SPRING Working Group Z. Li Internet-Draft C. Li Intended status: Standards Track Huawei Technologies Expires: August 28, 2020 C. Xie China Telecom K. LEE LG U+ H. Tian F. Zhao CAICT J. Guichard Futurewei Technologies C. Li China Telecom S. Peng Huawei Technologies February 25, 2020 Compressed SRv6 Network Programming draft-li-spring-compressed-srv6-np-02 Abstract Segment Routing can be applied to the IPv6 data plane by leveraging a new type of Routing Extension Header, called Segment Routing Header (SRH). However, the overhead introduced by SRH may be a challenge for existing hardware, which may influence on the forwarding performance and the payload efficiency. This document defines a compressed SRv6 network programming mechanism in order to reduce the overhead of SRv6 by introducing the Compressed Segment Identifier (C-SID) and the Compressed SRH (C-SRH). The C-SRH can be a new Routing Header or an enhancement of SRH. 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 Li, et al. Expires August 28, 2020 [Page 1] Internet-Draft Compressed SRv6 NP February 2020 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 August 28, 2020. Copyright Notice Copyright (c) 2020 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 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 3. Compressed SID (C-SID) . . . . . . . . . . . . . . . . . . . 4 4. Compressed Segment Routing Header (C-SRH) . . . . . . . . . . 5 5. C-SRH Processing . . . . . . . . . . . . . . . . . . . . . . 10 6. Control Plane Consideration . . . . . . . . . . . . . . . . . 13 7. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1. Reference Diagram . . . . . . . . . . . . . . . . . . . . 15 7.2. Compressed SRv6 Forwarding Example . . . . . . . . . . . 15 8. Inter-domain Routing Using C-SRH . . . . . . . . . . . . . . 17 9. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 18 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 11. Security Considerations . . . . . . . . . . . . . . . . . . . 20 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 14.1. Normative References . . . . . . . . . . . . . . . . . . 20 14.2. Informative References . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node by inserting an ordered list of instructions, called segments. Li, et al. Expires August 28, 2020 [Page 2] Internet-Draft Compressed SRv6 NP February 2020 When segment routing is deployed on the IPv6 data plane, it is called SRv6 [I-D.ietf-6man-segment-routing-header].An SRv6 Segment ID (SID) is a 128-bit value, and it can be represented as LOC:FUNCT where LOC is the L most significant bits and FUNCT is the 128-L least significant bits [I-D.ietf-spring-srv6-network-programming]. L is called the locator length and is flexible. Each network operator is free to use the locator length it chooses. The LOC part of the SID is routable and leads to the node which instantiates that SID. For support of SR, a new routing header called Segment Routing Header (SRH), which contains a list of SIDs and other information, has been defined in [I-D.ietf-6man-segment-routing-header]. In use cases like Traffic Engineering, an ordered SID List with multiple SIDs is inserted into the SRH to steer packets along an explicit path. However, the overhead of SIDs (16 bytes per SID) may be a challenge for existing hardware processing, as the size of the SRH may affect the forwarding performance. When the packet is small, the payload efficiency is not ideal due to the large overhead of the SRH. When the packet is large, the overhead of the SRH may cause the packet to be dropped due to PMTU [RFC8200]. This document defines a compressed SRv6 network programming mechanism in order to reduce the overhead of SRv6 by introducing the Compressed Segment Identifier (C-SID) and the Compressed SRH (C-SRH). The C-SRH can be a new Routing Header or an enhancement of SRH, in either case, compatibility with the existing SRH is maintained. 2. Terminology This document makes use of the terms defined in [I-D.ietf-6man-segment-routing-header], [RFC8402] and [RFC8200], and the reader is assumed to be familiar with that terminology. This document introduces the following new terms: C-SRH: Compressed Segment Routing Header C-SID: Compressed Segment Identifier C-Tag: Compressed Tag 2.