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 provisions of BCP 78 and BCP 79. This document may not be modified, and derivative works of it may not be created, except to publish it as an RFC and to translate it into languages other than English. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 8, 2010. Bi Expires September 8, 2010 [Page 1] Internet-Draft savi-dhcp March 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 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 Bi Expires September 8, 2010 [Page 2] Internet-Draft savi-dhcp March 2010 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]. Bi Expires September 8, 2010 [Page 3] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 4] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 5] Internet-Draft savi-dhcp March 2010 +---------+----------+ |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. Bi Expires September 8, 2010 [Page 6] Internet-Draft savi-dhcp March 2010 +--------+ | 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. Bi Expires September 8, 2010 [Page 7] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 8] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 9] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 10] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 11] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 12] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 13] Internet-Draft savi-dhcp March 2010 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 - Bi Expires September 8, 2010 [Page 14] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 15] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 16] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 17] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 18] Internet-Draft savi-dhcp March 2010 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, Bi Expires September 8, 2010 [Page 19] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 20] Internet-Draft savi-dhcp March 2010 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. Bi Expires September 8, 2010 [Page 21] Internet-Draft savi-dhcp March 2010 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 Bi Expires September 8, 2010 [Page 22]