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SAVI                                              J. Bi, J. Wu, G. Yao
Internet Draft                                                 CERNET
Intended status: Standard Tracks                             F. Baker
Expires: September 2010                                         Cisco
                                                         March 8, 2010



                          SAVI Solution for DHCP
                        draft-ietf-savi-dhcp-01.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 8, 2010.




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Copyright Notice

   Copyright (c) 2010 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
   (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.

Abstract

   This document specifies the procedure for creating bindings between a
   DHCPv4 [RFC2131]/DHCPv6 [RFC3315] assigned source IP address and an
   anchor (refer to [SAVI-framework]) on SAVI (Source Address Validation
   Improvements) device. The bindings can be used to filter packets
   generated on the local link with forged IP addresses.

Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................4
   3. Mechanism Overview.............................................4
   4. Background and Related Protocols...............................4
   5. Terminology....................................................5
   6. Conceptual Data Structures.....................................5
      6.1. Binding State Table (BST).................................5
      6.2. Filtering Table (FT)......................................5
   7. Binding States Description.....................................6
   8. DHCP Scenario..................................................6
   9. Anchor Attributes..............................................7
      9.1. SAVI-Validation Attribute.................................7
      9.2. SAVI-DHCP-Trust Attribute.................................7
      9.3. SAVI-SAVI Attribute.......................................8
   10. Prefix Configuration..........................................8
   11. Binding Set Up................................................9
      11.1. Process of DHCP Snooping.................................9
         11.1.1. Initialization......................................9
            11.1.1.1. Trigger Event..................................9
            11.1.1.2. Event Validation...............................9
            11.1.1.3. Following Actions.............................10


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         11.1.2. From START to LIVE.................................10
            11.1.2.1. Trigger Event.................................10
            11.1.2.2. Event Validation..............................10
            11.1.2.3. Following Actions.............................10
         11.1.3. From LIVE to DETECTION.............................12
            11.1.3.2. Event Validation..............................12
            11.1.3.3. Following Actions.............................12
         11.1.4. From DETECTION to BOUND............................13
            11.1.4.1. Trigger Event.................................13
            11.1.4.2. Following Actions.............................13
         11.1.5. After BOUND........................................13
      11.2. State Machine of DHCP Snooping..........................14
   12. Filtering Specification......................................15
      12.1. Data Packet Filtering...................................16
      12.2. Control Packet Filtering................................16
   13. Format and Delivery of Probe Messages........................17
      13.1. Duplicate detection.....................................17
   14. Binding Remove...............................................17
   15. Handle Anchor Off-link event.................................18
   16. About Collision in Detection.................................18
      16.1. Whether to notify the DHCP server.......................18
      16.2. The result of detection without host aware..............18
   17. Filtering during detection...................................18
   18. Binding Number Limitation....................................19
   19. Movement without DHCP Procedure..............................19
   20. MLD Consideration............................................19
   21. State Restoration............................................19
   22. Constants....................................................20
   23. Security Considerations......................................20
   24. IANA Considerations..........................................20
   25. References...................................................20
      25.1. Normative References....................................20
      25.2. Informative References..................................21
   26. Acknowledgments..............................................21

1. Introduction

   This document describes the procedure for creating bindings between
   DHCP assigned addresses and an anchor (refer to [savi-framework]).
   Other related details about this procedure are also specified in this
   document.

   These bindings can be used to filter packets with forged IP addresses.
   How to use these bindings is specified in [savi-framework], depending
   on the environment and configuration. The definition and examples of
   anchor is also specified in [savi-framework].



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   The binding process is inspired by the work of IP Source Guard. This
   specification differs from IP Source Guard in the specification for
   collision detection, which is essential in environments with multiple
   address assignment methods.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3. Mechanism Overview

   The mechanism specified in this document is designed to provide a
   host level source IP address validation granularity, as a supplement
   to BCP38 [BCP38]. This mechanism is deployed on the access device
   (including access switch, wireless access point/controller, etc), and
   performs mainly DHCP snooping to set up bindings between DHCP
   assigned IP addresses and corresponding anchors. The bindings can be
   used to validate the source address in the packets.

