Network Working Group M. Bagnulo Internet-Draft A. Garcia-Martinez Intended status: Standards Track UC3M Expires: April 28, 2011 October 25, 2010 SEND-based Source-Address Validation Implementation draft-ietf-savi-send-04 Abstract This memo describes SEND SAVI, a mechanism to provide source address validation using the SEND protocol. The proposed mechanism is intended to complement ingress filtering techniques to provide a higher granularity on the control of the source addresses used. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 28, 2011. 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. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 1] Internet-Draft SEND SAVI October 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Non-normative Background to SEND SAVI . . . . . . . . . . . . 3 2.1. Address Validation Scope . . . . . . . . . . . . . . . . . 3 2.2. SEND SAVI Enforcement Perimeter . . . . . . . . . . . . . 4 2.3. Binding Creation for SEND SAVI . . . . . . . . . . . . . . 5 3. Perimeter Configuration Guidelines for SEND SAVI . . . . . . . 6 4. SEND SAVI Specification . . . . . . . . . . . . . . . . . . . 9 4.1. SEND SAVI Data Structures . . . . . . . . . . . . . . . . 9 4.2. SEND SAVI Device Configuration . . . . . . . . . . . . . . 11 4.3. SEND SAVI Algorithm . . . . . . . . . . . . . . . . . . . 11 4.3.1. Traffic Processing . . . . . . . . . . . . . . . . . . 11 4.4. VLAN Support . . . . . . . . . . . . . . . . . . . . . . . 22 4.5. Protocol Constants . . . . . . . . . . . . . . . . . . . . 22 5. Security Considerations . . . . . . . . . . . . . . . . . . . 22 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 7. Normative References . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 2] Internet-Draft SEND SAVI October 2010 1. Introduction This memo describes SEND SAVI (Source-Address Validation Implementation), a mechanism to provide source address validation for IPv6 networks using the SEND protocol [RFC3971]. The proposed mechanism is intended to complement ingress filtering techniques to provide a higher granularity on the control of the source addresses used. SEND SAVI uses DAD_NSOL (Duplicate Address Detection Neighbor Solicitation), DAD_NADV (DAD Neighbor Advertisement), NUD_NSOL (Neighbor Unreachability Detection NSOL) and NUD_NADV (NUD Neighbor Advertisement) messages to validate the address ownership claim of a node. Ports and other layer-2 binding anchors can be associated to the IPv6 address of the neighbor, so that source address validation could be performed. Scalability of a distributed SAVI system comprised of multiple SEND SAVI devices is preserved by means of a deployment scenario in which SEND SAVI devices form a "protection perimeter" and validation is only performed when the packet ingress to the protection perimeter. The SEND SAVI specification, as defined in this document, is limited to links in which every IPv6 host and every IPv6 router uses the SEND protocol [RFC3971] to protect the exchange of Neighbor Discovery information. However, SEND SAVI is designed to be deployed in existing SEND networks requiring a minimum set of changes. In particular, SEND SAVI does not require any changes in the hosts whose source address is to be verified. Any verification must solely rely in the usage of already available protocols. This means that SEND SAVI does neither define a new protocol, nor define any new message on existing protocols, nor require that a host uses an existent protocol message in a different way. An overview of the general framework about Source Address Validation Implementation is presented in [I-D.ietf-savi-framework]. 2. Non-normative Background to SEND SAVI 2.1. Address Validation Scope The application scenario of SEND SAVI is limited to the local link. This means that the goal of SEND SAVI is to verify that the source address of the packets generated by the hosts attached to the local link have not been spoofed. In a link there usually are hosts and routers attached. Hosts Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 3] Internet-Draft SEND SAVI October 2010 generate packets with their own addresses as the source address. This is the so-called local traffic, while routers send packets containing a source address other than their own, since they are forwarding packets generated by other hosts (usually located in a different link). This is the so-called transit traffic. SEND SAVI allows the validation of the source address of the local- traffic, i.e. it allows to verify that the source address of the packets generated by the hosts attached to the local link has not been spoofed. In addition, since SEND does provide the means to verify that a node claiming to act as a router is indeed authorized to act as one, SEND SAVI also provides the means to verify that packets containing off-link prefixes in the source address are forwarded by authorized routers. However, SEND SAVI does not provide the means to verify if a given router is actually authorized to forward packets containing a specific off-link source address. Other techniques, like ingress filtering [RFC2827], are recommended to validate transit traffic. Hence, the security level is increased by the use of both SAVI and ingress filtering. 2.2. SEND SAVI Enforcement Perimeter SAVI devices prevent address spoofing by verifying that a layer-2 anchor is associated to the IPv6 address used as source address for the packets being exchanged. The layer-2 anchor, which must be difficult to spoof can be the port of the layer-2 switch through which a packet containing a given IPv6 address is received, or a layer-2 address. In this document we assume that MAC-specific mechanisms to secure data packets, such as IEEE 802.1AE, are not generally available, so SEND SAVI is defined to operate with ports as the only available layer-2 anchor. In order to reduce computing and state requirements in SEND SAVI devices, SEND SAVI is designed according to the perimetrical protection deployment model presented in the SAVI framework document [I-D.ietf-savi-framework]. In this model, source address validation is performed only when packets enter in a protected realm defined through the protection perimeter. This perimeter must be deployed in such a way that packets for which validation must be performed can only enter in the protected realm through a port belonging to the border performing the validation. The perimeter is defined by appropriate configuration of the roles of each port, which can be Validating ports and Trusted ports. Validating ports are the ports forming the protection perimeter, so they are the ports in which validation for incoming packets is performed. Trusted ports (TPs) are those in which SEND SAVI filtering is not performed. