allocated to identify both the network
segments and the set of resources allocated on the network segments
for the VTN. Such group of resource-aware SIDs, e.g., prefix-SIDs
and adj-SIDs are used as the data plane identifiers of the nodes and
links in the VTN.
In the underlying forwarding plane, there can be multiple ways of
allocating a subset of network resources to a VTN. The candidate
data plane technologies to support resource partitioning or
reservation can be found in [I-D.ietf-teas-enhanced-vpn]. The
resource-aware SIDs are considered as abstract data plane identifiers
in the network layer, which can work with various network resource
partitioning or reservation mechanisms in the underlying forwarding
plane.
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Prefix-SIDs: Prefix-SIDs:
r:101 r:102
g:201 g:202
b:301 r:1001:1G r:1001:1G b:302
+-----+ g:2001:2G g:2001:2G +-----+
| A | b:3001:1G b:3001:1G | B |
| +------------------------+ + r:1003:1G
+--+--+ +--+--+\g:2003:2G
r:1002:1G| r:1002:1G| \
g:2002:2G| g:2002:2G| \ r:1001:1G
b:3002:3G| b:3002:2G| \g:2001:2G
| | \ +-----+Prefix-SIDs:
| | \+ E | r:105
| | /+ | g:205
r:1001:1G| r:1002:1G| / +-----+
g:2001:2G| g:2002:2G| /r:1002:1G
b:3001:3G| b:3002:2G| / g:2002:2G
+--+--+ +--+--+ /
| | | |/r:1003:1G
| C +------------------------+ D + g:2003:2G
+-----+ r:1002:1G r:1001:1G +-----+
Prefix-SIDs: g:2002:1G g:2001:1G Prefix-SIDs:
r:103 b:3002:2G b:3001:2G r:104
g:203 g:204
b:303 b:304
Figure 1. SID and resource allocation for multiple VTNs
Figure 1 shows an example of providing multiple VTNs in an SR based
network. The prefix-SIDs are labels as such in the figure. All
other SIDs in the figure are adj-SIDs. Note that the format of the
SIDs in this figure is for illustration, both SR-MPLS and SRv6 can be
used as the data plane. In this example, three VTNs: red (r) , green
(g) and blue (b) are created to carry traffic of different customers
or services. Both the red and green VTNs consist of nodes A, B, C,
D, and E with all their interconnecting links, whilst the blue VTN
only consists of nodes A, B, C and D with all their interconnecting
links. Note that different VTNs may have a set of shared nodes and
links. On each node, a resource-aware prefix-SID is allocated for
each VTN it participates in. And on each link, a resource-aware adj-
SID is allocated for each VTN it participates in.
In Figure 1, the notation x:nnnn:y means that in VTN x, the adj-SID
nnnn will steer the packet over a link which has bandwidth y reserved
for that VTN. For example, r:1002:1G in link C->D says that the VTN
red has a reserved bandwidth of 1Gb/s on link C->D, and will be used
by packets arriving at node C with an adj-SID 1002 at the top of the
label stack. Similarly, on each node, a resource-aware prefix-SID is
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allocated for each VTN it participates in. Each resource-aware adj-
SID can be associated with a set of link resources (e.g., bandwidth)
allocated to a specific VTN, so that different adj-SIDs can be used
to steer service traffic into different set of link resources in
packet forwarding. A resource-aware prefix-SIDs in a VTN can be
associated with the set of network resources allocated to this VTN on
each involved network node and link. Thus, the prefix-SIDs can be
used to build loose SR path within a VTN, and can be used by the
transit nodes to steer traffic into the set of local network
resources allocated to the VTN.
3.3. Construction of SR based VTNs
The network controller needs to obtain the information about all the
VTNs in the network it oversees, including the resource-aware SIDs
and their associated network resources and topology information.
