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SAVI                                              J. Bi, J. Wu, G. Yao
Internet Draft                                     Tsinghua University
Intended status: Standard Tracks                             F. Baker
Expires: May 2011                                        Cisco Systems
                                                     November 26, 2010


                          SAVI Solution for DHCP
                        draft-ietf-savi-dhcp-07.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 May 26, 2011.





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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 a
   binding 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 source IP address.

Table of Contents


   Copyright Notice ............................................... 2
   Abstract ....................................................... 2
   1. Introduction ................................................ 3
   2. Conventions used in this document............................ 4
   3. Terminology ................................................. 4
   4. SAVI-DHCP Scenario .......................................... 4
   5. Data Structures ............................................. 5
      5.1. Control Plane Data Structure: Binding State Table (BST). 5
      5.2. Data Plane Data Structure: Filtering Table (FT)......... 6
   6. Binding Anchor Attributes.................................... 6
      6.1. No Attribute ........................................... 7
      6.2. SAVI-Validation Attribute............................... 7
      6.3. SAVI-DHCP-Trust Attribute............................... 7
      6.4. SAVI-SAVI Attribute..................................... 7
      6.5. SAVI-BindRecovery Attribute............................. 7
   7. Binding Set Up .............................................. 8
      7.1. Rationale .............................................. 8
      7.2. Binding States Description.............................. 8
      7.3. Events ................................................. 8
         7.3.1. Timer expiration event............................. 8
         7.3.2. Control message arriving events ................... 8


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      7.4. Process of DHCP Packet Snooping ........................ 9
         7.4.1. From NO_BIND to other states ...................... 9
            7.4.1.1. Trigger Event................................. 9
            7.4.1.2. Following Actions............................ 10
         7.4.2. From INIT_BIND to other states ................... 11
            7.4.2.1. Trigger Event................................ 11
            7.4.2.2. Following Actions............................ 12
         7.4.3. From BOUND to other states ....................... 12
            7.4.3.1. Trigger Event................................ 12
            7.4.3.2. Following Actions............................ 12
      7.5. State Machine of DHCP Snooping ........................ 13
   8. Supplemental Binding Process................................ 14
      8.1. Binding Recovery Process............................... 14
   9. Filtering Specification..................................... 15
      9.1. Data Packet Filtering.................................. 16
      9.2. Control Packet Filtering............................... 16
   10. State Restoration ......................................... 16
   11. Handle Binding Anchor Off-link Event ...................... 17
   12. Constants ................................................. 17
   13. Security Considerations.................................... 17
      13.1. Binding Number Limitation............................. 17
      13.2. Risk from Link Layer Routing Dynamic ................. 18
      13.3. Duplicate Bindings of Same Address ................... 18
   14. IANA Considerations........................................ 18
   15. References ................................................ 19
      15.1. Normative References.................................. 19
      15.2. Informative References................................ 19
   16. Acknowledgments ........................................... 20
   17. Change Log ................................................ 21

1. Introduction

   This document describes the procedure for creating bindings between
   DHCP addresses and binding anchor on SAVI device (refer to [I-D.ietf-
   savi-framework]). Other related details about this procedure are also
   specified in this document. The definition and examples of binding
   anchor are specified in [I-D.ietf-savi-framework].

   Bindings can be used to filter packets with forged IP address.
   Section 9 suggests usage of these bindings for common practice.
   [savi-framework] may specify different usages of binding, depending
   on the environment and configuration.

   The mechanism specified in this document is designed to provide a
   binding anchor granularity validation, as a supplement to BCP38
   [BCP38]. This mechanism is deployed on the access device (including
   access switch, wireless access point/controller, etc), and performs


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   mainly DHCP snooping to set up bindings between IP addresses assigned
   by DHCP and corresponding binding anchors. The binding process is
   inspired by the work of IP Source Guard [IP Source Guard].

   This solution is designed for stateful DHCP scenario [RFC2131,
   RFC3315]. In stateless DHCP scenarios [RFC3736], DHCP is used to
   configure other parameters but rather IP address. The address of the
   client SHOULD be bound based on other SAVI solutions, but rather this
   solution.

   This solution is primarily designed for a pure DHCP scenario in which
   only DHCP address is legitimate global address. How to use this
   mechanism in multiple address assignments scenario is discussed in
   [draft-bi-savi-mixed].

