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SAVI                                                      J. Bi, J. Wu
Internet Draft                                                 CERNET
Intended status: Standard Tracks                               G. Yao
Expires: March 2011                                     Tsinghua Univ.
                                                             F. Baker
                                                                Cisco
                                                     September 8, 2010



                          SAVI Solution for DHCP
                        draft-ietf-savi-dhcp-06.txt


Status of this Memo

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   This Internet-Draft will expire on January 8, 2010.

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. Mechanism Overview .......................................... 4
   4. Terminology ................................................. 4
   5. Conceptual Data Structures................................... 4
      5.1. Control Plane Data Structure: Binding State Table(BST).. 4
      5.2. Data Plane Data Structure: Filtering Table(FT).......... 5
   6. DHCP Scenario ............................................... 5
   7. Binding Anchor Attributes.................................... 6
      7.1. No Attribute ........................................... 6
      7.2. SAVI-Validation Attribute............................... 6
      7.3. SAVI-DHCP-Trust Attribute............................... 7
      7.4. SAVI-SAVI Attribute..................................... 7
      7.5. SAVI-BindRecovery Attribute............................. 7
      7.6. SAVI-ExtSnooping Attribute.............................. 7
   8. Binding Set Up .............................................. 7
      8.1. Rationale .............................................. 8


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      8.2. Binding States Description.............................. 8
      8.3. Events ................................................. 8
         8.3.1. Timer expiration event............................. 8
         8.3.2. Control message arriving event..................... 8
      8.4. Process of Control Packet Snooping...................... 9
         8.4.1. From INIT to other states.......................... 9
            8.4.1.1. Trigger Event................................. 9
            8.4.1.2. Following Actions............................ 10
         8.4.2. From START to other states........................ 11
            8.4.2.1. Trigger Event................................ 11
            8.4.2.2. Following Actions............................ 11
         8.4.3. From BOUND to other states........................ 12
            8.4.3.1. Trigger Event................................ 12
            8.4.3.2. Following Actions............................ 12
      8.5. State Machine of DHCP Snooping......................... 12
   9. Supplemental Binding Process: Handling Link Topology Change. 13
      9.1. Binding Recovery Process............................... 14
      9.2. Extended Control Packet Snooping Process............... 15
   10. Filtering Specification.................................... 16
      10.1. Data Packet Filtering................................. 16
      10.2. Control Packet Filtering.............................. 16
   11. Handle Binding Anchor Off-link Event....................... 17
   12. Binding Number Limitation.................................. 17
   13. State Restoration ......................................... 17
   14. Confirm Triggered Binding.................................. 18
   15. Consideration on Link Layer Routing Complexity............. 18
   16. Duplicate Bindings of Same Address......................... 19
   17. Constants ................................................. 19
   18. Security Considerations.................................... 19
   19. IANA Considerations........................................ 19
   20. References ................................................ 19
      20.1. Normative References.................................. 19
      20.2. Informative References................................ 19
   21. Acknowledgments ........................................... 20
   22. Change Log ................................................ 21

1. Introduction

   This document describes the procedure for creating bindings between
   DHCP assigned addresses and a binding 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 address.
   Section 12 suggests usage of these bindings for common practice.
   [savi-framework] may specify different usages of binding, depending



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   on the environment and configuration. The definition and examples of
   binding anchor is specified in [savi-framework].

   The binding process is inspired by the work of IP Source Guard [IP
   Source Guard].

   In a stateless DHCP scenario [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 designed for stateful DHCP.

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 an
   address 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 binding anchors. The
   bindings can be used to validate the source address in the packets.

4. Terminology

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

5. 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.

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


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   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 in DHCP request. Before a binding is
   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 1 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 2 Instance of FT

6. 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.
   However, this solution is primarily designed for a pure DHCP scenario,
   in which only DHCP servers can assign valid global address. In a
   mixed address assignment scenario where multiple address assignment


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   methods such as DHCPv6 and SLAAC, or DHCPv4 and manually
   configured assign addresses that share the common prefix, the SAVI
   device may need additional state in the state machine to detect and
   avoid address conflict. The SAVI solution for mixed environment
   is proposed in a separate document [draft-bi-savi-mixed].