Based on this information, the controller can have a global view of
the VTN topologies, network resources and the associated SIDs, so as
to perform VTN-specific explicit path computation, taking both the
topology and resource constraints of the VTNs into consideration, and
use the resource-aware SIDs to build the SID list for the explicit
path. The controller may also compute the shortest paths in the VTN
based on the resource-aware prefix-SIDs.
The network nodes also need to obtain the information about the VTNs
they participate in, including the resource-aware SIDs and their
associated network resources and topology information. Based on the
collected information, the network nodes which are the headend of a
path can perform VTN-specific path computation, and build the SID
list using the collected resource-aware adj-SIDs and prefix-SIDs.
The network nodes also need to generate the forwarding entries for
the resource-aware prefix-SIDs in each VTN they participates in, and
associate these forwarding entries with the set of local network
resources (e.g., bandwidth on the outgoing interface) allocated to
the corresponding VTN.
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Thus, after receiving the network controller's instruction about
network resource and SID allocation, each network node needs to
advertise the identifier of the VTNs it participates in, the group of
resource-aware SIDs allocated to each VTN, and the resource
attributes (e.g., bandwidth) associated with the resource-aware SIDs
in the network. Each resource-aware adj-SID is advertised with the
set of associated link resources, and each resource-aware prefix-SID
is advertised with the identifier of the associated VTN, as all the
prefix-SIDs in a VTN are associated with the same set of network
resources allocated to the VTN. Note that, as described in section
2.3, the VTNs can be identified in the control plane either using
existing identifiers, such as the MT-ID or Flex-Algo ID, or using a
newly defined VTN ID.
The IGP mechanisms which reuse the existing IDs such as Multi-
Topology [RFC5120] or Flex-Algo [I-D.ietf-lsr-flex-algo] as the
identifier of VTNs, and distribute the resource-aware SIDs and the
associated topology and resource information may be based on the
mechanisms described in [I-D.ietf-lsr-isis-sr-vtn-mt] and
[I-D.zhu-lsr-isis-sr-vtn-flexalgo] respectively. The corresponding
BGP-LS mechanisms which can be used to distribute both the intra-
domain VTN information and the inter-domain VTN-specific link
information to the controller may be based on the mechanisms
described in [I-D.ietf-idr-bgpls-sr-vtn-mt] and
[I-D.zhu-idr-bgpls-sr-vtn-flexalgo] respectively. Note that with
these mechanisms, the number of VTNs supported relies on the number
of topologies or algorithms supported.
The IGP mechanisms described in [I-D.dong-lsr-sr-enhanced-vpn]
introduce a new VTN-ID in the control plane, so that multiple VTNs
can be mapped to the same <topology, algorithm> tuple, while each VTN
can have different resource attributes. This provides a mechanism
which allows flexible combination of network topology and network
resources attributes to build a large number of VTNs with a
relatively small number of topologies or algorithms. The
corresponding BGP-LS mechanisms which may be used to distribute the
intra-domain VTN information and the inter-domain VTN-specific link
information to the controller are described in
[I-D.dong-idr-bgpls-sr-enhanced-vpn].
Figure 2 shows the three SR based VTNs created in the network in
Figure 1.
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1001 1001 2001 2001 3001 3001
101---------102 201---------202 301---------302
| | \1003 | | \2003 | |
1002| 1002| \ 1001 2002| 2002| \ 2001 3002| 3002|
| | 105 | | 205 | |
1001| 1002| / 1002 2001| 2002| / 2002 3001| 3002|
| | / 1003 | | / 2003 | |
103---------104 203---------204 303---------304
1002 1001 2002 2001 3002 3001
VTN Red VTN Green VTN Blue
Figure 2. SR based VTNs with different groups of SIDs
For each SR based VTN, SR paths are computed within the VTN, taking
the VTN topology and resources as constraints. The SR path can be an
explicit path instantiated using SR policy [RFC9256], in which the
SID-list is built only with the SIDs allocated to the VTN. The SR
path can also be an IGP computed path associated with a prefix-SID or
SRv6 End SID allocated by a node for the VTN, the IGP path
computation is also based on the topology and/or algorithm
constraints of the VTN. Different SR paths in the same VTN may use
shared network resources when they use the same resource-aware SIDs
allocated to the VTN, while SR paths in different VTNs use different
set of network resources even when they traverse the same network
links or nodes. These VTN-specific SR paths need to be installed in
the corresponding forwarding tables.