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. Terminology

   Lease time:   Lease time in IPv4 [RFC2131] and valid lifetime in
   IPv6 [RFC3315]

4. SAVI-DHCP Scenario

   Figure 1 shows the main elements in a DHCP 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. Multiple SAVI devices and
   non-SAVI devices can co-exist on link. A SAVI device can be attached
   by client, DHCP relay (even DHCP server), SAVI device and non-SAVI
   device.

   Other address assignment mechanisms may be also used in such network.
   However, this solution is primarily designed for a pure DHCP scenario,
   in which only DHCP servers can assign valid global address.

   Note that in IPv6 environment, DHCP procedure cannot be performed on
   an interface without a link-local or global address pre-assigned.
   Thus, to make this solution work, a SAVI solution for link-local
   address MUST be enabled.






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                             /------------\
              +--------+     |            |
              | DHCP   |-----|   Router   |
              | Server |     |            |
              +--------+     \------------/
                                   |
                     --------------|-----------------.
                     |             |                 |
                     |             |                 |
                     |             |                 |
                     |             |                 |
                     |             |                 |
               +-----\----+    +----'-----+      +---\'-----+
               |  SAVI    |    |  SAVI    |      |  Non SAVI|
               |  Device  |    |  Device  |      |  Device  |
               +/---.-----+    +-.------.-+      +-----.----+
                |   |            |      |              |
           /----|   |            |      |              |
           |        |            |      |              |
   +-------/--++----/-----+ +----\-+   +\-----+     +--\---+
   |  SAVI    ||  Non SAVI| |DHCP  |   |Client|     |Client|
   |  Device  ||  Device  | |Relay |   |      |     |      |
   +----------++----------+ +------+   +------+     +------+
                          Figure 1 DHCP Scenario



5. Data Structures

   This section describes the 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.

  5.1.   Control Plane Data Structure: Binding State Table (BST)

   This table contains the state of binding between source address and
   binding anchor. Entries are keyed on the binding 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. The lifetime field
   is used to help remove expired bindings. The state field is used to
   identify state. The other field is used to keep temporary information,
   e.g., the transaction ID (TID, Refer to Section 2 in [RFC2131] and
   Section 4.2 in [RFC3315]) in DHCP request. Before a binding is


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   finished, the lease time of the address is also kept in this field
   because it is improper to keep it in the lifetime field which keeps
   the lifetime of the binding entry but not the address.

             +---------+----------+-------+-----------+-------+
             | Anchor  | Address  | State | Lifetime  |Other  |
             +---------+----------+-------+-----------+-------+
             | A       | IP_1     | Bound |  65535    |       |
             +---------+----------+-------+-----------+-------+
             | A       | IP_2     | Bound |  10000    |       |
             +---------+----------+-------+-----------+-------+
             | B       | IP_3     |_Start |      1    |       |
             +---------+----------+-------+-----------+-------+
                         Figure 2 Instance of BST


  5.2.   Data Plane Data Structure: Filtering Table (FT)

   This table contains the bindings between binding anchor and address,
   keyed on binding anchor and address. 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.

                          +---------+----------+
                          | Anchor  |Address   |
                          +---------+----------+
                          |A        |IP_1      |
                          +---------+----------+
                          |A        |IP_2      |
                          +---------+----------+
                          Figure 3 Instance of FT

6. Binding Anchor Attributes

   This section specifies the binding anchor attributes used in this
   mechanism.

   Attribute of each binding anchor is configurable. By default, binding
   anchor has no attribute. A binding anchor MAY be configured to have
   one or more compatible attributes. However, a binding anchor MAY
   always have no attribute.







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  6.1. No Attribute

   By default, a binding anchor has no attribute. Server type DHCP
   message from binding anchor with no attribute MUST be dropped.
   However, other packets SHOULD NOT be dropped.

  6.2. SAVI-Validation Attribute

   SAVI-Validation attribute is used on binding anchor on which the
   source address is to be validated. The filtering process on binding
   anchor with such attribute is described in section 9.

  6.3. SAVI-DHCP-Trust Attribute

   SAVI-DHCP-Trust Attribute is used on binding anchor on the path to a
   trustable DHCP server/relay.

   DHCP server/relay message coming from binding anchor with this
   attribute will be forwarded.

  6.4. SAVI-SAVI Attribute

   This attribute is used on binding anchor from which the data traffic
   is not to be checked. Binding will not be set up on binding anchor
   with this attribute. Except for message from DHCP server, all packets
   will not be let pass directly.

