Dynamic Host Configuration (DHC) W. Cheng Internet Draft R. Han Intended status: Standards Track China Mobile Expires: March 22, 2023 C. Lin Y. Qiu New H3C Technologies September 21, 2022 Distribute SRv6 Locator by DHCP draft-cheng-dhc-distribute-srv6-locator-by-dhcp-02 Abstract In SRv6 network, locators need to be assigned to each SRv6 Endpoint, and segments are created based on locators. This document describes the method of assigning locators to SRv6 Endpoints through DHCPv6. 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), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on March 22 2023. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Cheng, et al. Expire March, 2023 [Page 1] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 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 1.1. Requirements Language .................................. 3 2. Terminology ................................................. 3 3. Scenario for Locator......................................... 3 4. DHCPv6 extension ............................................ 5 4.1. Identity Association for SRv6 Locator Option ........... 5 4.2. IA SRv6 Locator Option ................................. 8 5. Process of Assigning Locator ............................... 10 5.1.1. DHCP Client Behavior ............................. 10 5.1.2. DHCP Server Behavior ............................. 11 5.1.3. DHCP Relay Agent Behavior ........................ 12 6. IANA Considerations ........................................ 12 7. Security Considerations .................................... 13 8. References ................................................. 13 8.1. Normative References .................................. 13 Authors' Addresses ............................................ 14 1. Introduction Segment Routing (SR) allows a headend node to steer a packet flow along any path. Per-path states of Intermediate nodes are eliminated thanks to source routing. The headend node steers a flow into an SR Policy. The packets steered into an SR Policy carry an ordered list of segments associated with that SR Policy. When deploying SRv6, each SRv6 endpoint needs to be assigned a unique IPv6 prefix, that is, locator. As the identity of the endpoint, the locator could be distributed to other IPv6 nodes in the SRv6 domain through IGP, so that other IPv6 nodes could learn the locator route. SRv6 endpoint allocates segments of various behaviors based on its locator. Cheng, et al. Expires March, 2023 [Page 2] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 In some specific scenarios, some SRv6 endpoints do not deploy IGP with other routers. In this case, the locator route cannot be distributed in the normal way. This document describes a method of assigning locators to SRv6 Endpoints through DHCPv6. The existing processing flow of DHCPv6 can be used to simplify the allocation of locators and route distributing. 1.1. 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. 2. Terminology This document leverages the terms defined in [RFC8415] and [RFC8986]. The reader is assumed to be familiar with this terminology. This document introduces the following new terms: IA_SRV6_LOCATOR: Identity Association for SRv6 Locator, an IA that carries delegated SRv6 locator prefixes. See Section 4.1 for detail on the IA_SRV6_LOCATOR option. 3. Scenario for Locator Telecom provider use IP Metro network and Backbone network to realize the interconnection between access users in different regions. In the IP backbone network, deploy the network PE (PE-N) for access users in different regions and the cloud PE (PE-C) for the cloud. CPEs for access users are connected to the local MAN in various ways. CPEs are responsible for assigning addresses to access users, so CPEs apply for DHCPv6 PD from DHCPv6 server.DHCPv6 server is usually enabled on BRAS. After the DHCPv6 server allocates PD, BRAS will add a network route corresponding to PD to local routing table and distribute the network route to the upstream routers. Cheng, et al. Expires March, 2023 [Page 3] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 In this networking environment, it is expected to deploy end-to-end SRv6 to realize interconnection between access users, or between access users and clouds. For example, for the traffic from host1 to host2, CPE1 should be the SRv6 headend node and CPE2 should be the SRv6 endpoint node. When accessing the cloud, CPE should be the SRv6 headend node and vCPE should be the SRv6 endpoint node. To deploy SRv6, the CPE should be configured, such as SRv6 locator. The locator