IDR Working Group Louis Chan INTERNET-DRAFT Intended status: Experimental Juniper Networks Expires: Sep 6, 2021 Mar 6, 2021 Color Operation with BGP Label Unicast draft-chan-idr-bgp-lu2-03.txt Abstract This document specifies how to carry colored path advertisement via an enhancement to the existing protocol BGP Label Unicast. It would allow backward compatibility with RFC8277. The targeted solution is to use stack of labels advertised via BGP Label Unicast 2.0 for end to end traffic steering across multiple IGP domains. The operation is similar to Segment Routing. This proposed protocol will convey the necessary reachability information to the ingress PE node to construct an end to end path. Another two problems addressed here are the interworking with Flex-Algo, and the MPLS label space limit problem. Please note that there is a major change of protocol format starting from version 01 draft. Except the optional BGP capability code, these rest of BGP attributes used in this draft are defined in previous RFC or in use today in other scenario. 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 http://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 Sep 6, 2021. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. Chan Expires Sep 6, 2021 [Page 1] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://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. Conventions used in this document .................................... 4 3. Carrying Label Mapping Information with Color and Label Stack ........ 4 3.1. Use of Add-path to advertise multiple color paths ............... 4 3.2. Color extended community for BGP Labeled Unicast ................ 4 3.3. Color extended community for service prefixes ................... 5 3.4. Color Slicing Capability ........................................ 6 4. Uniqueness of path entries ........................................... 7 5. AIGP consideration ................................................... 8 6. Explicit Withdraw of a ................... 8 7. Error Handling Procedure ............................................. 8 8. Controller Compatibility ............................................. 8 9. Interworking with Flex Algo .......................................... 8 10. Label stacking to increase label space .............................. 9 11. Security Considerations ............................................. 9 12. IANA Considerations ................................................. 9 13. References ......................................................... 9 13.1. Normative References ........................................... 9 13.2. Informative References ......................................... 9 14. Acknowledgments ................................................... 10 1. Introduction The proposed protocol is aimed to solve interdomain traffic steering, with different transport services in mind. One application is low latency service across multiple IGP domains, which could scale up to 100k or more routers network. BGP is a flexible protocol. With additional of color attribute to BGP Label Unicast, a path with specific color would be given a meaning in application - a low latency path, a fully protected path, or a path for diversity. The stack of labels would mean an end to end path across domains through each ABR or ASBR. Each ABR or ASBR will take one label from the stack, and hence pick the forwarding path to next ABR, ASBR, or the final destination. And the label in the stack may be derived from any of the below - Prefix SID - Binding SID for RSVP LSP Chan Expires Sep 6, 2021 [Page 2] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 - Binding SID for SR-TE LSP - Local assigned label The enhancement to the original RFC8277 is to add color extended community, with multiple advertisement allowed. The result is similar to multi-topology BGP-LU with different colors. With Add-path [RFC7911] feature, non color RIB and colored RIB could be advertised to the BGP neighbors without new additional attributes. Add-path capability is required advertise multiple paths with same prefix but different colors. A new [BGP-CAP] should be required to enforce such slicing operation during negotiation. On the other hand, to enable the service prefixes to be mapped accordingly, the L3VPN, L2VPN, EVPN and IP prefix with BGP signaling, the color extended community is also added there. In the PE node, the service prefixes with color will be matched to a transport tunnel with the same color. The following is an example. Between PE1 and PE2, there is a VPN service running with label 16, which is associated with color 100. PE1----ABR1-----ABR2-----PE2 PE1 will send the following labels with a color 100 path plus VPN label [2001 13001 801 16], where 2001 - SR label to reach ABR1 13001 - a Binding-SID label for ABR1-ABR2 tunnel. Underlying tunnel type is RSVP-TE 801 - a Binding-SID label for ABR2-PE2 tunnel. Underlying tunnel type is SR-TE 16 - a VPN label, which is signaled via other means [2001 13001 801] - denotes the label stack for this color 100 path to reach PE2 The document here is going to describe how PE1 gains enough information to build this label stack across routing domains. If PE1 wants to reach PE2 with another colored path, say color 200, the label stack could be different. At the same time, this architecture is also controller friendly, since all the notation is Segment Routing compatible, like use of Binding-SID. The above architecture could be used in conjunction with Flex-Algo [FLEXAGLO] where one color could represent a Flex Algorithm. e.g. color 128 equals to Algo 128 When using with Flex Algo in huge network, there could be label space limit. The MPLS label 20 bits long and the maximum label space is around 1 million. In order to represent more IPv4 or IPv6 nodes, label stacking method is recommended. One IP Chan Expires Sep 6, 2021 [Page 3] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 loopback address could be represent by one or more labels. In this case, (20 bits x n) of label address space is possible. 