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Li, et al. Expires August 28, 2020 [Page 3] Internet-Draft Compressed SRv6 NP February 2020 3. Compressed SID (C-SID) This document defines a Compressed SID (C-SID) to carry the last 16 - N bytes of the original SRv6 SID, where N is the length of the common prefix among SIDs in the SID list. N is calculated by comparing the difference of each SID with other SIDs on the SID list. The common prefix part contains the common part of all Locators in the SID list, while the C-SID contains the different part, if any, of all Locators and the Function ID of an SRv6 SID. Generally, in an SRv6 domain, the common prefix can be the SRv6 SID block as per [I-D.ietf-spring-srv6-network-programming], and the C-SID consists of the Node ID and Function ID. The IPv6 DA contains a 128-bits (16 Bytes) SRv6 SID, and it can be separated into two parts: the common prefix among all SIDs, and the current C-SID on the SID list. 0 N 16 bytes +--------------------------------------------------------------+ | Common Prefix | C-SID | +--------------------------------------------------------------+ |<----------------- Locator ------------------->|<-FunctionID->| |<--->| | Different part of Locator Figure 1. C-SID in IPv6 DA In this way, the common prefix is carried by the IPv6 DA only, and the SIDs in the SID list will not carry the common prefix, but only the last 16 - N bytes of the original SRv6 SID. Therefore, this document does not define any new SRv6 segment types. Editor's Note: A C-SID can be a fixed length value, such as 32 bits, and actually authors suggest 32 bits. Also, the C-SID does not have to be the last part of SRv6 SID. An SRv6 SID may contains three parts: Common prefix, C-SID and argument. By default, the argument is 0, and it is treated as padding. The format is shown in Figure 2. In this case, operators can allocate a appropriate length common prefix for their networks. Li, et al. Expires August 28, 2020 [Page 4] Internet-Draft Compressed SRv6 NP February 2020 For example, the Common Prefix is A::/48, the C-SID is a 32 bits value, and the argument can be 48 bits zero, then only the 80 bits(Common prefix + C-SID) are used for routing, and only the C-SIDs will be carried in the SRH and updated to DA. 0 Variable Length 32 bits 128 bits +--------------------------------------------------------------+ | Common Prefix | C-SID | Argument | +--------------------------------------------------------------+ |<-------- Locator ---------------->|<-FuctID->|<---Argument-->| |<--->| | Different part of Locator Figure 2. 32 bits C-SID in IPv6 DA 4. Compressed Segment Routing Header (C-SRH) In order to carry the C-SID, this document defines the Compressed Segment Routing Header (C-SRH). The C-SRH can be a new Routing Header (with new Routing Type (TBD)) or an enhancement of the SRH (Note: the latter is preferred in this document). The C-SRH provides a more efficient encoding mechanism for SRv6, and is compatible with the existing SRv6 architecture. Li, et al. Expires August 28, 2020 [Page 5] Internet-Draft Compressed SRv6 NP February 2020 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Entry |E| Flag | C-Tag | Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[0](16 or 16 - C-Tag bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[1](16 - C-Tag bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[n](16 - C-Tag bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Padding to align with 64 bits Boundary ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // // Optional Type Length Value objects (variable) // // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3. Compressed Segment Routing Header where: o Next Header: Defined in [RFC8200] o Hdr Ext Len: Defined in [RFC8200] o Routing Type: 4 when C-SRH is an enhancement of SRH, or new type (TBD) when C-SRH is a new Routing Header. o Segments Left: Defined in [RFC8200] o Last Entry: contains the index (zero based), in the Segment List, of the last element of the Segment List. o Flags: Li, et al. Expires August 28, 2020 [Page 6] Internet-Draft Compressed SRv6 NP February 2020 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |E|U U U U U U U| +-+-+-+-+-+-+-+-+ U: Unused and for future use. MUST be 0 on transmission and ignored on receipt. E: Exclude flag, set when the last SID is excluded in compression. 