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Internet Engineering Task Force (IETF) Y. FuRequest for Comments: 8389 CNNICCategory: Standards Track S. JiangISSN: 2070-1721 B. Liu Huawei Technologies Co., Ltd J. Dong Y. Chen Tsinghua University December 2018Definitions of Managed Objects forMapping of Address and Port with Encapsulation (MAP-E)Abstract This memo defines a portion of the Management Information Base (MIB) for Mapping of Address and Port with Encapsulation (MAP-E) for use with network management protocols.Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available inSection 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8389.Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 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.Fu, et al. Standards Track [Page 1]
RFC 8389 MAP-E MIB December 2018Table of Contents1. Introduction ....................................................22. The Internet-Standard Management Framework ......................23. Terminology .....................................................34. Structure of the MIB Module .....................................34.1. The mapMIBObjects ..........................................34.1.1. The mapRule Subtree .................................34.1.2. The mapSecurityCheck Subtree ........................34.2. The mapMIBConformance Subtree ..............................45. Definitions .....................................................46. IANA Considerations ............................................127. Security Considerations ........................................128. References .....................................................138.1. Normative References ......................................138.2. Informative References ....................................14 Acknowledgements ..................................................15 Authors' Addresses ................................................161. Introduction Mapping of Address and Port with Encapsulation (MAP-E) [RFC7597] is a stateless, automatic tunneling mechanism for providing an IPv4 connectivity service to end users over a service provider's IPv6 network. This document defines a portion of the Management Information Base (MIB) for use with monitoring MAP-E devices.2. The Internet-Standard Management Framework For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer tosection 7 of RFC 3410 [RFC3410]. Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. MIB objects are generally accessed through the Simple Network Management Protocol (SNMP). Objects in the MIB are defined using the mechanisms defined in the Structure of Management Information (SMI). This memo specifies a MIB module that is compliant to the SMIv2, which is described in STD 58,RFC 2578 [RFC2578], STD 58,RFC 2579 [RFC2579] and STD 58,RFC 2580 [RFC2580].Fu, et al. Standards Track [Page 2]
RFC 8389 MAP-E MIB December 20183. Terminology 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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.4. Structure of the MIB Module The IF-MIB [RFC2863] defines generic managed objects for managing interfaces. Each logical interface (physical or virtual) has an ifEntry. Tunnels are handled by creating a logical interface (ifEntry) for each tunnel. Each MAP-E tunnel endpoint also acts as a virtual interface that has a corresponding entry in the IF-MIB. Those corresponding entries are indexed by ifIndex. The MAP-E MIB is configurable on a per-interface basis, so it depends on several parts (ifEntry) of the IF-MIB [RFC2863].4.1. The mapMIBObjects4.1.1. The mapRule Subtree The mapRule subtree describes managed objects used for managing the multiple mapping rules in MAP-E. According to [RFC7597], the mapping rules are divided into two categories: Basic Mapping Rule (BMR) and Forwarding Mapping Rule (FMR). According toSection 4.1 of [RFC7598], an F-flag specifies whether the rule is to be used for forwarding (FMR). If set, this rule is used as an FMR; if not set, this rule is BMR only and MUST NOT be used for forwarding. A BMR can also be used as an FMR for forwarding if the F-flag is set. So, the RuleType definition in the MAP-E MIB (seeSection 5) defines bmrAndfmr to specify this scenario.4.1.2. The mapSecurityCheck Subtree The mapSecurityCheck subtree provides statistics for the number of invalid packets that have been identified. [RFC7597] defines two kinds of invalid packets: o The Border Relay (BR) will validate the received packet's source IPv6 address against the configured MAP domain rule and the destination IPv6 address against the configured BR IPv6 address. o The MAP node (Customer Edge (CE) and BR) will check that the received packet's source IPv4 address and port are in the range derived from the matching MAP rule.Fu, et al. Standards Track [Page 3]
