[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01 02 03 04
Network Working Group J. Dong
Internet-Draft S. Bryant
Intended status: Standards Track Huawei Technologies
Expires: September 12, 2019 Z. Li
China Mobile
T. Miyasaka
KDDI Corporation
March 11, 2019
Segment Routing for Enhanced VPN Service
draft-dong-spring-sr-for-enhanced-vpn-03
Abstract
Enhanced VPN (VPN+) is an enhancement to VPN technology to enable it
to support the needs of new applications, particularly applications
that are associated with 5G services. These applications require
better isolation from both control and data plane's perspective and
have more stringent performance requirements than can be provided
with overlay VPNs. The characteristics of an enhanced VPN as
perceived by its tenant needs to be comparable to those of a
dedicated private network. This requires tight integration between
the overlay VPN and the underlay network resources in a scalable
manner. An enhanced VPN may form the underpinning of 5G network
slicing, but will also be of use in its own right. This document
describes the use of segment routing based mechanisms to provide the
enhanced VPN service with dedicated network resources. The proposed
mechanism is applicable to both SR with MPLS data plane and SR with
IPv6 data plane (SRv6).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019.
Dong, et al. Expires September 12, 2019 [Page 1]
Internet-Draft SR for VPN+ March 2019
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
3. Segment Routing with Resource Awareness . . . . . . . . . . . 4
3.1. SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Singe SID Identifying both Topology and Resource . . 4
3.1.2. Dedicated SID Identifying Network Resource . . . . . 5
3.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Topology and Resource Computation . . . . . . . . . . . . 8
5.2. Network Resource and SID Allocation . . . . . . . . . . . 8
5.3. Construction of SR Virtual Networks . . . . . . . . . . . 10
5.4. VPN Service to SR Virtual Network Mapping . . . . . . . . 11
5.5. Network Visibility to Customer . . . . . . . . . . . . . 11
6. Benefits of the Proposed Mechanism . . . . . . . . . . . . . 12
6.1. MPLS-TP . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.3. Basic SR . . . . . . . . . . . . . . . . . . . . . . . . 13
6.4. SR with Resource Awareness . . . . . . . . . . . . . . . 13
7. Service Assurance . . . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
Dong, et al. Expires September 12, 2019 [Page 2]
Internet-Draft SR for VPN+ March 2019
1. Introduction
Driven largely by needs arising from the 5G mobile network design,
the concept of network slicing has gained traction [NGMN-NS-Concept]
[TS23501][TS28530] [BBF-SD406]. Network slicing requires the
transport network to support partitioning the network resources to
provide the client with dedicated (private) networking, computing,
and storage resources drawn from a shared pool. The slices may be
seen as (and operated as) virtual networks.
Thus there is a need to create virtual networks with enhanced
characteristics. The tenant of such a virtual network can require a
degree of isolation and performance that previously could only be
satisfied by dedicated networks. Additionally the tenant may ask for
some level of control to their virtual network e.g. to customize the
service paths in the network slice.
The enhanced VPN service (VPN+) as described in
[I-D.ietf-teas-enhanced-vpn] is targeted at new applications which
require better isolation from both control plane and data plane's
perspective and have more stringent performance requirements than can
be provided with existing overlay VPNs. An enhanced VPN may form the
underpinning of network slicing, but will also be of use in its own
right.
Although each VPN can be associated with a set of dedicated RSVP-TE
[RFC3209] LSPs with bandwidth reservation to provide some guarantee
to service performance, such mechanisms would introduce per-VPN per-
path states into the network, which is known to have scalability
issues [RFC5439] and has not been widely adopted in production
networks.
Segment Routing (SR) [RFC8402] specifies a mechanism to steer packets
through an ordered list of segments. It can achieve explicit source
routing without introducing per-path state into the network. Like
RSVP-TE, SR also supports source specification of the packet path.