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

7. Binding Anchor Attributes

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

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

7.1. 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.

7.2. SAVI-Validation Attribute

   SAVI-Validation attribute is used on binding anchor on which the
   source addresses are to be validated. The filtering process on
   binding anchor with such attribute is described in section 13.



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7.3. 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.

7.4. SAVI-SAVI Attribute

   This attribute is used on binding anchor from which the traffic is
   not to be checked. All traffic from binding anchor with this
   attribute will be forwarded without check. Note that DHCP server
   message and router message will also be trusted.

   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.

7.5. SAVI-BindRecovery Attribute

   This attribute is used on binding anchor that requires binding
   recovery described in section 10.1.

   This attribute is mutually exclusive with SAVI-SAVI.

7.6. SAVI-ExtSnooping Attribute

   This attribute is used on binding anchor that requires extended
   control packet snooping described in section 10.2.

   This attribute is mutually exclusive with SAVI-SAVI.

8. Binding Set Up

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


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8.1. Rationale

   The rationale of this mechanism is that if a node attached to a
   binding anchor intends to use a valid DHCP address, the DHCP
   procedure which assigns the address to the node goes first on the
   same binding anchor. This basis stands when the link layer routing is
   stable. However, unstable link layer routing may result in that data
   packet is received from a different binding anchor with the DHCP
   messages. Infrequent link layer path change can be handled (but not
   perfectly) by the mechanism described in section 10. Section 15
   discusses the situation that link layer routing is naturedly unstable.
   To handle this situation is above the scope of this document.

8.2. Binding States Description

   This section describes the binding states of this mechanism.

   INIT       The state before a binding has been set up.

   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.

   BOUND       The address is authorized to the client.

8.3. Events

8.3.1. Timer expiration event

   EVE_ENTRY_EXPIRE: The lifetime of an entry expires

8.3.2. Control message arriving events

   EVE_DHCP_REQUEST: A DHCP Request 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_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.




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   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, which has an entry in the state of START. The
   TID field in the entry matches the TID in the message.

   EVE_DHCP_REPLY_NULL: 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, which has no entry in the state of START or
   matches the TID field.

   EVE_DHCP_DECLINE: A DHCP Decline message is received from a binding
   anchor with SAVI-Validation attribute. The message declines an
   address bound with the binding anchor in state of LIVE or DETECTION
   or BOUND.

   EVE_DHCP_RELEASE: A DHCP Release message is received from a binding
   anchor with SAVI-Validation attribute. The message releases an
   address bound with the binding anchor in state of LIVE or DETECTION
   or BOUND.

   EVE_DHCP_REPLY_RENEW: A DHCPv4 Acknowledgement or DHCPv6 Reply
   message is received, which suggests a new lease time of address in
   state of BOUND.

8.4. Process of Control Packet Snooping

8.4.1. From INIT to other states

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

   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.


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

8.4.1.2. 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 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 MUST be recorded in the
     entry, except that the mapping from link layer address to binding
     anchor is secure as specified in section 9.2.1.1.

   +---------+----------+-------+-----------------------+-------+
   | Anchor  | Address  | State | Lifetime              |Other  |
   +---------+----------+-------+-----------------------+-------+
   | A       |          | START |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 the actions above, the address to be confirmed MUST be
     recorded in the entry.

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

   If the triggering event is EVE_DHCP_REPLY_NULL:

     The SAVI device MUST deliver the message to the destination.

     The SAVI device MUST generate a new entry in BST and FT. The
     binding anchor in entry is looked up based on the destination link
     layer address, from mapping table from link layer address to


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     binding anchor (e.g., the MAC-Port mapping table in case that port
     is used as binding anchor). The state of the corresponding entry is
     set to be BOUND. The lifetime of the entry MUST be set to be the
     lease time.

   +---------+----------+-------+------------------------+-------+
   | Anchor  | Address  | State | Lifetime               |Other  |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr     | BOUND |   Lease time           |       |
   +---------+----------+-------+------------------------+-------+
      Figure 6 Binding entry in BST on Reply triggered initialization

                          +---------+----------+
                          | Anchor  |Address   |
                          +---------+----------+
                          |A        |Addr      |
                          +---------+----------+
       Figure 7 Binding entry in FT on Reply triggered initialization



8.4.2. From START to other states

8.4.2.1. Trigger Event

   EVE_DHCP_REPLY, EVE_ENTRY_EXPIRE.