4. Background and Related Protocols

   This mechanism is an instance of a SAVI [savi-framework] solution,
   specialized for addresses assigned using the DHCP protocol.

   Dynamic Host Configuration Protocol version 4 [RFC2131] and Dynamic
   Host Configuration Protocol version 6 [RFC3315] specify the
   procedures for providing a client with assigned address and other
   configuration information from a DHCP server. If a client gets an
   address through the DHCP protocol, the address should be regarded as
   a potential "authorized" or "registered" address of the client.

   In IPv6, IPv6 Stateless Autoconfiguration [RFC4862] is used as
   another address assignment mechanism. A node can use this mechanism
   to auto-configure an IPv6 address. A DHCPv6 client may use a
   stateless address to send message to DHCP server. Even in a DHCPv6-
   only environment, a node must assign its link-local address through
   this mechanism. [RFC4862] clearly requires that duplicated address
   detection must be performed on any IPv6 address, including DHCPv6
   address.

   [RFC4861] specifies the Neighbor Discovery protocol, which is an
   essential part of IPv6 address assignment.

   [RFC5227] specifies the procedure to detect IPv4 address collision.
   It is not required currently. However, this feature is useful to


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   determine the uniqueness of an IPv4 address on the link. Considering
   not all the operating systems support [RFC5227], this solution is
   designed to be compatible with operating systems not complying with
   [RFC5227].

5. Terminology

   Main terms used in this document are described in [savi-framework],
   [RFC2131] and [RFC3315].

6. Conceptual Data Structures

   This section describes the possible conceptual data structures used
   in this mechanism.

   Two main data structures are used to record bindings and their states
   respectively. There is redundancy between the two structures, for the
   consideration of separation of data plane and control plane.

6.1.  Binding State Table (BST)

   This table contains the state of binding between source address and
   anchor. Entries are keyed on the anchor and source IP address. Each
   entry has a lifetime field recording the remaining lifetime of the
   entry, a state field recording the state of the binding and a field
   recording other information.

             +---------+----------+-------+-----------+-------+
             | Anchor  | Address  | State | Lifetime  |Other  |
             +---------+----------+-------+-----------+-------+
             | A       | IP_1     | Bound |  65535    |       |
             +---------+----------+-------+-----------+-------+
             | A       | IP_2     | Bound |  10000    |       |
             +---------+----------+-------+-----------+-------+
             | B       | IP_3     |_Start |      1    |       |
             +---------+----------+-------+-----------+-------+
                         Figure 1 Instance of BST


6.2.  Filtering Table (FT)

   This table contains the bindings between anchor and address, keyed on
   anchor. This table doesn't contain any state of the binding. This
   table is only used to filter packets. An Access Control List can be
   regarded as a practical instance of this table.




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                          +---------+----------+
                          |Anchor   |Address   |
                          +---------+----------+
                          |A        |IP_1      |
                          +---------+----------+
                          |A        |IP_2      |
                          +---------+----------+
                          Figure 2 Instance of FT

7. Binding States Description

   This section describes the binding states of this mechanism.

   START        A DHCP request (or a DHCPv6 Confirm, or a DHCPv6
   Solicitation with Rapid Commit option) has been received from host,
   and it may trigger a new binding.

   LIVE       A DHCP address has been acknowledged by a DHCP server.

   DETECTION    A gratuitous ARP or Duplicate Address Detection NSOL
   has been sent by the host (or the SAVI device).

   BOUND       The address has passed duplicate detection and
             it is bound with the anchor.

8. DHCP Scenario

   Figure 3 shows the main elements in a DHCP enabled network. At least
   one DHCP server MUST be deployed in the network, and DHCP relay MAY
   be used to relay message between client and server. Other address
   assignment mechanisms may be also used in such network.

