RFC 8389 MAP-E MIB December 20184.2. The mapMIBConformance Subtree The mapMIBConformance subtree provides conformance information of MIB objects.5. Definitions The following MIB module imports definitions from [RFC2578], [RFC2579], [RFC2580], [RFC2863], and [RFC4001]. MAP-E-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, mib-2, Unsigned32, Counter64 FROM SNMPv2-SMI --RFC 2578 TEXTUAL-CONVENTION FROM SNMPv2-TC --RFC 2579 ifIndex FROM IF-MIB --RFC 2863 InetAddressIPv6, InetAddressIPv4, InetAddressPrefixLength FROM INET-ADDRESS-MIB --RFC 4001 OBJECT-GROUP, MODULE-COMPLIANCE FROM SNMPv2-CONF; --RFC 2580 mapMIB MODULE-IDENTITY LAST-UPDATED "201811260000Z" ORGANIZATION "IETF Softwire Working Group" CONTACT-INFO "Yu Fu CNNIC No. 4 South 4th Street, Zhongguancun Beijing 100190 China Email: eleven711711@foxmail.com Sheng Jiang Huawei Technologies Co., Ltd Q14, Huawei Campus, No. 156 Beiqing Road Hai-Dian District, Beijing 100095 China Email: jiangsheng@huawei.com Bing Liu Huawei Technologies Co., Ltd Q14, Huawei Campus, No. 156 Beiqing RoadFu, et al. Standards Track [Page 4]
RFC 8389 MAP-E MIB December 2018 Hai-Dian District, Beijing 100095 China Email: leo.liubing@huawei.com Jiang Dong Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 China Email: knight.dongjiang@gmail.com Yuchi Chen Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 China Email: chenycmx@gmail.com" DESCRIPTION "This MIB module is defined for management of objects for MAP-E BRs or CEs. Copyright (c) 2018 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth inSection 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info)." REVISION "201811260000Z" DESCRIPTION "Initial version. Published asRFC 8389." ::= { mib-2 242 } mapMIBObjects OBJECT IDENTIFIER ::= {mapMIB 1} mapRule OBJECT IDENTIFIER ::= { mapMIBObjects 1 } mapSecurityCheck OBJECT IDENTIFIER ::= { mapMIBObjects 2 } -- ============================================================== -- Textual Conventions Used in This MIB Module -- ==============================================================Fu, et al. Standards Track [Page 5]
RFC 8389 MAP-E MIB December 2018 RulePSID ::= TEXTUAL-CONVENTION DISPLAY-HINT "0x:" STATUS current DESCRIPTION "Indicates that the Port Set ID (PSID) is represented as hexadecimal for clarity." SYNTAX OCTET STRING (SIZE (2)) RuleType ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Enumerates the type of the mapping rule. It defines three types of mapping rules here: bmr: Basic Mapping Rule (not Forwarding Mapping Rule) fmr: Forwarding Mapping Rule (not Basic Mapping Rule) bmrAndfmr: Basic and Forwarding Mapping Rule The Basic Mapping Rule may also be a Forwarding Mapping Rule for mesh mode." REFERENCE "bmr, fmr:Section 5 of RFC 7597. bmrAndfmr:Section 5 of RFC 7597,Section 4.1 of RFC 7598." SYNTAX INTEGER { bmr(1), fmr(2), bmrAndfmr(3) } mapRuleTable OBJECT-TYPE SYNTAX SEQUENCE OF MapRuleEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The (conceptual) table containing rule information for a specific mapping rule. It can also be used for row creation." ::= { mapRule 1 } mapRuleEntry OBJECT-TYPE SYNTAX MapRuleEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Each entry in this table contains the information on a particular mapping rule." INDEX { ifIndex, mapRuleID } ::= { mapRuleTable 1 }Fu, et al. Standards Track [Page 6]