2. Conventions used in this document 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]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying significance described in RFC 2119. 3. Carrying Label Mapping Information with Color and Label Stack 3.1. Use of Add-path to advertise multiple color paths The use of Path Identifier is to allow multiple advertisement of the same prefix but with different colors or null color. The extended NLRI format would be like this +--------------------------------+ | Path Identifier (4 octets) | +--------------------------------+ | Length (1 octet) | +--------------------------------+ | Label (3 octets) ~ +--------------------------------+ ~ Label (3 octets) | +--------------------------------+ | Prefix (variable) | +--------------------------------+ 3.2. Color extended community for BGP Labeled Unicast The addition of Color Extended Community is an opaque extended community from RFC4360 and RFC5512. The draft allows multiple color values advertisement. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Chan Expires Sep 6, 2021 [Page 4] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x03 | 0x0b |C|O| Reserved |X|X|X| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color Value ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 0x03 | 0x0b |C|O| Reserved |X|X|X| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Color value advertisement format Both in BGP update and MP_UNREACH_NLRI message, multiple color extended communities could be included. It means that multiple colors, indicating different kind of services, could share the same label stack. With the use of Path-ID, the multiple colors are considered as one bundled update. Any subsequent update is based on Path-ID. If color extended community is not present in a BGP update message, it would be treated as normal BGP-LU without any color. 3 bits of XXX is reserved here for the draft. The meaning for XXX is interpreted as sub-slice of color, with 0 to 7 in decimal, or 000b and 111b in binary. These sub-slice could be used in either of the following case. a) Primary path and fallback paths in order of preference 0 - primary path 1 - first and most preferred backup path .... 7 - least preferred backup path b) ECMP paths up to 8, since all paths should be active in forwarding plane. Color value 0 is reserved for future interoperability purpose. Color value 1 - 31 are not recommended to use, and this range is reserved for future use. 3.3. Color extended community for service prefixes The same format of color extended community is advertised with service prefixes, which could be VPN prefixes or IP prefixes. The order of the color extended community could be interpreted as - Order of primary and fallback colors - Or, ECMP of equal split between color paths The above would be interpreted by the receiving PE upon its local configuration. It is optional to enable sub-slice notation. Chan Expires Sep 6, 2021 [Page 5] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 But if sub-slice bits are used, it will be used to map directly to each of the sub- slice path. If sub-slice path is not available for mapping, it should just fallback to resolving by color. 3.4. Color Slicing Capability The Color Slicing Capability is a BGP capability [RFC5492], with Capability Code xx (TBD). The color slicing capability is an optional but preferred to have capability. It could be configurable parameters at both side of BGP session but with assumption of BGP add-path support [RFC7911]. If the specific BGP capability is not negotiated, it is assumed version 0 without sub-slice notation. In this case, multiple paths with color attribute are advertised through BGP add-path. The Capability Length field of this capability is variable. The Capability Value field consists of one or more of the following tuples: +------------------------------------------------+ | Address Family Identifier (2 octets) | +------------------------------------------------+ | Subsequent Address Family Identifier (1 octet) | +------------------------------------------------+ | version (1 octet) | +------------------------------------------------+ | Reserved (3 octet) | +------------------------------------------------+ The meaning and use of the fields are as follows: Address Family Identifier (AFI): This field is the same as the one used in [RFC4760]. Subsequent Address Family Identifier (SAFI): This field is the same as the one used in [RFC4760]. Version: This field is for capability negotiation. 