BGP Colorful Prefix Routing (CPR) for SRv6 based Services
draft-wang-idr-cpr-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Haibo Wang , Jie Dong , Jingrong Xie , Xinjun Chen | ||
| Last updated | 2023-03-25 | ||
| Replaced by | draft-ietf-idr-cpr | ||
| RFC stream | (None) | ||
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draft-wang-idr-cpr-01
Interdomain Routing Working Group H. Wang
Internet-Draft J. Dong
Intended status: Informational J. Xie
Expires: 27 September 2023 X. Chen
Huawei Technologies
26 March 2023
BGP Colorful Prefix Routing (CPR) for SRv6 based Services
draft-wang-idr-cpr-01
Abstract
This document describes a mechanism to advertise different IPv6
prefixes which are associated with different color attributes to
establish end-to-end intent-aware paths for SRv6 services. Such IPv6
prefixes are called "Colorful Prefixes", and this mechanism is called
Colorful Prefix Routing (CPR). In SRv6 networks, the colorful
prefixes are the SRv6 locators associated with different intent.
SRv6 services (e.g. SRv6 VPN services) with specific intent could be
assigned with SRv6 SIDs under the corresponding SRv6 locators, which
are advertised as colorful prefixes. This allows the SRv6 service
traffic to be steered into end-to-end intent-aware paths simply based
on the SRv6 Service SIDs. The existing IPv6 Address Family could be
used for the advertisement of IPv6 colorful prefixes, thus this
mechanism is easy to interoperate and allows incremental deployment
in multi-domain networks.
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 27 September 2023.
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Copyright Notice
Copyright (c) 2023 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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BGP CPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Colorful Prefix Allocation . . . . . . . . . . . . . . . 4
2.2. Colorful Prefix Advertisement . . . . . . . . . . . . . . 4
2.3. CPR to Intra-domain Path Resolution . . . . . . . . . . . 5
2.4. SRv6 Service Route Advertisement . . . . . . . . . . . . 6
2.5. SRv6 Service Steering . . . . . . . . . . . . . . . . . . 6
3. Encapsulation and Forwarding Processes . . . . . . . . . . . 6
3.1. CPR over SRv6 Intra-Domain Paths . . . . . . . . . . . . 7
3.2. CPR over MPLS Intra-Domain Paths . . . . . . . . . . . . 7
4. Operational Considerations . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
With the trend of using one common network to carry multiple types of
services, each service type can have different requirements on the
network. Such requirements are usually considered as the "intent" of
the service or customer, and is represented as an abstract notion
called "color".
In network scenarios where the services are delivered across multiple
network domains, there is need to provide the services with different
end-to-end paths to meet the intent.
[I-D.hr-spring-intentaware-routing-using-color] describes the problem
statements and requirements for inter-domain intent-aware routing.
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The inter-domain path can be established using either MPLS or IP data
plane. In MPLS based networks, the traditional inter-domain approach
is to establish an end-to-end LSP based on the BGP-LU mechanisms as
defined in [RFC8277]. Each domain or area border node needs to
perform label swapping for the end-to-end BGP-LU LSP, and encapsulate
the label stack which are used for the intra-domain LSP within the
subsequent network domain or area.
While in IP based networks, the IP reachability information can be
advertised to network nodes in different domains using BGP, so that
all the domain or area border nodes have the routes to the IP
prefixes of the destination node in other domains. With the
introduction of SRv6 [RFC8986], services are assigned with SRv6
Service SIDs [RFC9252], which are routable in the network according
to its SRv6 locator prefix. Thus the inter-domain path can be
established simply based on the inter-domain prefix routes, and the
BGP-LU inter-domain LSP mechanism is not necessary for IPv6 and SRv6
based networks.
This document describes a mechanism to advertise different IPv6
prefixes which are associated with different color attributes to
establish end-to-end intent-aware paths for SRv6 services. Such IPv6
prefixes are called "Colorful Prefixes", and this mechanism is called
Colorful Prefix Routing (CPR). In SRv6 networks, the colorful
prefixes are the SRv6 locators associated with different intent.
SRv6 services (e.g. SRv6 VPN services) with specific intent could be
assigned with SRv6 SIDs under the corresponding SRv6 locators, which
are advertised as colorful prefixes. This allows the SRv6 service
traffic to be steered into end-to-end intent-aware paths simply based
on the SRv6 Service SIDs. The existing IPv6 Address Family could be
used for the advertisement of IPv6 colorful prefixes, thus this
mechanism is easy to interoperate and allows incremental deployment
in multi-domain networks.
