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Versions: (draft-bagnulo-savi-fcfs) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6620

Network Working Group                                        E. Nordmark
Internet-Draft                                                       Sun
Intended status: Standards Track                              M. Bagnulo
Expires: April 29, 2010                                             UC3M
                                                        E. Levy-Abegnoli
                                                           Cisco Systems
                                                        October 26, 2009


FCFS-SAVI: First-Come First-Serve Source-Address Validation for Locally
                           Assigned Addresses
                        draft-ietf-savi-fcfs-02

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 29, 2010.

Copyright Notice

   Copyright (c) 2009 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
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   Please review these documents carefully, as they describe your rights
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Abstract

   This memo describes FCFS SAVI a mechanism to provide source address
   validation for IPv6 networks using the First-Come First-Serve
   approach.  The proposed mechanism is intended to complement ingress
   filtering techniques to provide a higher granularity on the control
   of the source addresses used.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Design considerations  . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Scope of FCFS SAVI . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Constraints for FCFS SAVI  . . . . . . . . . . . . . . . .  4
     2.3.  Address ownership proof  . . . . . . . . . . . . . . . . .  4
     2.4.  Layer-2 Anchor considerations  . . . . . . . . . . . . . .  5
     2.5.  Special cases  . . . . . . . . . . . . . . . . . . . . . .  5
   3.  SAVI topology and port configuration . . . . . . . . . . . . .  5
     3.1.  SAVI enforcement perimeter . . . . . . . . . . . . . . . .  6
     3.2.  SAVI port configuration guidelines . . . . . . . . . . . .  9
     3.3.  VLAN support . . . . . . . . . . . . . . . . . . . . . . . 10
   4.  FCFS SAVI specification  . . . . . . . . . . . . . . . . . . . 10
     4.1.  FCFS SAVI Data structures  . . . . . . . . . . . . . . . . 10
     4.2.  FCFS SAVI algorithm  . . . . . . . . . . . . . . . . . . . 10
       4.2.1.  Processing of transit traffic  . . . . . . . . . . . . 10
       4.2.2.  Processing of local traffic. . . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18



















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1.  Introduction

   This memo describes FCFS SAVI, a mechanism to provide source address
   validation for IPv6 networks using the First-Come First-Serve
   approach.  The proposed mechanism is intended to complement ingress
   filtering techniques to provide a higher granularity on the control
   of the source addresses used.


2.  Design considerations

2.1.  Scope of FCFS SAVI

   The application scenario for FCFS SAVI is limited to the local-link.
   This means that the goal of FCFS SAVI is verify that the source
   address of the packets generated by the hosts attached to the local
   link have not been spoofed.

   In any link there usually are hosts and routers attached.  Hosts
   generate packets with their own address 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 what the so-called transit traffic.

   The applicability of FCFS SAVI is limited to the local traffic i.e.
   to verify if the traffic generated by the hosts attached to the local
   link contains a valid source address.  The verification of the source
   address of the transit traffic is out of the scope of FCFS SAVI.
   Other techniques, like ingress filtering [RFC2827], are recommended
   to validate transit traffic.  In that sense, FCFS SAVI complements
   ingress filtering, since it relies on ingress filtering to validate
   transit traffic but is provides validation of local traffic, which is
   not provided by ingress filtering.  Hence, the security level is
   increased by using these two techniques.

   In addition, FCFS SAVI is designed to be used with locally assigned
   addresses, in particular with address configured through stateless
   address autoconfiguration [RFC4862].  Manually configured addresses
   can be supported by FCFS SAVI, but manual configuration of the
   binding on the SAVI device provides higher security and seems
   compatible with manual address management.  Additional considerations
   about how to use FCFS SAVI depending on the type of address
   management used and the nature of the addresses is discussed in the
   framework document (add reference when available).






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2.2.  Constraints for FCFS SAVI

   FCFS SAVI is designed to be deployed in existing networks requiring a
   minimum set of changes.  For that reason, FCFS SAVI does not require
   any changes in the hosts which source address is to be verified.  Any
   verification must solely rely in the usage of already available
   protocols.  This means that FCFS SAVI cannot 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.  In other
   words, the requirement is no host changes.