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                                +--------+
                                | DHCP   |
                                | Server |
                                +-------,+
                                    |
                                    |
                                    |
                               +----'-----+
                               |  SAVI    |
                               |  Device  |
                               +-/------/-+
                                 |      |
                            +----\-+   +\-----+
                            |DHCP  |   |Client|
                            |Relay |   |      |
                            +------+   +------+
                          Figure 3 DHCP Scenario

9. Anchor Attributes

   This section specifies the anchor attributes involved in this
   mechanism.

   Anchor is defined in the [savi-framework]. Attribute of each anchor
   is configurable. In default, anchor has no attribute. An anchor MAY
   be configured to have one or more compatible attributes. However, an
   anchor MAY have no attribute.

   If an anchor has no attribute, server type DHCP message from this
   anchor MUST be dropped. However, other packets SHOULD NOT be dropped.

9.1. SAVI-Validation Attribute

   If and only if source address validation must be performed on the
   traffic from an anchor, this anchor MUST be set to have SAVI-
   Validation attribute. The filtering process on anchor with such
   attribute is described in section 12.

9.2. SAVI-DHCP-Trust Attribute

   If and only if an anchor is associated with a trustable DHCP
   server/relay, it SHOULD be set to have this attribute.

   If DHCP is used to assign address in the network, there MUST be at
   least one anchor with this attribute. DHCP Reply message not coming
   from such ports MUST be dropped.



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9.3. SAVI-SAVI Attribute

   If and only if an anchor is associated with another SAVI device, it
   SHOULD be set to have this attribute. All traffic from anchor with
   this attribute will be forwarded without check.

   This attribute is mutually exclusive with SAVI-Validation.

10. Prefix Configuration

   In DHCP scenario, address advertised by DHCP server should be
   believed in. However, in this solution, a node shares the same anchor
   as the DHCP server can disguise as the DHCP server and offer the
   client incorrect configuration information. Without fully deployment
   of SAVI, this problem is difficult to solve. Thus, it is SUGGESTED
   that correct address prefix should be configured, and DHCP server
   message which assigns address out of the scope should be dropped.
   This mechanism can ensure the client can at least get an address with
   proper prefix.

   This document suggests set 3 prefix scopes:

   IPv4 Prefix:

         The allowed scope of any kind of IPv4 addresses. It can be set
         manually.

   IPv6 SLAAC Prefixes:

         The allowed scope of SLAAC and manually configured IPv6
         addresses. It can be set through snooping RA message from port
         with SAVI-RA-Trust attribute, DHCP-PD or manual configuration.

       FE80::/64 MUST be set to a feasible prefix.

   IPv6 DHCPv6 Prefixes:

         The allowed scope of DHCPv6 addresses. It can be set through RA
         snooping, DHCP-PD protocol, or manual configuration.

   There is no need to explicitly present these prefix scopes. But these
   restrictions SHOULD be used as premier check in binding set up.

   Refer to security consideration for other discussions.





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11. Binding Set Up

   This section specifies the procedure of setting up bindings based on
   control packet snooping. All binding entries are set up on anchor
   with SAVI-Validation attribute.

11.1. Process of DHCP Snooping

11.1.1. Initialization

   A binding entry is initialized in this step.

   This step MAY NOT be performed if:

   1. Option 82 is used to keep anchor in DHCP Request and Reply, or

   2. Unspoofable MAC is used as anchor(802.11i,802.1ae/af), or

   3. The mapping table from MAC to anchor is secure.

   If none of these three requirements are satisfied, this step SHOULD
   be performed.

   If this step is not performed, then binding entry will be initialized
   in the next step.

   This step is performed for the consideration that anchor and DHCP
   assigned address can be bound with security in the next step.
   Otherwise the security of binding setup is based on the mapping
   mechanism from MAC to anchor on SAVI device, which may be vulnerable.