For example, to create an explicit path A-B-D-E in VTN red in
Figure 2, the SR SID-list encapsulated in the service packet would be
(1001, 1002, 1003). For the same explicit path A-B-D-E in VTN green,
the SR segment list would be (2001, 2002, 2003). In the case where
we wish to construct a loose path A-D-E in VTN green, the service
packet should be encapsulated with the SR SID-list (201, 204, 205).
At node A, the packet can be sent towards D via either node B or C
using the network resources allocated by these nodes for VTN green.
At node D the packet is forwarded to E using the link and node
resource allocated for VTN green. Similarly, a packet to be sent via
loose path A-D-E in VTN red would be encapsulated with segment list
(101, 104, 105). In the case where an IGP computed path can meet the
service requirement, the packet can be simply encapsulated with the
prefix-SID of egress node E in the corresponding VTN.
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3.4. Mapping Services to SR based VTN
Network services can be provisioned using SR based VTNs as the
virtual underlay networks. For example, different services may be
provisioned in different SR based VTNs, each of which would use the
network resources allocated to the VTN, so that their data traffic
will not interfere with each other. In another case, a group of
services which have similar characteristics and requirements may be
provisioned in the same VTN, in this case the network resources
allocated to the VTN are only shared among this group of services,
but will not be shared with other services in the network. The
steering of service traffic to SR based VTNs can be based on either
local policy or, for example, the mechanisms as defined in [RFC9256].
3.5. VTN Visibility to Customers
VTNs can be used by network operators to organize and split their
network infrastructure into different virtual underlay networks for
different customers or services. Some customers may also request
different granularity of visibility into the VTN which is used to
deliver the service. Depending on the requirement and the network
operator's policy, VTNs may be exposed to the customer either as a
virtual network with both the edge nodes and the intermediate nodes,
as a set of paths with some of the transit nodes, or simply as a set
of virtual connections between the endpoints without any transit node
information. The visibility may be delivered through different
mechanisms, such as IGPs (e.g., IS-IS, OSPF), BGP-LS or Netconf/YANG.
On the other hand, a network operator may want to restrict the
visibility of the underlay network information it delivers to the
customer by either hiding the transit nodes between sites (and only
delivering information about the endpoint connectivity), or by hiding
some of the transit nodes (summarizing the path into fewer nodes).
The information about VTNs which are not used by the customer should
also be filtered. Mechanisms such as BGP-LS allow the flexibility of
the advertisement of aggregated virtual network information and
configurable filtering policies.
4. Characteristics of SR based VTNs
The mechanism described in this document provides several key
characteristics:
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* Customization: Different customized VTNs can be created in a
shared network to meet different customers' connectivity and
service requirement. The customers are only aware of the topology
and attributes of their own VTNs, and provision services on the
VTN instead of the physical network. This provides a practical
mechanism to support network slicing
[I-D.ietf-teas-ietf-network-slices].
* Resource Isolation: The computation and instantiation of SR paths
in one VTN can be independent from other VTNs or other services in
the network. In addition, a VTN can be associated with a set of
dedicated network resources, which can avoid resource competition
and performance interference from other VTNs or other services in
the network. This mechanism also allows resource sharing between
different service flows of the same customer, or between a group
of services which are provisioned in the same VTN. This gives the
operators and the customers the flexibility in network planning
and service provisioning. In a VTN, the performance of critical
services can be further ensured using other mechanisms, e.g.,
those as defined in [DetNet].