2. BGP CPR
This section describes the BGP CPR mechanisms. More specifically,
section 2.1 describes the allocation of the IPv6 colorful prefixes,
section 2.2 describes the advertisement of colorful prefixes in BGP,
section 2.3 describes the resolution of CPR routes to the intra-
domain paths, and section 2.4 describes the steering of SRv6 services
to CPR routes.
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2.1. Colorful Prefix Allocation
In SRv6 networks, an SRv6 locator needs to be allocated for each
node. In order to distinguish N different intent, a PE node needs to
be allocated with N SRv6 locators, each of which is associated a
different intent. This can be achieved by splitting the base SRv6
locator of the node into N sub-locators, and these sub-locators are
called colorful locators.
For example, node PE2 is allocated with the base SRv6 Locator
2001:db8:aaaa:1::/64. In order to provide 16 different intent, this
base SRv6 Locator is split into 16 sub-locators from
2001:db8:aaaa:1:0000::/68 to 2001:db8:aaaa:1:F000::/68, each of these
sub-locators is associated with a different intent, such as low-
delay, high-bandwidth, etc.
2.2. Colorful Prefix Advertisement
After the allocation of colorful prefixes on a PE node, routes to
these colorful prefixes need to be advertised both in the local
domain and also to other domains using BGP, so that the SRv6 services
routes could be resolved using the corresponding CPR route.
In a multi-domain IPv6 network, the IPv6 unicast Address Family/
Subsequent Address Family (AFI/SAFI = 2/1) [RFC2545] is used for the
advertisement of the colorful prefix routes. The color extended
community [RFC9012] is carried with the colorful prefix route. The
procedure of colorful prefix advertisement is described using an
example with the following topology:
Color Domain: Color Domain: Color Domain:
C11, C12,... C21, C22,... C31, C32,...
+--------------+ +--------------+ +-------------+
| | | | | |
| [ASBR11]---[ASBR21] [ASBR23]---[ASBR31] |
--[PE1] [P1] | X | [P2] | X | [P3] [PE3]--
| [ASBR12]---[ASBR22] [ASBR24]---[ASBR32] |
| | | | | |
+--------------+ +--------------+ +-------------+
AS1 AS2 AS3
Colorful Prefixes of PE3:
Low delay: 2001:db8:aaaa:1:1000::/68
high bandwidth: 2001:db8:aaaa:1:2000::/68
...
Figure 1. Example Topology for CPR Route Illustration
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Assume PE3 is provisioned with two different colorful prefixes CLP-1
and CLP-2 for two different intent such as "low-delay" and "high-
bandwidth" respectively. Note that in different network domains, the
color representing the same intent may be different. In this
example, the color used for "low-delay" in AS1, AS2 and AS3 are C11,
C21 and C31 respectively, and the color used for "high-bandwidth" in
AS1, AS2 and AS3 are C12, C22 and C32 respectively.
* PE3 originates BGP IPv6 unicast (AFI/SAFI=2/1) route for the
colorful prefixes PE3:CL1:: and PE3:CL2::. Each route should carry
the corresponding color extended community C31 or C32. PE3 also
advertises a route for the base SRv6 Locator prefix PE3:BL, and
there is no color extended community carried with this route.
* ASBR31 and ASBR32 receive the CPR routes of PE3, and advertise the
CPR routes further to ASBR23 and ASBR24 with next-hop set to
itself.
* ASBR23 and ASBR24 receive the CPR routes of PE3. As the color-to-
intent mapping in AS2 is different from AS3, the color in the
received CPR routes are changed to the corresponding color in AS2,
e.g. C21 and C22. ASBR23 and ASBR 24 advertise the CPR routes
further in AS2 with the next-hop set to itself.
* The behavior of ASBR21 and ASBR22 are similar to the behavior of
ASBR31 and ASBR32.
* The behavior of ASBR11 and ASBR12 are similar to behavior of
ASBR31 and ASBR32. The color in the received CPR routes are
changed to the corresponding color in AS1, e.g. C11 and C12.
In network scenarios where some of the intermediate network domains
are MPLS based, the CPR routes may still be advertised using the IPv6
unicast address family (AFI/SAFI=2/1) in the MPLS-based intermediate
domains, and at the MPLS domain border nodes, some route resolution
policy could be used to make the CPR routes resolved to intra-domain
intent-aware MPLS LSPs. Another possible mechanism is to use the
IPv6 Labeled Unicast address family (AFI/SAFI=2/4) to advertise the
CPR routes in the MPLS domains, the detailed procedure is described
in Section 7.1.2.1 of [I-D.agrawal-spring-srv6-mpls-interworking].
