Internet DRAFT - draft-xie-spring-srv6-network-migration
draft-xie-spring-srv6-network-migration
Network Working Group C. Xie
Internet-Draft C. Li
Intended status: Informational China Telecom
Expires: January 9, 2020 S. Peng
Z. Li
Y. Xiao
Huawei Technologies
July 8, 2019
SRv6 Network Migration
draft-xie-spring-srv6-network-migration-00
Abstract
SRv6 has significant advantages over SR-MPLS which has attracted more
and more attentions and interests from operators and verticals. The
smooth network migration towards SRv6 is a key focal point for the
SRv6 deployers. This document provides network migration guidance
and recommendations on solutions in various scenarios.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 January 9, 2020.
Xie, et al. Expires January 9, 2020 [Page 1]
Internet-Draft SRv6 Network Migration July 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Advantages of SRv6 . . . . . . . . . . . . . . . . . . . . . 3
2.1. IP Route Aggregation . . . . . . . . . . . . . . . . . . 3
2.2. End-to-end Service Auto-start . . . . . . . . . . . . . . 4
2.3. On-Demand Upgrade . . . . . . . . . . . . . . . . . . . . 5
3. Incremental Deployment Guidance for SRv6 Migration . . . . . 6
4. Migration Guidance for SRv6/SR-MPLS Co-existence Scenario . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
SRv6 [I-D.ietf-spring-srv6-network-programming] has significant
advantages over SR-MPLS and has attracted more and more attentions
and interests from operators and verticals. The smooth network
migration towards SRv6 is a key focal point for the SRv6 deployers.
SRv6 is the Segment Routing deployed on the IPv6 data plane[RFC8200].
Therefore, in order to support SRv6, the network needs to support
IPv6 first. As being actively promoted all over the world, the
deployments of IPv6 have been ever-increasing which provides the
strong base for the deployments of SRv6.
With the IPv6 as its data plane, for network migration towards SRv6,
both software and hardware need to be upgraded. Compared with other
new protocols, only IGP and BGP need to be extended to support SRv6,
which significantly simplifies the software upgrade required. While
Xie, et al. Expires January 9, 2020 [Page 2]
Internet-Draft SRv6 Network Migration July 2019
in the hardware it needs to support the new SRv6 header
SRH[I-D.ietf-6man-segment-routing-header], the design of SRv6 assures
the compatibility with the existing IPv6 network. An SRv6 SID is
designed as an IPv6 address with 128bits long. From the
encapsulation aspect an SRv6 packet is the same as an IPv6 packet.
When only L3VPN over SRv6 BE (Best-Effort) is deployed, there will be
no SRH. Therefore, no additional hardware capabilities are required
but only software upgrade for protocol extensions.
As the services supported by SRv6 increase, e.g. SFC, network
slicing, more SIDs in the SRH may impose new requirements on the
hardware. Besides hardware upgrading, various solutions
[I-D.peng-spring-srv6-compatibility] have already been proposed to
relief the imposed pressure on the hardware, such as BSID etc. to
guarantee the compatibility with the existing network. On the other
hand SRv6 has much more advantages over SR-MPLS for the network
migration to support new services.
This document summarizes the advantages and provides network
migration guidance and recommendations on solutions in various
scenarios.
2. Advantages of SRv6
Compared with SR-MPLS, SRv6 has significant advantages especially in
the large scale networking scenario.
2.1. IP Route Aggregation
It has been many years that the operators are troubled by the
complexity of the service deployments, especially in the large scale
networking scenario. With the solutions such as multi-segment PW and
Option A, the service-touch points are increased, and the services or
OAM cannot be deployed end-to-end.
o With Seamless MPLS or SR-MPLS, since the MPLS label itself does
not have reachability information, it must be attached to a
routable address. The 32-bit host route needs to leak across
domains. For an extreme case, as shown in Figure 1a, in a large
scale networking scenario, millions of host routes LSPs might need
to be imported, which places big challenges on the capabilities of
the edge nodes.
o With SRv6, owning to its native IP feature of route
aggregatability as shown in Figure 1b, the aggregated routes can
be imported across network domains. For the large scale
networking, only very few aggregated routes are needed in order to
Xie, et al. Expires January 9, 2020 [Page 3]
Internet-Draft SRv6 Network Migration July 2019
start end-to-end services, which also reduces the scalability
requirements on the edge nodes.