1: the last SID is excluded in compression, and it is a 16 bytes (128 bits) value 0: the last SID is included in compression, and it is a 16 - C-Tag bytes value o C-Tag: 4-bit unsigned integer to indicate the length of the common prefix. Therefore, the length of the C-SID in C-SRH is 16 - C-Tag bytes except the last segment if and only if the E-flag is set. When the C-Tag is 0, the length of C-SIDs in C-SRH is 16 bytes, which is compatible with the existing SRH [I-D.ietf-6man-segment-routing-header]. o Tag: 12 bits value to tag a packet as part of a class or group of packets, e.g., packets sharing the same set of properties as per [I-D.ietf-6man-segment-routing-header]. o Segment List[0]: 16 bytes (128 bits ) IPv6 address when E-flag is set, and last 16 - C-Tag bytes of SID when E-flag is unset. o Segment List[n]: a compressed SRv6 SID, which is the last 16 - C-Tag bytes value of the original nth SRv6 SID. The Segment List is encoded starting from the last segment of the SR Policy, i.e., the first element of the segment list (Segment List [0]) contains the last segment of the SR Policy, the second element contains the penultimate segment of the SR Policy and so on. o Type Length Value (TLV) are described in [I-D.ietf-6man-segment-routing-header]. In some use cases, the last SID may be a normal SID, which has a different prefix against all other SIDs, so it can be excluded in C-SID generation for better compression. The E-flag indicates whether the last SID is excluded in compression. When E-flag is set, Segment List[0] will carry the original SID, Li, et al. Expires August 28, 2020 [Page 7] Internet-Draft Compressed SRv6 NP February 2020 otherwise, it carries the compressed SID, i.e. the last 16 - C-Tag bytes of the original Segment List[0]. Padding is needed after the SID List[Last entry] to align with 64 bits. Editor's Note: The authors had consided that there are some mechanisms to indicate compression, authors would like to have the comments from the working group, to see which option is the best, so welcome to send your comments. 1. Option 1: Compression Tag: C-tag in SRH * Compression tag indicates the length of Common prefix explicitly. * Indicate the length of C-SID as well, if the length of C-SID is a well-known length value. * No need to modify the control plane to distribute new type of SIDs. * SRH is modified, some bits are needed. * A SID can be used for normal SRv6 routing or Compression SRv6 routing. * New SID space for compression is optional. 2. Option 2: Compression Flag: C-flag in SRH * C-flag indicates compression, and the length of common prefix is learned from the control plane or configuration. * Indicate the length of C-SID as well, if the length of C-SID is a well-known length value. * Need to distribute the length of Common prefix or configure it in the SRv6 domain. * SRH is modified, a bit in flag for indicating compression is needed. * A SID can be used for normal SRv6 routing or Compression SRv6 routing. * New SID space for compression is optional. Li, et al. Expires August 28, 2020 [Page 8] Internet-Draft Compressed SRv6 NP February 2020 3. Option 3: Compression Flavor/SID/Locator/SID Space: C Flavor/C Type in Control plane * New compression type of SIDs or SIDs with C flavor, they should be distributed via control plane, such as IGP. * The format of SID should be distributed via control plane, such as the length of common prefix. * SRH is not modified. * C-SID is used for compression SRv6 routing only. * New SID space for compression is required. The format of C-SRH of Option 2 and 3 are shown below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Entry |C| Flag | Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[0](N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[1] (N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[n](N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Padding to align with 64 bits Boundary ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // // Optional Type Length Value objects (variable) // // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4. Compressed Segment Routing Header with C-flag 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Li, et al. Expires August 28, 2020 [Page 9] Internet-Draft Compressed SRv6 NP February 2020 | Next Header | Hdr Ext Len | Routing Type | Segments Left| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Entry | Flag | Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[0](N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[1](N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment List[N](N bytes) | . ... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Padding to align with 64 bits Boundary ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // // Optional Type Length Value objects (variable) // // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5. C-SRH without changing Common header of SRH 5. C-SRH Processing The compressed SID List can be generated by the ingress node by comparing the SIDs to get the C-Tag value according to the length of the common prefix. The compressed SID List can also be generated by a Controller and be sent to the ingress node, and the necessary protocol extensions for this are outside the scope of this document. (Note: The former is preferred in this document) When the ingress node applies SRv6 policy to packets, a C-SRH can be encapsulated in a new IPv6 header (Encapsulation Mode). The first SID is carried along with the common prefix in the DA, and the remaining C-SIDs are carried in the SID List of the C-SRH. The last SID is inserted according to the E-flag. When an SRv6 endpoint node receives the packet, the node will follow the same processing procedure as with an SRH, that is, to inspect whether the DA is a local SID or not, if yes, then process the SID according to its function. Otherwise, it will perform regular IPv6 forwarding. Li, et al. Expires August 28, 2020 [Page 10] Internet-Draft Compressed SRv6 NP February 2020 When the DA is a local SID, then the node will process the C-SRH and the C-SIDs, and the current C-SID on the segment-list will replace the last 16 - C-Tag bytes of the IPv6 DA. Regarding the last SID, if the E-flag is set, the entire 128 bits of Segment List[0] is updated to IPv6 DA. Otherwise, the C-SID will be updated to replace the last 16 - C-Tag bytes of IPv6 DA. After updating the IPv6 DA, the packet will be forwarded accordingly. The pseudo code of C-SRH processing is shown below. Editor's Note: The pseudo code will be updated when the options of Compression SRv6 NP are converged. Li, et al. Expires August 28, 2020 [Page 11] Internet-Draft Compressed SRv6 NP February 2020 01. When a C-SRH is processed { 02. If Segments Left is equal to zero { 03. Proceed to process the next header in the packet, whose type is identified by the Next Header field in the Routing header. 04. } 05. Else { 06. If local configuration requires TLV processing { 07. Perform TLV processing 08 //If E-flag is unset: 09. // TLV begins at SID length + Padding Length 10. // SID Length = Last Entry * (16 - C-Tag) 11. // Padding Length = 8 - Last Entry * (16 - C-Tag)%8 12. //Else: // TLV begins at SID length + Padding Length 13. // SID Length = Last Entry * (16 - C-Tag) + C-Tag 14. If (Segments Left is greater than (Last Entry+1)) { 15. Send an ICMP Parameter Problem, Code 0, message to the Source Address, pointing to the Segments Left field, and discard the packet. 16. } 17. Else { 18. Decrement Segments Left by 1. 19. if Segments Left > 0 or Segments Left = 0 and E-flag = 0: 20. // Update the C-SID to the DA 21. Copy Segment List[Segments Left] from the SRH to replace the last 16 - C-Tag bytes of destination address of the IPv6 header. 22. else: 23. // Segment Left = 0 and E-flag = 1 // Segment List[0] is a 16 bytes value. 24. Copy Segment List[Segments Left] from the SRH to destination address of the IPv6 header. 25. If the IPv6 Hop Limit is less than or equal to 1 { 26. Send an ICMP Time Exceeded -- Hop Limit Exceeded in Transit message to the Source Address and discard the packet. 27. } 28. Else { 29. Decrement the Hop Limit by 1 30. Resubmit the packet to the IPv6 module for transmission to the new destination. 31. } 32. } 33. } 34. } Li, et al. Expires August 28, 2020 [Page 12] Internet-Draft Compressed SRv6 NP February 2020 6. Control Plane Consideration Editor's note: Control Plane consideration will be described in separate drafts in the future. Note that, some extensions may be not needed in some Compression options. For indicating compression, the node should advertise the capabilities of SRv6 compression via control plane. A C-flag should be added in: o SRv6 Capabilities sub-TLV in IS-IS [I-D.ietf-lsr-isis-srv6-extensions] o SRv6-Capabilities TLV in OSPF [I-D.li-ospf-ospfv3-srv6-extensions], o OPEN Object/PATH-SETUP-TYPE-CAPABILITIES TLV/SRv6 Capabilities sub-TLV in PCEP [I-D.ietf-pce-segment-routing-ipv6] For distributing the C-SID in control plane, the C-flag should be added to the following TLV or sub-TLV in IGP/BGP/BGP-LS and PCEP. o IS-IS [I-D.ietf-lsr-isis-srv6-extensions]: * SRv6 Locator TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. * SRv6 END.X/ LAN END.X sub-TLV o OSPF [I-D.li-ospf-ospfv3-srv6-extensions] * SRv6 Locator TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. * SRv6 END.X/ LAN END.X sub-TLV , when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. o BGP [I-D.ietf-bess-srv6-services] * SRv6 SID Information sub-TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. o BGP-LS [I-D.ietf-idr-bgpls-srv6-ext] * SRv6 