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 4] Internet-Draft SEND SAVI October 2010 2.3. Binding Creation for SEND SAVI Filtering is performed according to the bindings existing between a layer-2 anchor and an IPv6 address. These bindings should allow legitimate nodes to use the binding IPv6 address as source address, and prevent illegitimate nodes to do so. When a protection perimeter is defined, the binding must be created for a port of the border to which a legitimate node is attached to, and must not be created in other case. SEND provides tools to assure that a ND message containing a CGA option and signed by a RSA option has been generated by the legitimate owner of the CGA IPv6 address. It also provides tools to verify that a RADV message signed by a RSA option with a key bounded to a CGA or a certificate has been generated by a legitimate router. SEND SAVI benefits from SEND ability to prove address ownership and router authorization to create SAVI bindings. SEND SAVI assumes that a successfully validated SEND message ingressing to the protection perimeter from a validating port guarantees that the host legitimatelly issuing the message is connected to that port. In this case, a binding for the host to this layer-2 port is created. The events that trigger the binding creation process in a Validating port of a SEND SAVI device are: o The reception from a Validating port of a DAD_NSOL message, indicating the attempt of a node to configure an address. This may occur when a node configure an address after being idle for sometime, or because the node has changed the physical attachment point to the layer-2 infrastructure. o The reception from a Validating port of any other packet (including data packets) with a source address for which no binding exists. This would occur if a DAD_NSOL message was lost before arriving to the Validating port, or if a node has changed the physical attachment point to the layer-2 infrastructure without issuing a DAD_NSOL message. When the binding creation process is triggered, the SEND SAVI device has to assure that the host for which the binding is to be created is the legitimate owner of the address. For a binding creation process initiated by a DAD_NSOL exchange, the messages to consider for address ownership validation are other DAD_NSOL messages arriving from other locations or a DAD_NADV message indicating that other host has configured the address before. For other packets initiating the creation of the binding, the SEND SAVI device asks the host to prove address ownership by issuing a NUD_NSOL which has to be answered by a NUD_NADV by the probed node. Note that it is not required to ask other SEND SAVI devices, as it is done in the non-SEND FCFS Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 5] Internet-Draft SEND SAVI October 2010 specification [I-D.ietf-savi-fcfs], since in this case a SEND host can prove authoritatively the ownership of its address. Bindings are refreshed periodically by means of a NUD_NSOL message issued by the SEND SAVI device through the bounded port which has to be answered by a valid NUD_NADV message by the node for which the binding exist. SEND SAVI could be sensible to replay attacks, i.e. situations in which a secured SEND message is replayed by a non-legitimate node. For example, a node could immediatelly re-inject a valid SEND message being received from other node, to force the creation of a binding for which it is not authorized. SEND provides some means to prevent the replaying of ND messages, in particular, the use of nonces to validate advertisements that were previously solicited, and the use of timestamps to validate solicitation messages and unsolicited advertisements. However, the emphasis for SEND anti-replay protection is to assure that confidence in some information (for example, the relationship between an IPv6 address and a layer-2 address) is not hold for more time than reasonable, while in SEND SAVI truthful information (in SEND sense, like the relationship of an IPv6 address and a layer-2 address) can be used to create a SAVI binding in a time span shorter than the time reasonable to consider the information aged. As a consequence, SEND SAVI relies only in messages with a low chance of being replayed from different ports to the legitimate one and still being considered valid by SEND. The messages being used by SEND SAVI to create bindings are: o Unsolicited DAD_NSOL messages. According to the SEND SAVI specification Section 4.3.1.1 These messages can only be forwarded to ports through which a previous binding for the same IPv6 address existed. o NUD_NADV messages in response to a NUD_NSOL sent by the SEND SAVI device, both exchanged through the same Validating port. In this case, anti-replay protection is assured by nonce exchange. This message exchange is also used to refresh the binding. Any validated RADV can be used to determine that a node for which a binding exists in a Validating port is a router, since the topological part of the binding has been assured before. In addition, the acquisition of prefix information, required to determine local and transit traffic, is not tied to topological considerations too, so for this case regular SEND validating rules are applied. 3. Perimeter Configuration Guidelines for SEND SAVI As it has been discussed before, the perimeter is defined by Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 6] Internet-Draft SEND SAVI October 2010 appropriate port configuration. Ports in SEND SAVI devices may assume two roles according to its behavior when filtering and validating SEND messages: Validating ports and Trusted ports. o Validating ports (VPs) are those in which SEND SAVI filtering and binding creation is performed. o Trusted ports (TPs) are those in which neither SEND SAVI filtering nor binding creation are performed. So, packets received through Trusted ports are not filtered by SEND SAVI. The only SEND messages received through a Trusted port which are processed are those related with certificates, prefix information and Neighbor Advertisements for Duplicate Address Detection (DAD_NADV). The following figure shows a typical topology involving trusted and untrusted infrastructure. +--------+ +--+ +--+ +--+ | +--+ | |H1| |H2| |H3| | |R1| | +--+ +--+ +--+ | +--+ | | | | | | | +----------SEND SAVI-ENFORCEMENT-PERIMETER---+ | | | | | | | | +-1-----2-+ +-1-----2-+ | | | SEND- | | SEND- | | | | SAVI1 | | SAVI2 | | | +-3--4----+ +--3------+ | | | | +--------------+ | | | | +----------| |--------+ | | | | SWITCH-A | | | | +----------| |--------+ | | | | +--------------+ | | | +-1--2----+ +--1------+ | | | SEND- | | SEND- | | | | SAVI3 | | SAVI4 | | | +-3-----4-+ +----4----+ | | | | | | | +----SEND SAVI-ENFORCEMENT-PERIMETER----------+ | | | | | | +--+ | +--+ +---------+ | |R2| | |H4| |SWITCH-B | | +--+ | +--+ +---------+ | | | | +-------+ +--+ +--+ |H5| |H6| +--+ +--+ Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 7] Internet-Draft SEND SAVI October 2010 Trusted ports are used for connections with trusted infrastructure, including the communication between SEND SAVI devices, the communication with other switches which are not SEND SAVI devices, routers or other trusted nodes. Port 3 of SEND-SAVI1 and port 1 of SEND-SAVI3 are trusted because the connect two SAVI devices. Port 4 of