SAVI J. Bi, J. Wu Internet Draft CERNET Intended status: Standard Tracks G. Yao Expires: October 2010 Tsinghua Univ. F. Baker Cisco April 16, 2010 SAVI Solution for DHCP draft-ietf-savi-dhcp-02.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. 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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 Bi Expires October 16, 2010 [Page 1] Internet-Draft savi-dhcp April 2010 This Internet-Draft will expire on October 16, 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 IP addresses. Table of Contents Copyright Notice ............................................... 2 Abstract ....................................................... 2 1. Introduction ................................................ 4 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).................................... 6 7. Binding States Description................................... 6 8. DHCP Scenario ............................................... 7 9. Anchor Attributes ........................................... 7 9.1. SAVI-Validation Attribute............................... 7 9.2. SAVI-DHCP-Trust Attribute............................... 8 9.3. SAVI-SAVI Attribute..................................... 8 9.4. Optional Attributes..................................... 8 10. Prefix Configuration........................................ 8 11. Binding Set Up ............................................. 9 Bi Expires October 16, 2010 [Page 2] Internet-Draft savi-dhcp April 2010 11.1. Process of Control Packet 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............................ 9 11.1.2. From START to LIVE............................... 11 11.1.2.1. Trigger Event............................... 11 11.1.2.2. Event Validation............................ 11 11.1.2.3. Following Actions........................... 11 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.......................... 12 11.1.4.1. Trigger Event............................... 12 11.1.4.2. Following Actions........................... 13 11.1.5. Binding Deletion in DETECTION State.............. 13 11.1.5.1. Trigger Event............................... 13 11.1.5.2. Following Actions........................... 13 11.1.6. After BOUND...................................... 13 11.2. State Machine of DHCP Snooping........................ 14 12. Supplemental Binding Process............................... 15 12.1. Rate-limited Data Triggered Binding Process........... 16 12.1.1. SAVI-DataTrigger Attribute....................... 16 12.1.2. Data Triggered Binding Process................... 16 12.2. Counter Triggered Process............................. 17 12.2.1. SAVI-CounterTrigger Attribute.................... 17 12.2.2. Counter Triggered Process........................ 18 12.3. External Control Packet Snooping Process.............. 18 12.3.1. SAVI-ExtSnooping Attribute....................... 18 12.3.2. Extended Control Packet Snooping................. 18 13. Filtering Specification.................................... 19 13.1. Data Packet Filtering................................. 19 13.2. Control Packet Filtering.............................. 20 14. Format and Delivery of Probe Messages...................... 20 14.1. Duplicate detection................................... 20 15. Binding Remove ............................................ 21 16. Handle Anchor Off-link event............................... 21 17. About Collision in Detection............................... 21 17.1. Whether to Notify the DHCP Server..................... 22 17.2. The Result of Detection without Host Aware............ 22 18. Filtering during Detection................................. 22 19. Binding Number Limitation.................................. 22 20. MLD Consideration ......................................... 23 21. State Restoration ......................................... 23 22. Stateless DHCP ............................................ 23 23. Confirm Triggered Binding.................................. 23 24. Handle Layer 2 Path Change................................. 24 Bi Expires October 16, 2010 [Page 3] Internet-Draft savi-dhcp April 2010 25. Duplicate Bindings on Same Address......................... 24 26. Constants ................................................. 24 27. Security Considerations.................................... 25 28. IANA Considerations........................................ 25 29. References ................................................ 25 29.1. Normative References.................................. 25 29.2. Informative References................................ 25 30. Acknowledgments ........................................... 26 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]. The binding process is inspired by the work of IP Source Guard [IP Source Guard]. This solution differs from IP Source Guard in the specification for collision detection, which is essential in environments with multiple address assignment methods. There are also other differences in details. 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. Bi Expires October 16, 2010 [Page 4] Internet-Draft savi-dhcp April 2010 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 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. Bi Expires October 16, 2010 [Page 5] Internet-Draft savi-dhcp April 2010 +---------+----------+-------+-----------+-------+ | 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. +---------+----------+ |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. Bi Expires October 16, 2010 [Page 6] Internet-Draft savi-dhcp April 2010 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. +--------+ | 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 13. Bi Expires October 16, 2010 [Page 7] Internet-Draft savi-dhcp April 2010 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. 