Link Attributes: SRv6 END.X SID TLV/LAN END.X SID TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. Li, et al. Expires August 28, 2020 [Page 13] Internet-Draft Compressed SRv6 NP February 2020 * SRv6 Prefix Attributes: SRv6 Locator TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. * SRv6 SID Attributes: SRv6 Endpoint Function TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. * SRv6 SID Attributes: SRv6 BGP Peer Node SID TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. For distributing SRv6 Policy with compression SIDs, a C-flag should be added in BGP and PCEP. o BGP SR Policy [I-D.ietf-idr-segment-routing-te-policy] * SRv6 Segment List sub-TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. Candidate path and SR Policy level's extensions will be described in the future revision. * Segment sub-TLV, when C-flag is set, the Locator Block length is less than 96 if the C-SID is a 32 bits value. The entire SID is still carried in the SR Policy, while the C-flag will indicate this is a compression SID with C-SID. + Type 2: SRv6 SID + Type 9: IPv6 Node addr with opt SRv6 SID + Type 10: IPv6 addr+intf ID for Local and remote pair for SRv6 with opt SID o PCEP * PATH-SETUP-TYPE TLV [RFC8408]: When PST is 2, the the C-flag indicates the SID list of the Path should be Compression SID. * SRv6 ERO Subobject [I-D.ietf-pce-segment-routing-ipv6] * SRv6 RRO Subobject [I-D.ietf-pce-segment-routing-ipv6] 7. Illustration This section describes a simple example to illustrate the usage of C-SID. Similar to [I-D.filsfils-spring-srv6-net-pgm-illustration], Li, et al. Expires August 28, 2020 [Page 14] Internet-Draft Compressed SRv6 NP February 2020 in order to ease the reading of the example, we introduce a simple reference diagram and simplified SID allocations. Editor's note: the following part will be updated accordingly when the compression option is converged in WG. 7.1. Reference Diagram Nodes 1 - 8 are SRv6 enabled nodes within the network domain. Nodes CE1, CE2, and CE3 are outside the domain. CE1 and CE2 are tenants of VPN 10. Nodes 1 and 8 act as PE respectively to nodes CE1 and CE3. All the links within the domain have the same IGP metric. The IGP metric shortest-path from 1 to 8 is 1-2-7-8, while the latency-metric shortest-path from 1 to 8 is 1-2-3-4-5-6-7-8. CE2 \ 4------5 | | +-----3------6 | | / | | | / | | |/ | Tenant10 CE1---1-----2------7---8---CE3 Tenant10 with IPv4 20/8 Figure 3: Reference topology 7.2. Compressed SRv6 Forwarding Example This section describes a simple example to show how efficiently C-SRH can reduce the overhead of SRv6. In order to ease the reading of the example, it is better to introduce a simplified SID allocation schema. We assume: o B::/112 is dedicated to the internal SRv6 SID space, which is the common prefix. Therefore, the C-SID is a 16-bit value. Li, et al. Expires August 28, 2020 [Page 15] Internet-Draft Compressed SRv6 NP February 2020 o A locator expressed in 120 bits and a function expressed in 8 bits. o Node k has B::0k/120 for its local SID space. Its SIDs will be explicitly allocated from that block. o Node k advertises B::0k/120 in its IGP. o Function 01 represents the End function with PSP support. o B::0k01 represents the End function with PSP support allocated by node K, such as B::0601 represents the End function with PSP support allocated by node 6. o B::0810 is an END.DT4 SID initiated by node 8, which is associated with the VRF10. In SRH based SRv6, the PE 1 encapsulates the packets from CE1 to CE3 in an outer IPv6 header with DA = B::0201 and SRH (B::0810, B::0701, B::0601, B::0501, B::0401, B::0301, B::0201; SL=6; NH=4). follows the latency-metric shortest-path. The total length of SRH is 8+16*7=120 bytes. In Compressed SRv6, PE 1 encapsulates the packets from CE1 to CE3 in an outer IPv6 header with DA = B::0201 and C-SRH (0810, 0701, 0601, 0501, 0401, 0301, 0201, SL=6; NH=4) with E-flag unset. The C-Tag is 14, since the length of the common prefix is 112 bits. Therefore, the total length of C-SRH is 8 + (16-14)*7 = 22 bytes, reducing the encapsulation overhead by 98 bytes (81.7% less overhead than SRH) or 87.5% reduction in SIDs overhead. The packet leaves node 1 to node 2 according to the FIB associated with the IPv6 DA B::0201. The packet can be presented as: (A::1, B::0201) (0810, 0701, 0601, 0501, 0401, 0301, 0201, SL=6; NH=4) (CE1, CE3) When 2 receives the packet, 2 matches B::0201 in its "My SID Table" and executes the END function behavior to update the IPv6 DA. Since the updated