SEND-SAVI1, port 3 of SEND- SAVI2, port 2 of SEND-SAVI3 and port 1 of SEND-SAVI4 are trusted because they connect to SWITCH-A to which only trusted nodes are connected. Port 2 of SEND-SAVI2 and port 3 of SEND-SAVI3 are trusted ports, because they connect to routers. Validating ports are used for connection with non-trusted infrastructure. Therefore, hosts are normally connected to validating ports. Non-SEND SAVI switches that are outside of the SAVI enforcement perimeter also are connected through validating port. In particular, non-SEND SAVI devices which connect directly to hosts or which have no SEND SAVI capable device between themselves and the hosts are connected through a validating port. So, in the figure above, ports 1 and 2 of SEND-SAVI1, port 1 of SEND-SAVI2, port 4 of SEND-SAVI3 are validating ports because they connect to hosts. Port 4 of SEND-SAVI4 is also a validating port because it is connected to SWITCH-B which is a non- SEND SAVI capable switch which is connected to hosts H5 and H6. SEND SAVI requires all devices performing SAVI function to implement SEND SAVI (for example, coexistence with non-SEND aware FCFS SAVI [I-D.ietf-savi-fcfs] switches is not allowed). The detailed guidelines for port configuration in SEND SAVI devices are: o Ports that are connected to another SEND SAVI device SHOULD be configured as Trusted ports. Not doing so will at least increase significantly the CPU time, memory consumption and signaling traffic due to SEND SAVI validation, in both the SEND SAVI devices and the node whose address is being validated. o Ports connected to hosts SHOULD be configured as Validating ports. Not doing so will allow the host connected to that port to send packets with spoofed source address. o Ports connected to routers SHOULD be configured as Validating ports. However, the SEND SAVI specification also allows the routers to be connected to Trusted ports, as they are assumed to be part of the trusted infrastructure. When connected through a trusted port, a router can generate traffic with any source address, even those belonging to the link, while when connected through a Validating port it can only send traffic using off-link source addresses, or its own source addresses. When routers are connected to Validating, authorization for the routing function is Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 8] Internet-Draft SEND SAVI October 2010 bound to the router itself, instead of being bound to a port configured in a switch. o Ports connected to a chain of one or more legacy switches that have hosts connected SHOULD be configured as Validating ports. Not doing so will allow the host connected to any of these switches to send packets with spoofed source address. o Ports connected to a chain of one or more legacy switches that have other SEND SAVI devices and/or routers connected but had no hosts attached to them SHOULD be configured as Trusted ports. Not doing so will at least significantly increase the memory consumption in the SEND SAVI devices and increase the signaling traffic due to SEND SAVI validation. o Ports connected to a chain of one or more legacy switches that have a mix of SEND SAVI devices and/or routers with hosts, SHOULD be configured as Validating ports. Not doing so will allow the host connected to that port to send packets with spoofed source address. 4. SEND SAVI Specification 4.1. SEND SAVI Data Structures The following data structures are defined for SEND SAVI operation: SEND SAVI Port list. This structure defines an entry per port in the SAVI device. Each entry indicates the role configured for the port (Trusted port or Validating port). In addition, only for Validating ports, the entry indicates the presence or absence of a router connected through the port has been stated by successful validation of a RADV message received from this port. This data structure is used to determine the filtering behavior for each port when local- link and off-link traffic is received. If the port is a Trusted Port, both local-link and off-link traffic coming from the port is accepted. If the port is a Validating port but not a Routing port, then only local-link traffic coming from the port for which a binding exists is accepted. If the port is a Validating port and a Routing port, then off-link traffic coming from the port is accepted, but only local-link traffic coming from the port for which a binding exists is accepted. Each entry of the SEND SAVI Port list contains the following information: o Layer-2 Validating port o Configured port role (either Trusted port or Validating port). The default configuration is Validating port. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 9] Internet-Draft SEND SAVI October 2010 o Router port bit. This value is only meaningful for ports with a configured port role set to Validating port. It indicates whether a RADV message received from the port has been successfully validated, indicating that a router is connected to the port. For this bit to be set, an entry containing this layer-2 port MUST exist in the SEND SAVI Address table for an IP address of an entry in the SEND SAVI Router table. SEND SAVI Address list. The SEND SAVI function relies on state information binding the source IPv6 address used in data packets to the port through which the legitimate host connects. Such information is stored in SEND SAVI Address table. The SEND SAVI Address table contains one entry for each of the IPv6 source addresses in use on a Validating port of the SEND SAVI device. The SEND SAVI Address list is populated with the contents of successfully validated SEND messages. Each entry contains the following information: o IP source address o Layer-2 Validating port to which the host is connected. o Lifetime o Status: TENTATIVE_DAD, TENTATIVE_NUD, VALID, TESTING_VP, TESTING_VP'. SEND SAVI Prefix list. In addition to this, a SEND SAVI device needs to know which are the link prefixes in order to identify local and off-link traffic. This information is obtained from validated RADV messages. This information is not specific to a given port. Note that the information in this table is equivalent to the Prefix List conceptual data structure defined in [RFC4861]. The SEND SAVI Prefix list contains one entry per prefix in use, as follows: o Prefix o Lifetime SEND SAVI Router list. SEND SAVI keeps a table with one entry for each authorized router in use connected to a Validating port of the SAVI device. In particular, it contains the address for which a successfully validated RADV has been received. The information in this table is used to populate the SEND SAVI port table when at least one router has been validated in a layer-2 Validating port (the layer-2 port can be obtained by looking-up for the IPv6 address of the router in the SEND SAVI Address list). It can also be used to issue a RSOL in case the entry is about to expire, in order to ensure that the node is still performing as a router. Note that the information in this table is equivalent to the Default Router List conceptual