   This step can also help limit the request rate of client to prevent
   Denial of Services attack against DHCP server.

11.1.1.1. Trigger Event

   A DHCPv4/v6 Request or a DHCPv6 Confirm or a DHCPv6 Solicitation with
   Rapid Commit option is received.

11.1.1.2. Event Validation

   The SAVI device checks current BST as follows:

   1. Whether the limitation on binding entry number of this anchor will
      be exceeded if a new entry is triggered.




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11.1.1.3. Following Actions

   If the check is passed:

   The SAVI device MUST forward the message.

   The SAVI device MUST generate an entry for the anchor in the Binding
   State Table (BST) and set the state field to START. The lifetime of
   this entry MUST set to be MAX_DHCP_RESPONSE_TIME. The Transaction ID
   (Refer to Section 2 in [RFC2131] and Section 4.2 in [RFC3315]) field
   of the request packet SHOULD be recorded in the entry.

   +---------+----------+-------+-----------------------+-------+
   | Anchor  | Address  | State | Lifetime              |Other  |
   +---------+----------+-------+-----------------------+-------+
   | A       |          | START |MAX_DHCP_RESPONSE_TIME | TID   |
   +---------+----------+-------+-----------------------+-------+
              Figure 4 Binding entry in BST on initialization

   The TID is kept for assurance that the assigned address can be bound
   with anchor securely. It is suggested to keep TID in entry. However,
   TID MAY NOT be contained in the entry.

11.1.2. From START to LIVE

11.1.2.1. Trigger Event

   A DHCPv4 DHCPACK or DHCPv6 REPLY message is received.

11.1.2.2. Event Validation

   The SAVI device checks the message and BST as follows:

   1. Whether the message is received from an anchor which has the SAVI-
      DHCP-Trust attribute;

   2. Whether the entry in the BST with corresponding TID is in the
      START state. Or if the prior step is not performed, check whether
      the binding number limitation will be exceeded.

11.1.2.3. Following Actions

   If the check is passed:

   The SAVI device MUST deliver the message to the destination.




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   The SAVI device MUST set the state of the corresponding entry to be
   LIVE. If prior step is not performed, a new entry MUST be generated
   in the BST. The lifetime of the entry MUST be set to be
   MAX_ARP_PREPARE_DELAY or MAX_DAD_PREPARE_DELAY respectively. The
   lease time MUST be recorded in the entry.

   +---------+----------+-------+------------------------+-------+
   | Anchor  | Address  | State | Lifetime               |Other  |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr     | LIVE  |MAX_ARP_PREPARE_DELAY or| Lease |
   |         |          |       |MAX_DAD_PREPARE_DELAY   | Time  |
   +---------+----------+-------+------------------------+-------+
                Figure 5 Binding entry in BST on assignment

   Then, the SAVI device MAY set the state of the corresponding entry to
   be DETECTION, and send two or more ARP Request or NSOL for the
   assigned address. If the SAVI device sends detection packet directly,
   the next step MUST be omitted.

   +---------+----------+-----------+-----------------+-------+
   | Anchor  | Address  | State     | Lifetime        |Other  |
   +---------+----------+-----------+-----------------+-------+
   | A       | Addr     | DETECTION |MAX_ARP_DELAY or | Lease |
   |         |          |           |MAX_DAD_DELAY    | Time  |
   +---------+----------+-----------+-----------------+-------+
         Figure 6 Binding entry in BST on assignment: another case

   The SAVI device MUST insert an entry into the Filtering Table if the
   assigned address is not bound with another anchor in current BST. If
   the address has been bound with another anchor in current BST, the
   SAVI device MUST check if the node associated with that anchor is
   off-line. If yes, bind the address with the new entry and delete the
   original binding; if no, keep the original entry and delete the new
   entry in BST. This mechanism can handle local link movement, and
   avoid attacker grabbing assigned bindings from other nodes. However,
   if several hosts share the same anchor, and one of them moves to
   another anchor, this mechanism may cause problem.