However, currently SR does not have the capability of reserving or
identifying different network resources for different services or
customers. Although the controller can have global view of network
state and can provision different services onto different SR paths,
in the data plane it still relies on traditional DiffServ QoS model
[RFC2474] [RFC2475] to provide coarse-grained traffic differentiation
in the network. While this may be sufficient for some traditional
services, it cannot meet the requirement of the enhanced VPN service.
This document extends the SR paradigm by allocating different Segment
Identifiers (SIDs) to represent the different subset of resources
allocated on each network elements (links or nodes). The SIDs
Dong, et al. Expires September 12, 2019 [Page 3]
Internet-Draft SR for VPN+ March 2019
associated with a particular group of network resources can be used
to construct customized virtual networks for different services, the
SID can also be used to steer the service traffic to be processed
with the corresponding allocated resources. This mechanism can be
used to provide the enhanced VPN service with dedicated network
resources. The proposed mechanism is applicable to both SR with MPLS
data plane and SR with IPv6 data plane (SRv6).
2. Requirements Notation
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 RFC 2119 [RFC2119] RFC8174 [RFC8174][when, and only when, they
appear in all capitals, as shown here.
3. Segment Routing with Resource Awareness
In segment routing, several types of segments are defined to
represent either topological elements or service instructions. A
topological segment may be a node segment or an adjacency segment.
Some other types of segments may be associated with specific service
functions for service chaining purpose. However, so far none of the
SR segments are associated with network resources for the QoS
purpose.
In order to support the enhanced VPNs which require guaranteed
performance and isolation from other services in the network, the
overlay VPN needs to be integrated with part of the underlay
networks. Some dedicated network resources need to be allocated to
an enhanced VPN or a group of enhanced VPNs. When segment routing is
used to provide enhanced VPNs, it is necessary to associate the
segments with network resources. By extending the segment routing
paradigm, different set of network resources can be allocated on
network elements, and associated with different SIDs.
This section describes the possible mechanisms to bring resource-
awareness into two SR data plane instantiations: SR-MPLS and SRv6.
3.1. SR-MPLS
3.1.1. Singe SID Identifying both Topology and Resource
In SR-MPLS [I-D.ietf-spring-segment-routing-mpls], Adjacency Segment
(Adj-SID) is an IGP-segment attached to a unidirectional adjacency or
a set of unidirectional adjacencies. Node segment is an IGP-Prefix
segment that identifies a specific router (e.g., a loopback). These
Dong, et al. Expires September 12, 2019 [Page 4]
Internet-Draft SR for VPN+ March 2019
two types of SIDs can be extended to represent both topological
elements and the resources allocated on a particular network element.
On one particular network link, multiple adjacency segment
identifiers (Adj-SIDs) can be allocated, each of which is associated
with a subset of the link resource allocated, such as logical sub-
interface, bandwidth, queues, etc. For one particular node, multiple
node-SIDs can be allocated, each of which may be associated with a
subset of resource allocated from the node, such as the processing
resources. Per-segment resource allocation complies to the SR
paradigm, which avoids introducing per-path state into the network.
Different groups of adj-SIDs and node-SIDs which represent different
set of network resources can be used to build different virtual
networks, which could be further used to provide different enhanced
VPNs, so that the isolation and performance requirement of enhanced
VPNs could be met. The adj-SIDs are used to steer traffic of
different enhanced VPNs into different set of link resources. The
node SIDs can be used to steer traffic of different enhanced VPNs
into different node resources. The node SIDs can also be used to
build loose SR paths for different enhanced VPNs. In this case, the
node-SIDs are used by transit nodes to steer traffic into the local
resources allocated for the corresponding enhanced VPN. Note in this
case Penultimate Hop Popping (PHP) [RFC3031] MUST be disabled, as the
node-SID is used to identify the SR virtual network and the
corresponding network resources allocated to the enhanced VPN.
3.1.2. Dedicated SID Identifying Network Resource
Another option to bring resource-awareness into SR-MPLS data plane is
to define a dedicated SID called "resource-SID" to identify the group
of network resources allocated on a particular link or node. In SR
label stack, the resource-SID MUST be encapsulated under the
topological SIDs (adj-SID or node-SIDs) which identifies the network
element it applies to.
