



intarea                                                      L. Zhu, Ed.
Internet-Draft                                             Y. Zhang, Ed.
Intended status: Standards Track                            China Unicom
Expires: 16 August 2026                                 12 February 2026


 Broadband Network UP-Specific Information Suboption for the DHCP Relay
                              Agent Option
            draft-zhul-intarea-bnc-up-specific-suboption-00

Abstract

   This document defines a new Broadband Network UP-Specific Information
   suboption for the Dynamic Host Configuration Protocol’s (DHCP) relay
   agent information option.  The suboption allows the DHCP relay agent
   (Broadband Network CP) to include UP-specific information in the DHCP
   messages it forwards, to ensure that subscribers within the same SGRP
   under the same UP are assigned IP addresses from the same address
   space by the DHCP server.

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
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   This Internet-Draft will expire on 16 August 2026.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.










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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Broadband Network UP-Specific Information Suboption . . . . .   4
   4.  DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . .   5
   5.  DHCP Server Behavior  . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In the broadband network with CU separation, subscribers connecting
   via IPOE first send DHCP Request messages.  These messages are sent
   via the AN to a group of UPs.  UPs implement encapsulating the DHCP
   messages with a tunnel header, then send them to the CP.  After
   successful authentication of the subscribers, the CP selects an
   appropriate UP to carry the subscriber’s services and acts as a DHCP
   Relay Agent to forward the DHCP Request messages to the DHCP SERVER
   to obtain an IP address.




















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+--------------+
| Subscriber 1 |----|                                            1,3_SGRP1
+--------------+    |    +--------------+                   +--------------+
                    |----|      AN      |---------|---------|      UP      |----|
+--------------+    |    +--------------+         |         +--------------+    |
| Subscriber 2 |----|                             |                             |
+--------------+                                  |                             |
                                                  |              5_SGRP1        |
+--------------+         +--------------+         |         +--------------+    |
| Subscriber 3 |---------|      AN      |---------|---------|      UP      |----|      +---------------+     +---------------+
+--------------+         +--------------+                   +--------------+    |      |       CP      |     |               |
                                                                                |------| (Relay Agent) |-----|   DHCP Sever  |
                                                                                |      +---------------+     +---------------+
                                                                  2_SGRP2       |
+--------------+         +--------------+                   +--------------+    |
| Subscriber 4 |---------|      AN      |---------|---------|      UP      |----|
+--------------+         +--------------+         |         +--------------+    |
                                                  |                             |
+--------------+                                  |                             |
| Subscriber 5 |----|                             |              4,6_SGRP2      |
+--------------+    |    +--------------+         |         +--------------+    |
                    |----|      AN      |---------|---------|      UP      |----|
+--------------+    |    +--------------+                   +--------------+
| Subscriber 6 |----|
+--------------+

                 Figure 1: Broadband network diagram

   However, since the DHCP server cannot know that subscribers are borne
   by different UPs, it may assign addresses from different address
   segments to different subscribers accessing through the same UP,
   which is not conducive to address aggregation on the UP.  The best
   practice is that one SGRP on the specific UP should be assigned from
   the same address segment.

   Therefore, this document adds a new suboption, enabling the CP to add
   SGRP information and UP information involved in the DHCP request
   message.  After receiving the message, the DHCP server can divide the
   address pool into several continuous address segments, so that users
   accessing through the same UP can obtain addresses from the same
   address segment.  In this way, the UP can maximize route aggregation
   when advertising prefixes to the IP core network, reducing the
   advertisement of /32 host routes.

2.  Conventions and Definitions

   The following terms and acronyms are used in this document:




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   *  DHCP Relay Agent: This is a concept in all of the following
      protocols, although the details differ between them: BOOTP
      [RFC951] [RFC1542], DHCPv4 [RFC2131] [RFC2132], and DHCPv6[draft-
      ietf-dhc-rfc8415bis].

   *  Subscriber Group(or SGRP): Refers to group subscribers together
      that share states and resources; for example, subscribers sharing
      the same back-up state or subscribers sharing the same IP prefix.

   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.

3.  Broadband Network UP-Specific Information Suboption

   Format of the Broadband Network UP-Specific Information suboption:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Code    |      Len      |          Reserverd            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           SGRP-ID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      UP-Identifier(variable)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 2: Broadband Network UP-Specific Information suboption Format

   Where:

   *  Code: TBA

   *  Len: the number of octets in the sub-option (excluding the sub-
      option ID and length fields); the minimum length is 7.

   *  Reserved: Reserved fields, can be defined according to
      requirements in the future.

   *  SGRP-ID: the ID of SGRP, which is any integer value between 0 to
      2^32-1

   *  UP-Identifier: the identifier of UP which is currently carrying
      the group of users corresponding to the aforementioned SGRP-ID





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   The SGRP-ID has to be stable.  The CP (relay agent) SHOULD use a
   single identifier value consistently for a SGRP.  The SGRP-ID used by
   a relay device SHOULD be comitted to stable storage, unless the relay
   device can regenerate the value upon reboot.

   The UP-Identifier has to be stable and unique.  If the UP-Identifier
   configured in a relay agent is not unique within its administrative
   domain, resource allocation problems may occur as the DHCP server
   attempts to allocate the same resource to subscribers behind two
   different UPs, then UPs can’t implement ip prefix convergence.
   Therefore, a UP-Identifier configured in a relay agent MUST be unique
   within its administrative domain.

   DHCP server attempts to allocate the same resource to subscribers
   behind two different UPs, then UPs can’t implement ip prefix
   convergence.  Therefore, a UP-Identifier configured in a relay agent
   MUST be unique within its administrative domain.

4.  DHCP Relay Agent Behavior

   DHCP relay agent (THE CP) MAY be configured to include a Broadband
   Network UP-Specific Suboption if the include a relay agent
   information option in relayed DHCP messages.  The SGRP-ID strings
   themselves are preferred to be consistent with SGRP provisioning
   parameter.  The UP-Identifier strings themselves can be a loopback
   address of UP or some other ID.

5.  DHCP Server Behavior

   This suboption provides additional information to the DHCP server.
   If it is configured to support this option, the DHCP server may use
   this information to 1) divide the address pool into a smaller block
   using the SGRP-ID and UP-Identifier as indexes, 2) allocate an
   address in the address block indexed by the SGRP-ID and UP-
   Identifier.  There is no special additional processing for this
   suboption.

6.  Security Considerations

   TBD.

7.  IANA Considerations

   A registry is requested to be created for the sub-options in the
   option above.

8.  Normative References




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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC3396]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
              Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
              DOI 10.17487/RFC3396, November 2002,
              <https://www.rfc-editor.org/info/rfc3396>.

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, DOI 10.17487/RFC3046, January 2001,
              <https://www.rfc-editor.org/info/rfc3046>.

Authors' Addresses

   Lin Zhu (editor)
   China Unicom
   Beijing
   China
   Email: zhul14@chinaunicom.cn


   Yutao Zhang (editor)
   China Unicom
   Beijing
   China
   Email: zhangyt118@chinaunicom.cn




















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