                          +---------+----------+
                          |Anchor   |Address   |
                          +---------+----------+
                          |A        |Addr      |
                          +---------+----------+
                Figure 7 Binding entry in FT on assignment

   The following steps after this step MAY NOT be performed. It is
   SUGGESTED to perform following steps unless in some specified


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   scenario, e.g., a DHCP-only scenario. If the following steps are not
   performed because of implementation or configuration, the state of
   the corresponding entry MUST be changed to BOUND, and the lifetime is
   set to lease time.

11.1.3. From LIVE to DETECTION

11.1.3.1. Trigger Event

   A gratuitous ARP Request or Duplicate Address Detection Neighbor
   Solicitation is received from anchor. Or a timeout event of an entry
   with state LIVE happens.

11.1.3.2. Event Validation

   The SAVI device checks the message and BST as follows:

   1. Whether the Target IP Address field of the ARP Request or Neighbor
      Solicitation has been bound with the corresponding anchor in BST
      or FT.

11.1.3.3. Following Actions

   If the check is passed:

   If timeout event of an entry with state LIVE happens, the SAVI device
   MAY send one or more ARP Request or a DAD NSOL, with Target Address
   set to the recorded address in the entry. If detection packets are
   sent, the SAVI device MUST set the state of the entry to be DETECTION.
   The lifetime of the entry MUST be set to be MAX_ARP_DELAY or
   MAX_DAD_DELAY respectively. If no detection packet is sent, the entry
   MUST be removed from BST and FT. If the SAVI device chooses not to
   send detection packet, valid packets may get dropped because a number
   of operating systems don't fully support [RFC4862] and [RFC5227] and
   don't send detection packets themselves. Thus, it is SUGGESTED the
   SAVI device SHOULD send detection packet in case the client doesn't
   send that itself.

   +---------+----------+-----------+-----------------+-------+
   | Anchor  | Address  | State      | Lifetime       |Other  |
   +---------+----------+-----------+-----------------+-------+
   | A       | Addr     | DETECTION  |MAX_ARP_DELAY or| Lease |
   |         |          |            |MAX_DAD_DELAY   | Time  |
   +---------+----------+-----------+-----------------+-------+
                Figure 8 Binding entry in BST on detection




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11.1.4. From DETECTION to BOUND

11.1.4.1. Trigger Event

   A timeout event of an entry with state DETECTION occurs or an ARP
   Response or NA for an address in BST with state DETECTION is received.

11.1.4.2. Following Actions

   If a timeout event of an entry with state DETECTION occurs, set the
   state of the entry to be BOUND. The lifetime of the entry is set to
   be the Lease time acknowledged by DHCP server.

   +---------+----------+-----------+----------------+-------+
   | Anchor  | Address  | State     | Lifetime       |Other  |
   +---------+----------+-----------+----------------+-------+
   | A       | Addr     | BOUND     | Lease time     |       |
   +---------+----------+-----------+----------------+-------+
               Figure 9 Binding entry in BST on finalization

   If an ARP Response or NA for an address in BST with state DETECTION
   is received, remove the corresponding entry in BST and FT. The ARP
   Response or NA MUST be delivered to the client.

11.1.5. After BOUND

   Once a binding entry is set up for an anchor, the binding will be
   used to filter packet with the anchor, as specified in section 12. On
   the other hand, DHCP messages with the anchor will affect the binding.
   The binding is also affected by DHCP server message toward the anchor.

   Before a DHCP message is found that it may change the corresponding
   binding, its validity MUST be checked as described in section 12.2.

   Whenever a DHCP Decline is received, delete the corresponding entry
   in BST and FT.

   Whenever a DHCP Release is received, if the state of the entry is
   BOUND, delete the entry in BST and FT.