Note that a network node can participate in multiple topologies. For
each network topology it participates in, a dedicated node-SID is
needed for topology-specific path computation and next hop
resolution. Dedicated adj-SIDs could also be allocated for different
network topologies.
In packet forwarding, the adj-SID and node-SID are used to determine
the next-hop and the outbound interface in a particular virtual
network, then the resource-SID is used to identify the fine granular
forwarding plane resource to be used for the processing of the
received packet.
Dong, et al. Expires September 12, 2019 [Page 5]
Internet-Draft SR for VPN+ March 2019
The benefit of this approach is that it decouples the topology
identification and resource identification. In some cases where
multiple virtual networks share a same topology but map to different
set of network resources, it is possible that the topology-specific
processing (for example, SPF computation) could be shared, so that
the scalability can be improved. The cost is it increases the depth
of the MPLS label stack.
The resource-SID can be a global significant identifier, which
represents the collection of network resources allocated in the whole
network domain to a particular virtual network. In this case, the
resource-SID SHOULD appear only once in the label stack, and it
SHOULD be parsed by each transit node which performs per virtual
network resource reservation. This resource-SID can be either a new
type of SID, or it could be embedded in some existing MPLS labels.
For example, some fields in the Entroy Label Indicator (ELI) /
Entropy Label (EL) [RFC6790] may be used as the resource identifier,
the details will be provided in a future version.
The resource-SID may be a local significant identifier, which only
represents the network resource locally allocated on each network
segment to a particular virtual network. In this case, it has to be
added to the label stack for each hop which performs per-virtual
network resource reservation. As this approach would increase the
label stack depth significantly, this approach is NOT RECOMMENDED.
3.2. SRv6
An SRv6 Segment (SID) is a 128-bit value which consists of a locator
(LOC) and a function (FUNCT), optionally it may also contain
additional arguments (ARG)
[I-D.filsfils-spring-srv6-network-programming]. The locator is used
for routing towards a particular node, it needs to be parsed by all
nodes in the network. The function and arguments are only parsed by
the owner of the SRv6 SID to determine the local behavior on receipt
of the SRv6 packet.
In order to build multiple virtual networks in an SRv6 network, each
node SHOULD allocate a dedicated locator for each virtual network it
participates in. In packet forwarding, the locator can be used to
identify the virtual network the packet belongs to, so that a virtual
network specific next-hop can be determined. In addition, the
locator can also be used to identify the group of local network
resources allocated to the virtual network. All the SRv6 functions
associated with a particular virtual network MUST use the locator of
that virtual network as the prefix to construct the SRv6 SID.
Dong, et al. Expires September 12, 2019 [Page 6]
Internet-Draft SR for VPN+ March 2019
In some cases where multiple virtual networks share a same topology
but maps to different set of network resources, it is possible that
the topology-specific processing (for example, SPF computation) could
be shared, so that the scalability can be improved. This requires to
decouple the topology identification and resource identification in
SRv6. The locator can still be used as the identifier of the
topology, while another identifier is needed to identify the network
resources allocated to a particular virtual network. There are some
candidates for the resource identifier in the IPv6 [RFC8200] or SRv6
header [I-D.ietf-6man-segment-routing-header], such as the IPv6 Flow
Label or the Hop-by-Hop Option. More details will be provided in a
future version.
4. Control Plane
The architecture described in this document makes use of a
centralized controller that collects the information about the
network (configuration, state, routing databases, etc.) as well as
the service information (traffic matrix, performance statistics,
etc). The controller is also responsible for the centralized
computation and optimization of the virtual networks used for
enhanced VPNs. A distributed control plane is needed for the
collection and distribution of the topology and state information of
the virtual networks. Distributed routing computation for some
services in the enhanced VPNs is also possible.
5. Procedures
This section describes the procedures of provisioning an enhanced VPN
service based on segment routing with resource awareness.