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 can also be set on other anchors if the administrator decides not to validate the traffic from the anchor. Note that DHCP server message and router message will also be trusted. This attribute is mutually exclusive with SAVI-Validation. 9.4. Optional Attributes Section 12 describes some optional attributes. At least one of these attributes MUST be implemented. 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. The SAVI device enabled this solution SHOULD set allowed prefix 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 October 16, 2010 [Page 8] Internet-Draft savi-dhcp April 2010 11. 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 anchor with SAVI-Validation attribute. 11.1. Process of Control Packet Snooping 11.1.1. Initialization A binding entry is initialized in this step. 11.1.1.1. Trigger Event A DHCPv4/v6 Request or a DHCPv6 Confirm or a DHCPv6 Solicitation with Rapid Commit option is received. Or a DHCP Reply is received from anchor with SAVI-DHCP-Trust attribute. Note that vulnerability may be caused by DHCP Reply triggered initialization. The binding of assigned address and anchor may be threatened if the binding mechanism between 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 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. It is SUGGESTED not to initialize a binding based on DHCP Reply, until the associated mechanism is also implemented. 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. 11.1.1.3. Following Actions If the check fails, the triggering message SHOULD be discarded. This event MAY be announced on console interface. If the check is passed: Bi Expires October 16, 2010 [Page 9] Internet-Draft savi-dhcp April 2010 If the triggering message is DHCP Request/Confirm/Solicitation with Rapid Commit Option: 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 client triggered initialization The TID is kept as a mediator of assigned address and the anchor of requesting node, to assure that the assigned address can be bound with anchor secure. If the triggering message is DHCP Reply: The SAVI device MUST deliver the message to the destination. The SAVI device MUST generate a new entry in BST and FT. The anchor in entry is looked up based on the destination link layer address, from mapping table from link layer address to anchor (e.g., the MAC- Port mapping table in case that port is used as anchor). The state of the corresponding entry is set to be LIVE. 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 Reply triggered initialization Bi Expires October 16, 2010 [Page 10] Internet-Draft savi-dhcp April 2010 +---------+----------+ |Anchor |Address | +---------+----------+ |A |Addr | +---------+----------+ Figure 6 Binding entry in FT on Reply triggered initialization 11.1.2. From START to LIVE 11.1.2.1. Trigger Event A DHCPv4 DHCPACK or DHCPv6 REPLY message is received from SAVI-DHCP- Trust anchor. 11.1.2.2. Event Validation The SAVI device checks the message and BST as follows: 1. Whether there exists an entry in the BST with corresponding TID in the START state. 11.1.2.3. Following Actions If the check fails, the message may be used to trigger binding initialization, specified in section 11.1.1. If the check is passed: The SAVI device MUST deliver the message to the destination. The state of the corresponding entry is changed to be LIVE. 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 7 From START to LIVE A corresponding entry MUST also be generated in FT. Bi Expires October 16, 2010 [Page 11] Internet-Draft savi-dhcp April 2010 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, and the state in BST must be LIVE. 11.1.3.3. Following Actions If the check fails because of the Target Address is not in BST, the packet MUST be discarded. If the entry state is not LIVE, the message MUST be forwarded. If the check is passed: If the event is triggered by client, SAVI device MUST set the state of the corresponding entry to be DETECTION. +---------+----------+-----------+-----------------+-------+ | Anchor | Address | State | Lifetime |Other | +---------+----------+-----------+-----------------+-------+ | A | Addr | DETECTION |MAX_ARP_DELAY or | Lease | | | | |MAX_DAD_DELAY | Time | +---------+----------+-----------+-----------------+-------+ Figure 8 From LIVE to DETECTION If the triggering event is timeout event, the SAVI device MUST send one or more ARP Request or DAD NSOL, with Target Address set to the recorded address in the entry. The format of detection packet is specified in section 14. The state MUST be changed to DETECTION. The lifetime of the entry MUST be set to be MAX_ARP_DELAY or MAX_DAD_DELAY respectively. 11.1.4. From DETECTION to BOUND 11.1.4.1. Trigger Event A timeout event of an entry with state DETECTION occurs. Bi Expires October 16, 2010 [Page 12] Internet-Draft savi-dhcp April 2010 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. Binding Deletion in DETECTION State 11.1.5.1. Trigger Event An ARP Response or NA/DAD NS targeting at an address in BST with state DETECTION is received from a different anchor. 