   If a DHCPv4 Acknowledgement or DHCPv6 Reply with Renew/Rebind sign is
   received from the server, set lifetime of the entry in BST to be the
   new lease time.

   If the lifetime of an entry with state BOUND expires, delete the
   entry in BST and Filter Table.



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   The binding may also be affected by control messages with or toward
   another anchor. The binding MAY be move to another anchor to handle
   local link movement, as described in section 11.1.2.3. In this
   situation, the node assigned a DCHP address changes to associate with
   another anchor, thus the address should be bound with the anchor
   which the node migrates to. Other than this situation, the binding
   will not be changed, for the consideration of simplicity. Even if an
   attached node becomes inactive and doesn't reply to any NS or ARP
   Request, the associated bindings will not be removed.

   Switch port down event (or more general, anchor turns off-link) will
   change the corresponding entry, as described in section 15.

11.2. State Machine of DHCP Snooping

   The main state transits are listed as follows. Note that the anchor
   migration of binding entry is not included.

   State      Message/Event       Action                      Next State

   -          REQ/CFM/SOL+RC      Generate entry                   START

   *-         ACK/RPL             Generate entry with lease         LIVE

   *-         ACK/RPL             Generate entry with lease        BOUND

   **-        ACK/RPL             Generate entry with lease    DETECTION

                                 , send probe

   START      ACK/RPL             Record lease time                 LIVE

   **START    ACK/RPL             Send probe                   DETECTION

   START      Timeout             Remove entry                         -

   LIVE       Gra ARP REQ/DAD NS  -                            DETECTION

   LIVE       DECLINE             Remove entry                         -

   LIVE       Timeout             Send probe                   DETECTION

   *LIVE      Timeout             Remove entry                         -

   DETECTION  Timeout             -                                BOUND

   DETECTION  ARP RES/DAD NA      Remove entry                         -


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   DETECTION  DECLINE             Remove entry                         -

   BOUND      RELEASE/DECLINE     Remove entry                         -

   BOUND      Timeout             Remove entry                         -

   BOUND      RENEW/REBOUND       Set new lifetime                 BOUND

   *: optional but NOT SUGGESTED.

   **: optional and MAY conflict other transits

   REQ: DHCP REQUEST

   CFM: DHCP CONFIRM

   SOL: DHCP SOLICITATION

   RC:  Rapid Commit option

   ACK: DHCP ACKNOWLEDGEMENT

   RPL: DHCP REPLY

   Probe Gratuitous ARP REQUEST or Duplicate Address Detection Neighbor
   Solicitation, described in section 13.1

   Gra ARP REQ: Gratuitous ARP REQUEST

   ARP RES: ARP RESPONSE

   DAD NS: Duplicate Address Detection Neighbor Solicitation

   DAD NA: Neighbor Advertisement targeting at a tentative address

   DECLINE: DHCP DECLINE

   RELEASE: DHCP RELEASE

   RENEW: DHCP RENEW

   REBOUND: DHCP REBOUND

12. Filtering Specification

   This section specifies how to use bindings to filter packets. Because
   the Filtering Table is an allow-table, packet with source address not


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   in the table will be filtered. Considering DHCP may coexist with
   other address assignment methods, e.g., Stateless Auto-configuration,
   the specification made here is based on the assumption that other
   SAVI solutions will also use BST and FT to keep bindings and filter
   packets. Otherwise this solution will conflict with other SAVI
   solutions.

   Filtering policies are different for data packet and control packet.
   DHCP and ND messages that may cause state transit are classified into
   control packet. Neighbor Advertisement and ARP Response are also
   included in control packet, because the Target Address of NA and ARP
   Response should be checked to prevent spoofing. All other packets are
   considered to be data packets.

12.1. Data Packet Filtering

   Data packets with an anchor which has attribute SAVI-Validation MUST
   be checked.

   If the source of a packet associated with its anchor is in the FT,
   this packet SHOULD be forwarded; or else the packet MUST be discarded.