According to the requirement of an enhanced VPN service, a
centralized network controller calculates a subset of the underlay
network topology to support this enhanced VPN. Within this topology,
the network resources needed on each network element can also be
determined. The network resources are allocated in a per-segment
manner, and are associated with different node-SIDs and adj-SIDs.
The group of the node-SIDs and adj-SIDs allocated for the enhanced
VPN will be used by network nodes and the network controller to build
a SR virtual topology, which is used as the logical underlay of the
enhanced VPN service. The extensions to IGP protocol to distribute
the SIDs and the associated resources allocated for a virtual network
is specified in [I-D.dong-lsr-sr-enhanced-vpn].
Suppose that customer requests for an enhanced VPN service from the
network operator. The fundamental requirement is that customer A's
service does not experience interference from other services in the
network, such as other customers' VPN services, or the non-VPN
Dong, et al. Expires September 12, 2019 [Page 7]
Internet-Draft SR for VPN+ March 2019
services in the network. The detailed requirements can be described
with characteristics such as the following:
o Service topology: the service sites and the connectivity between
them
o Service bandwidth: the bandwidth requirement between service sites
o Isolation: the level of isolation from other services in the
network
o Reliability: whether fast repair or end-to-end protection is
needed or not.
o Latency
o Jitter
o Visibility: the customer may want to have some form of visibility
of the network deliversing the service.
5.1. Topology and Resource Computation
As described in section 4, a centralized network controller is
responsible for the provisioning of enhanced VPNs. The controller
needs to determine the information of network connectivity, network
resources, network performance and other relevant network state of
the underlay network. This is often done using either IGP [RFC5305]
[RFC3630] [RFC7471] [RFC7810] or BGP-LS [RFC7752]
[I-D.ietf-idr-te-pm-bgp].
Based on the network information collected from the underlay network,
the controller computes the underlay topology (possibly using
multiple algorithms) and knows the resources that are available and
allocated. When a request is received from a tenant, the controller
computes the subgraph of the underlay network, along with the
resources to be allocated on each network element (e.g. links and
nodes) in the topology to meet the tenant's requirements, whilst
maintaining the needs of the existing tenants that are using the same
network.
5.2. Network Resource and SID Allocation
According to the output of computation, the network controller
instructs the network devices involved in the subgraph to allocate
the required network resources for the enhanced VPN. This can be
done with either PCEP [RFC5440] or Netconf/YANG [RFC6241] [RFC7950]
with necessary extensions. The network resources are allocated in a
Dong, et al. Expires September 12, 2019 [Page 8]
Internet-Draft SR for VPN+ March 2019
per-segment manner. In addition, dedicated segment identifiers, e.g.
node-SIDs and adj-SIDs are also allocated to represent the network
resources allocated for the enhanced VPN on each network segment.
In the forwarding plane, there are multiple ways of allocating or
reserving network resources to different enhanced VPNs. For example,
FlexE may be used to partition the link resource into different sub-
channels to achieve hard isolation between each other. The candidate
data plane technologies of enhanced VPN can be found in
[I-D.ietf-teas-enhanced-vpn]. The SR SIDs are used as a good
abstraction of the various types of network resource reservation
mechanisms in the forwarding plane.
Node-SIDs: Node-SIDs:
r:101 r:102
g:201 Adj-SIDs: 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 |Adj-SIDs:
| +------------------------+ + r:1003:1G
Adj-SIDs +--+--+ +--+--+\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
| | \ +-----+ Node-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 +-----+
Node-SIDs: g:2002:1G g:2001:1G Node-SIDs:
r:103 b:3002:2G b:3001:2G r:104
g:203 g:204
b:303 b:304
Figure 1. SIDs identify resources allocated to different virtual networks
Figure 1 shows a network fragment of enhanced VPN supported by SR.