of each CPE uniquely identifies the CPE, and other network nodes need to be able to learn the locator route. There are difficulties in achieving these requirements for the following reasons: o configuration complexity In Metro network, the number of CPEs is very large and widely distributed geographically. Moreover, the mobility requirements of CPE are relatively high, and the access location of the same CPE often changes, so the IP address of CPE cannot be fixed. In order to simplify the deployment procedure, zero touch provisioning (ZTP) deployment technology is often used when deploying CPE, such as USB-based deployment. The configuration file is recorded in the USB flash disk, and CPE reads the corresponding configuration file to complete the basic configuration. In this way, the configuration file in the USB flash disk should only contain general configuration, and the personalized configuration of the CPE, such as IP address, should be avoided as far as possible. Usually, the public network side IPv6 address of CPE is applied for through the stateless address automatic configuration (SLAAC) of ND or through DHCPv6. At present, SRv6 locator can only be configured on each CPE through the controller or CLI, which increases the configuration complexity. o locator route learning CPE can be connected to the BRAS of local MAN through various types of networks, such as leased line, 4/5G network, optical fiber, etc. Due to the diversity of connections, IGP is usually only enabled within the MAN, that is, IGP will not be deployed between CPE and BRAS. The locator route of CPE could not be distributed to the BRAS node through IGP, and the static route can only be configured manually on Cheng, et al. Expires March, 2023 [Page 4] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 the BRAS or the controller. CPE and BRAS often belong to different administration domains. Configuring routes to CPE on BRAS increases the cost and workload of communication and coordination. Metropolitan area network +---------------------------+ | | +------+ +------+ | +-----+ +------+ | |Host1 +-----+ CPE1 +----+--+BRAS1+--------+ CR1 | | +------+ +------+ | +-----+ +---+--+ | | | | +---------------------+-----+ | +--------+-------------+ | | | Backbone Network | | | +-------+--------+----+ | | +--------------------+------+ | | | | | +------+ +------+ | +-----+ +--+---+ | | |Host2 +-----+ CPE2 +----+--+BRAS2+--------+ CR2 | | | +------+ +------+ | +-----+ +------+ | | +---------------------------+ | | +--+-+ ,----+vCPE+---. ,-' +----+ `-. ,' `. ( ) `. Cloud ,' `-. ,-' `-------------' Figure 1: Telecom IPv6 Network To solve these difficulties this document proposes a method to allocate SRv6 locators to CPE through DHCPv6, and distribute locator routes by using the workflow of DHCPv6. 4. DHCPv6 extension 4.1. Identity Association for SRv6 Locator Option The Identify Association for SRv6 Locator (IA_SRV6_LOCATOR) option is used to carry an IA_SRV6_LOCATOR, the parameters associated with Cheng, et al. Expires March, 2023 [Page 5] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 the IA_SRV6_LOCATOR, and the SRv6 locator associated with the IA_SRV6_LOCATOR. The format of the IA_SRV6_LOCATOR option is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_IA_SRV6_LOCATOR | Option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IAID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | T1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | T2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . IA_SRV6_LOCATOR-options . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Identify Association for SRv6 Locator Option Format Where: - Option-code: OPTION_IA_SRV6_LOCATOR (TBD). - Option-len: 12 + length of IA_SRV6_LOCATOR-options field. - IAID: The unique identifier for this IA_SRV6_LOCATOR. The IAID must be unique among the identifiers for all of this client's IA_SRV6_LOCATORs. The number space for IA_SRV6_LOCATOR IAIDs is separate from the number space for other IA option types (i.e., IA_TA, IA_NA and IA_PD). A 4-octet field containing an unsigned integer. - T1: The time interval after which the client should contact the server from which the SRv6 locator in the IA_SRV6_LOCATOR were obtained to extend the lifetimes of the SRv6 locators to the IA_SRV6_LOCATOR; T1 is a time duration relative to the message reception time expressed in units of seconds. A 4-octet field containing an unsigned integer. - T2: The time interval after which the client should contact any available server to extend the lifetimes of the SRv6 locators assigned to the