11.1.5.2. Following Actions If ARP Response or NA is received from anchor with SAVI-Validation attribute, but the address is not bound with the anchor, the packet MUST be dropped. If DAD NS is received from anchor with SAVI- Validation, the message MUST be delivered to the former detecting node. The binding SHOULD be removed. If the message is received from anchor with SAVI-Validation attribute, and the address is bound with anchor, the message MUST be delivered to the detecting node, and the binding MUST be removed. If the message is received from anchor without SAVI-Validation attribute, the message MUST be delivered to the detecting node. The binding SHOULD be removed. 11.1.6. 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 13. 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. Bi Expires October 16, 2010 [Page 13] Internet-Draft savi-dhcp April 2010 Before a DHCP message is found that it may change the corresponding binding, its validity MUST be checked as described in section 13.2. 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. Switch port down event (or in a more general expression, anchor turns off-link) will change the corresponding entry, as described in section 16. 11.2. State Machine of DHCP Snooping The main state transits are listed as follows. Note that precondition of state transit is not included. Triggering message/event must satisfy the preconditions before changing the state. State Message/Event Action Next State - REQ/CFM/SOL+RC Generate entry START *- ACK/RPL Generate entry with lease LIVE START ACK/RPL Record lease time LIVE START Timeout Remove entry - LIVE Gra ARP REQ/DAD NS - DETECTION LIVE DECLINE/RELEASE Remove entry - LIVE Timeout Send probe DETECTION DETECTION Timeout - BOUND DETECTION ARP RES/DAD NS/NA Remove entry - DETECTION DECLINE/RELEASE Remove entry - Bi Expires October 16, 2010 [Page 14] Internet-Draft savi-dhcp April 2010 BOUND RELEASE/DECLINE Remove entry - BOUND Timeout Remove entry - BOUND RPL with REN/REB Set new lifetime BOUND *: optional but NOT SUGGESTED. 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 11.1.3 and section 14. 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 REN: DHCP RENEW REB: DHCP REBOUND 12. 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 layer-2 path changes after the binding has been set up, 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. In DHCP Bi Expires October 16, 2010 [Page 15] Internet-Draft savi-dhcp April 2010 scenario, till this document is finished, layer-2 path change and local link movement are the only two events that must be handled through this supplemental binding process. This 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 this binding process. At least one of the following techniques MUST be implemented in SAVI device which deploys this solution: 1. Rate-limited Data Triggered Binding Process; 2. Counter Triggered Process; 3. Extended Control Packet Snooping Process. 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. 12.1. Rate-limited Data Triggered Binding Process 12.1.1. SAVI-DataTrigger Attribute If data trigger binding process is implemented as the supplemental binding process, an additional anchor attribute, named SAVI- DataTrigger, MUST be implemented. This attribute is mutually exclusive with SAVI-SAVI. Data triggered binding process will be performed on the anchor with such attribute. 12.1.2. Data Triggered Binding Process If an anchor is set to have SAVI-DataTrigger attribute, data packet whose source address is not bound with the anchor, may not be filtered directly; instead, the SAVI device will check whether the address can be used by the 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. Bi Expires October 16, 2010 [Page 16] Internet-Draft savi-dhcp April 2010 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 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. The data triggered process MUST be rate limited to avoid Denial of Services attack against the SAVI device itself. A constant DATA_TRIGGER_INTERVAL is used to control the frequency. Two data trigger processes on one anchor must have a minimum interval time DATA_TRIGGER_INTERVAL. This constant SHOULD be configured prudently to avoid Denial of Services. Data triggered process is not strict secure. The node with data- trigger 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. Data triggered process may fail if any DHCP server doesn't support LEASEQUERY. 12.2. Counter Triggered Process 12.2.1. SAVI-CounterTrigger Attribute If counter triggered binding process is implemented as the supplemental binding process, an additional anchor attribute, named SAVI-CounterTrigger, MUST be implemented. This attribute is mutually exclusive with SAVI-SAVI. Bi Expires October 16, 2010 [Page 17] Internet-Draft savi-dhcp April 2010 Counter triggered binding process will be performed on the anchor with such attribute. 12.2.2. Counter Triggered Process In this process, a counter is used to record the number of filtered packets by this solution or all the enabled SAVI solutions on anchor with SAVI-CounterTrigger attribute. A constant TRIGGER_COUNT is set with the counter. Whenever the counter reaches TRIGGER_COUNT, this event MUST be handled by the SAVI device. The SAVI device performs following steps: 1. Set the counter to 0; 2. If the SAVI device is a layer-3 device, it MUST perform LEASEQUERY to check whether the source address of the triggering packet can be bound with the triggering anchor. If it is a layer-2 device, DHCP Confirm can be used to replace LEASEQUERY. The security degree may degrade for the address may not be assigned by DHCP server. 3. This event MUST be announced to network administrator. For example, a SNMP trap may be triggered; or an alert on console interface may be generated. The constant TRIGGER_COUNT MUST be prudently configured to fit the specified deployment scenario. In extreme situation, it can be set to 1. 