   Through configuring this attribute on binding anchor that joins two
   or more SAVI devices, SAVI-Validation and SAVI-SAVI attributes
   implement the security perimeter concept in [savi-framework]. Since
   no binding entry is needed on such binding anchor, the binding entry
   resource requirement can be reduced greatly.

   This attribute can also be set on other binding anchors if the
   administrator decides not to validate the traffic from the binding
   anchor.

   This attribute is mutually exclusive with SAVI-Validation.

  6.5. SAVI-BindRecovery Attribute

   This attribute is used on binding anchor that requires data-triggered
   binding recovery described in section 8.1.

   This attribute is mutually exclusive with SAVI-SAVI.




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7. Binding Set Up

   This section specifies the procedure of setting up bindings based on
   DHCP message snooping. The binding procedure specified here is
   exclusively designed for binding anchor with SAVI-Validation
   attribute.

  7.1. Rationale

   The rationale of this mechanism is that if a node attached to a
   binding anchor is legitimate to use a DHCP address, the DHCP
   procedure which assigns the address to the node must has been
   performed on the same binding anchor. This basis stands when the link
   layer routing is stable. However, layer-2 mobility and unstable link
   layer routing may result in that data packet is received from a
   different binding anchor. Infrequent link layer path change can be
   handled (but not perfectly) by the mechanism described in section 8.
   Section 13.2 discusses the situation that link layer routing is
   naturedly unstable. To handle this situation is above the scope of
   this document.

  7.2. Binding States Description

   This section describes the binding states of this mechanism.

   NO_BIND       The state before a binding has been set up.

   INIT_BIND       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.

   BOUND         The address is authorized to the client.

  7.3. Events

7.3.1. Timer expiration event

   EVE_ENTRY_EXPIRE: The lifetime of an entry expires

7.3.2. Control message arriving events

   Only if a control message can pass the check in section 9.2, the
   corresponding event is a valid event.

   EVE_DHCP_REQUEST: A DHCP Request message is received from a binding
   anchor with SAVI-Validation attribute, and the binding entry limit



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   (discussed in "Security Considerations") on the binding anchor has
   not been reached.

   EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received from a binding
   anchor with SAVI-Validation attribute, and the binding entry limit on
   the binding anchor has not been reached.

   EVE_DHCP_OPTION_RC: A DHCPv6 Solicitation message with Rapid Commit
   option is received from a binding anchor with SAVI-Validation
   attribute, and the binding entry limit on the binding anchor has not
   been reached.

   EVE_DHCP_REPLY: A DHCPv4 Acknowledgement or DHCPv6 Reply message is
   received from a binding anchor with SAVI-DHCP-Trust attribute, and
   the message should be forwarded to a binding anchor with SAVI-
   Validation attribute.

   EVE_DHCP_REPLY_NULL: A DHCPv4 Acknowledgement or DHCPv6 Reply message
   is received from a binding anchor with SAVI-DHCP-Trust attribute.

   EVE_DHCP_DECLINE: A DHCP Decline message is received from a binding
   anchor with SAVI-Validation attribute.

   EVE_DHCP_RELEASE: A DHCP Release message is received from a binding
   anchor with SAVI-Validation attribute.

   EVE_LEASEQUERY_REPLY: A successful DHCP LEASEQUERY_REPLY is received
   from a binding anchor with SAVI-DHCP-Trust attribute.

  7.4. Process of DHCP Packet Snooping

7.4.1. From NO_BIND to other states

7.4.1.1. Trigger Event

   EVE_DHCP_REQUEST, EVE_DHCP_CONFIRM, EVE_DHCP_OPTION_RC,
   EVE_DHCP_REPLY_NULL.

   Note that vulnerability may be caused by DHCP Reply triggered
   initialization. The binding of assigned address and binding anchor
   may be threatened if the binding mechanism between binding anchor and
   link layer address is not secure. If one of the following conditions
   is satisfied, the security can be ensured.

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



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

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

   It is NOT RECOMMENDED to initialize a binding based on DHCP Reply,
   until the associated mechanism is also implemented.

7.4.1.2. Following Actions

   If the triggering event is EVE_DHCP_REQUEST/EVE_DHCP_OPTION_RC:

               The SAVI device MUST forward the message.

