Network Working Group H. Tian
Internet-Draft F. Zhao
Intended status: Informational CAICT
Expires: May 7, 2020 C. Xie
China Telecom
T. Li
J. Ma
China Unicom
S. Peng
Z. Li
Y. Xiao
Huawei Technologies
November 4, 2019
SRv6 Deployment Consideration
draft-tian-spring-srv6-deployment-consideration-00
Abstract
SRv6 has significant advantages over SR-MPLS and has attracted more
and more attention and interest from network operators and verticals.
Smooth network migration towards SRv6 is a key focal point and this
document provides network migration guidance and recommendations on
solutions in various scenarios. Deployment cases with SRv6 are also
introduced.
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."
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This Internet-Draft will expire on May 7, 2020.
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
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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. Deployment cases . . . . . . . . . . . . . . . . . . . . . . 8
5.1. China Telecom Si'chuan . . . . . . . . . . . . . . . . . 9
5.2. China Unicom . . . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
SRv6 is the instantiation of Segment Routing deployed on the IPv6
data plane[RFC8200]. Therefore, in order to support SRv6, the
network must first be enabled for IPv6. Over the past several years,
IPv6 has been actively promoted all over the world, and the
deployments of IPv6 have been ever-increasing which provides the
basis for the deployments of SRv6.
With IPv6 as its data plane, for network migration towards SRv6, both
software and hardware need to be upgraded. Compared with other new
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protocols, only IGP and BGP need to be extended to support SRv6,
which significantly simplifies the software upgrade required. While
the hardware needs to support the new SRv6 header
SRH[I-D.ietf-6man-segment-routing-header], the design of SRv6 assures
compatibility with the existing IPv6 network as an SRv6 SID is
designed as a 128-bit IPv6 address and the encapsulation of 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 number of services supported by SRv6 increase, e.g. SFC,
network slicing, iOAM etc., more SIDs in the SRH may impose new
requirements on the hardware. Besides upgrading the hardware,
various solutions [I-D.peng-spring-srv6-compatibility] have already
been proposed to relieve the imposed pressure on the hardware, such
as Binding SID (BSID) etc. to guarantee the compatibility with the
existing network. On the other hand SRv6 has many more advantages
over SR-MPLS for the network migration to support new services.
This document summarizes the advantages of SRv6 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
large scale networking scenarios.
2.1. IP Route Aggregation
The increasing complexity of service deployment is of concern for
network operators, especially in large-scale networking scenarios.
With solutions such as multi-segment PW and Option A [RFC4364], the
number of service-touch points has increased, and the services, with
associated OAM features 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 route LSPs might need
to be imported, which places big challenges on the capabilities of
the edge nodes.
o With SRv6, owing to its native IP feature of route aggregation as
shown in Figure 1b, the aggregated routes can be imported across
network domains. For large scale networking, only very few
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aggregated routes are needed in order to 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 need to be imported to other
domains.
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o With SR-MPLS, SRGB and Node SID need overall network-wide
planning, and in the cross-domain scenario, it is difficult or
sometimes even impossible to perform as the node SIDs in different
domains may collide. BGP Prefix SID can be used for the cross-
domain SID import, but the network operator must be careful when
converting the SID to avoid SID collision. Moreover, the pre-
allocated SRGB within each domain needs to consider the total
number of devices in all other domains, which raises difficulties
for the network-wide planning.
o With SRv6, owing to its native IP feature of route reachability,
if the IPv6 address space is carefully planned, and the aggregated
routes are imported by using BGP4+ (BGP IPv6), 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
Regardless of which migration option is chosen, big changes in a wide
area is required at the initial stage therefore causing a long time-
to-market.
In contrast, the network can be migrated to SRv6 on demand. Wherever
the services need to be turned 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 be aware of SRv6. When Traffic
Engineering (TE) services are needed, only the key nodes along the
path need to be upgraded to support SRv6.
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(~~~~~~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
Incremental deployment is the key for a smooth network 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 practical deployment
experience earned from the use cases described in
[I-D.matsushima-spring-srv6-deployment-status].
The referenced network topology is shown in Figure 3.
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/---- 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 a possible service provided
by upgrading some of the network devices.
Step 4. All the network devices are upgraded to support SRv6. In
this case, it is now possible to deploy strict TE, which enables the
deterministic networking 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, 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.
To support 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, to support
X2 interface between the eNB and gNB, network services also need to
be deployed between the CSG 1 and CSG 2.
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+-----+
| 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 services.
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, a dual-stack solution
can be adopted which deploys 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 support of
5G services, but continue to use 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. Deployment cases
With the current network, the launch of leased line service is slow,
the network operation and maintainence is complex, and the
configuration points are many. SRv6 can solve the issues above.
There have already been several successful SRv6 deployments following
the incremental deployment guidance shown in Section 3.
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5.1. China Telecom Si'chuan
China Telecom Si'chuan (Si'chuan Telecom) has enabled SRv6 at the PE
node of the Magic-Mirror DC in Mei'shan, Cheng'du, Pan'zhihua and
other cities. The SRv6 BE tunnel has been deployed through the 163
backbone network which has the IPv6 capability. It enables the fast
launch of the Magic-Mirror video service, the interconnection of the
DCs in various cities, and the isolation of video services. The
deployment case is shown in Figure 6.