2.3. CPR to Intra-domain Path Resolution
A domain border node which receives a CPR route can resolve the CPR
route to an intra-domain color-aware path based on the tupple (N, C),
where N is the next-hop of the CPR route, and C is the color extended
community of the CPR route. The intra-domain color-aware path could
be built with any of the following mechanisms:
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* SRv6 or SR-MPLS Policy
* SRv6 or SR-MPLS Flex-Algo
* RSVP-TE
For example, PE1 receives a CPR route to PE3:CL1 with color C31 and
next-hop ASBR11, it can resolve the CPR routes to an intra-domain
SRv6 Policy based on the tupple (ASBR11, C31).
The intra-domain path resolution scheme could be based on any
existing tunnel resolution policy, and new tunnel resolution
mechanisms could be introduced if needed.
2.4. SRv6 Service Route Advertisement
For an SRv6 service which is associated with a specific intent, the
SRv6 Service SID could be allocated under the corresponding colorful
locator prefix. For example, on PE3 in the example topology, an SRv6
VPN service with the low delay intent can be allocated with the SRv6
End.DT4 SID 2001:db8:aaaa:1:1000::0100, where
2001:db8:aaaa:1:1000::/68 is the SRv6 colorful prefix for low delay
service.
The SRv6 service routes are advertised using the mechanism defined in
[RFC9252], the SRv6 Service SID is carried using the BGP Prefix-SID
attribute [RFC8669]. The inter-domain VPN Option C is used, which
means the next-hop of the SRv6 service route is set to the
originating PE and not changed. Since the intent of the service is
embedded in the SRv6 service SID, the SRv6 service route does not
need to carry the color extended community.
2.5. SRv6 Service Steering
With the CPR routing mechanism, the ingress PE node which receives
the SRv6 service routes follows the behavior of SRv6 best-effort
forwarding. The SRv6 service SID carried in the service route is
used as the destination address in the outer IPv6 header encapsulated
to the service packet. If the corresponding CPR route has been
received and installed, the SRv6 service SID can match with the
colorful prefix of the CPR route, then the intra-domain color-aware
path which the CPR route is resolved to is used for forwarding the
SRv6 service traffic.
3. Encapsulation and Forwarding Processes
This section describes the encapsulation and forwarding process of
data packets which are matched with the corresponding CPR route.
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3.1. CPR over SRv6 Intra-Domain Paths
Following is an illustration of the packet encapsulation and
forwarding process of CPR over SRv6 Policy. The abstract
representation of IPv6 and SRH in section 6 of [RFC8754] is used.
PE3 is provisioned with a colorful prefix PE3:C1 for "low-delay".
In AS1, the SRv6 Policy for (ASBR11, C11) is represented with SID
list (P1, BR11).
In AS2, the SRv6 Policy for (ASBR23, C21) is represented with the SID
list (P2, BR23).
In AS3, the SRv6 Policy for (PE3, C31) is represented with the SID
list (P3, PE3).
For packets which belong to an SRv6 VPN service associated with the
SRv6 Service SID PE3:CL1.DT, the packet encapsulation and forwarding
process is shown as below:
PE1 ->P1 : (PE1, P1)(PE3:CL1.DT, BR11; SL=2)(C-pkt)
P1 ->BR11: (PE1, BR11)(PE3:CL1.DT, BR11; SL=1)(C-pkt)
BR11->BR21: (PE1, PE3:CL1.DT)(C-pkt)
BR21->P2 : (PE1, P2)(PE3:CL1.DT, BR23; SL=2)(C-pkt)
P2 ->BR23: (PE1, BR23)(PE3:CL1.DT, BR23; SL=1)(C-pkt)
BR23->BR31: (PE1, PE3:CL1.DT)(C-pkt)
BR31->P3 : (PE1, P3)(PE3:CL1.DT, PE3; SL=2)(C-pkt)
P3 ->PE3 : (PE1, PE3)(PE3:CL1.DT, PE3; SL=1)(C-pkt)
In some network domains, SRv6 Flex-Algo may be used to provide intent
aware intra-domain path. The encapsulation is similar to the case
with SRv6 Policy.
3.2. CPR over MPLS Intra-Domain Paths
In network scenarios where some of the network domains use MPLS based
data plane, the CPR route can be resolved over a color-aware intra-
domain MPLS LSP. Such intra-domain MPLS LSP may be established using
SR-MPLS Policy, SR-MPLS Flex-Algo or RSVP-TE.
The encapsulation and forwarding of SRv6 service packets over an
intra-domain MPLS LSP is based on the MPLS mechanisms as defined in
[RFC3031] [RFC3032] and [RFC8660].