data structure defined in [RFC4861]. The information stored in the table is the following: Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 10] Internet-Draft SEND SAVI October 2010 o Router IPv6 address o Lifetime 4.2. SEND SAVI Device Configuration In order to perform SEND SAVI operation, some basic parameters of a SEND SAVI device have to be configured. A SEND SAVI device operates as a full-fledged SEND node in some cases: it may generate NUD_NSOL, RSOL or CPS messages. Therefore, a SEND SAVI device o MUST be configured with a valid CGA address. Note that when the SEND SAVI device configures this address, it must follow the same rules as regular SEND hosts (such as using secured NSOL messages to perform DAD, etc.) o MUST be configured with at least one Trust anchor to validate the Certification Paths that authorizes route operation. o MUST be configured with Certification Paths, either manually or by means of issuing Certification Path Solicitation messages, as detailed in the SEND specification [RFC3971]. In addition, the port role for each port of the SEND SAVI Port list SHOULD be configured. Otherwise, every port would be labeled as Validating port, and performance may be degraded, as discussed in [I-D.ietf-savi-framework]. 4.3. SEND SAVI Algorithm 4.3.1. Traffic Processing In this section we describe how packets are processed. First, the source address of packet is analysed to determine if it is local or transit traffic, by checking if the prefix of the source address is included in the SEND SAVI Prefix List (local traffic) or not included (transit traffic). A special case of local traffic is the traffic destined to the SEND SAVI device itself, either specifically, or through a multicast address to which the SEND SAVI device is registered (such as the all-nodes address, ff02::1). Transit traffic processing occurs as follows: o If the transit traffic packet is received through a Trusted port, the data packet is forwarded and no SAVI processing performed. o If the transit traffic packet is received through a Validating port, the packet is only forwarded if the port appears with the Routing bit set in the SEND SAVI Port list, indicating that a router has been validated through SEND procedures at this port. If transit traffic is received from a Validating port, and the Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 11] Internet-Draft SEND SAVI October 2010 port does not appear with the Routing bit set in the SEND SAVI Port list, the SAVI SEND device SHOULD send a RSOL message through the considered port. Processing of traffic addressed to the SEND SAVI device itself occurs as follows: o Packets received from Trusted ports are not filtered. In particular, if a successfully validated CPA message is received through a Trusted port, the certificate information is accepted by the SEND SAVI device. If a successfully validated RADV message is received through a Trusted port, the SEND SAVI Prefix list in the SEND SAVI device is updated accordingly. o NUD_NADV messages corresponding to SEND SAVI operation are processed according to the specification of Section 4.3.1.1. o Packets received from Validating ports are only processed by the SEND SAVI device if a binding exists for the source IPv6 address of the packet, and the state for the binding is VALID or TESTING (see next section). In particular, If a successfully validated RADV message is received through a Trusted port, the SEND SAVI Prefix list in the SEND SAVI device is updated accordingly. The Router bit of the SEND SAVI Port list is set only if the destination address of the RADV message is not a multicast address. If a SEND SAVI device receives a RADV sent to a multicast address, it SHOULD issue a RSOL message to the port through which this message has been received. We next consider how local traffic is processed. 4.3.1.1. Processing of Local Traffic If the verification of the source address of a packet shows that it belongs to local traffic, this packet is processed using the state machine described in this section. For the rest of the section, the following assumptions hold: o When it is stated that a secured NUD_NSOL message is issued by a SEND SAVI device through a given port, this means the following: the SEND SAVI device performs a Neighbor Unreachability Detection procedure as described in [RFC4861] with SEND secured messages as defined in [RFC3971] addressed to the IPv6 target address (source address of the packet triggering the procedure). The source address used for issuing the NUD_NSOL is the source address of the SEND SAVI device. o When it is stated that a validated NUD_NADV message is received by a SEND SAVI device through a port P, this means that: a SEND secured NUD_NADV message has been received by the same port through which the corresponding NUD_NSOL message was issued, and the NUD_NADV message has been validated according to [RFC3971] to Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 12] Internet-Draft SEND SAVI October 2010 prove ownership for the IPv6 address under consideration, and being a response for the previous NUD_NSOL message issued by the SEND SAVI device (containing the same nonce value as the NUD_NSOL message to which it answers). We use VP to refer to a Validating port, and TP for Trusted port. The state machine is defined for a binding of a given source IP address in a given SAVI device. In the transitions considered, packets described as inputs refer to the IPaddr IPv6 address associated to the state machine. The possible states are o NO_BIND. This state represents that no binding exists for the address. This is the state for all addresses unless a binding is explicitly created. o TENTATIVE_DAD. This state is reached when the SEND SAVI device has received a validated DAD_NSOL message. The SEND SAVI device waits for a possible DAD_NADV. Packets with the source address of the binding are not forwarded. o TENTATIVE_NUD. A packet different from a valid DAD_NSOL message has been received from port VP and the SEND SAVI device has sent a NUD_NSOL message to the port. Packets with the source address of the binding are not forwarded. o VALID. The binding for the source address has been verified. Packets with the source address of the binding are forwarded. o TESTING_VP. The lifetime of the binding has expired so SEND SAVI device has sent a NUD_NSOL message to the port, or a DAD_NSOL coming from other SEND SAVI device has been received. The SEND SAVI device waits for a validated NADV. Packets with the source address of the binding are allowed to be forwarded. o TESTING_VP'. A validated DAD_NSOL message has been received from a Validating port of the SEND SAVI device. The device waits for a DAD_NADV coming from port VP, or changes the binding to port VP' if no response is received after TENT_LT milliseconds. Packets coming from port VP with the source address of the binding are allowed to be forwarded. The states can be classified into forwarding states, i.e. states in which packets coming for the port associated to the IPv6 address different