RFC 8389 MAP-E MIB December 2018 MapRuleEntry ::= SEQUENCE { mapRuleID Unsigned32, mapRuleIPv6Prefix InetAddressIPv6, mapRuleIPv6PrefixLen InetAddressPrefixLength, mapRuleIPv4Prefix InetAddressIPv4, mapRuleIPv4PrefixLen InetAddressPrefixLength, mapRuleBRIPv6Address InetAddressIPv6, mapRulePSID RulePSID, mapRulePSIDLen Unsigned32, mapRuleOffset Unsigned32, mapRuleEALen Unsigned32, mapRuleType RuleType } mapRuleID OBJECT-TYPE SYNTAX Unsigned32 (1..4294967295) MAX-ACCESS not-accessible STATUS current DESCRIPTION "A unique identifier used to distinguish mapping rules." ::= { mapRuleEntry 1 } -- The object mapRuleIPv6Prefix is IPv6 specific; hence, it does -- not use the version-agnostic InetAddress. mapRuleIPv6Prefix OBJECT-TYPE SYNTAX InetAddressIPv6 MAX-ACCESS read-only STATUS current DESCRIPTION "The IPv6 prefix defined in the mapping rule that will be assigned to CEs." ::= { mapRuleEntry 2 } mapRuleIPv6PrefixLen OBJECT-TYPE SYNTAX InetAddressPrefixLength MAX-ACCESS read-only STATUS current DESCRIPTION "The length of the IPv6 prefix defined in the mapping rule that will be assigned to CEs." ::= { mapRuleEntry 3 } -- The object mapRuleIPv4Prefix is IPv4 specific; hence, it does -- not use the version-agnostic InetAddress.Fu, et al. Standards Track [Page 7]
RFC 8389 MAP-E MIB December 2018 mapRuleIPv4Prefix OBJECT-TYPE SYNTAX InetAddressIPv4 MAX-ACCESS read-only STATUS current DESCRIPTION "The IPv4 prefix defined in the mapping rule that will be assigned to CEs." ::= { mapRuleEntry 4 } mapRuleIPv4PrefixLen OBJECT-TYPE SYNTAX InetAddressPrefixLength MAX-ACCESS read-only STATUS current DESCRIPTION "The length of the IPv4 prefix defined in the mapping rule that will be assigned to CEs." ::= { mapRuleEntry 5 } -- The object mapRuleBRIPv6Address is IPv6 specific; hence, it does -- not use the version-agnostic InetAddress. mapRuleBRIPv6Address OBJECT-TYPE SYNTAX InetAddressIPv6 MAX-ACCESS read-only STATUS current DESCRIPTION "The IPv6 address of the BR that will be conveyed to CEs. If the BR IPv6 address is anycast, the relay must use this anycast IPv6 address as the source address in packets relayed to CEs." ::= { mapRuleEntry 6 } mapRulePSID OBJECT-TYPE SYNTAX RulePSID MAX-ACCESS read-only STATUS current DESCRIPTION "The PSID value algorithmically identifies a set of ports assigned to a CE." REFERENCE "PSID:Section 5.1 of RFC 7597." ::= { mapRuleEntry 7 } mapRulePSIDLen OBJECT-TYPE SYNTAX Unsigned32(0..16) MAX-ACCESS read-only STATUS currentFu, et al. Standards Track [Page 8]
RFC 8389 MAP-E MIB December 2018 DESCRIPTION "The bit length value of the number of significant bits in the PSID field. When it is set to 0, the PSID field is to be ignored." ::= { mapRuleEntry 8 } mapRuleOffset OBJECT-TYPE SYNTAX Unsigned32(0..15) MAX-ACCESS read-only STATUS current DESCRIPTION "The number of the mapRuleOffset is 6 by default to exclude the system ports (0-1023). It is provided via the Rule Port Mapping Parameters in the Basic Mapping Rule." DEFVAL {6} ::= { mapRuleEntry 9 } mapRuleEALen OBJECT-TYPE SYNTAX Unsigned32(0..48) MAX-ACCESS read-only STATUS current DESCRIPTION "The length of the Embedded Address (EA) defined in mapping rule that will be assigned to CEs." REFERENCE "EA:Section 3 of RFC 7597." ::= { mapRuleEntry 10 } mapRuleType OBJECT-TYPE SYNTAX RuleType MAX-ACCESS read-only STATUS current DESCRIPTION "Indicates the type of mapping rule. '1' represents a BMR. '2' represents an FMR. '3' represents a BMR that is also an FMR for mesh mode." REFERENCE "bmr, fmr:Section 5 of RFC 7597. bmrAndfmr:Section 5 of RFC 7597,Section 4.1 of RFC 7598." ::= { mapRuleEntry 11 } mapSecurityCheckTable OBJECT-TYPE SYNTAX SEQUENCE OF MapSecurityCheckEntry MAX-ACCESS not-accessible STATUS currentFu, et al. Standards Track [Page 9]
RFC 8389 MAP-E MIB December 2018 DESCRIPTION "The (conceptual) table containing information on MAP security checks. This table can be used for statistics on the number of invalid packets that have been identified." ::= { mapSecurityCheck 1 } mapSecurityCheckEntry OBJECT-TYPE SYNTAX MapSecurityCheckEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Each entry in this table contains information on a particular MAP security check." INDEX { ifIndex } ::= { mapSecurityCheckTable 1 } MapSecurityCheckEntry ::= SEQUENCE { mapSecurityCheckInvalidv4 Counter64, mapSecurityCheckInvalidv6 Counter64 } mapSecurityCheckInvalidv4 OBJECT-TYPE SYNTAX Counter64 MAX-ACCESS read-only STATUS current DESCRIPTION "Indicates the number of received