/------Metro------\ /----Core----\ /------Metro-------\
LB PE1 ASBR ASBR PE2 LB
1.1.1.1 2.2.2.2
+--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+
|A | |B | |ER| | | |PE| | | |PE| | | |ER| |B | |A |
+--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+
SR-LSP SR-LSP SR-LSP SR-LSP SR-LSP
|<--->|<---------->| |<--------->| |<--------->|<--->|
BGP-LSP
|<---------------------------------------------------------->|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+IP + +IP + +IP + +IP + +IP + +IP + +IP + +IP + +IP +
+ETH+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +ETH+
+---+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +---+
+SR + +SR + +ETH+ +SR + +ETH+ +SR + +SR +
+ETH+ +ETH+ +---+ +ETH+ +---+ +ETH+ +ETH+
+---+ +---+ +---+ +---+ +---+
(a) SR-MPLS
/------Metro------\ /----Core----\ /------Metro-------\
LOC PE1 ASBR ASBR PE2 LOC
A1::100:: A2::200::
+--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+
|A | |B | |ER| | | |PE| | | |PE| | | |ER| |B | |A |
+--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+
\_____A1::/80____/ \__A0::/80__/ \____A2::/80____/
Aggregated Route Aggregated Route Aggregated Route
+---+ +----------+ +----------+ +----------+ +---+
+IP + + IP + + IP + + IP + +IP +
+ETH + +w./wo.SRH + +w./wo.SRH + +w./wo.SRH + +ETH+
+---+ + ETH + + ETH + + ETH + +---+
+----------+ +----------+ +----------+
(b) SRv6
Figure 1. Large-scale Networking with (a) SR-MPLS vs. (b) SRv6
2.2. End-to-end Service Auto-start
In the SR cross-domain scenario, in order to set up end-to-end SR
tunnels, the SIDs in each domain needs to be imported to other
domains.
Xie, et al. Expires January 9, 2020 [Page 4]
Internet-Draft SRv6 Network Migration July 2019
o With SR-MPLS, SRGB and Node SID need the overall network-wide
planning. However, in the cross-domain scenario, it is difficult
or sometimes even impossible to perform the overall planning. The
node SIDs in different domains may collide. BGP Prefix SID can be
used for the cross-domain SID import, but it must be careful when
converting the SID to avoid the SID collision. Moreover, the pre-
allocated SRGB within each domain needs to consider the total
number of devices in all other domains, which raises the
difficulties of the network-wide planning.
o With SRv6，owning to its native IP feature of route
reachability, as long as the IPv6 address space is carefully
planned, and the aggregated routes are imported by using BGP4+,
the services will auto-start in the cross-domain scenario.
2.3. On-Demand Upgrade
The MPLS label itself does not hold any reachability information, so
it must be attached to a routable address, which means that the
matching relationship between the label and FEC needs to be
maintained along the path.
SR-MPLS uses the MPLS data plane. When the network migrates to SR-
MPLS, there are two ways, as shown in Figure 2:
1. MPLS/SR-MPLS Dual stack: the entire network is upgraded first and
then deploy SR-MPLS.
2. MPLS and SR-MPLS interworking: mapping servers are deployed at
some of the intermediate nodes and then removed once the entire
network is upgraded
With either way, big changes in a wide area are required at the
initial stage therefore causes a long time-to-market.
On the contrary, the network can be migrated to SRv6 on demand.
