IDR R. Chen
Internet-Draft Ch. Dai
Intended status: Standards Track Sh. Peng
Expires: 8 September 2022 ZTE Corporation
7 March 2022
Inter-domain Network Slicing via BGP-LU
draft-zhou-idr-inter-domain-lcu-04
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/multiple prefix to stitch multiple
network segments.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Advertising multiple paths . . . . . . . . . . . . . . . . . 3
4. Assigning Label(s) . . . . . . . . . . . . . . . . . . . . . 4
5. Inter-domain Network Slicing via BGP-LU . . . . . . . . . . . 4
5.1. Colored BGP-LU Capability Advertisement . . . . . . . . . 4
5.2. Colored BGP-LU realized . . . . . . . . . . . . . . . . . 5
6. SRv6 support . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Deploy Considerations . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
In the traditional end to end inter-domain network slicing, BGP-LU is
used to build inter-domain MPLS LSP, and overlay service will be
directly over BGP-LU LSP. For an E2E BGP-LU LSP, if overlay service
has TE requirements that defined by a color, the BGP-LU LSP need also
have a sense of color, i.e., BGP-LU label could be allocated per
color.
[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 contains two
options:
* One is to define the multiple paths for the same destination
prefix and advertise in BGP UPDATE message, and each UPDATE
message can contain the color Extended Community [RFC9012] with
different color value, which helps to select the underlying
resources.This mode require additional path function defined in
[RFC7911].
* The other is that multiple prefixes and multiple colors are
configured on PE. One prefixes corresponds to one color. This
mode does not require to additional path function.
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1.1. 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].
2. Color
[RFC9012] 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.
TO help routing decisions , each UPDATE may contain a Color Extended
Community with a specific color value, the Color Sub-TLV is only an
opaque extended community.
3. 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) |
+--------------------------------+
Figure 1
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
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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].
4. Assigning Label(s)
[RFC8277] describes how to use BGP to bind MPLS label(s) to the
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
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).
5. Inter-domain Network Slicing via BGP-LU
5.1. Colored BGP-LU Capability Advertisement
A BGP speaker that uses Colored BGP-LU Extensions SHOULD use the
Capability Advertisement procedures [RFC3392] to determine whether
the speaker could use Colored BGP-LU Extensions with a particular
peer.
The fields in the Capabilities Optional Parameter are set as
follows：
* The Capability Code field TBD1 (which indicates Colored BGP-LU
Extensions capabilities).
* The Capability Length field is set to 4.
* The Capability Value field is defined as:
+------------------------------------------------+
| Address Family Identifier (2 octets) |
+------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+
| reseve (1 octet) |
+------------------------------------------------+
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Figure 2
where:
AFI-Address Family Identifier (16 bit), The values is 1 "IPV4"or 2
"IPV6".
SAFI-Subsequent Address Family Identifier (8 bit), The values is 1
"Unicast"or 4(BGP LU).
Res.-Reserved (8 bit) field. SHOULD be set to 0 by the sender and
ignored by the receiver.
Note that not setting the field value to 0 may create issues for a
receiver not ignoring the field. In addition, this definition is
problematic if it is ever attempted to redefine the field.
5.2. Colored BGP-LU realized
[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
[RFC9012] with different color value. That is a simple existing way
to realize BGP-LU color function, and only an extension of Colored
BGP-LU capability advertisement is 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 3
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 underlay
SR-BE/TE tunnels according to their colors.
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6. SRv6 support
Colored BGP-LU can be also used to setup end-to-end color-aware
connectivity using Segment Routing over IPv6 (SRv6) [RFC8402].
As defined in [I-D.ietf-bess-srv6-services],to provide SRv6 service
with underlay SRv6 policy connectivity, the egress PE signals the BGP
overlay service route with SRv6 Service SID and color extended
community . The ingress PE encapsulates the payload in an outer IPv6
header which contains the underlay SRv6 policy segment list and the
overlay Service SID.
In addition, another solution is to provide SRv6 servcie with
underlay SRv6 best-effort connectivity that is created by global IPv6
(AFI/SAFI 2/1) with color extended community. The underlay SRv6 SID
is allocated based on <global IPv6, path-id, color>. The ingress PE
encapsulates the payload in an outer IPv6 header which contains the
underlay SRv6 SID and the Service SID.
7. Deploy Considerations
All BGP routers (PE1--ASBR1, ASBR1---ASBR2, ASBR2---PE2) SHOULD be
Colored BGP-LU neighbors in advance. There may be multiple border
routers to ensure multipath backup. All routers require the Colored
BGP-LU Capability Advertisement.If transit network domains that do
not support Colored BGP-LU，Processed as follows：
* When the Colored BGP-LU neighbor receives the BGP-LU routes, if it
continues to advertise the BGP-LU routes to the upstream neighbor
that supports the Colored BGP-LU, the BGP-LU routes shouldn't be
changed to the Colored BGP-LU routes.
* When receiving the Colored BGP-LU advertisement from the neighbor
that supports Colored BGP-LU, if the advertisement continues to be
advertised to the upstream neighbor that does not support Colored
BGP-LU, the advertisement should be changed to BGP-LU
advertisement, that is, advertise one out of multiple path.
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.
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8. Acknowledgements
TBD.
9. IANA Considerations
TBD.
10. Security Considerations
TBD.
11. Normative References
[I-D.ietf-bess-srv6-services]
Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
Overlay Services", Work in Progress, Internet-Draft,
draft-ietf-bess-srv6-services-12, 5 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
srv6-services-12>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-19, 5 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
segment-routing-policy-19>.
[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>.
[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>.
[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>.
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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>.
Authors' Addresses
Ran Chen
ZTE Corporation
Nanjing
China
Email: chen.ran@zte.com.cn
Chunning Dai
ZTE Corporation
Nanjing
China
Email: dai.chunning@zte.com.cn
Shaofu Peng
ZTE Corporation
Nanjing
China
Email: peng.shaofu@zte.com.cn
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