12.2. Control Packet Filtering

   For anchors with SAVI-Validation attribute:

   The source address of DHCPv4 Discovery SHOULD be set to all zeros.
   The source address of DHCPv4 Request SHOULD be set to all zeros or a
   bound address in FT.

   The source address of DHCPv6 Request MUST be an address associated
   with the corresponding anchor in FT. The source address of DHCPv6
   Confirm MUST be a link local address associated with the
   corresponding anchor in FT. The source address of DHCPv6 Solicit MUST
   be a link layer address bound with corresponding anchor. The link
   layer address MAY be bound based on SAVI-SLAAC solution or other
   solutions.

   The source address of other types of DHCP messages MUST be a address
   bound with the corresponding anchor.

   The source address of IPv6 NS and IPv4 gratuitous ARP MUST pass the
   check on FT.

   The target address and source address in all the Neighbor
   Advertisement packets and ARP replies MUST also pass the checks on FT.



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   For other anchors:

   All DHCP Reply/Ack packets MUST be from anchor with the SAVI-DHCP-
   Trust attribute.

13. Format and Delivery of Probe Messages

   As described in section 11.1.2.3 and 11.1.3.3, the SAVI device MAY
   send detection probes on behavior of client to determine whether the
   assigned address is duplicated. Currently no other probes are
   designed in this solution.

13.1. Duplicate detection

      Message Type: DAD NS, Gratuitous ARP Request

      Format:

                   Link layer source - link layer address of host;

                   Link layer destination - For IPv6, use multicast address
      specified in [RFC3307]; For IPv4, use broadcast address;

                   IP source - Unspecified address for IPv6; The tentative

      address for IPv4;

                   IP destination - For IPv6, multicast address specified in
      section 5.4.2 of [RFC4861]; For IPv4, the tentative address;

      Delivery:

         MUST not be delivered to the host which the SAVI device is
      performing DAD on behavior of.

14. Binding Remove

   If the lifetime of an entry with state BOUND expires, the entry MUST
   be removed.

   When the SAVI device receives a DAD NS/Gra ARP request target at an
   address bound and there is no replies from the anchor, if the anchor
   is a SAVI-Validation anchor, hold the binding entry through sending
   NA/ARP Reply, or remove the binding.





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15. Handle Anchor Off-link event

   Port DOWN event MUST be handled if switch port is used as anchor. In
   more general case, if an anchor turns off-link, this event MUST be
   handled.

   Whenever an anchor with attribute SAVI-Validation turns down, the
   bindings with the anchor MUST be kept for a short time.

   To handle movement, if receiving DAD NS/Gra ARP request targeting at
   the address during the period, remove the entry.

   If the anchor turns on-link during the period, recover bindings. It
   may result in some security problem, e.g., a malicious node
   immediately associates with the anchor got off by a previous node,
   then it can use the address assigned to the previous node. However,
   this situation is very rare in reality. Authors decide not to handle
   this situation.

16. About Collision in Detection

   The SAVI device may receive a response in detection. Some related
   details are specified here.

16.1. Whether to notify the DHCP server

   It is unnecessary for the SAVI device to notify the DHCP server,
   because the host will send a DECLINE message to it once it finds the
   advertised address is conflict.

16.2. The result of detection without host aware

   In case the SAVI device send detection packet instead of the host,
   the host will not be aware of the detection result. If the detection
   succeeds, there is no problem. However, if the detection fails, the
   packets from the host with the assigned address will be filtered out.
   This result can be regarded as a reasonable punishment for not
   performing duplicate detection and using a collision address. The
   SAVI device MAY choose to notice the client that the assigned address
   has been used, through a NA message. This mechanism is not required
   in this solution.

17. Filtering during detection

   In this mechanism, whenever the DHCP server replies an address, this
   address will be allowed immediately even before duplicate detection
   is completed. This design is in consideration of a host may start to


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   send packets straightway without detection. Also this design is to be
   compatible with optimistic DAD [RFC4429].

