IDR Working Group R. Chen
Internet-Draft Ch. Dai
Intended status: Standards Track Sh. Peng
Expires: July 14, 2021 ZTE Corporation
January 10, 2021
Inter-domain Network Slicing via BGP-LU
draft-zhou-idr-inter-domain-lcu-02
Abstract
This document aims to solve inter-domain network slicing problems
using existing technologies. It attempts to establish multiple BGP-
LU LSPs of different colors for a prefix to stitch multiple network
segments.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 2
3. Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Advertising multiple paths . . . . . . . . . . . . . . . . . 3
5. Assigning Label(s) . . . . . . . . . . . . . . . . . . . . . 3
6. Inter-domain Network Slicing via BGP-LU . . . . . . . . . . . 4
7. Deploy Considerations . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Information References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
As described in [I-D.peng-teas-network-slicing], in the traditional
end to end inter-domain network slicing, BGP-LU to build inter-domain
MPLS LSP, and overlay service will be directly over BGP-LU LSP.
[RFC8277] specifies a set of procedures for using BGP to advertise
that a specified router has bound a specified MPLS label to a
specified address prefix. It's an effective way for inter-domain
labels, but it does not have the ability to select the underlying
network resources.
This document describes the colored BGP-LU LSP, which defines the
multiple paths for the same destination prefix can be advertised in
BGP UPDATE message, and each UPDATE message can contain the color
Extended Community [I-D.ietf-idr-tunnel-encaps] with different color
value, which helps to select the underlying resources.
2. Requirements notation
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 [RFC2119].
3. Color
[I-D.ietf-idr-tunnel-encaps] introduces the concept of color, which
is used as one of the KEY of SR policy
[I-D.ietf-spring-segment-routing-policy]. The color of SR policy
defines a TE purpose, which includes a set of constraints such as
bandwidth, delay, TE metric, etc.
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Color is used a policy keyword to help routing decisions and can be
carried through Community attribute [I-D.ietf-idr-tunnel-encaps] in
BGP. Each UPDATE SHOULD contain a Color Extended Community with a
specific color value, the Color Sub-TLV is only an opaque extended
community.
4. Advertising multiple paths
A BGP speaker can advertise multiple paths for a particular address
prefix by a Path identifier in the Extended NLRI Encoding as defined
in [RFC7911].
+--------------------------------+
| Path Identifier (4 octets) |
+--------------------------------+
| Length (1 octet) |
+--------------------------------+
| Prefix (variable) |
+--------------------------------+
The Path Identifier only identifies a path, not carrying any
particular semantics.In this document, it can be generated by the
<Prefix,Color> tuple. The assignment to the Path Identifier for a
path by a BGP speaker is purely a local matter.
Therefore, if a BGP speaker has two colors for the prefix P, which
correspond to two different paths, it may advertise two UPDATE NLRIs,
<prefix, pathid1> with color1 extended community and <prefix,
pathid2> with color2 extended community. Pathid1 and pathid2 in two
UPDATE NLRIs MUST be different.
Note that in this document, BGP speakers acting as border routers
that interact with external neighbors need to support advertising
multiple paths corresponding to the same prefix. Although multiple
paths have differnet path ids, they have the same next hop. As for
the procedures of mutual backup paths with the same prefix and the
differnet next hops, refer to [RFC7911].
5. Assigning Label(s)
[RFC8277] describes how to use BGP to bind MPLS label(s) to address
prefixes. The specific format of the UPDATE message is detailed in
Section 2 of [RFC8277].
[RFC8277] Section 3.2 details the process of modifying the Label
field during propagation. When propagating a SAFI-4 or SAFI-128
route, if the Network Address of Next Hop field has never changed,
the label field must remain unchanged. Otherwise, if the Network
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Address of Next Hop field is changed, the label field(s) of the
propagating route must contain the label(s) that is (are) bound to
the prefix at the new next hop. What the label changes to depends on
the local policy. However, LSPs with different color paths need to
have different label(s).