SL is greater than 0, and the C-Tag is 14, then it copies the C-SID that is a 2 bytes value to replace the last 2 bytes of the IPv6 DA, and then forwards the packet according to the new IPv6 DA B::0301. The packet can be presented as: Li, et al. Expires August 28, 2020 [Page 16] Internet-Draft Compressed SRv6 NP February 2020 (A::1, B::0301) (0810, 0701, 0601, 0501, 0401, 0301, 0201, SL=5; NH=4) (CE1, CE3) Like node 2, the nodes 3, 4, 5, and 6 perform the END function behavior to update the IPv6 DA with the corresponding C-SID and then forward the packet by looking up the IPv6 DA in their FIB accordingly. Therefore, the packet leaving node 6 can be presented as: (A::1, B::0701) (0810, 0701, 0601, 0501, 0401, 0301, 0201, SL=1; NH=4) (CE1, CE3) When 7 receives the packet, 7 matches B::0701 in its "My SID Table" and executes the END function behavior to update the IPv6 DA. Since the updated SL is 0 and E-flag is unset, then it copies the C-SID that is a 2 bytes value to replace the last 2 bytes of the IPv6 DA. Also, the C-SRH is popped since the B::0701 is an END SID with PSP flavor. Node 7 then performs a lookup on the updated IPv6 DA B::0810 to forward the packet along the shortest path to node 8. The packet can be presented as: (A::1, B::0810) (CE1, CE3) When 8 receives the packet, 8 matches B::0810 in its "My SID Table" and executes the END.DT4 function behavior to sends the IP packet (CE1, CE3) to its VPN destination. This example illustrates the procedure of C-SRH based SRv6 forwarding, and shows that the longer the common prefix, the more the SRv6 overhead can be reduced. More benefits are described in section 7. 8. Inter-domain Routing Using C-SRH Considering privacy and security of SRv6 domain, when SRv6 is used for inter-domain routing, the detailed SIDs will not be leaked between domains, and the Binding SID [RFC8402] SHOULD be used. The typical inter-domain using SRv6 is illustrated in Figure 4. When receiving the packet from CE1 to CE2, the Ingress node of SRv6 domain A can generate an SRv6 packet with SID List . BSID1 is bound to an SR Policy, which contains a list of SID list in SRv6 Domain B, for example [B1::1, B2::1, B3::1, B4::1, B5::1]. Li, et al. Expires August 28, 2020 [Page 17] Internet-Draft Compressed SRv6 NP February 2020 Similarly, BSID2 is bound to an SR Policy in SRv6 Domian C, for example [C1::1, C2::1, C3::1, C4::1, C5::1]. VPN1 SID can be an END.DT4 SID associated with CE2. In this way, the SIDs should be inserted at the ingress node are reduced from 11 to 3. BSID1 BSID2 VPN1 +---------+ +---------+ +---------+ | | | | | | CE1---*---------*----------*-*-*-*-*-*--------*-*-*-*-*-*---CE2 | | | | | | +---------+ +---------+ +---------+ SRv6 Domain A SRv6 Domain B SRv6 Domain C (A1::1,BSID1) (VPN1,BSID2,BSID1) (CE1, CE2) Figure 4.SRv6 Inter-domain Routing using BSID Normally, when a BSID is processed , a new IPv6 and SRH will be added to the packet, and the SRH carries the SID list representing the sub- path of this domain. C-SRH can be used to carry Compressed SID list within the SRv6 domain for reducing the overhead of SRv6. In this way, a Binding SID can be associated with an SR Policy, which contains a C-SID list to be carried by a C-SRH. Therefore, in inter-domain SRv6 routing, C-SRH can be used in each domain, while the SRH is used for inter-domian. In addition, if the common prefixs of SIDs in SRH can be compressed, C-SRH can be used for carring these SIDs as well. 9. Benefits 1. Seamless integration with SRv6 Network Programming o No new type (Functions, such as END) of SRv6 SIDs is defined. A C-SID is a sub-set of an SRv6 SID. o Does not redefine the IPv6 address space nor requires any specific IPv6 space. 2. Support for full set of SRv6 functionalities Li, et al. Expires August 28, 2020 [Page 18] Internet-Draft Compressed SRv6 NP February 2020 o Full set of SRv6 functionality (BE, Loose TE and Strict TE, etc.) are supported without any extra route advertisements. o Function ID information is maintained. 3. Control-Plane friendly o No need to make any extensions in Control-Plane to advertise new type of SIDs or binding information. o No indexed mapping table is required o No routing extension is required. o No new route advertisement is required if without new Locators 4. Hardware-friendly o Hardware has the mature capability to overwrite the IPv6 DA. o Avoids any extra lookup in indexed mapping table 5. Efficient MTU overhead o C-SRH has the smallest MTU overhead among alternative solutions (VxLAN with SR-MPLS, CRH, uSID), when all the Segment endpoint nodes information is maintained in the packet. 