   However, this feature may allow an attacker to send quantities of
   packets with source addresses already assigned to other nodes. A
   practical solution for this vulnerability is configuring the address
   pool and allocation algorithm of the DHCP server carefully.

18. Binding Number Limitation

   It is suggested to configure some mechanism in order to prevent a
   single node from exhausting the binding table entries on the SAVI
   device. Either of the following mechanism is sufficient to prevent
   such attack.

   1. Set the upper bound of binding number for each anchor with SAVI-
      Validation.

   2. Reserve a number of binding entries for each anchor with SAVI-
      Validation attribute and all anchors share a pool of the other
      binding entries.

   3. Limit DHCP Request rate per anchor, using the bound entry number
      of each anchor as reverse indicator.

19. Movement without DHCP Procedure

   This mechanism currently doesn't handle any movement without DHCP
   procedure, which means the change of anchor without triggering any
   DHCP procedure. The scenario includes several hosts are attached a
   SAVI-Validation port through a hub, and the hub changes from its
   attaching port to another SAVI-Validation port.

   For handling this situation will necessarily lead to a data packet
   triggering procedure on SAVI device, and may violate the semantic of
   DHCP protocol, this situation is not handled in this solution.

20. MLD Consideration

   The SAVI device MUST join the tentative address multicast group
   whenever perform duplicate detection on behavior of host.

21. State Restoration

   If a SAVI device reboots accidentally or designedly, the states kept
   in volatile memory will get lost. This may cause hosts indirectly
   attached to the SAVI device to be broken away from the network,


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   because they can't recover bindings on the SAVI device of themselves.
   Thus, it is SUGGESTED that binding entries can be saved into non-
   volatile storage manually or regularly. Immediately after reboot, the
   SAVI device can restore binding states from the non-volatile storage.

22. Constants

   MAX_DHCP_RESPONSE_TIME     120s

   MAX_ARP_PREPARE_DELAY      Default 1s but configurable

   MAX_ARP_DELAY              Default 1s but configurable

   MAX_DAD_PREPARE_DELAY      Default 1s but configurable

   MAX_DAD_DELAY              Default 1s but configurable

23. Security Considerations

   For prefix level granularity filtering is the basis of host level
   granularity filtering, to learn and configure correct prefix is of
   great importance to this mechanism. Thus, it's important to keep RA
   and DHCP-PD secure. [draft-ietf-v6ops-ra-guard-03] describes a
   mechanism to improve the security of RA message.

24. IANA Considerations

   There is no IANA consideration currently.

25. References

25.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4862] Thomson, S., Narten, T. and Jinmei, T., "IPv6 Stateless
             Autoconfiguration", RFC4862, September, 2007.

   [RFC5227] S. Cheshire, "IPv4 Address Conflict Detection", RFC5227,
             July 2008.








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25.2. Informative References

26. Acknowledgments

Thanks to Christian Vogt, Eric Levy-Abegnoli, Mark Williams, Erik
Nordmark, Marcelo Bagnulo Braun, Alberto Garcia, Jari Arkko, David
Harrington, Pekka Savola, Xing Li, Lixia Zhang, Robert Raszuk, Greg
Daley, Joel M. Halpern, Mikael Abrahamsson and Tao Lin for their
valuable contributions.







































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Authors' Addresses

   Jun Bi
   CERNET
   Network Research Center, Tsinghua University
   Beijing 100084
   China
   Email: junbi@cernet.edu.cn

   Jianping Wu
   CERNET
   Computer Science, Tsinghua University
   Beijing 100084
   China
   Email: jianping@cernet.edu.cn

   Guang Yao
   CERNET
   Network Research Center, Tsinghua University
   Beijing 100084
   China
   Email: yaog@netarchlab.tsinghua.edu.cn


   Fred Baker
   Cisco Systems
   Email: fred@cisco.com





















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