to the ones used for signalling are forwarded (VALID, TESTING_VP and TESTING_VP'), and non-forwarding states, i.e. states in which packets coming from the port associated to the IPv6 address different to the ones used for signalling are not forwarded (NO_BIND, TENTATIVE_DAD and TENTATIVE_NUD). The state machine defined for SEND SAVI operation adheres to the following design guidelines: Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 13] Internet-Draft SEND SAVI October 2010 o The only events which triggers state changes from forwarding to non-forwarding states and vice versa are the reception of DAD_NSOL, DAD_NADV and NUD_NADV, or the expiration of a timer. Besides, DAD_NADV and NUD_NADV are only processed when expected as a response to a DAD_NSOL or a NUD_NSOL message. The other possible input to consider is 'any other packet', which could generate changes to states belonging to the same class as the original state (i.e. when 'any other packet' is received, the state cannot move from being forwarding to non-forwarding and vice versa). Note that non-validated SEND messages always belong to the 'any other packet' cathegory. The reduced set of messages being able to trigger a change simplifies the processing at SEND SAVI devices. It is also convenient for defining a comprehensive model regarding to anti-replay protection. o The SEND SAVI device is only required to generate NUD_NSOL messages for SEND SAVI operation. This also simplifies the state machine. o Well-behaved hosts are expected to initiate communication by sending secured DAD_NSOL messages. The SEND SAVI state machine is designed to process these events in an optimal way. The reception of other packet types without receiving previously validated DAD_NSOL messages is assumed to be the result of either bad- behaving hosts or the lost of packets. While these events may occur and a binding will ultimately be created for such hosts, the case in which data packets are received without receiving previously a DAD_NSOL message is not always optimized, for the sake of simplicity of the state machine. It is also worth to note that a validated DAD_NSOL provides a reliable hint about the address ownership of a host attached to a given port, while this is not the case for data packets, for example. o If a host has an address configured, and it can prove the ownership of this address, the state is preserved regardless of any indication that a binding for the same source address could be configured in other SEND SAVI device. Bindings for the same source address in two (or more) SEND SAVI devices may occur due to several reasons, for example when a host moves (the two bindings exist just for a short period of time), if accidentally two hosts generate the same address and the DAD procedure has failed. In these unfrequent cases, connectivity is honored over security. The SEND SAVI device must join the Solicited Node Multicast group for all the addresses which state is other than NO_BIND. This is needed to make sure that the SEND SAVI device will receive the DAD_NSOL for those addresses. Please note that it may not be enough to relay on the host behind the Validating port doing so, since the node may move and after a while, the packets for that particular solicited node multicast group will no longer be forwarded to the SEND SAVI device. So, the SAVI device SHOULD join the solicited node multicast groups Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 14] Internet-Draft SEND SAVI October 2010 for all the addresses that are in a state other than NO_BIND. We next describe how different inputs are processed depending on the state of the binding of the IP address 'IPaddr'. A Waiting_lifetime timer is associated to each binding. A simplified version is depicted in the next figure: Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 15] Internet-Draft SEND SAVI October 2010 +-------------+ | | | TESTING_VP' | | | +-------------+ | ^ Timeout / VP=VP' | | VP_NUD_NADV | | VP'_DAD_NSOL/ | | NUD_NSOL | | v | VP_DAD_NSOL +--------+ +------------- | | | | VALID |< -------------------+ | +-------- >| | | | | +--------+ | | | ^ | | | | VP_NUD_ | | Timeout, | | | NADV/- | | TP_DAD_NSOL/NUD_NSOL | | | | v | | | +------------+ | | | | | | | | | TESTING_VP | | | | | | | | | +------------+ | | | | | | | | Timeout | | | VP*, | | | | Timeout/- | VP_NUD_NADV | v | | | +---------------+ | +---------------+ | | | | | | TENTATIVE_DAD | | | TENTATIVE_NUD | | | | | | +---------------+ | +---------------+ ^ | | | ^ | | | Timeout/- | | | | TP_DAD_NSOL, | | | | | TP_DAD_NADV/- | | | | | v | | | | +---------+ | | | +--------- >| |< -----+ | | | NO_BIND | | +--------------| |-----------------+ VP_DAD_NSOL/- +---------+ VP*/VP_NUD_NSOL NO_BIND Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 16] Internet-Draft SEND SAVI October 2010 Relevant inputs for this state: When the node is in this state, there are no unresolved DAD_NSOL or NUD_NSOL messages (generated by SEND SAVI), so the only relevant inputs are DAD_NSOL messages coming either from VP or TP, or any packet other than DAD_NSOL coming from VP or TP. There are no timers too. o If a validated DAD_NSOL message is received from a Validating port VP, the SEND SAVI device forwards this message to all appropriate Trusted ports (the subset of Trusted ports which belong to the forwarding layer-2 topology, and with the restrictions imposed by the MLD snooping mechanism, if applied). The DAD_NSOL messages are not sent through any of the ports configured as Validating Ports. The SEND SAVI device sets the Waiting_timer to TENT_LT, stores all the information required for future validation of the corresponding DAD_NADV message (such as the nonce of the message) and changes the state to TENTATIVE_DAD. Note that in this case it is not possible to check address ownership by sending a NUD_NSOL because while the host is waiting for a possible DAD_NADV its address is in tentative state and it cannot respond to NSOL messages ([RFC4862]). o If any packet other than a DAD_NSOL is received through a Validating port VP, the SEND SAVI device issues a secured NUD_NSOL through port VP. The SEND SAVI device sets the Waiting_timer to TENT_LT. The state is changed to TENTATIVE_NUD. o Validated DAD_NSOL message containing IPAddr as the target address received through a Trusted port are NOT forwarded through any of the Validating ports but they are sent through the proper Trusted Ports (as defined by the switch behavior that will depend on whether it performs MLD snooping or not). The SEND SAVI device MAY assume that any DAD_NSOL message received from a Trusted port has been successfully validated by other SEND SAVI device, so that no additional validation is required. The state is not changed. o Any packet other than a DAD_NSOL received from a Trusted port is forwarded to its destination. This packet is assumed to come from a SEND SAVI device that has securely validated the attachment of the host to its Validating port according to SEND SAVI rules (unless the SEND SAVI perimeter has been breached). The state is not changed. TENTATIVE_DAD To arrive to this state, the SEND SAVI device has received a validated DAD_NSOL coming from port VP and forwarded to TP. The possible events occuring in this state are: the reception of a DAD_NADV message from a TP (the corresponding DAD_NSOL was forwarded to this port), a DAD_NSOL message from VP, other validating port VP' or TP, and the expiration of the timer initiated when the DAD_NSOL was received at port VP. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 17] Internet-Draft SEND SAVI October 2010 o If a validated DAD_NADV is received from a Trusted port, the binding cannot be configured for port VP. The state is changed to NO_BIND, and the Waiting_timer cleared. o If a validated DAD_NSOL is received from a Trusted port, a host connected to another SEND SAVI device may be trying to configure the same address at the same time. The DAD_NSOL message is forwarded to port VP, so that the host at port VP will not configure the address, as stated in [RFC4862]. The DAD_NSOL message is also forwarded to all appropriate Trusted ports. Then, the Waiting_timer is cleared, and the state is changed to NO_BIND. o Any packet other than a validated DAD_NSOL or DAD_NADV received from a Trusted port is forwarded to its destination. This packet is assumed to come from a SEND SAVI device that has securely validated the attachment of the host to its Validating port according to SEND SAVI rules (unless the SEND SAVI perimeter has been breached). The state is not changed. o If a validated DAD_NSOL is received from a Validating port VP' different to VP, a host connected to VP' may be trying to configure the same address at the same time. The DAD_NSOL message is forwarded to port VP, so that the host at port VP will not configure the address, as stated in [RFC4862]. The DAD_NSOL message is also forwarded to all appropriate Trusted ports. Then, the Waiting_timer is set to TENT_LT, and the state remains in TENTATIVE_DAD, although in this case with VP=VP'. o Any other packet than a validated DAD_NSOL is received from a Validating port VP' different from VP is discarded. The state is not changed. o If a validated DAD_NSOL is received from port VP, the Waiting_timer is set to TENT_LT, and the state remains in TENTATIVE_DAD. o If any packet other than a validated DAD_NSOL is received from VP, it is assumed that the host has configured its address, although it has done it in less time than expected by the SEND SAVI device (less than TENT_LT). Since the host proved address ownership by means of the validated DAD_NSOL message, the binding is created. The Waiting_timer is set to DEFAULT_LT, and the state is changed to VALID. o If Waiting_timer expires, it is assumed that no other host has configured this address. Therefore, the Validating port VP could be bound to this IPv6 address. The Waiting_timer is set to DEFAULT_LT, and the state is changed to VALID. VALID To arrive to this state, successful validation of address ownership has been completed. Relevant transitions for this state are triggered by the reception of DAD_NSOL from ports VP, VP' or TP, and any packet other than DAD_NSOL from VP' or TP. The expiration of Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 18] Internet-Draft SEND SAVI October 2010 Waiting_timer is also relevant to check again for address ownership. o If a validated DAD_NSOL with IPaddr as source address is received through Validating port VP, this message is forwarded to the appropriate trusted ports. The Waiting_timer is set to TENT_LT and the state is changed to TENTATIVE_DAD. o Any packet other than a validated DAD_NSOL containing IPaddr as a source address arriving from Validating port VP is forwarded appropriately. The state is not changed. Note that in the SEND SAVI case Timeout_valid for the entry MUST NOT be set to DEFAULT_LT (as occurs for FCFS SAVI), since regular sending of packets does not provide the required security, which is achieved by performing secured NUD periodically with the sending host. o If a validated DAD_NSOL with IPaddr as source address is received through a Trusted port, the message is forwarded to VP. The Waiting_timer is set to TENT_LT, a secured NUD_NSOL message is sent to IPaddr through VP and the state is changed to TESTING_VP. o If any packet other than a DAD_NSOL with IPaddr as source address is received through a Trusted port, the packet is forwarded to VP and to other appropriate Trusted ports. A secured NUD_NSOL is sent to VP, the Waiting_timer is set to TENT_LT, and the state is changed to TESTING_VP. o If a DAD_NSOL packet with IPaddr as source address is received through a Validating Port VP' (VP' different from the current Validating port for this binding), the message is forwarded to VP. In addition, a secured NUD_NSOL is sent to VP, the Waiting_timer is set to TENT_LT, and the state is changed to TESTING_VP'. o If any packet other than a DAD_NSOL with IPaddr as source address is received from a Validating Port VP', different from the current Validating port for this binding, VP, the packet is discarded. The SEND SAVI device MAY issue a secured NUD_NSOL through port VP, set the Waiting_timer to TENT_LT, and change the state to TESTING_VP'. An alternative to this behavior is that the SEND SAVI device MAY not do anything (in this case, the state would eventually change after a maximum DEFAULT_LT time, if the node at VP does not respond to a NUD_NSOL at TESTING_VP, the state is moved to NO_BIND, and a packet arrives from VP'. o If Waiting_timer expires, a secured NUD_NSOL message is sent through port VP to the IPv6 address, the Waiting_timer is set to TENT_LT, and the state is changed to TESTING_VP. In the TESTING_VP state packets are still being forwarded until the timer expires without receiving a NUD_NADV. TESTING_VP When the SEND SAVI device enters in the TESTING_VP state, the current Validating port is under check through a secured NUD_NSOL message generated by the SEND SAVI device. While testing, packets from the current Validating port are forwarded. Packets coming from Trusted Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 19] Internet-Draft SEND SAVI October 2010 ports are also forwarded. The relevant events for this state are the reception of a secured NUD_NADV message from VP, the reception of a secured DAD_NSOL message from VP, VP' or TP, the reception of any packet other than the previous cases from VP, VP' or TP, and the expiration of the timer waiting for NUD_NADV. o If a validated NUD_NADV message is received from VP, the message is discarded, the Waiting_timer is changed to DEFAULT_LT, and the state is changed to VALID. o If a validated DAD_NSOL message is received from VP, the message is forwarded to the appropriate Trusted ports, the Waiting_timer is set to DEFAULT_LT, and the state is changed to TENTATIVE_DAD. o Any packet other than DAD_NSOL or NUD_NADV containing IPaddr as a source address arriving from Validating port VP is forwarded. Neither the Waiting_timer nor the state are changed. o If a DAD_NSOL