0 1 2 3 4 5 6 7 Chan Expires Sep 6, 2021 [Page 6] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 +-+-+-+-+-+-+-+-+ |v v v v| |s| +-+-+-+-+-+-+-+-+ Each of 4 bits of v represents a flag of version from 0 to 4, where LSB denotes support of version 1, and MSB denotes version 4. Version 0 is the default mode of operation, which is described in this document. To determine the common capability between the two BGP PEER, logical AND function to use determine the highest denominator of protocol version. For example, if BGP receive 0b0110 from its peer and perform AND function with its own capability 0b0010, the result is 0b0010. Version 2 is selected. The other examples are - 0b0110 AND 0b0110, version 3 is selected - 0b0100 AND 0b0010, version 0 is selected Version 1 (0b0001) is reserved. S-flag is the indication of use of sub-slice. Set to 1 if sub-slice notation is enforced. If either side is set to 0 for S-flag, sub-slice is not in use. Reserved: This field is reserved for future use. 4. Uniqueness of path entries a) Use of color can be considered to slice into multiple BGP Label Unicast RIB. Therefore, it should be treated as unique entries for the . e.g. , [labels] <123, 100, 10.1.1.1/32>, [1000 2000] <124, 200, 10.1.1.1/32>, [1000 2000] <222, {300,400}, 10.1.1.1/32>, [1000 2000] <223, null, 10.1.1.1/32>, [1000 2000] All these 4 NLRI are considered different but valid entries for different color instances. b) With sub-slice notation , [labels] <901, 100-0, 10.1.1.1/32>, [1000 2000] <902, 100-1, 10.1.1.1/32>, [1001 3000] Chan Expires Sep 6, 2021 [Page 7] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 <903, 100-7, 10.1.1.1/32>, [1002 4000] These 3 NLRI are distinct, and the second and third NLRI could be used for backup or ECMP purpose. 5. AIGP consideration AIGP (RFC7311) would be also used in here to embed certain metric across. 6. Explicit Withdraw of a According to RFC8277, MP_UNREACH_NLRI can be used to remove binding of a . If a path-id is associated with a prefix with multiple colors, the withdrawal would be applied to all associated colors. To withdraw color(s) partially from the same path-id advertisement, BGP update should be used instead. 7. Error Handling Procedure If BGP receiver could not handle the NLRI, it should silently discard with error logging. 8. Controller Compatibility The proposed architecture is compatible with controller for end to end provisioning. Persistent label, like Binding-SID is recommended to be used. Hence, controller could learn these labels from the network, and program specific end to end path. In this case, BGP-LU2 will provide a second best path to an ingress PE node, while a controller, with more external information, could provide a best path from overall perspective. Controller could also be deployed based on domain by domain perspective. e.g. Optimizing latency of a RSVP LSP, or maintain the bandwidth and loading between SR- TE LSPs. 9. Interworking with Flex Algo Flex Algo is a way of network slicing, but it is only an IGP protocol. In order to scale across different domains, BGP is recommended as the method to distribute the information across. Chan Expires Sep 6, 2021 [Page 8] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 With color notation in this proposal, one router can distribute to another domain via BGP. There are two ways of mapping Flex-Algo to color attribute in BGP-LU2 a) Color 128 equals Flex Algo 128 b) Or, Color 400 is mapped to Flex Algo 128 10. Label stacking to increase label space Due to the use of Flex-Algo [FLEXALGO], the MPLS label space might run into limit. Each node will need extra labels for each Algo. The idea is to use multiple labels to represent a single node. In this case, the label space becomes (2^20)^n, depending on n stacking level. For IPv6 address, there would be enough label space even if running with SR-MPLS. For example, for node 1.1.1.1, 2 consecutive labels are used to represent the node. Algo 0: [100101 100001] Algo 128: [400101 400001] How the forwarding plane treats the stacked labels is out of the discussion here. 11. Security Considerations TBD 12. IANA Considerations TBD. It will require a new BGP capability code to enable such color operation. New SAFI might be required as well. 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 13.2. Informative References [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001, . [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006 . Chan Expires Sep 6, 2021 [Page 9] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 [RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation Subsequent Address Family Identifier (SAFI) and the BGP Tunnel Encapsulation Attribute", RFC 5512, April 2009. . [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., and D. McPherson, "Dissemination of Flow Specification Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009, . [RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro, "The Accumulated IGP Metric Attribute for BGP", RFC 7311, DOI 10.17487/RFC7311, August 2014, . [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", RFC 7911, DOI 10.17487/RFC7911, July 2016, . [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, . [BGP-CAP] Chandra, R. and J. Scudder, "Capabilities Advertisement with BGP-4", RFC 2842, May 2000. [FLEXAGLO] S. Hegde, P. Psenak and etc, IGP Flexible Algorithm 14. Acknowledgments The following people have contributed to this document: Jeff Haas, Juniper Networks Shraddha Hedge, Juniper Networks Santosh Kolenchery, Juniper Networks Shihari Sangli, Juniper Networks Krzysztof Szarkowicz, Juniper Networks Chan Expires Sep 6, 2021 [Page 10] Internet-Draft draft-chan-idr-bgp-lu2-03.txt March 2021 Yimin Shen, Juniper Networks Author Address Louis Chan (editor) Juniper Networks 2604, Cityplaza One, 1111 King's Road Taikoo Shing Hong Kong Phone: +85225876659 Email: louisc@juniper.net Chan Expires Sep 6, 2021 [Page 11]