Wherever the services need to turn on, only the relevant devices need
to be upgraded to enable SRv6, and all other devices only need to
support IPv6 forwarding and need not to be aware of SRv6. When the
TE services are needed, only the key nodes along the path needs to be
upgraded to support SRv6.
Xie, et al. Expires January 9, 2020 [Page 5]
Internet-Draft SRv6 Network Migration July 2019
(~~~~~~MPLS/SR-MPLS~~~~~~~)
( +---+ +---+ +---+ )
MPLS Migration Options Option 1 ( |SM | |SM | |SM | )
--->( +---+ +---+ +---+ )
/ ( +---+ +---+ +---+ )
(~~~~~~~~~~MPLS~~~~~~~~~~~) / ( |SM | |SM | |SM | )
( +---+ +---+ +---+ ) / ( +---+ +---+ +---+ )
( | M | | M | | M | ) / ~~~~~~~~~~~~~~~~~~~~~~~~~~
( +---+ +---+ +---+ ) \
( +---+ +---+ +---+ ) \ (~~MPLS~~|~~~~~SR-MPLS~~~~~)
( | M | | M | | M | ) \ ( +---+ | +---+ +---+ )
( +---+ +---+ +---+ ) \ ( | M | | |SM | |SM | )
~~~~~~~~~~~~~~~~~~~~~~~~~~ --->( +---+ | +---+ +---+ )
Option 2 ( +---+ | +---+ +---+ )
( | M | | |SM | |SM | )
( +---+ | +---+ +---+ )
~~~~~~~~~~~~~~~~~~~~~~~~~~
SRv6 Migration
(~~~~~~~~~~MPLS~~~~~~~~~~~) (~~~~~~SRv6 on demand~~~~~)
( +---+ +---+ +---+ ) ( +---+ +---+ +---+ )
( | M | | M | | M | ) ( |S6 | | M | | M | )
( +---+ +---+ +---+ ) ----------> ( +---+ +---+ +---+ )
( +---+ +---+ +---+ ) ( +---+ +---+ +---+ )
( | M | | M | | M | ) ( | M | | M | |S6 | )
( +---+ +---+ +---+ ) ( +---+ +---+ +---+ )
~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~
Figure 2. MPLS Domain Migration vs. SRv6 On-Demand Upgrade
3. Incremental Deployment Guidance for SRv6 Migration
The incremental deployment is the key for smooth migration to SRv6.
In order to quickly launch SRv6 network services and enjoy the
benefits brought by SRv6, the recommended incremental SRv6 deployment
steps are given as follows. These are based on the practical
deployment experience earned from the cases such as China Telecom
described in [I-D.matsushima-spring-srv6-deployment-status].
The referenced network topology is shown in Figure 3.
Xie, et al. Expires January 9, 2020 [Page 6]
Internet-Draft SRv6 Network Migration July 2019
/---- Path 1 ----\
+------+ +----+ +---/--+ +---\--+ +----+ +------+
|Site 1|----|PE 1|----|ASBR 1| IP Core |ASBR 2|----|PE 2|----|Site 2|
+------+ +----+ +---\--+ +---/--+ +----+ +------+
\---- Path 2 ----/
Figure 3. Reference Network Topology
Step1. All the network devices are upgraded to support IPv6.
Step 2. According to service demands, only a set of selected PE
devices are upgraded to support SRv6 in order to immediately deploy
SRv6 overlay VPN services. For instance, in Figure 3, PE1 and PE2
are SRv6-enabled.
Step 3. Besides the PE devices, some P devices are upgraded to
support SRv6 in order to deploy loose TE which enables network path
adjustment and optimization. SFC is also the possible service
provided by upgrading part of network devices.
Step 4. All the network devices are upgraded to support SRv6. In
this case, it is able to deploy strict TE, which enables the
deterministic network and other strict security inspection.
4. Migration Guidance for SRv6/SR-MPLS Co-existence Scenario
As the network migration to SRv6 is progressing, in most cases
SRv6-based services and SR-MPLS-based services will coexist.