message is received from a Trusted port, the message is forwarded to VP and the appropriate Trusted ports. Neither the Waiting_timer nor the state are changed. The host at VP port is under check: if it still is at port VP, it should answer with a NUD_NADV, and also with a DAD_NADV. If it is not there, neither the NUD_NADV nor the DAD_NADV will be received, the timer will expire, the local state will move to NO_BIND, and the state at the remote node will change to VALID. o If a packet other than a DAD_NSOL arrives from a Trusted port, the packet is forwarded. Neither the Waiting_timer nor the state are changed. o If a DAD_NSOL is received from a validating port VP', the message is forwarded to VP and the appropriate Trusted ports. In addition, a secured NUD_NSOL is sent to VP, the Waiting_timer is set to TENT_LT, and the state is changed to TESTING_VP'. o Any other packet received from a validating port VP' is discarded. This may occur because the host has moved but have not issued a DAD_NSOL or the DAD_NSOL message has been lost. The state will eventually move to NO_BIND, and then the packets sent from VP' will trigger the creation of the binding for VP'. o If the Waiting_timer expires, the Waiting_timer is cleared and the state is changed to NO_BIND. TESTING_VP' To arrive to this state an indication that a host at VP' wants to send data with IPaddr as source address while a binding existed for VP. The SEND SAVI device has issued a NUD_NSOL to the host through port VP. The possible events that may occur in this case are the reception of a NUD_NADV from port VP, the reception of DAD_NSOL from VP, VP', TP and VP" (VP" different from VP and VP'), the reception of any other packet from VP, VP', TP or VP", and the expiration of the timer. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 20] Internet-Draft SEND SAVI October 2010 o If a validated NUD_NADV is received from port VP, then the host at VP is defending its address. VP is kept as the Validating port, the Waiting_timer is set to DEFAULT_LT, and the state is changed to VALID. o If a validated DAD_NSOL is received from port VP, the message is forwarded to VP'. The Waiting_timer is set to TENT_LT and the state is changed to TENTATIVE_DAD. If the host at VP is reconfiguring its address; when forwarding the DAD_NSOL message, the node at VP' is expected to unconfigure its address. o Any packet other than a validated DAD_NSOL or a validated NUD_NADV coming from port VP is forwarded, and the state is not changed. o If a validated DAD_NSOL is received from port VP', the message is forwarded to VP. The Waiting_timer is set to DEFAULT_LT, and the state is not changed. o Any packet other than a validated DAD_NSOL coming from port VP is discarded, and the state is not changed. o If a validated DAD_NSOL is received from port VP", different from VP and VP', the message is forwarded to VP and VP'. VP' is expected to unconfigure its address if it was a VP'_DAD_NSOL message (and not any other packet) the message triggering the transition to this state. The state remains in TESTING_VP' although with VP'=VP". The Waiting_timer is not changed. o Any packet other than a validated DAD_NSOL received from port VP" is discarded and does not affect to the state. o If a validated DAD_NSOL is received from a Trusted port, the message is forwarded to ports VP, VP' and other appropriate Trusted ports. The Waiting_timer is left unchanged and the state is changed to TESTING_VP. VP' is expected to unconfigure its address if it was a VP'_DAD_NSOL message (and not any other packet) the message triggering the transition to this state. o Any packet other than a validated DAD_NSOL coming from a Trusted port is forwarded appropriately, but the state is not changed. o If Waiting_timer expires, it is assumed that the host for which the binding existed is no longer connected through port VP. Therefore, the Validating port VP' could be bound to this IPv6 address. The Waiting_timer is set to DEFAULT_LT and the state is changed to VALID. TENTATIVE_NUD To arrive to this state a data packet has been received through port VP without any existing binding in the SEND SAVI device. The SEND SAVI device has sent a NUD_NSOL message to VP. The relevant events for this case are the reception of a NUD_NADV from port VP, the reception of DAD_NSOL from port VP, VP' or TP, and the reception of any packet other than DAD_NSOL and NUD_NADV for port VP, and different from DAD_NSOL for VP' or TP. In addition, the Waiting_timer may expire. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 21] Internet-Draft SEND SAVI October 2010 o If a validated NUD_NADV message is received through port VP, the message is discarded, the Waiting_timer is set to TENT_LT, and the state is changed to VALID. o If a validated DAD_NSOL message is received through port VP, the message is forwarded to the appropriate Trusted ports, the Waiting_timer is set to TENT_LT and the state is changed to TENTATIVE_DAD. o Any packet other than NUD_NADV or DAD_NSOL received through port VP is discarded. o If a validated DAD_NSOL message is received through port VP' different from port VP, the message is forwarded to the appropriate Trusted ports, the Waiting_timer is set to TENT_LT with VP=VP', and the state is changed to TENTATIVE_DAD. o Any packets other than DAD_NSOL received through port VP' are discarded, and the state is left unchanged. o If a validated DAD_NSOL message is received through a Trusted port, the message is forwarded to port VP, and the state is left unchanged. o Any other packet received from a Trusted port are forwarded appropriately. These packets may come from a SEND SAVI device that has securely validated the attachment of the host to its Validating port according to SEND SAVI rules. The state is left unchanged. o If Waiting_timer expires, the Waiting_timer is cleared and the state is changed to NO_BIND. 4.4. VLAN Support In the case the SAVI device is a switch that supports VLANs, the SAVI implementation will behave as if there was one SAVI process per VLAN. The SAVI process of each VLAN will store the binding information corresponding the nodes attached to that particular VLAN. 4.5. Protocol Constants TENT_LT is 500 milliseconds. DEFAULT_LT is 5 minutes. 