IPv4 packets that do not have a payload source IPv4 address or port within the range defined in the matching MAP rule. It corresponds to the second kind of invalid packet described inSection 4.1.2." ::= { mapSecurityCheckEntry 1 } mapSecurityCheckInvalidv6 OBJECT-TYPE SYNTAX Counter64 MAX-ACCESS read-only STATUS current DESCRIPTION "Indicates the number of received IPv6 packets that do not have a source or destination IPv6 address matching a Basic Mapping Rule. It corresponds to the first kind of invalid packet described inSection 4.1.2." ::= { mapSecurityCheckEntry 2 } -- Conformance InformationFu, et al. Standards Track [Page 10]
RFC 8389 MAP-E MIB December 2018 mapMIBConformance OBJECT IDENTIFIER ::= {mapMIB 2} mapMIBCompliances OBJECT IDENTIFIER ::= { mapMIBConformance 1 } mapMIBGroups OBJECT IDENTIFIER ::= { mapMIBConformance 2 } -- compliance statements mapMIBCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "Describes the minimal requirements for conformance to the MAP-E MIB." MODULE -- this module MANDATORY-GROUPS { mapMIBRuleGroup , mapMIBSecurityGroup } ::= { mapMIBCompliances 1 } -- Units of Conformance mapMIBRuleGroup OBJECT-GROUP OBJECTS { mapRuleIPv6Prefix, mapRuleIPv6PrefixLen, mapRuleIPv4Prefix, mapRuleIPv4PrefixLen, mapRuleBRIPv6Address, mapRulePSID, mapRulePSIDLen, mapRuleOffset, mapRuleEALen, mapRuleType } STATUS current DESCRIPTION "The group of objects used to describe the MAP-E mapping rule." ::= { mapMIBGroups 1 } mapMIBSecurityGroup OBJECT-GROUP OBJECTS { mapSecurityCheckInvalidv4, mapSecurityCheckInvalidv6 } STATUS current DESCRIPTION "The group of objects used to provide information on the MAP-E security checks." ::= { mapMIBGroups 2 } ENDFu, et al. Standards Track [Page 11]
RFC 8389 MAP-E MIB December 20186. IANA Considerations The MIB module in this document uses the following IANA-assigned OBJECT IDENTIFIER values recorded in the SMI Numbers registry: Descriptor OBJECT IDENTIFIER value ---------- ----------------------- MAP-E-MIB { mib-2 242 }7. Security Considerations There are no management objects defined in this MIB module that have a MAX-ACCESS clause of read-write and/or read-create. So, if this MIB module is implemented correctly, then there is no risk that an intruder can alter or create any management objects of this MIB module via direct SNMP SET operations. Some of the objects in this MIB module may be considered sensitive or vulnerable in some network environments. This includes INDEX objects with a MAX-ACCESS of not-accessible, and any indices from other modules exposed via AUGMENTS. It is thus important to control even GET and/or NOTIFY access to these objects and possibly to even encrypt the values of these objects when sending them over the network via SNMP. These are the tables and objects and their sensitivity/vulnerability: mapRuleIPv6Prefix mapRuleIPv6PrefixLen mapRuleIPv4Prefix mapRuleIPv4PrefixLen mapRuleBRIPv6Address mapRulePSID mapRulePSIDLen mapRuleOffset mapRuleEALen mapRuleTypeFu, et al. Standards Track [Page 12]
RFC 8389 MAP-E MIB December 2018 Some of the MIB model's objects are vulnerable because the information that they hold may be used for targeting an attack against a MAP node (CE or BR). For example, an intruder could use the information to help deduce the customer IPv4 and IPv6 topologies and address-sharing ratios in use by the ISP. SNMP versions prior to SNMPv3 did not include adequate security. Even if the network itself is secure (for example by using IPsec), there is no control as to who on the secure network is allowed to access and GET/SET (read/change/create/delete) the objects in this MIB module. Implementations SHOULD provide the security features described by the SNMPv3 framework (see [RFC3410]), and implementations claiming compliance to the SNMPv3 standard MUST include full support for authentication and privacy via the User-based Security Model (USM) [RFC3414] with the AES cipher algorithm [RFC3826]. Implementations MAY also provide support for the Transport Security Model (TSM) [RFC5591] in combination with a secure transport such as SSH [RFC5592] or TLS/DTLS [RFC6353]. Further, deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to enable cryptographic security. It is then a customer/operator responsibility to ensure that the SNMP entity giving access to an instance of this MIB module is properly configured to give access to the objects only to those principals (users) that have legitimate rights to indeed GET or SET (change/create/delete) them.8. References8.1. 