IA_SRV6_LOCATOR; T2 is a time duration relative to the message reception time expressed in units of seconds. A 4-octet field containing an unsigned integer. Cheng, et al. Expires March, 2023 [Page 6] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 - IA_SRV6_LOCATOR-options: Options associated with this IA_SRV6_LOCATOR. A variable-length field (12 octets less than the value in the Option-len field). The IA_SRV6_LOCATOR-options field encapsulates those options that are specific to this IA_SRV6_LOCATOR. For example, all of the IA SRv6 Locator options (see Section 4.2) carrying the SRv6 locators associated with this IA_SRV6_LOCATOR are in the IA_SRV6_LOCATOR- options field. An IA_SRV6_LOCATOR option may only appear in the options area of a DHCP message. A DHCP message may contain multiple IA_SRV6_LOCATOR options (though each must have a unique IAID). The status of any operations involving this IA_SRV6_LOCATOR is indicated in a Status Code option (see Section 21.13 of [RFC8415]) in the IA_SRV6_LOCATOR-options field. Note that an IA_SRV6_LOCATOR has no explicit "lifetime" or "lease length" of its own. When the valid lifetimes of all of the SRv6 locators in an IA_SRV6_LOCATOR have expired, the IA_SRV6_LOCATOR can be considered as having expired. T1 and T2 fields are included to give the server explicit control over when a client should contact the server about a specific IA_SRV6_LOCATOR. In a message sent by a client to a server, the T1 and T2 fields SHOULD be set to 0. The server MUST ignore any values in these fields in messages received from a client. In a message sent by a server to a client, the client MUST use the values in the T1 and T2 fields for the T1 and T2 timers, unless values in those fields are 0. The values in the T1 and T2 fields are the number of seconds until T1 and T2. The server selects the T1 and T2 times to allow the client to extend the lifetimes of any SRv6 locators in the IA_SRV6_LOCATOR before the lifetimes expire, even if the server is unavailable for some short period of time. Recommended values for T1 and T2 are 0.5 and 0.8 times the shortest preferred lifetime of the SRv6 locators in the IA_SRV6_LOCATOR that the server is willing to extend, respectively. If the time at which the SRv6 locators in an IA_SRV6_LOCATOR are to be renewed is to be left to the discretion of the client, the server sets T1 and T2 to 0. The client MUST follow the rules defined in Section 14.2 of [RFC8415]. If a client receives an IA_SRV6_LOCATOR with T1 greater than T2 and both T1 and T2 are greater than 0, the client discards the Cheng, et al. Expires March, 2023 [Page 7] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 IA_SRV6_LOCATOR option and processes the remainder of the message as though the server had not included the IA_SRV6_LOCATOR option. If the device does not support IA_SRV6_LOCATOR, this IA_SRV6_LOCATOR option should be ignored. 4.2. IA SRv6 Locator Option The IA SRv6 Locator option is used to specify a SRv6 locator associated with an IA_SRV6_LOCATOR. The IA SRv6 Locator option must be encapsulated in the IA_SRV6_LOCATOR-options field of an IA_SRV6_LOCATOR option (see Section 4.1). The terms Locator Block and Locator Node correspond to the B and N parts, respectively, of the SRv6 Locator that is defined in Section 3.1 of [RFC8986]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_IALOCATOR | Option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preferred-lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid-lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LOC-len | Func-len | Args-len | LB-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | SRv6-Locator | | (16 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . IALocator-options . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: IA SRv6 Locator Option Format Where: - Option-code: OPTION_IALOCATOR (TBD). - Option-len: 28 + length of IALocator-options field. - Preferred-lifetime: The preferred lifetime for the SRv6 locator in the option, expressed in units of seconds. A value of 0xffffffff represents "infinity" (see Section 7.7 of [RFC8415]). A 4-octet field containing an unsigned integer. Cheng, et al. Expires March, 2023 [Page 8] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 - Valid-lifetime: The valid lifetime for the SRv6 locator in the option, expressed in units of seconds. A value of 0xffffffff represents "infinity". A 4-octet field containing an unsigned integer. - LOC-len: The locator (LOC) length of SRv6 SID in bits. A 1-octet unsigned integer. - Func-len: The function (FUNCT) length of SRv6 SID in