5. Security Considerations It should be noted that any SAVI solution is as strong as the lower layer anchor that it uses. In particular, if the lower layer anchor is forgeable, then the resulting SAVI solution will be weak. For example, if the lower layer anchor is a MAC address that can be easily spoofed, then the resulting SAVI will not be stronger than that. On the other hand, if we use switch ports as lower layer Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 22] Internet-Draft SEND SAVI October 2010 anchors (and there is only one host connected to each port) it is likely that the resulting SAVI solution will be considerably more secure. SEND SAVI improves protection compared to conventional SAVI, as a result of the increased ability of SEND hosts to prove address ownership. A critical security consideration regarding to SEND SAVI deals with the need of proper configuration of the roles of the ports in a SEND SAVI deployment scenario. Regarding to security, the main requirement is that ports defining the protected perimeter SHOULD be configured as Validating. Not doing so will generate security breaches through which an attacker could send packets using any source address, regardless of the bindings established in other SEND SAVI devices. However, SEND SAVI is designed to allow even in this case communication for legitimate users. The worst case for the misconfiguration of the perimeter is then that two hosts may use the same source IPv6 address. The reasons for having a misconfigured perimeter, apart from initial misconfiguration, are the dynamic operations performed by layer-2 routing mechanisms, for example, as a result of a failure in a link or switching device. To prevent the security risks associated, in the case of changes in the topology of the SEND SAVI devices, all ports of a SEND SAVI device MAY be changed automatically to Validating. Note that neither connectivity nor the protection offered are compromised by operating in a mode in which all ports of the SEND SAVI devices operate in Validating mode (only performance is affected by this setting). SEND SAVI does not protect against spoofers being attached to the same port as a legitimate host. For this reason it is RECOMMENDED that only one host attaches at the same time to a given port. One possible concern about SEND SAVI is its behavior when an attacker tries to forge the identity of a legitimate host by replaying messages. Note that information that can be valid for SEND a short period after being generated (the binding between an IPv6 address and a layer-2 MAC address) is not valid for SEND SAVI if it arrives from an non-legitimate port. We now perform a security analysis of such a replay attack for SEND SAVI. On one hand, there is some information for which the security risks are equivalent to those of SEND operation, which are situations in which the information received is not tied to port-related state in SEND SAVI operation. Such situations are the reception of CPA messages containing certificates, or the processing of an unsolicited RADV message, which can be used in SEND SAVI to associate the router condition to the IPv6 address of an existing binding in the SEND SAVI Port list. On the other hand, all the messages which can be create a SEND SAVI binding may be Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 23] Internet-Draft SEND SAVI October 2010 sensible for the replaying of valid SEND messages. SEND SAVI creates and maintains bindings as a result of the reception of DAD_NSOL messages and of the exchange of NUD_NSOL/NUD_NADV messages. o To prevent DAD_NSOL replay attacks, DAD_NSOL messages are not forwarded to ports through which an existing binding existed. Therefore, to capture a message that could be used to launch a replay attack, an attacker must be located either in the port through which the legitimate host is (in which case the attack is useless), or in a port in which a legitimate host was before and for which a binding still exists. For this latter case, an attacker can prevent the configuration of binding for a legitimate host in other port (which could have moved from the initial location), and the binding would be available for the attacker for DEFAULT_LT ms. The attacker can do this either in the port for which a binding existed, or in other port to which it is connected or to which it can convey this information for a third node to perform this attack. This risk is inherent to allowing layer-2 host mobility in an scenario in which many hosts can attach to the same port (either at the same time or in instants very close one to the other). Another consideration is that this situation reflect the fact that it is impossible to determine the legitimacy of a node with a more secure NUD_NSOL/NUD_NADV exchange when the nodes claim to be configuring the address. o When a NUD_NSOL/NUD_NADV exchange is used to create or maintain a state, the messages are only forwarded to the port in which the host claiming to be legitimate is located. In this case, an attacker must be connected to the same port of the legitimate host to be able to capture a message which could be replayed. The replay of NUD_NSOL is useless, since it is not used to trigger the creation of a binding. The replay of a NUD_NADV message through the same port is useless, since SEND SAVI does not protect against spoofers attached to the same port. The replay of a NUD_NADV message through a different port does result neither in the creation of a binding in other SEND SAVI device, nor in the binding created in the SEND SAVI device originating the NUD_NSOL message, since this SEND SAVI device only considers NUD_NADV message received from the same port through which the NUD_NSOL message was sent. It is worth to note that the potential of Denial of Service attacks against the SEND SAVI network is increased due to the use of costly cryptographic operations in order to validate the address of the hosts. An attacker could generate packets using new source addresses in order to make the closest SEND SAVI device spend CPU time to validate DAD_NSOL messages or generate a NUD_NSOL and create a state in which a NUD_NADV is waited for. This attack can be used to drain CPU resources of SEND SAVI devices with a very low cost for the attacker. In order to solve this problem, a rate-limiting mechanism Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 24] Internet-Draft SEND SAVI October 2010 SHOULD be enforced in a per-port basis. 6. Acknowledgments Thanks to Ana Kukec for her review and comments on this document. The text has also benefited from feedback provided by Tony Cheneau. Marcelo Bagnulo is partly funded by Trilogy, a research project supported by the European Commission under its Seventh Framework Program. Alberto Garcia-Martinez is partly funded by T2C2, a Spanish R&D project. 7. Normative References [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. [I-D.ietf-savi-framework] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, "Source Address Validation Improvement Protocol Framework", draft-ietf-savi-framework-00 (work in progress), September 2010. [I-D.ietf-savi-fcfs] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS- SAVI: First-Come First-Serve Source-Address Validation for Locally Assigned Addresses", draft-ietf-savi-fcfs-05 (work in progress), October 2010. Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 25] Internet-Draft SEND SAVI October 2010 Authors' Addresses Marcelo Bagnulo Universidad Carlos III de Madrid Av. Universidad 30 Leganes, Madrid 28911 SPAIN Phone: 34 91 6248814 Email: marcelo@it.uc3m.es URI: http://www.it.uc3m.es Alberto Garcia-Martinez Universidad Carlos III de Madrid Av. Universidad 30 Leganes, Madrid 28911 SPAIN Phone: 34 91 6248782 Email: alberto@it.uc3m.es URI: http://www.it.uc3m.es Bagnulo & Garcia-Martinez Expires April 28, 2011 [Page 26]