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, <https://www.rfc-editor.org/info/rfc2119>. [RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58,RFC 2578, DOI 10.17487/RFC2578, April 1999, <https://www.rfc-editor.org/info/rfc2578>. [RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD 58,RFC 2579, DOI 10.17487/RFC2579, April 1999, <https://www.rfc-editor.org/info/rfc2579>.Fu, et al. Standards Track [Page 13]
RFC 8389 MAP-E MIB December 2018 [RFC2580] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Conformance Statements for SMIv2", STD 58,RFC 2580, DOI 10.17487/RFC2580, April 1999, <https://www.rfc-editor.org/info/rfc2580>. [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",RFC 2863, DOI 10.17487/RFC2863, June 2000, <https://www.rfc-editor.org/info/rfc2863>. [RFC4001] Daniele, M., Haberman, B., Routhier, S., and J. Schoenwaelder, "Textual Conventions for Internet Network Addresses",RFC 4001, DOI 10.17487/RFC4001, February 2005, <https://www.rfc-editor.org/info/rfc4001>. [RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S., Murakami, T., and T. Taylor, Ed., "Mapping of Address and Port with Encapsulation (MAP-E)",RFC 7597, DOI 10.17487/RFC7597, July 2015, <https://www.rfc-editor.org/info/rfc7597>. [RFC7598] Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec, W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for Configuration of Softwire Address and Port-Mapped Clients",RFC 7598, DOI 10.17487/RFC7598, July 2015, <https://www.rfc-editor.org/info/rfc7598>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.8.2. Informative References [RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction and Applicability Statements for Internet- Standard Management Framework",RFC 3410, DOI 10.17487/RFC3410, December 2002, <https://www.rfc-editor.org/info/rfc3410>. [RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", STD 62,RFC 3414, DOI 10.17487/RFC3414, December 2002, <https://www.rfc-editor.org/info/rfc3414>.Fu, et al. Standards Track [Page 14]
RFC 8389 MAP-E MIB December 2018 [RFC3826] Blumenthal, U., Maino, F., and K. McCloghrie, "The Advanced Encryption Standard (AES) Cipher Algorithm in the SNMP User-based Security Model",RFC 3826, DOI 10.17487/RFC3826, June 2004, <https://www.rfc-editor.org/info/rfc3826>. [RFC5591] Harrington, D. and W. Hardaker, "Transport Security Model for the Simple Network Management Protocol (SNMP)", STD 78,RFC 5591, DOI 10.17487/RFC5591, June 2009, <https://www.rfc-editor.org/info/rfc5591>. [RFC5592] Harrington, D., Salowey, J., and W. Hardaker, "Secure Shell Transport Model for the Simple Network Management Protocol (SNMP)",RFC 5592, DOI 10.17487/RFC5592, June 2009, <https://www.rfc-editor.org/info/rfc5592>. [RFC6353] Hardaker, W., "Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP)", STD 78,RFC 6353, DOI 10.17487/RFC6353, July 2011, <https://www.rfc-editor.org/info/rfc6353>.Acknowledgements The authors would like to thank the following individuals for their valuable comments: David Harrington, Mark Townsley, Shishio Tsuchiya, Yong Cui, Suresh Krishnan, Bert Wijnen, Ian Farrer, and Juergen Schoenwaelder.Fu, et al. Standards Track [Page 15]
RFC 8389 MAP-E MIB December 2018Authors' Addresses Yu Fu CNNIC No. 4 South 4th Street, Zhongguancun Beijing 100190 China Email: eleven711711@foxmail.com Sheng Jiang Huawei Technologies Co., Ltd Q14, Huawei Campus, No. 156 Beiqing Road Hai-Dian District, Beijing 100095 China Email: jiangsheng@huawei.com Bing Liu Huawei Technologies Co., Ltd Q14, Huawei Campus, No. 156 Beiqing Road Hai-Dian District, Beijing 100095 China Email: leo.liubing@huawei.com Jiang Dong Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 China Email: knight.dongjiang@gmail.com Yuchi Chen Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 China Email: flashfoxmx@gmail.comFu, et al. Standards Track [Page 16]
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