Note that the format of the SIDs in this figure are for illustration,
both SR-MPLS and SRv6 can be utilized as the data plane. In this
example, there are three virtual topologies created for enhanced VPNs
red (r) , green (g) and blue (b). The red and green topologies
consist of nodes A, B, C, D, and E with all their interconnecting
links, whilst the blue topology only consists of nodes A, B, C and D
Dong, et al. Expires September 12, 2019 [Page 9]
Internet-Draft SR for VPN+ March 2019
with all their interconnecting links. Each node allocates a
dedicated adjacency SID for each link participating in a particular
topology. Each node is also allocated with a dedicated node SID for
each topology it participates in. The adj-SIDs are associated with
the link resources (e.g. bandwidth) allocated to each topology, so
that the adj-SIDs can be used to steer service of different enhanced
VPNs into different set of reserved resources in the data plane. The
node-SIDs can be associated with dedicated nodal resources allocated
for each topology. In addition, the node-SIDs of different
topologies can be used to build loose SR path within each virtual
topology, and steer service of different enhanced VPNs into the
different set of reserved resources in the data plane.
In Figure 1, the notation x:nnnn:y that in topology colour x, the
adj-SID nnnn will steer the packet over that link which has a total
bandwidth of y assigned to that topology. Thus the note r:1002:1G in
link C->D says that the red topology over link C->D has a reserved
bandwidth of 1Gb/s and will be used by packets arriving at node C
with an adj-SID 1002 at the top of the label stack.
5.3. Construction of SR Virtual Networks
Each node MUST advertise its set of resources (allocated and
available) and the associated SIDs both to the centralized controller
and into the network. This can be achieve by many different means
such as (non-exhaustive list) IGP extensions
[I-D.dong-lsr-sr-enhanced-vpn], BGP-LS [RFC7752] with possible
extensions, NETCONF/YANG [RFC6241] [RFC7950].
With the collected network resource and SIDs information, the
controller and network nodes are able to construct the SR virtual
topologies and forwarding entries using the node-SIDs and adj-SIDs
allocated for each enhanced VPN. Unlike classic segment routing in
which network resources are shared by all services and customers, the
SR virtual networks are associated with dedicated resource allocated
in the underlay, so that they can be used to meet the service
requirement of enhanced VPN and provide the required isolation from
other services in the same network.
Figure 2 shows the virtual SR topologies created from the underlay
network in Figure 1.
Dong, et al. Expires September 12, 2019 [Page 10]
Internet-Draft SR for VPN+ March 2019
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 1002 2001 3002 3001
Topology Red Topology Green Topology Blue
Figure 2. SR virtual topologies using different groups of SIDs
5.4. VPN Service to SR Virtual Network Mapping
The services of an enhanced VPN customer can be provisioned using the
customized SR virtual network as the underlay. In this way, services
of different enhanced VPNs will only use the network resources
allocated and will not interfere with each other. For each enhanced
VPN customer, the service paths can be customized for different
services within the SR virtual topology, and the allocated network
resources are shared by different services of the same enhanced VPN
customer.
For example, to create a strict path along the path A-B-D-E in the
red topology in Figure 2, the SR segment list in the service packet
would be (1001, 1002, 1003). For the same strict path in green
topology, the SR segment list would be (2001, 2002, 2003). In the
case where we wish to construct a loose path A-D-E in the green
topology, the service packet SHOULD be set with the SR segment list
(201, 204, 205). At node A the packet is sent towards D via either
node B or C using the link and node resources allocated for the green
topology. At node D the packet is forwarded to E using the link and
node resource allocated for the green topology. Similarly, a packet
for the loose path A-D-E in the red topology would arrive at node A
with the SID list (101, 104, 105).
5.5. Network Visibility to Customer
The tenants of enhanced VPNs may request different granularity of
visibility to the network which deliver the service. Depending on
the requirement, the network can be exposed to the tenant either as a
virtual network topology, or a set of computed paths with transit
nodes, or simply the connectivity between endpoints without any path
information. The visibility can be delivered through different
possible mechanisms, such as IGPs (e.g. IS-IS, OSPF) or BGP-LS. In
addition, the network operator may want to restrict the visibility of
the information it delivers to the tenant by either hiding the
Dong, et al. Expires September 12, 2019 [Page 11]
Internet-Draft SR for VPN+ March 2019
transit nodes between sites (and only delivering the endpoints
connectivity) or by hiding portions of the transit nodes (summarizing
the path into fewer nodes). Mechanisms such as BGP-LS allow the
flexibility of the advertisement of aggregated network information.