/----------163--------\
+------+ / \ +-------+
| Magic| +----+ +--/-+ +--\-+ +----+ | Magic |
|Mirror|----|PE 1|----|CR 1| IP Backbone |CR 2|----|PE 2|----|Mirror |
| DC 1 | +----+ +--\-+ +--/-+ +----+ | DC 2 |
+------+ \ / +-------+
+-\---+ +---/-+
|ASBR1|-----CN2-----|ASBR2|
+-----+ +-----+
IGP/IBGP EBGP IGP/IBGP
|<------->|<-------------------------->|<-------->|
EBGP VPNv4 Peer
|<----------------------------------------------->|
L3VPN over SRv6
|<----------------------------------------------->|
Figure 6. China Telecom Si'chuan deployment case
As shown in Figure 6, IGP (some cities such as Chengdu deploy ISIS,
while other cities such as Panzhihua deploy OSPF) and IBGP are
deployed between PE and CR, and EBGP is deployed between CRs of
cities in order to advertise the aggregation route. EBGP VPNv4 peers
are set up between PEs in different cities to deliver VPN private
network routes.
The packet enters the SRv6 BE tunnel from the egress PE of DC, and
the packet is forwarded according to the Native IP of the 163
backbone network. When the packet reaches the peer PE, the SRH is
decapsulated, and then the IP packet is forwarded in the VRF
according to the service SID (for example, End.DT4).
In order to further implement the path selection, ASBRs can be
upgraded to support SRv6. Different SRv6 policies are configured on
the DC egress PE so that different VPN traffic reaches the peer PE
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through the 163 backbone network and the CN2 backbone network
respectively.
5.2. China Unicom
China Unicom has deployed SRv6 L3VPN over 169 IPv6 backbone network
from Guangzhou to Beijing to provide inter-domain Cloud VPN service.
The deployment case is shown in Figure 7.
/-------------\ /------------\ /-----------\
+-/-+ Guangzhou +-\-+ +-/-+ IPv6 +-\-+ +-/-+ Beijing +-\-+
|PE1| |CR1|---|CR2| Backbone |CR3|---|CR4| |PE2|
+-\-+ Metro +-/-+ +-\-+ 169 +-/-+ +-\-+ Metro +-/-+
\-------------/ \------------/ \-----------/
|<--OSPF/ISIS-->|<-EBGP->|<-Native IPv6->|<-EBGP->|<-OSPF/ISIS->|
|<----------------------- EBGP VPNv4 Peer --------------------->|
|<----------------------- L3VPN over SRv6 --------------------->|
Figure 7. China Unicom SRv6 L3VPN case
In Guangzhou and Beijing metro networks, routers exchange basic
routing information using IGP(OSPF/ISIS). The prefixes of IPv6
loopback address and SRv6 locator of routers are different, and both
of them need to be imported into the IGP. The 169 backbone is a
native IPv6 network. Between metro and backbone, the border routers
establish EBGP peer with each other, e.g. CR1 with CR2, CR3 with
CR4, to form basic connectivity. All of these constitute the
foundation of overlay services, and have not been changed.
PE1 and PE2 establish EBGP peer and advertise VPNv4 routes with each
other. If one site connects to two PEs, metro network will use multi
RD, community and local preference rules to choose one best route and
one backup.
After basic routing among networks and VPN routes between the two PEs
are all ready, two PEs encapsulate and forward VPN traffic within
SRv6 tunnel. The tunnel is SRv6 best effort (BE) tunnel. It
introduces only outer IPv6 header but not SRH header into traffic
packets. After encapsulation, the packet is treated as common IPv6
packet and forwarded to the egress PE, which performs decapsulation
and forwards the VPN traffic according to specific VRF.
Guangdong Unicom has also lauched the SRv6 L3VPN among Guangzhou,
Shenzhen, and Dongguan, which has passed the interop test between
different vendors.
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With SRv6 enabled at the PE devices, the VPN service can be launched
very quickly without impact on the existing traffic. With SRv6 TE
further deployed, more benefits of using SRv6 can be exploited.
6. IANA Considerations
There are no IANA considerations in this document.
7. Security Considerations
TBD.
8. Contributors
Hailong Bai
China Unicom
China
Email:
Jichun Ma
China Unicom
China
Email:
Ruizhao Hu
Huawei
China
Email: huruizhao@huawei.com
Jianwei Mao
Huawei
China
Email: maojianwei@huawei.com
9. References
9.1. Normative References
[]
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-26 (work in progress), October 2019.
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[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-05 (work in progress), October 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>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
DOI 10.17487/RFC5659, October 2009,
<https://www.rfc-editor.org/info/rfc5659>.
[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>.
9.2. 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-02 (work in progress),
October 2019.
[I-D.peng-spring-srv6-compatibility]
Peng, S., Li, Z., Xie, C., and L. Cong, "SRv6
Compatibility with Legacy Devices", draft-peng-spring-
srv6-compatibility-01 (work in progress), July 2019.
Authors' Addresses
Hui Tian
CAICT
China
Email: tianhui@caict.ac.cn
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Feng Zhao
CAICT
China
Email: zhaofeng@caict.ac.cn
Chongfeng Xie
China Telecom
China
Email: xiechf.bri@chinatelecom.cn
Tong Li
China Unicom
China
Email: litong@chinaunicom.cn
Jichun Ma
China Unicom
China
Email: majc16@chinaunicom.cn
Shuping Peng
Huawei Technologies
China
Email: pengshuping@huawei.com
Zhenbin Li
Huawei Technologies
China
Email: lizhenbin@huawei.com
Yaqun Xiao
Huawei Technologies
China
Email: xiaoyaqun@huawei.com
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