bits. A 1- octet unsigned integer. - Args-len: The arguments (ARG) length of SRv6 SID in bits. A 1- octet unsigned integer. - LB-len: The Locator Block length of SRv6 SID in bits. A 1-octet unsigned integer. - SRv6-locator: A SRv6 locator prefix. A 16-octet field. - IALocator-options: Options associated with this SRv6 locator. A variable-length field (28 octets less than the value in the Option- len field). For compressible SID, the length of Locator Node is LOC-len minus LB-len. In a message sent by a client to a server, the preferred-lifetime and valid-lifetime fields SHOULD be set to 0. The server MUST ignore any received values in these lifetime fields. The client SHOULD NOT send an IA SRv6 Locator option with 0 in the "LOC-len" field (and an unspecified value (::) in the "SRv6-Locator" field). A client MAY send a non-zero value in the "LOC-len" field and the unspecified value (::) in the "SRv6-Locator" field to indicate a preference for the size of the SRv6 locator to be delegated. The LOC-len hint of IA_SRV6_LOCATOR is the same as prefix-length hint of IA_PD. For further details on LOC-len hints, see [RFC8168]. The client MUST discard any SRv6 locators for which the preferred lifetime is greater than the valid lifetime. The values in the preferred-lifetime and valid-lifetime fields are the number of seconds remaining in each lifetime. For more details on how these values are used to assign locators, see section 18.2.10.1 of [RFC8415], which is the same as prefix delegation. Cheng, et al. Expires March, 2023 [Page 9] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 As per Section 7.7 of [RFC8415], the value of 0xffffffff for the preferred lifetime or the valid lifetime is taken to mean "infinity" and should be used carefully. An IA SRv6 Locator option may appear only in an IA_SRV6_LOCATOR option. More than one IA SRv6 Locator option can appear in a single IA_SRV6_LOCATOR option. The status of any operations involving this IA SRv6 Locator option is indicated in a Status Code option (see Section 21.13 of [RFC8415]) in the IALocator-options field. 5. Process of Assigning Locator This document assumes that a client SHOULD use a single transaction for all of the IA options required on an interface. This simplifies the client implementation and reduces the potential number of transactions required (for the background on this design choice, refer to Section 4 of [RFC7550]). If a client requests multiple IA option types, follow [RFC7550]. 5.1.1. DHCP Client Behavior A client uses the Solicit message to discover DHCPv6 servers configured to assign leases or return other configuration parameters on the link to which the client is attached. A client uses Request, Renew, Rebind, Release, and Decline messages during the normal lifecycle of addresses and delegated prefixes. The process of applying for SRv6 locator is the same as that of applying for PD. When applying for SRv6 locator, the DHCPv6 client sends a request message carrying the IA_SRV6_LOCATOR option to the DHCPv6 server. Upon the receipt of a valid reply message with IA_SRV6_LOCATOR option in response to a Solicit with a Rapid Commit option, Request, Confirm, Renew, or Rebind message, the client SHOULD process the Reply message according to the requirements of Section 18.2 of [RFC8415], and configure the delegated locator in the client device automatically. When the client uses a delegated locator prefix to configure SRv6 locator locally, the preferred and valid lifetimes of those locators MUST be no longer than the remaining preferred and valid lifetimes respectively for the delegated SRv6 locator at any time. Cheng, et al. Expires March, 2023 [Page 10] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 To extend the preferred and valid lifetimes for the leases assigned to the IAs and obtain new delegated SRv6 locators for IAs, the client sends a Renew/Rebind message to the server with IA_SRV6_LOCATOR option. When the valid lifetime of the SRv6 locator expires, or the new lifetime replied by the server is 0, delete the corresponding SRv6 locator. If the client no longer uses the delegated SRv6 locator, the client can actively send a Release message to notify the server to reclaim locator prefixes and delete the corresponding SRv6 locator. The client MUST include options containing the IAs for the locators it is releasing in the IA_SRV6_LOCATOR-options of IA_SRV6_LOCATOR option. 