* Scalability: The introduction of resource aware SIDs for different
VTNs would increase the amount of SIDs and state in the network.
While the increased network state is considered an inevitable
price in meeting the requirements of some customers or services,
the SR based VTN mechanism seeks to achieve a balance between the
state limitations of traditional end-to-end TE mechanism and the
lack of resource awareness in classic segment routing. Following
the segment routing paradigm, network resources are allocated on
network segments in a per VTN manner and represented as SIDs, this
ensures that there is no per-path state introduced in the network.
In addition, operators can choose the granularity of resource
allocation on different network segments. In network segments
where resource is scarce such that the service requirement may not
always be met, this approach can be used to allocate a set of
resources to a VTN which contains such network segment to avoid
possible competition. By contrast, in other segment of the
network where resource is considered plentiful, the resource may
be shared between a number of VTNs. The decision to do this is in
the hands of the operator.
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5. Service Assurance of VTNs
In order to provide assurance for services provisioned in the SR
based VTNs, it is necessary to instrument the network at multiple
levels, e.g., in both the underlay network level and the VTN level.
The operator or the customer may also monitor and measure the
performance of the services carried by the VTN. In principle these
can be achieved using existing or in development techniques in IETF,
such as network telemetry [RFC9232]. The detailed mechanisms are out
of the scope of this document.
In case of failure or service performance degradation in a VTN, it is
necessary that some recovery mechanisms, e.g., local protection or
end-to-end protection mechanism is used to switch the traffic to
another path in the same VTN which could meet the service performance
requirement. Care must be taken that the service or path recovery
mechanism in one VTN does not impact other VTNs in the same network.
6. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
7. Security Considerations
The security considerations of segment routing [RFC8402] [RFC8754]
and resource-aware SIDs [I-D.ietf-spring-resource-aware-segments] are
applicable to this document.
The SR VTNs may be used carry services with specific SLA parameters.
An attack can be directly targeted at the customer application by
disrupting the SLA, and can be targeted at the network operator by
causing them to violate their SLA, triggering commercial
consequences. By rigorously policing ingress traffic and carefully
provisioning the resources provided to the VTN, this type of attack
can be prevented. However care needs to be taken when shared
resources are provided between VTNs at some point in the network, and
when the network needs to be reconfigured as part of ongoing
maintenance or in response to a failure.
Considering the scalability of the SR VTN mechanism, the system may
be destabilised by an attack or accident) that causes a large number
of VTNs to be configured. This can be mitigated by placing
thresholds (for alarms or cut-off) in the configuration process.
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Traffic within a network may marked as belonging to a specific VTN
and this makes it possible to carry out targetted attacks on traffic
and to deduce customer-sensitive traffic patterns.
The details of the underlying network should not be exposed to third
parties, some abstraction would be needed, this is also to prevent
attacks aimed at exploiting a shared resource between VTNs.
8. Contributors
Zhenbin Li
Email: lizhenbin@huawei.com
Zhibo Hu
Email: huzhibo@huawei.com
9. Acknowledgements
The authors would like to thank Mach Chen, Stefano Previdi, Charlie
Perkins, Bruno Decraene, Loa Andersson, Alexander Vainshtein, Joel
Halpern, James Guichard, Adrian Farrel and Shunsuke Homma for the
valuable discussion and suggestions to this document.
10. References
10.1. Normative References
[I-D.ietf-spring-resource-aware-segments]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Introducing Resource Awareness to SR
Segments", Work in Progress, Internet-Draft, draft-ietf-
spring-resource-aware-segments-06, 11 October 2022,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-spring-resource-aware-segments/>.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Network (VPN+)",
Work in Progress, Internet-Draft, draft-ietf-teas-
enhanced-vpn-11, 19 September 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
vpn-11.txt>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
10.2. Informative References
[DetNet] "DetNet WG", 2016,
<https://datatracker.ietf.org/wg/detnet>.