In AS1, the SR-MPLS Policy for (ASBR11, C11) is represented with
Label-stack (P1, BR11).
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In AS2, the SR-MPLS Flex-Algo for (ASBR23, C21) is represented with
Label-stack (BR23).
In AS3, the SR-MPLS Policy for (PE3, C31) is represented with Label-
stack (P3, PE3).
For packets which belong to an SRv6 VPN service associated with the
SRv6 Service SID PE3:CL1.DT, the packet encapsulation and forwarding
process is shown as below:
PE1 ->P1 : Label-stack (P1, BR11) (PE1, PE3:CL1.DT)(C-pkt)
P1 ->BR11: Label-stack (BR11) (PE1, PE3:CL1.DT)(C-pkt)
BR11->BR21: (PE1, PE3:CL1.DT)(C-pkt)
BR21->P2 : Label-stack (BR23) (PE1, PE3:CL1.DT)(C-pkt)
P2 ->BR23: Label-stack (BR23) (PE1, PE3:CL1.DT)(C-pkt)
BR23->BR31: (PE1, PE3:CL1.DT)(C-pkt)
BR31->P3 : Label-stack (P3, PE3) (PE1, PE3:CL1.DT)(C-pkt)
P3 ->PE3 : Label-stack (PE3) (PE1, PE3:CL1.DT)(C-pkt)
4. Operational Considerations
When the colorful prefixes are assigned as the sub-locators of the
node's base SRv6 locator, the IPv6 unicast route of the base locator
prefix is the covering prefix of all the colorful locator prefixes.
To make sure the colorful locator prefixes can be distributed to the
ingress PE nodes along the border nodes, it is required that route
aggregation be disabled for IPv6 unicast routes which carries the
color extended community.
All the border nodes and the ingress PE nodes needs to install the
colorful locator prefixes into the RIB and FIB. For transit domains
which support the CPR mechanism, the border nodes can use the tupple
(N, C) to resolve the CPR routes to intent-aware intra-domain paths.
For transit domains which do not support the CPR mechanism, the
border nodes could resolve the CPR routes over a best effort intra-
domain path to the next-hop N, while the CPR route will be advertised
further to the downstream domains with only the next-hop changed to
itself. This allows the CPR routes to be resolved to intent-aware
intra-domain paths in any network domains which support the CPR
mechanism, while can fall back to resolve over best-effort intra-
domain paths in the legacy network domains.
5. IANA Considerations
This document makes no request of IANA.
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6. Security Considerations
The mechanism described in this document provide an approach for
inter-domain intent-aware routing based on existing BGP protocol
mechanisms. It does not introduces any additional security
considerations than those described in [RFC4271] and [RFC4272].
7. Acknowledgements
The authors would like to thank Shunwan Zhuang and Zhibo Hu for the
review and discussion.
8. References
8.1. Normative References
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
DOI 10.17487/RFC2545, March 1999,
<https://www.rfc-editor.org/info/rfc2545>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
[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>.
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[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
8.2. Informative References
[I-D.agrawal-spring-srv6-mpls-interworking]
Agrawal, S., Ali, Z., Filsfils, C., Voyer, D., Dawra, G.,
and Z. Li, "SRv6 and MPLS interworking", Work in Progress,
Internet-Draft, draft-agrawal-spring-srv6-mpls-
interworking-11, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-agrawal-
spring-srv6-mpls-interworking-11>.
[I-D.hr-spring-intentaware-routing-using-color]
Hegde, S., Rao, D., Sangli, S. R., Agrawal, S., Filsfils,
C., Talaulikar, K., Patel, K., Uttaro, J., Decraene, B.,
Bogdanov, A., Jalil, L., Alston, A., Xu, X., Gulko, A.,
Khaddam, M., Contreras, L. M., Steinberg, D., Guichard,
J., Henderickx, W., and Co-authors, "Problem statement for
Inter-domain Intent-aware Routing using Color", Work in
Progress, Internet-Draft, draft-hr-spring-intentaware-
routing-using-color-01, 14 March 2023,
<https://datatracker.ietf.org/doc/html/draft-hr-spring-
intentaware-routing-using-color-01>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
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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>.
Authors' Addresses
Haibo Wang
Huawei Technologies
China
Email: rainsword.wang@huawei.com
Jie Dong
Huawei Technologies
China
Email: jie.dong@huawei.com
Jingrong Xie
Huawei Technologies
China
Email: xiejingrong@huawei.com
Xinjun Chen
Huawei Technologies
China
Email: ifocus.chen@huawei.com
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