   FCFS SAVI validation is performed by the FSFC SAVI function.  Such
   function can be placed in different type of devices, including a
   router or a layer-2 bridge.  The basic idea is that the FCFS SAVI
   function is located in the points of the topology that can enforce
   the correct usage of source address by dropping the non-compliant
   packets.

2.3.  Address ownership proof

   The main function performed by FCFS SAVI is to verify that the source
   address used in data packets actually belongs to the originator of
   the packet.  Since FCFS SAVI scope is limited to the local link, the
   originator of the packet is attached to the local link.  In order to
   define any source address validation solution, we need to define some
   address ownership proof concept i.e. what it means to be able to
   proof that a given host owns a given address in the sense that the
   host is entitled to send packet with that source address.

   Since no host changes are acceptable, we need to find the means to
   proof address ownership without requiring a new protocol.  In FCFS
   SAVI the address ownership proof is based in the First-Come first
   Serve approach.  This means that the first host that claims a given
   source address is the owner of the address until further notice.
   More precisely, whenever a source address is used for the first time,
   a state is created in the device that is performing the FCFS SAVI
   function binding the source address to the layer-2 information that
   the FCFS SAVI box has available (e.g. the port in a switched LAN).
   Following data packets containing that IP source address must use the
   same layer-2 information in order to be compliant.

   There are however additional considerations to be taken into account.
   For instance, consider the case of a host that moves from one segment
   of a LAN to another segment of the same subnetwork and it keeps the
   same IP address.  In this case, the host is still the owner of the IP
   address, but the associated layer-2 information has changed.  In
   order to cope with this case, the defined FCFS SAVI behaviour implies
   the verification whether the host is still reachable using the



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   previous layer-2 information.  In order to do that FCFS SAVI uses ND
   protocol.  If the host is no longer reachable at the previously
   recorded layer-2 information, FCFS SAVI assumes that the new location
   is valid and creates a new binding using the new layer-2 information.
   In case the host is still reachable using the previously recorded
   information, the packets coming from the new layer-2 information are
   dropped.

   Note that this only applies to local traffic.  Transit traffic
   generated by a router would be verified using alternative techniques,
   such as ingress filtering.  SAVI checks would not be fulfilled by the
   transit traffic, since the router is not the owner of the source
   address contained in the packets.

2.4.  Layer-2 Anchor considerations

   Any SAVI solution is not stronger than the Layer-2 anchor it uses.
   If the Layer-2 anchor is easily spoofable (e.g. a MAC address), then
   the resulting solution will be weak.  The treatment of non-compliant
   packets needs to be tuned accordingly.  In particular, if the Layer-2
   anchor is easily spoofable and the SAVI device is configured to drop
   no compliant packets, then the usage of SAVI may open a new vector of
   Denial of Service attacks, based on spoofed Layer-2 anchors.  For
   that reason, in this document, we assume that the Layer-2 anchors
   used by the SAVI solution are not easily spoofable (e.g. ports of a
   switched network) and that the SAVI device MAY be configured to drop
   non- compliant packets.  If the SAVI solution proposed in this
   document is to be used with weaker Layer-2 anchors (such as MAC
   addresses), logging is RECOMMENDED instead of dropping non-compliant
   packets.  For the rest of the document, we will assume that the
   Layer-2 anchors are ports of a switched network.

2.5.  Special cases

   The following special cases that need to be considered
   o  Hosts with multiple physical interfaces connected to the same
      link.
   o  Anycast i.e. multiple hosts using the same source address to send
      packets.
   o  Proxy ND i.e. host sending packets on behalf of other, in a
      layer-3 transparent manner.


3.  SAVI topology and port configuration







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3.1.  SAVI enforcement perimeter

   SAVI provides perimetrical security.  This means that the SAVI
   devices form what can be called a SAVI enforcement perimeter and they
   verify that any packet that crosses the perimeter is compliant (i.e.
   the source address related information is validated).  Once the
   packet is inside the perimeter, no further validations are performed
   to the packet.  This model has implications both on how SAVI devices
   are deployed in the topology and on the configuration of the SAVI
   boxes.