6. Benefits of the Proposed Mechanism
The proposed mechanism provides several key characteristics:
o Flexibility
o Scalability
o Resource isolation
In addition to isolation, the proposed mechanism allows resource
sharing between different services of the same enhanced VPN customer.
This gives the customer more flexibility and control in service
planning and provisioning, the experience would be similar to using a
dedicated private network. The performance of critical services
flows in a particular enhanced VPN can be further ensured using the
mechanisms defined in [DetNet].
The detailed comparison with other candidates technologies are given
in the following subsections.
6.1. MPLS-TP
MPLS-TP could be enhanced to include the allocation of specific
resources along the path to a specific LSP. This would require that
the SDN system set up and maintain every resource at every path for
every customer, and map this to the LSP in the data plane, hence at
every hop unique LSP label is needed for each path. Whilst this
would be a way to produce a proof of concept for network slicing of
an MPLS underlay, delegation would be difficult, resulting in a high
overhead and a system needing too much administration. This leads to
scaling concerns. The number of labels needed at any node would be
the total number of services passing through that node. Experience
with early pseudowire designs shows that this can lead to scaling
issues.
6.2. RSVP-TE
RSVP-TE has the same scaling concern as MPLS-TP in terms of the
number of LSPs that need to be maintained being equal to the number
of services passing through any given node. It also has the two RSVP
disadvantages that basic SR seeks to address:
Dong, et al. Expires September 12, 2019 [Page 12]
Internet-Draft SR for VPN+ March 2019
o The use of RSVP for path establishment in addition to the routing
protocol used to discover the topology and the network resources.
o The overhead of the soft-state maintenance associated with RSVP.
The impact of this overhead would be exacerbated by the increased
number of end to end paths requiring state maintenance.
6.3. Basic SR
Compared to RSVP, SR reduces the number of control protocols to only
the routing protocol. It also attempts to minimize the core state by
pushing state into the packet, although in some cases the binding
SIDs are required to overcome the limitations in the ability of some
nodes to push large label stacks. Moreover, currently SR does not
support resource allocation or identification below the level of
link, and none at node level. This restricts the extent to which
some particular tenant traffic can be isolated from other traffic in
the network.
6.4. SR with Resource Awareness
The approach described in this document seeks to achieve a compromise
between the state limitations of traditional TE systems and the lack
of resource awareness in basic SR.
By segmenting the path and allocating network resources to each
element of the virtual network topologies, the operator can choose
the granularity of resource to path binding within a virtual
topology. In network segments where resource is scarce such that the
service requirement may not always be met, the SR approach can
allocate specific resources to a particular high priority service.
By contrast, in other parts of the network where resource is
plentiful, the resource may be shared by a number of services. The
decision to do this is in the hands of the operator. Because of the
segmented nature of the path, resource aggregation is possible in a
way that is more difficult with RSVP-TE and MPLS-TP due to the use of
dedicated label to identify each end-to-end path.
7. Service Assurance
In order to provide service assurance it is necessary to instrument
the network at multiple levels. The network operator needs to
ascertain that the underlay is operating correctly. A tenant needs
to ascertain that their services are correctly operating. In
principle these can use existing techniques. These are well known
problems and solutions either exist or are in development to address
them.
Dong, et al. Expires September 12, 2019 [Page 13]
Internet-Draft SR for VPN+ March 2019
New work is needed to instrument the virtual networks that are
created. Such instrumentation needs to operate without causing
disruption to other services using the network. Given the
sensitivity of some applications, care needs to be taken to ensure
that the instrumentation itself does not cause disruption either to
the service being instrumented or to other services.
8. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
9. Security Considerations
The normal security considerations of VPNs are applicable and it is
assumed that industry best practise is applied to an enhanced VPN.