[I-D.dong-idr-bgpls-sr-enhanced-vpn]
Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS
Extensions for Scalable Segment Routing based Enhanced
VPN", Work in Progress, Internet-Draft, draft-dong-idr-
bgpls-sr-enhanced-vpn-04, 4 March 2022,
<https://www.ietf.org/archive/id/draft-dong-idr-bgpls-sr-
enhanced-vpn-04.txt>.
[I-D.dong-lsr-sr-enhanced-vpn]
Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., and S.
Bryant, "IGP Extensions for Scalable Segment Routing based
Enhanced VPN", Work in Progress, Internet-Draft, draft-
dong-lsr-sr-enhanced-vpn-08, 11 July 2022,
<https://www.ietf.org/archive/id/draft-dong-lsr-sr-
enhanced-vpn-08.txt>.
[I-D.ietf-idr-bgpls-sr-vtn-mt]
Xie, C., Li, C., Dong, J., and Z. Li, "BGP-LS with Multi-
topology for Segment Routing based Virtual Transport
Networks", Work in Progress, Internet-Draft, draft-ietf-
idr-bgpls-sr-vtn-mt-01, 12 September 2022,
<https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-sr-
vtn-mt-01.txt>.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-25, 6 October
2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
flex-algo-25.txt>.
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[I-D.ietf-lsr-isis-sr-vtn-mt]
Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi-
Topology (MT) for Segment Routing based Virtual Transport
Network", Work in Progress, Internet-Draft, draft-ietf-
lsr-isis-sr-vtn-mt-03, 10 July 2022,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-sr-
vtn-mt-03.txt>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "Framework for IETF
Network Slices", Work in Progress, Internet-Draft, draft-
ietf-teas-ietf-network-slices-14, 3 August 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
network-slices-14.txt>.
[I-D.ietf-teas-nrp-scalability]
Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N.,
Mishra, G., Qin, F., Saad, T., and V. P. Beeram,
"Scalability Considerations for Network Resource
Partition", Work in Progress, Internet-Draft, draft-ietf-
teas-nrp-scalability-00, 11 July 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-nrp-
scalability-00.txt>.
[I-D.zhu-idr-bgpls-sr-vtn-flexalgo]
Zhu, Y., Dong, J., and Z. Hu, "BGP-LS with Flex-Algo for
Segment Routing based Virtual Transport Networks", Work in
Progress, Internet-Draft, draft-zhu-idr-bgpls-sr-vtn-
flexalgo-01, 22 February 2021,
<https://www.ietf.org/archive/id/draft-zhu-idr-bgpls-sr-
vtn-flexalgo-01.txt>.
[I-D.zhu-lsr-isis-sr-vtn-flexalgo]
Zhu, Y., Dong, J., and Z. Hu, "Using Flex-Algo for Segment
Routing (SR) based Virtual Transport Network (VTN)", Work
in Progress, Internet-Draft, draft-zhu-lsr-isis-sr-vtn-
flexalgo-05, 11 July 2022,
<https://www.ietf.org/archive/id/draft-zhu-lsr-isis-sr-
vtn-flexalgo-05.txt>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
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[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/info/rfc7471>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
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[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
[RFC9232] Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
A. Wang, "Network Telemetry Framework", RFC 9232,
DOI 10.17487/RFC9232, May 2022,
<https://www.rfc-editor.org/info/rfc9232>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
Authors' Addresses
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
Stewart Bryant
University of Surrey
Email: stewart.bryant@gmail.com
Takuya Miyasaka
KDDI Corporation
Email: ta-miyasaka@kddi.com
Yongqing Zhu
China Telecom
Email: zhuyq8@chinatelecom.cn
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Fengwei Qin
China Mobile
Email: qinfengwei@chinamobile.com
Zhenqiang Li
China Mobile
Email: li_zhenqiang@hotmail.com
Francois Clad
Cisco Systems
Email: fclad@cisco.com
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