     The SAVI device MUST generate an entry for the binding anchor in
     the Binding State Table (BST) and set the state field to INIT_BIND.
     The lifetime of this entry MUST set to be MAX_DHCP_RESPONSE_TIME.
     The TID field of the request packet MUST be recorded in the entry,
     except that the mapping from link layer address to binding anchor
     is secure as specified in section 7.2.1.1.

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

     The TID is kept as a mediator of assigned address and the binding
     anchor of requesting node, to assure that the assigned address can
     be bound with binding anchor secure.

   If the triggering event is EVE_DHCP_CONFIRM:

     Other than forwarding the message and generating corresponding
     entry, the address to be confirmed MUST be recorded in the entry.
     Because no lease time will be contained in the REPLY from DHCP
     server, the SAVI device MUST send a LEASEQUERY [RFC5007] message
     querying by IP address to All_DHCP_Relay_Agents_and_Servers
     multicast address [RFC3315] or a configured server address.

   +---------+--------+---------+-----------------------+-------+
   | Anchor  | Address| State   | Lifetime              |Other  |
   +---------+--------+---------+-----------------------+-------+
   | A       | Addr   |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID   |
   +---------+--------+---------+-----------------------+-------+
     Figure 5 Binding entry in BST on Confirm triggered initialization



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   If the triggering event is EVE_DHCP_REPLY_NULL:

     The SAVI device MUST deliver the message to the destination.

     The SAVI device MUST generate as many new entries in BST and FT as
     the number of IADDR found in the message. The binding anchor in
     entry is looked up based on the destination link layer address,
     from mapping table from link layer address to binding anchor (e.g.,
     the MAC-Port mapping table in case that port is used as binding
     anchor). The states of the corresponding entries are set to be
     BOUND. The lifetime of the entries MUST be set to be the lease time.

     The binding entry limit can be exceeded when setting up bindings
     for all addresses in a REPLY message. If there is enough binding
     entry resource, corresponding new entries MUST be generated even
     the binding number limit is exceeded. In case that there is not
     enough resource left, as many as possible entries SHOULD be set up.

   +---------+----------+-------+------------------------+-------+
   | Anchor  | Address  | State | Lifetime               |Other  |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr1    | BOUND |   Lease time 1         |       |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr2    | BOUND |   Lease time 2         |       |
   +---------+----------+-------+------------------------+-------+
         Binding entry in BST on Reply triggered initialization

                          +---------+----------+
                          | Anchor  |Address   |
                          +---------+----------+
                          |A        |Addr1     |
                          +---------+----------+
                          |A        |Addr2     |
                          +---------+----------+

       Figure 6 Binding entry in FT on Reply triggered initialization



7.4.2. From INIT_BIND to other states

7.4.2.1. Trigger Event

   EVE_DHCP_REPLY, EVE_ENTRY_EXPIRE, EVE_LEASEQUERY_REPLY.





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7.4.2.2. Following Actions

   If the trigger event is EVE_DHCP_REPLY:

     The SAVI device MUST deliver the message to the destination.

      If the Address field is null, the lease time in Reply message MUST
      be recorded in the entry with matched TID. The state of the entry
      is changed to be BOUND. If more than one IADDR is found in the
      message, if there is enough binding entry resource, corresponding
      new entries MUST be generated even the binding number limit is
      exceeded. In case that there is not enough resource left, as many
      as possible entries SHOULD be set up.

      If the Address field is not null, the Reply is in response to a
      Confirm message. If the Reply message is of Status Code Success,
      set the Lifetime of corresponding entry to be MAX_LEASEQUERY_DELAY.
      The state of the entry is changed to be BOUND.

   +---------+----------+-------+------------------------+-------+
   | Anchor  | Address  | State | Lifetime               |Other  |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr     | BOUND |  Lease time            |       |
   +---------+----------+-------+------------------------+-------+
                     Figure 7 From INIT_BIND to BOUND

      A corresponding entry MUST also be generated in FT.

   If the trigger event is EVE_ENTRY_EXPIRE:

      The entry MUST be deleted from BST.

   If the trigger event is EVE_LEASEQUERY_REPLY:

     The Lifetime field of entry with corresponding IP address MUST be
   set to the lease time in the LEASEQUERY_REPLY.

7.4.3. From BOUND to other states

7.4.3.1. Trigger Event

   EVE_ENTRY_EXPIRE, EVE_DHCP_RELEASE, EVE_DHCP_DECLINE,
   EVE_DHCP_REPLY_RENEW.