8.4.2.2. Following Actions

   If the trigger event is EVE_DHCP_REPLY:

     The SAVI device MUST deliver the message to the destination.

      The state of the corresponding entry is changed to be BOUND.

      If the Address field is null, the lease time in Reply message MUST
      be recorded in the entry.

      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,
      perform the procedure in section 19 to fetch the lease time.
      Otherwise, delete the entry.







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   +---------+----------+-------+------------------------+-------+
   | Anchor  | Address  | State | Lifetime               |Other  |
   +---------+----------+-------+------------------------+-------+
   | A       | Addr     | BOUND |  Lease time            |       |
   +---------+----------+-------+------------------------+-------+
                       Figure 8 From START 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.

8.4.3. From BOUND to other states

8.4.3.1. Trigger Event

   EVE_ENTRY_EXPIRE, EVE_DHCP_RELEASE, EVE_DHCP_DECLINE,
   EVE_DHCP_REPLY_RENEW.

8.4.3.2. Following Actions

   If the trigger event is EVE_ENTRY_EXPIRE:

     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.

8.5. State Machine of DHCP Snooping

   The main state transits are listed as follows.

   State      Event               Action                      Next State

   INIT       REQ/CFM/RC          Generate entry                   START

   *INIT      RPL                 Generate entry with lease        BOUND

   START      RPL                 Record lease time                BOUND



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   START      Timeout             Remove entry                      INIT

   BOUND      RELEASE/DECLINE     Remove entry                      INIT

   BOUND      Timeout             Remove entry                      INIT

   BOUND      RPL_RENEW           Set new lifetime                 BOUND

   *: optional but NOT SUGGESTED.

   REQ: EVE_DHCP_REQUEST

   CFM: EVE_DHCP_CONFIRM

   RC:  EVE_DHCP_OPTION_RC

   RPL: EVE_DHCP REPLY

   DECLINE: DHCP DECLINE

   RELEASE: DHCP RELEASE

   RPL_RENEW: EVE_DHCP_RPL_RENEW

  Timeout: EVE_ENTRY_EXPIRE

9. Supplemental Binding Process: Handling Link Topology Change

   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, which
   can be regarded as a special case of link topology change. In DHCP
   scenario, till this document is finished, link topology change is the
   only two events that must be handled through this supplemental
   binding 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.

   For implementations that will face the above problem:



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   1. 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 blocking will happen until the node is re-
      configured.

   2. Extended Control Packet Snooping Process is a MUST.

   Other techniques may be prudently chosen as alternative if found to
   have equivalent or even better function to avoid permanently blocking
   after discussion, implementation and deployment.

9.1. Binding Recovery Process

   Refer to [draft-baker-savi-one-implementation-approach] for a
   detailed implementation suggestion. The process specified here can
   only be enabled in condition that implementation can meet the
   specified hardware requirements described in [draft-baker-savi-one-
   implementation-approach].

   If a binding anchor is set to have SAVI-BindRecovery attribute, a
   FIFO queue or register MUST be used to save recently filtered packets.
   The SAVI device will fetch packet from the queue/register to check
   the source address can be used by corresponding client on the local
   link with limited rate:

   1. If the address has a local conflict, meaning the DAD on the
      address fails, the packet MUST be discarded. If the address is not
      being used, go to the next step.

   2.

   IPv4 address:

   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


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   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 based processes on one
   binding anchor must have a minimum interval time
   BIND_RECOVERY_INTERVAL. This constant SHOULD be configured prudently
   to avoid Denial of Services.

   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 DAD probe.

   In case that the SAVI device is a pure layer-2 device, DHCP Confirm
   MAY be used to replace the DHCP LEASEQUERY. The security degree may
   degrade for the address may not be assigned by DHCP server.

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

9.2. Extended Control Packet Snooping Process

   In this snooping process, other than DHCP initialization messages,
   other types of control packets processed by processor of SAVI device,
   if the source address is not bound, may trigger the device to perform
   binding process.