5.1.2. DHCP Server Behavior As described in [RFC8415], when the server receives a valid Request message or a valid Solicit message with a Rapid Commit option, the server creates the bindings for that client according to the server's policy and configuration information and records the IAs and other information requested by the client. The DHCPv6 server treats the locator as the prefix of prefix pool, which is similar to the prefix allocation process. Upon the receipt of the IA_SRV6_LOCATOR option, the server searches locator prefix pool and allocates appropriate locators for the client. If there is an assignable locator prefix, the server records the locator binding entry and encapsulates the locator information into the DHCPv6 Reply message. The IA_SRV6_LOCATOR option fills with the locator prefix information assigned to the client. The IA SRv6 Locator option populates the SRv6 locator length, function length, arguments length and Locator Block length of SRv6 SID specified by the DHCPv6 server. For the scenario described in Section 2 where the BRAS device acts as a DHCPv6 server, after the locator is successfully delegated, the server generates a locator subnet route locally, and the outgoing interface of the route is the access interface connecting the client. Upon receiving the Release message from the client or when the locator lease expires, the server reclaims the locator prefix resource and deletes the locator binding entry. If the BRAS device acts as a DHCPv6 server, the server also SHOULD delete the corresponding locator subnet route locally. Cheng, et al. Expires March, 2023 [Page 11] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 For any IA_SRV6_LOCATOR option in the request message to which the server cannot assign any delegated SRv6 locator prefixes, the server MUST return the IA_SRV6_LOCATOR option in the Reply message with no prefixes in the IA_SRV6_LOCATOR and with a Status Code option containing status code NoPrefixAvail in the IA_SRV6_LOCATOR. 5.1.3. DHCP Relay Agent Behavior For the scenario described in Section 2, if an external DHCPv6 server is deployed to allocate locators, the DHCPv6 relay agent service needs to be enabled on the layer 3 network nodes close to CPE. As shown in the figure below, the DHCP relay function is enabled on the router directly connected to CPE. DHCP Relay +------+ +------+ +------+ +-----+ | Host +-----+ CPE +-------+Router+------+ BRAS| +------+ +------+ +------+ +--+--+ | | +------+-----+ | Backbone | | Network | +------------+ Figure 4: CPE accessed through DHCP relay When the first hop DHCPv6 relay agent device connected to the DHCPv6 PD client receives DHCPv6 Relay-reply messages, it extracts the IA_SRV6_LOCATOR option from the Relay Message option, and obtains the locator delegated by the DHCPv6 server according to IA SRv6 Locator option. The first DHCPv6 relay agent needs to record the locator delegated by the DHCPv6 server, including locator information, lifetime, etc. and generates locator route locally. The outgoing interface of the route is the access interface connecting the client. After receiving the DHCPv6 message releasing the locator prefix from the client or the valid lifetime of Locator prefix expires, the first DHCPv6 relay agent device SHOULD delete the locator route locally. 6. IANA Considerations IANA is kindly requested to assign new values for OPTION_IA_SRV6_LOCATOR (TBD) and OPTION_IALOCATOR (TBD) and add the values to the DHCPv6 Option Codes registry maintained at http://www.iana.org/assignments/dhcpv6-parameters. Cheng, et al. Expires March, 2023 [Page 12] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 7. Security Considerations See [RFC8415] for the DHCPv6 security considerations. 8. References 8.1. Normative References [RFC7550] Troan, O., Volz, B., Siodelski, M., "Issues and Recommendations with Multiple Stateful DHCPv6 Options", RFC 7550, DOI 10.17487/RFC7550, May 2015, . [RFC8168] Li, T., Liu, C., Cui, Y., "DHCPv6 Prefix-Length Hint Issues", RFC 8168, DOI 10.17487/RFC8168, May 2017, . [RFC8415] Mrugalski, T., Siodelski, M ., Volz, B., Yourtchenko, A., Richardson, M., Jiang, S., Lemon, T., and Winters, T., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 8415, DOI 10.17487/RFC8415, November 2018, . [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, February 2021, . Cheng, et al. Expires February, 2023 [Page 13] Internet-Draft Distribute SRv6 Locator by DHCP September 2022 Authors' Addresses Weiqiang Cheng China Mobile Email: chengweiqiang@chinamobile.com Ruibo Han China Mobile Email: hanruibo@chinamobile.com Changwang Lin New H3C Technologies Email: linchangwang.04414@h3c.com Yuanxiang Qiu New H3C Technologies Email: qiuyuanxiang@h3c.com Cheng, et al. Expires February, 2023 [Page 14]