7.4.3.2. Following Actions

   If the trigger event is EVE_ENTRY_EXPIRE:


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     Remove the corresponding entry in BST and FT.

   If the trigger event is EVE_DHCP_RELEASE or EVE_DHCP_DECLINE:

     Remove the corresponding entry in BST and FT. The Release or
     Decline message MUST be forwarded.

   If the trigger event is EVE_DHCP_REPLY_RENEW:

     Set the lifetime of the address to be the new lease time.

  7.5. State Machine of DHCP Snooping

   The main state transits are listed as follows.

   State        Event            Action                       Next State

   NO_BIND       REQ/RC    Generate entry                      INIT_BIND

   NO_BIND       CFM       Generate entry and send Leasequery  INIT_BIND

   *NO_BIND      RPL       Generate entry with lease               BOUND

   INIT_BIND     RPL       Record lease time/set LQ_DLY            BOUND

   INIT_BIND     Timeout   Remove entry                          NO_BIND

   BOUND         LQR       Record lease time                       BOUND

   BOUND         RLS/DCL   Remove entry                          NO_BIND

   BOUND         Timeout   Remove entry                          NO_BIND

   BOUND         RNW       Set new lifetime                        BOUND

   *: optional but NOT RECOMMENDED.

   REQ: EVE_DHCP_REQUEST

   CFM: EVE_DHCP_CONFIRM

   RC:  EVE_DHCP_OPTION_RC

   RPL: EVE_DHCP REPLY

   DCL: DHCP DECLINE



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   RLS: DHCP RELEASE

   RNW: EVE_DHCP_RPL_RENEW

   LQR: EVE_LEASEQUERY_REPLY

   Timeout: EVE_ENTRY_EXPIRE

   LQ_DLY: MAX_LEASEQUERY_DELAY

8. Supplemental Binding Process

   Supplemental binding process is designed to cover conditions that
   packet is sent by node without previous DHCP procedure sensed by the
   SAVI device. A typical situation is that the link topology change
   after the binding has been set up, and then the node will send packet
   to a different port with the bound port. Another scenario is that a
   node moves on the local link without re-configuration process.

   Supplemental binding process is designed to avoid permanent
   legitimate traffic blocking. It is not supposed to set up a binding
   whenever a data packet with unbound source address is received.
   Generally, longer time and more packets are needed to trigger
   supplemental binding processes.

   Binding Recovery Process is a conditional SHOULD. This function
   SHOULD be implemented if the vendor has such ability, unless the
   implementation is known to be directly attached to host. If the
   mechanism is not implemented and managed nodes are not directly
   attached, permanent legitimate traffic blocking can happen until the
   node is reconfigured.

  8.1. Binding Recovery Process

   If a binding anchor is set to have SAVI-BindRecovery attribute,
   packet without matched binding can trigger the SAVI device to check
   if the source address can be used by corresponding node:

   1. Check if the address has a local conflict through sending 2 DAD
      NS/ARP on the address. If duplicate detection fails, the packet
      MUST be discarded. Otherwise, go to the next step.

   2.

   IPv4 address:




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   Send a DHCPLEASEQUERY [RFC4388] message querying by IP address to all
   DHCPv4 servers for IPv4 address or a configured server address. The
   server addresses may be discovered through DHCPv4 Discovery. If no
   DHCPLEASEACTIVE message is received, discard the packet; otherwise
   generate a new binding entry for the address.

   IPv6 address:

   Send a LEASEQUERY [RFC5007] message querying by IP address to
   All_DHCP_Relay_Agents_and_Servers multicast address or a configured
   server address. If no successful LEASEQUERY-REPLY is received,
   discard the packet; otherwise generate a new binding entry for the
   address. The SAVI device may repeat this process if a LEASEQUERY-
   REPLY with OPTION_CLIENT_LINK is received, in order to set up binding
   entries for all the address of the client.

   This process MUST be rate limited to avoid Denial of Services attack
   against the SAVI device itself. A constant BIND_RECOVERY_INTERVAL is
   used to control the frequency. Two data-triggered recovery processes
   on one binding anchor MUST have a minimum interval time
   BIND_RECOVERY_INTERVAL. This constant SHOULD be configured prudently
   to avoid Denial of Service attacks.