   The control messages that MUST be processed include: (1) address
   resolution Neighbor Solicitation; (2) Neighbor Advertisement; (3)
   neighbor unreachability detection; (4) Multicast Listener Discovery;
   (5) Address Resolution Protocol; (6) DHCP Renew/Rebind. Other ICMP
   messages that may be processed by intermediate device may also
   trigger the binding process.

   The SAVI device MUST first perform DAD to check if the address has a
   local conflict, and then send DHCP LEASEQUERY or Confirm to recover
   binding based on DHCP server message.

   A minimum time interval EXT_SNOOPING_INTERVAL MUST be set to limit
   the rate of such triggering process.

   Note that this process may not be able to avoid permanent block, in
   case that only data packets are sent by node. Generally, this
   mechanism is still practical, because data packet sending without
   control plane communication is rare and suspicious in reality. Normal



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   traffic will contain control plane communication packets to help
   traffic setup and fault diagnosis.

10. 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
   Response should be checked to prevent spoofing. All other packets are
   considered to be data packets.

10.1. 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.

10.2. 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:


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

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,
   the bindings with the binding 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, the entry MAY be removed.

   If the binding 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 binding anchor got off by a
   previous node, and 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.

12. 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 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, using the bound entry
      number of each binding anchor as reverse indicator.

13. 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.
   Thus, binding entries MUST be saved into non-volatile storage
   whenever a new binding entry changes to BOUND state or a binding with


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   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.

   The possible alternatives proposed but not suitable for general cases
   are:

   If the SAVI device is also the DHCP relay, an alternative mechanism
   is fetching the bindings through bulk DHCP LEASEQUERY [RFC5460].

   If the network enables 802.1ag, the bindings can be recovered with
   the help of the first hop routers through snooping unicast Neighbor
   Solicitations sent by routers based on the Neighbor Table.

14. Confirm Triggered Binding

   If a binding entry is triggered by a CONFIRM message from the client,
   no lease time will be contained in the REPLY from DHCP server. The
   SAVI device MUST send LEASEQUERY message to get the lease time of the
   address to complete the binding entry. If no successful LEASEQUERY-
   REPLY is received, the binding entry SHOULD be removed. In this
   scenario, the address is not regarded as assigned by DHCP, and it MAY
   be bound through other SAVI solution.

   If the confirmed address has local conflict, the Client-ID field of
   Confirm and LEASEQUERY-REPLY MUST be compared. If they are not match,
   the new binding entry MUST be deleted.

15. Consideration on Link Layer Routing Complexity

   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, if the link layer routing between
   host and SAVI device is inconsistent from time to time, this
   assumption doesn't stand. 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.



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   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.

16. Duplicate Bindings of Same Address

   Note that 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.

   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.

17. Constants

   MAX_DHCP_RESPONSE_TIME     120s

   BIND_RECOVERY_INTERVAL     Device capacity depended and configurable

18. Security Considerations

   There is no security consideration currently.

19. IANA Considerations

   There is no IANA consideration currently.

20. References

20.1. Normative References

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

20.2. Informative References

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

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


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   [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.

   [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.

   [draft-baker-savi-one-implementation-approach] F. Baker, "An
   implementation approach to Source Address Validation",
   draft-baker-savi-one-implementation-approach-00.

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

21. Acknowledgments


Special thanks to Christian Vogt and Joel M. Halpern for careful review
and valuation comments on the state machine and text.
Thanks to Marcelo Bagnulo Braun, Eric Levy-Abegnoli, Mark Williams,
Erik Nordmark, Mikael Abrahamsson, Alberto Garcia, 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
   CERNET
   Beijing, China
   Email: junbi@cernet.edu.cn

   Jianping Wu
   CERNET
   Beijing, China
   Email: jianping@cernet.edu.cn

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

   Fred Baker
   Cisco Systems
   Email: fred@cisco.com


22. 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.

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

         -  Sub-section 9.1 "Rationale" is added.

         -  Section "Filtering during Detection" is removed.




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         -  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.

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

   Main change from 05 to 06:

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

































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