12.3. External Control Packet Snooping Process 12.3.1. SAVI-ExtSnooping Attribute If extended control packet snooping is implemented as the supplemental binding process, an additional anchor attribute, named SAVI-ExSnooping, MUST be implemented. This attribute is mutually exclusive with SAVI-SAVI. Extended control packet snooping process will be performed on the anchor with such attribute. 12.3.2. Extended Control Packet Snooping In this snooping process, other than DHCP initialization messages, other types of control packets processed by processor of SAVI device, Bi Expires October 16, 2010 [Page 18] Internet-Draft savi-dhcp April 2010 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 traffic will contain control plane communication packets to help traffic setup and fault diagnosis. 13. 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 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. 13.1. Data Packet Filtering Data packets with an anchor which has attribute SAVI-Validation MUST be checked. Bi Expires October 16, 2010 [Page 19] Internet-Draft savi-dhcp April 2010 If the source of a packet associated with its 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. 13.2. Control Packet Filtering For anchors with SAVI-Validation attribute: The source address of DHCPv4 Discovery MUST be set to all zeros. The source address of DHCPv4 Request MUST 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 an 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. For other anchors: All DHCP Reply/Ack packets MUST be from anchor with the SAVI-DHCP- Trust attribute. 14. Format and Delivery of Probe Messages As described in section 11.1.3, 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. 14.1. Duplicate detection Message Type: DAD NS, Gratuitous ARP Request Format: Bi Expires October 16, 2010 [Page 20] Internet-Draft savi-dhcp April 2010 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. 15. Binding Remove If the lifetime of an entry with state BOUND expires, the entry MUST be removed. 16. 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, the entry MAY be removed. 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, 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. 17. About Collision in Detection The SAVI device may receive a response in detection. Some related details are specified here. Bi Expires October 16, 2010 [Page 21] Internet-Draft savi-dhcp April 2010 17.1. 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. 17.2. 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. 18. 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 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. 19. 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. Bi Expires October 16, 2010 [Page 22] Internet-Draft savi-dhcp April 2010 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, because they can't recover bindings on the SAVI device of themselves. Thus, binding entries SHOULD be saved into non-volatile storage whenever a new binding entry changes to BOUND state or a binding with state BOUND is removed, unless other alternatives specified here is implemented. If binding is saved into non-volatile memory, 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 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. 22. Stateless DHCP 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. 23. 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. Bi Expires October 16, 2010 [Page 23] Internet-Draft savi-dhcp April 2010 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. 24. Handle Layer 2 Path Change Layer 2 path change is an important challenge on this control plane based solution. The SAVI device MUST be sensitive to any layer 2 path change. Whenever a layer 2 control protocol frame, including STP, RSTP, TRILL, is received from some anchor, which announces a layer 2 incoming path is changed to the anchor, data packet trigger process SHOULD be enabled on the anchor for a period, or alternatively the device SHOULD forward the packets directly for a period, and set up bindings from Neighbor Table. Although generally such events can be handled through pre-configuration of data-trigger attribute, the future layer 2 protocol may be flexible and hard to handle through manual configuration. 25. Duplicate Bindings on Same Address Note that the same address may be bound with multiple anchors, only if the binding processes are finished on each anchor successfully respectively. This mechanism is designed in consideration that a node may move on the local ink, and a node may have multiple 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 anchor of the moving node have the ability to use its address. 26. 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 DATA_TRIGGER_INTERVAL Device capacity depended and configurable TRIGGER_COUNT Device capacity depended and configurable Bi Expires October 16, 2010 [Page 24] Internet-Draft savi-dhcp April 2010 27. 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. 28. IANA Considerations There is no IANA consideration currently. 29. References 29.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 29.2. Informative References [RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC2131, March 1997. [RFC3307] B. Haberman, "Allocation Guidelines for IPv6 Multicast Addresses", RFC3307, August 2002. [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. Bi Expires October 16, 2010 [Page 25] Internet-Draft savi-dhcp April 2010 30. 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, John Kaippallimalil, Tao Lin , and Dong Zhang for their valuable contributions. Bi Expires October 16, 2010 [Page 26] Internet-Draft savi-dhcp April 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 October 16, 2010 [Page 27]