   This process is not strict secure. The node with SAVI-BindRecovery
   binding anchor has the ability to use the address of an inactive node,
   which doesn't reply to the detection probes.

   In case that SAVI device is pure layer-2 device without IP address,
   it is impossible to perform DHCP LEASEQUERY. It is SUGGESTED NOT to
   perform this data-triggered process. If binding recovery is still
   required, DHCP Confirm SHOULD be sent instead of DHCP LEASEQUERY. The
   security degree will degrade for the address may not be assigned by
   DHCP server. A default lifetime DEFAULT_LEASE SHOULD be set with the
   entry.

   This process may fail if any DHCP server doesn't support DHCP
   LEASEQUERY.

9. Filtering Specification

   This section specifies how to use bindings to filter packets.

   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



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   Response should be checked to prevent spoofing. All other packets are
   considered to be data packets.

  9.1. Data Packet Filtering

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

   If the source of a packet associated with its binding anchor is in
   the FT, this packet SHOULD be forwarded; or else the packet SHOULD be
   discarded, or alternatively the SAVI SHOULD record this violation.

  9.2. Control Packet Filtering

   For binding anchors with SAVI-Validation attribute:

   Discard/record DHCPv4 Discovery with non-all-zeros source IP address.
   Discard/record DHCPv4 Request whose source IP address is neither all
   zeros nor a bound address in FT.

   Discard/record DHCPv6 Request whose source is not bound with the
   corresponding binding anchor in FT. Discard/record DHCPv6 Confirm/
   Solicit whose source is not a link local address bound with the
   corresponding binding anchor in FT. The link layer address may be
   bound based on SAVI-SLAAC solution or other solutions.

   Discard/record other types of DHCP messages whose source is not an
   address bound with the corresponding binding anchor.

   Discard/record IPv6 NS and IPv4 gratuitous ARP whose source is not an
   address bound with the corresponding binding anchor.

   Discard/record NA and ARP Replies messages whose target address and
   source address are not bound with the corresponding binding anchor.

   For other binding anchors:

   Discard DHCP Reply/Ack messages not from binding anchor with the
   SAVI-DHCP-Trust attribute or SAVI-SAVI attribute.

10. 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,
   because they can't recover bindings on the SAVI device of themselves.
   Purely using the Binding Recovery Process is of great cost and delay


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   to recover a large number of bindings. Thus, recovery from non-
   volatile storage is designed.

   Binding entries MUST be saved into non-volatile storage whenever a
   new binding entry changes to BOUND state or a binding with state
   BOUND is removed in condition that this function is supported by
   hardware. Immediately after reboot, the SAVI device MUST restore
   binding states from the non-volatile storage. The lifetime and the
   system time of save process MUST be stored. Then the device MUST
   check whether the saved entries are obsolete when rebooting.

11. Handle Binding Anchor Off-link Event

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

   Whenever a binding anchor with attribute SAVI-Validation turns down,
   set a timer with OFFLINK_DELAY. Until the timer becomes zero, the
   bindings with the binding anchor SHOULD be kept. As an exception, to
   handle movement, if receiving DAD Neighbor Solicitation/Gratuitous
   ARP request targeting at the address during OFFLINK_DELAY, the entry
   MAY be removed.

   If the binding anchor turns on-link during OFFLINK_DELAY, turn off
   the timer and keep corresponding bindings.

12. Constants

   MAX_DHCP_RESPONSE_TIME     120s

   BIND_RECOVERY_INTERVAL     60s and configurable

   MAX_LEASEQUERY_DELAY       10s

   DEFAULT_LEASE              2h

   OFFLINK_DELAY              2s

13. Security Considerations

  13.1. 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.


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

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

   3. Limit DHCP Request rate per binding anchor.

  13.2. Risk from Link Layer Routing Dynamic

   An implicit assumption of this solution is that data packet must
   arrive at the same binding anchor with the binding anchor that the
   control packets have arrived at. If this assumption is not valid,
   this control packet based solution will fail or at least discard
   legitimate packet. Unfortunately, the link layer routing between host
   and SAVI device can be inconsistent from time to time. Time
   consistency of link layer routing is not assured by link layer
   routing protocol. For example, TRILL, a recent link layer routing
   protocol, is flexible and multiple link layer paths are allowed.

   To make the basic assumption stand, the best way is enforcing that
   there should be only one topology path from downstream host to the
   SAVI device. For example, SAVI device is directly attached by hosts.