The security considerations of segment routing are applicable and it
is assumed that these are applied to an enhanced VPN that uses SR.
Some applications of enhanced VPNs are sensitive to packet latency;
the enhanced VPNs provisioned to carry their traffic have latency
SLAs. By disrupting the latency of such traffic an attack can be
directly targeted at the customer application, or can be targeted at
the network operator by causing them to violate their SLA, triggering
commercial consequences. Dynamic attacks of this sort are not
something that networks have traditionally guarded against, and
networking techniques need to be developed to defend against this
type of attack. By rigorously policing ingress traffic and carefully
provisioning the resources provided to critical services this type of
attack can be prevented. However case needs to be taken when
providing shared resources, and when the network needs to be
reconfigured as part of ongoing maintenance or in response to a
failure.
The details of the underlay MUST NOT be exposed to third parties, to
prevent attacks aimed at exploiting a shared resource.
10. Acknowledgements
The authors would like to thank Mach Chen, Zhenbin Li, Stefano
Previdi, Charlie Perkins and Bruno Decraene for the discussion and
suggestions to this document.
Dong, et al. Expires September 12, 2019 [Page 14]
Internet-Draft SR for VPN+ March 2019
11. References
11.1. Normative References
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-18
(work in progress), December 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
11.2. Informative References
[BBF-SD406]
"BBF SD-406: End-to-End Network Slicing", 2016,
<https://wiki.broadband-forum.org/display/BBF/
SD-406+End-to-End+Network+Slicing>.
[DetNet] "DetNet WG", 2016,
<https://datatracker.ietf.org/wg/detnet>.
[I-D.dong-lsr-sr-enhanced-vpn]
Dong, J. and S. Bryant, "IGP Extensions for Segment
Routing based Enhanced VPN", draft-dong-lsr-sr-enhanced-
vpn-01 (work in progress), October 2018.
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-07 (work in progress), February 2019.
Dong, et al. Expires September 12, 2019 [Page 15]
Internet-Draft SR for VPN+ March 2019
[]
Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-16 (work in
progress), February 2019.
[I-D.ietf-idr-te-pm-bgp]
Ginsberg, L., Previdi, S., Wu, Q., Tantsura, J., and C.
Filsfils, "BGP-LS Advertisement of IGP Traffic Engineering
Performance Metric Extensions", draft-ietf-idr-te-pm-
bgp-18 (work in progress), December 2018.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Networks (VPN+)
Service", draft-ietf-teas-enhanced-vpn-01 (work in
progress), February 2019.
[NGMN-NS-Concept]
"NGMN NS Concept", 2016, <https://www.ngmn.org/fileadmin/u
ser_upload/161010_NGMN_Network_Slicing_framework_v1.0.8.pd
f>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[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>.
Dong, et al. Expires September 12, 2019 [Page 16]
Internet-Draft SR for VPN+ March 2019
[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>.
[RFC5439] Yasukawa, S., Farrel, A., and O. Komolafe, "An Analysis of
Scaling Issues in MPLS-TE Core Networks", RFC 5439,
DOI 10.17487/RFC5439, February 2009,
<https://www.rfc-editor.org/info/rfc5439>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[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>.
[RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
RFC 7810, DOI 10.17487/RFC7810, May 2016,
<https://www.rfc-editor.org/info/rfc7810>.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
Dong, et al. Expires September 12, 2019 [Page 17]
Internet-Draft SR for VPN+ March 2019
[TS23501] "3GPP TS23.501", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS28530] "3GPP TS28.530", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
Authors' Addresses
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
Stewart Bryant
Huawei Technologies
Email: stewart.bryant@gmail.com
Zhenqiang Li
China Mobile
Email: li_zhenqiang@hotmail.com
Takuya Miyasaka
KDDI Corporation
Email: ta-miyasaka@kddi.com
Dong, et al. Expires September 12, 2019 [Page 18]
Html markup produced by rfcmarkup 1.129c, available from
https://tools.ietf.org/tools/rfcmarkup/