6. Inter-domain Network Slicing via BGP-LU
[RFC7911] defined that multiple paths for a particular address prefix
by a Path identifier can be advertised in BGP UPDATE message, and
each UPDATE message can contain the Color Extended Community
[I-D.ietf-idr-tunnel-encaps] with different color value. That is a
simple existing way to realize BGP-LU color function, and no protocol
extension required.
Consider the following example of establishing multiple BGP-LU LSPs
per different colors in a cross-domain scenario.
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<1.1.1.1, path-id1> <1.1.1.1, path-id1> <1.1.1.1, path-id1>
<color1, label200> <color1, label201> <color1, label201>
------------------------------------------------------------------>
.----. .------.
( ) ( )
.-( )-. .-( )-.
+---+---color1----+----+ +---+----color1----+---+
|PE1|\---SR-TE1---/|AS |-sub-if1 with slice1-|AS |\---SR-TE1---/|PE2|
| |/---SR-TE2---\|BR1|-sub-if2 with slice2-|BR2|/---SR-TE2---\| |
+---+---color2---- +---+ +---+--color2------+---+
( ) ( )
'--( AS1 )--' '--( AS2 )--'
( ) ( )
'-' '-'
------------------------------------------------------------------->
<1.1.1.1, path-id2> <1.1.1.1, path-id2> <1.1.1.1, path-id2>
<color2, label200> <color2, label202> <color2, label202>
Label Exchange Tables:
ASBR1: ASBR2:
inLabel outLabel nextHop inLabel outLabel nextHop
201 200 SR-TE1 201 201 sub-if1
202 200 SR-TE2 202 202 sub-if2
PE2:
prefix color outLabel nextHop
1.1.1.1 1 201 SR-TE1
1.1.1.1 2 202 SR-TE2
Figure 1: Example of Inter-domain Network Slicing via BGP-LU
In figure 1, PE1 advertises two paths: <1.1.1.1, path-id1> carries
the color1 attribute and <1.1.1.1, path-id2> carries the color2
attribute to ASBR1.PE1 advertises the binding between the prefix
1.1.1.1 and label 200. Because of the end node, both paths have the
same label value 200.
ASBR1 receives these two paths from PE1, and when sending to ASBR2,
it modifies the next hop to itself. And allocate two new labels
based on <prefix, path-id, color>. As shown in Figure 1, ASBR1 sends
two paths to ASBR2, <1.1.1.1, path-id1> carries color1+label201, and
<1.1.1.1, path-id2> carries color2+label202.
Similarly, ASBR2 also generates two different labels based on the
<prefix, path-id, color>. As shown in Figure 1, multiple end to end
BGP-LU LSPs are established.Different BGP-LU LSPs select the lower
SR-BE/TE tunnels according to their colors.
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7. Deploy Considerations
All BGP routers (PE1--ASBR1, ASBR1---ASBR2, ASBR2---PE2) SHOULD be
BGP-LU neighbors in advance. There may be multiple border routers to
ensure multipath backup. All routers require the ADD-PATH Capability
which is described in chapter 4 of [RFC7911].
This document not only supports interprovider VPNs while the customer
sites belong to different ASs, but also supports the Carrier-of-
Carriers VPNs while the customer site belong to the same AS.
Multiple operators are involved, so AS border routers may involve
color mapping, color namespaces, or color service chains. These
services can be delivered by the controller configurations or the
local configurations.
8. Security Considerations
TBD
9. IANA Considerations
TBD.
10. References
10.1. Normative References
[I-D.ietf-idr-tunnel-encaps]
Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
encaps-22 (work in progress), January 2021.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
[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>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
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[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>.
10.2. Information References
[I-D.peng-teas-network-slicing]
Peng, S., Chen, R., Mirsky, G., and F. Qin, "Packet
Network Slicing using Segment Routing", draft-peng-teas-
network-slicing-04 (work in progress), October 2020.
Authors' Addresses
Ran Chen
ZTE Corporation
Email: chen.ran@zte.com.cn
Chunning Dai
ZTE Corporation
Email: dai.chunning@zte.com.cn
Shaofu Peng
ZTE Corporation
Email: peng.shaofu@zte.com.cn
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