   If the assumption doesn't stand, a better solution is requiring
   inter-operation between SAVI protocol and the link layer routing
   protocol to make SAVI protocol sensitive to the link layer routing
   change. This solution is above the scope of this document.

  13.3. Duplicate Bindings of Same Address

   The same address may be bound with multiple binding anchors, only if
   the binding processes are finished on each binding anchor
   successfully respectively. This mechanism is designed in
   consideration that a node may move on the local ink, and a node may
   have multiple binding anchors. However, the traceability of address
   is reduced.

   Note that the local link movement scenario is not handled perfectly.
   The former binding may not be removed, unless the node is directly
   attached to the SAVI device. The nodes sharing the same former
   binding anchor of the moving node have the ability to use its address.

14. IANA Considerations

   There is no IANA consideration currently.


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15. References

  15.1. Normative References

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

   [I-D.ietf-savi-framework] Wu, J., Bi, J., Bagnulo, M., Baker, F., and
   C. Vogt, "Source Address Validation Improvement Protocol Framework",
   draft-ietf-savi-framework-00 (work in progress), September 2010.

   [RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC2131,
   March 1997.

   [RFC3315] R. Droms, Ed. "Dynamic Host Configuration Protocol for IPv6
   (DHCPv6)", RFC3315, July 2003.

   [RFC4388] R. Woundy and K. Kinnear, "Dynamic Host Configuration
   Protocol (DHCP) Leasequery", RFC4388, February 2006.

   [RFC4861] T. Narten, E. Nordmark, W. Simpson, and H. Soliman,
   "Neighbor Discovery for IP version 6 (IPv6)", RFC4861, September 2007.

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

   [RFC5007] J. Brzozowski, K. Kinnear, B. Volz, S. Zeng, "DHCPv6
   Leasequery", RFC5007, September 2007.



  15.2. Informative References

   [BCP38] Ferguson, P. and D. Senie, "Network Ingress Filtering:
   Defeating Denial of Service Attacks which employ IP Source Address
   Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3307] B. Haberman, "Allocation Guidelines for IPv6 Multicast
   Addresses", RFC3307, August 2002.

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

   [IP Source Guard] Cisco, "Network Security Technologies and
   Solutions", chapter 7, Cisco Press, May 20, 2008.



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   [draft-bi-savi-mixed] Jun Bi, "Mixed scenario analysis and best
   effort solution", draft-bi-savi-mixed-00.

16. Acknowledgments

Special thanks to Christian Vogt, Joel M. Halpern, Eric Levy-Abegnoli
and Alberto Garcia for careful review and valuation comments on the
state machine and text.
Thanks to Marcelo Bagnulo Braun, Mark Williams, Erik Nordmark, Mikael
Abrahamsson, Jari Arkko, David Harrington, Pekka Savola, Xing Li, Lixia
Zhang, Robert Raszuk, Greg Daley, John Kaippallimalil and Tao Lin for
their valuable contributions.



































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Authors' Addresses

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

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

   Guang Yao
   Computer Science, Tsinghua University
   Beijing 100084
   China
   Email: yaog@netarchlab.tsinghua.edu.cn

   Fred Baker
   Cisco Systems
   Santa Barbara, California  93117
   US
   Email: fred@cisco.com


17. Change Log

   From 02 to 03:

         -  Section 12, data trigger and counter trigger are combined to
            binding recovery process. The expression "one of MUST" is
            changed to "conditional MUST. Conditions related with the
            implementation are specified. Related constants are changed
            in section 26."



   Main changes from 03 to 04:

         -  Section "Prefix configuration" is removed.




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         -  Section "Supplemental binding process" is modified in
            requirement level.

         -  Sub-section 9.1 "Rationale" is added.

         -  Section "Filtering during Detection" is removed.

         -  Section "Handling layer 2 path change" is changed to
            "Consideration on Link layer routing complexity"

         -  Section "Background and related protocols" is removed.

   Main changes from 04 to 05:

         -  Trigger events are listed explicitly in section 8.

         -  Detection and Live states are deleted, together with
            corresponding sections.

   Main change from 05 to 06:

         -  Section 8.1: reference to section 20 is changed to section
            15.

   Main changes from 06 to 07:

         -  So many changes in this modification. We suggest to track
            http://www.ietf.org/mailarchive/web/savi/current/msg01543.ht
            ml. Changes are made according to the comments.



















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