As shown in Figure 4, in the Non-Standalone (NSA) case specified by
3GPP Release 15 that 5G networks will be supported by existing 4G
infrastructure. 4G eNB connects to CSG 2, 5G gNB connects to CSG 1,
and EPC connects to RSG 1.
For supporting the 4G services, network services need to be provided
between CSG 2 and RSG 1 for interconnecting 4G eNB and EPC, while for
the 5G services, network services need to be deployed between CSG 1
and RSG 1 for interconnecting 5G gNB and EPC. Meanwhile, for
supporting X2 interface between the eNB and gNB, network services
also need to be deployed between the CSG 1 and CSG 2.
Xie, et al. Expires January 9, 2020 [Page 7]
Internet-Draft SRv6 Network Migration July 2019
+-----+
| eNB |------\
+-----+ \
+-----+
|CSG 2|-------+-----+ +-----+ +-----+
/+-----+ |ASG 1|-------------|RSG 1|------| EPC |
+-----+ +--/--+ +-----+ +-----+ +-----+
| gNB |-----|CSG 1| Domain 1 | Domain 2 |
+-----+ +--\--+ +-----+ +-----+
\+-----+ |ASG 2|-------------|RSG 2|
|CSG 3|-------+-----+ +-----+
+-----+
Figure 4. A 3GPP Non-Standalone deployment case
As shown in Figure 4, in most of the current network deployments,
MPLS-based network services may have already existed between CSG 2
and RSG 1 for interconnecting 4G eNB and EPC for 4G sevices.
When 5G services are to be supported, more stringent network services
are required, e.g. low latency and high bandwidth. SRv6-based
network services could be deployed between CSG 1 and RSG 1 for
interconnecting 5G gNB and EPC.
In order to perform smooth network migration, dual-stack solution can
be adopted which deploy both SRv6 and MPLS stack in one node.
With the dual-stack solution, only CSG 1 and RSG 1 need to be
upgraded with SRv6/MPLS dual stack. In this case, CSG 1 can
immediately start SRv6-based network services to RSG 1 for supporting
5G services, but continue to using MPLS-based services to CSG 2 for
X2 interface communications. The upgrade at CSG 1 will not affect
the existing 4G services supported by the MPLS-based network services
between CSG 2 and RSG 1. RSG1 can provide MPLS services to CSG2 for
4G services as well as SRv6 services to CSG 1 for 5G services.
5. IANA Considerations
There are no IANA considerations in this document.
6. Security Considerations
TBD.
Xie, et al. Expires January 9, 2020 [Page 8]
Internet-Draft SRv6 Network Migration July 2019
7. References
7.1. Normative References
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-21 (work in progress), June 2019.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-ietf-spring-srv6-network-
programming-01 (work in progress), July 2019.
[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>.
[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>.
7.2. Informative References
[I-D.matsushima-spring-srv6-deployment-status]
Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6
Implementation and Deployment Status", draft-matsushima-
spring-srv6-deployment-status-01 (work in progress), May
2019.
[I-D.peng-spring-srv6-compatibility]
Peng, S. and Z. Li, "SRv6 Compatibility with Legacy
Devices", draft-peng-spring-srv6-compatibility-00 (work in
progress), October 2018.
Authors' Addresses
Xie, et al. Expires January 9, 2020 [Page 9]
Internet-Draft SRv6 Network Migration July 2019
Chongfeng Xie
China Telecom
China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District
Beijing 102209
China
Phone: +86-10-50902116
Email: xiechf.bri@chinatelecom.cn
Cong Li
China Telecom
China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District
Beijing 102209
China
Phone: +86-10-50902556
Email: licong.bri@chinatelecom.cn
Shuping Peng
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: pengshuping@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
Yaqun Xiao
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: xiaoyaqun@huawei.com
Xie, et al. Expires January 9, 2020 [Page 10]