6. Scalable SR TE o 8 C-SIDs can be carried in 128 bits when C-SID is 16 bits value o 16 Segment endpoint nodes (1 in DA and 16 in C-SRH including the one in DA) in 40 bytes of overhead. o T.Encaps with a C-SRH of 40 bytes (8 fixed + 2 * 16 bytes) o ALL C-SIDs are maintained in C-SRH, which can be used for recording the explicit routing path. 7. Saving IPv6 address o Very limited IPv6 address are needed for SID space. Longer Common Prefix means smaller IPv6 address burning and smaller overhead of SRv6. o Very easy to meet the requirement of C-SRH since any operator Li, et al. Expires August 28, 2020 [Page 19] Internet-Draft Compressed SRv6 NP February 2020 or person can offer a 112/, 80/ or even 64/ prefix. 10. IANA Considerations TBD 11. Security Considerations TBD 12. Contributors Zhibo Hu Huawei Technologies huzhibo@huawei.com Zhongzheng Wang Huawei Technologies wangzhongzhen@huawei.com Bing Liu Huawei Technologies remy.liubing@huawei.com Yang Xia Huawei Technologies yolanda.xia@huawei.com Jianwei Mao Huawei Technologies MaoJianwei@huawei.com 13. Acknowledgements 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Li, et al. Expires August 28, 2020 [Page 20] Internet-Draft Compressed SRv6 NP February 2020 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . [I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing-header-26 (work in progress), October 2019. [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, . [I-D.ietf-lsr-isis-srv6-extensions] Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extension to Support Segment Routing over IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-05 (work in progress), February 2020. [I-D.li-ospf-ospfv3-srv6-extensions] Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, "OSPFv3 Extensions for SRv6", draft-li-ospf- ospfv3-srv6-extensions-07 (work in progress), November 2019. [I-D.ietf-pce-segment-routing-ipv6] Negi, M., Li, C., Sivabalan, S., Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment Routing leveraging the IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-03 (work in progress), October 2019. [I-D.ietf-idr-bgpls-srv6-ext] Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link State Extensions for SRv6", draft-ietf-idr-bgpls- srv6-ext-02 (work in progress), January 2020. [I-D.ietf-bess-srv6-services] Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based Overlay services", draft-ietf-bess-srv6-services-01 (work in progress), November 2019. Li, et al. Expires August 28, 2020 [Page 21] Internet-Draft Compressed SRv6 NP February 2020 [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Rosen, E., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", draft-ietf-idr-segment-routing- te-policy-08 (work in progress), November 2019. [RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. Hardwick, "Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408, July 2018, . 14.2. Informative References [I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "SRv6 Network Programming", draft-ietf-spring-srv6-network-programming-10 (work in progress), February 2020. [I-D.filsfils-spring-srv6-net-pgm-illustration] Filsfils, C., Camarillo, P., Li, Z., Matsushima, S., Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and J. Leddy, "Illustrations for SRv6 Network Programming", draft-filsfils-spring-srv6-net-pgm-illustration-01 (work in progress), August 2019. Authors' Addresses Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Cheng Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: chengli13@huawei.com Li, et al. Expires August 28, 2020 [Page 22] Internet-Draft Compressed SRv6 NP February 2020 Chongfeng Xie China Telecom China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District Beijing China Email: xiechf.bri@chinatelecom.cn Kihoon LEE LG U+ 71, Magokjungang 8-ro, Gangseo-gu Seoul Republic of Korea Email: soho8416@lguplus.co.kr Hui Tian CAICT Beijing China Email: tianhui@caict.ac.cn Feng Zhao CAICT Beijing China Email: zhaofeng@caict.ac.cn James N Guichard Futurewei Technologies 2330 Central Express Way Santa Clara USA Email: james.n.guichard@huawei.com Li, et al. Expires August 28, 2020 [Page 23] Internet-Draft Compressed SRv6 NP February 2020 Cong Li China Telecom China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District Beijing China Email: licong.bri@chinatelecom.cn Shuping Peng Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: pengshuping@huawei.com Li, et al. 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