   The implication of this perimetrical security approach, is that there
   is part of the topology that is inside the perimeter and part of the
   topology that is outside the perimeter.  This means that while
   packets coming from interfaces connected to the external part of the
   topology need to be validated by the SAVI device, packets coming from
   interfaces connected to the the internal part of the topology do not
   need to be validated.  This significantly reduces the processing
   requirements of the SAVI device.  It also implies that each SAVI
   device that is part of the perimeter, must be able to verify the
   source addresses of the packets coming from the interfaces connected
   to the external part of the perimeter.  In order to do so, the SAVI
   device binds the source address to a layer-2 anchor.

   One possible approach would be for every SAVI device to store binding
   information about every source addresses in the subnetwork This means
   that every SAVI device would store binding for each source address to
   the local layer-2 anchor through packets with that source address can
   be received through.  The problem with this approach is that it
   imposes significant memory burden on the SAVI devices.  In order to
   reduce the memory requirements imposed to each device, the SAVI
   solution described in this specification distributes the storage of
   SAVI binding information among the multiple SAVI devices of a
   subnetwork.  The SAVI binding state is distributed across the SAVI
   devices according to the following criteria: each SAVI device will
   store binding information about the source addresses bound to layer-2
   anchors corresponding to the interfaces that connect to the part of
   the topology that is outside of the SAVI enforcement perimeter.
   Since all the untrusted packet sources are by definition in the
   external part of the perimeter, this means that the packets generated
   by each of the untrusted sources will reach the perimeter through one
   interface of a SAVI device.  The binding information for that
   particular source address will be stored in this first SAVI device
   the packet reaches to.

   This means the SAVI binding information will be distributed across
   multiple devices.  In order to provide proper source address
   validation, it is critical that the information distributed among the



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   different SAVI devices is coherent.  In particular, it is important
   to avoid that the same source address is bound to different layer-2
   anchors in different SAVI devices.  Should that occur, then it would
   mean that two hosts are allowed to send packets with the same source
   address, which is what we are trying to prevent.  In order to
   preserve the coherency of the SAVI bindings distributed among the
   SAVI devices within a realm, the Neighbour Discovery (ND) protocol is
   used, in particular the Neighbour Solicitation (NSOL) and Neighbour
   Advertisement (NADV) messages.  Before creating a SAVI binding in the
   local SAVI database, the SAVI device will send a NSOL message
   querying for the address involved.  Should any host reply to that
   message with a NADV message, the SAVI device that sent the NADV will
   infer that a binding for that address exists in another SAVI device
   and will not create a local binding for it.  If no NADV message is
   received as a reply to the NSOL, then the local SAVI device will
   infer that no binding for that address exists in other SAVI device
   and will create the local SAVI binding for that address.  (NOTE that
   the description included here is overly simplified to illustrate the
   mechanism used to preserve the coherency of the binding databases of
   the different SAVI devices.  The actual SAVI mechanism as described
   below varies in the fact that in some cases it is the SAVI device
   that generates the NSOL while in other cases it simply forwards the
   NSOL generated by the end host, and that the SAVI device will send
   multiple copies of the NSOL in order to improve the reliability of
   the message exchange).

   So, summarizing, the proposed SAVI approach relies on the following
   design choices:
   o  SAVI provides perimetrical security, so some interfaces of a SAVI
      device will connect to the internal (trusted) part of the topology
      and other interfaces will connect to the external (untrusted) part
      of the topology.
   o  A SAVI device only verifies packets coming though one interface
      connected to the untrusted part of the topology.
   o  A SAVI device only stores binding information for the source
      addresses that are bound to layer-2 anchors that correspond to
      interfaces that connect to the untrusted part of the topology.
   o  SAVI uses the NSOL and NADV messages to preserve the coherency of
      the SAVI binding state distributed among the SAVI devices within a
      realm.

   So, in a link that is constituted of multiple L2 devices, some of
   which are SAVI capable and some of which are not, the SAVI capable
   devices SHOULD be deployed forming a connected perimeter (i.e. that
   no data packet can get inside the perimeter without passing through a
   SAVI device).  Packets that cross the perimeter will be validated
   while packets that do no cross the perimeter are not validated (hence
   SAVI protection is not provided for these packets).  Consider the



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   deployment of SAVI in the topology depicted in the following picture:

      +--+   +--+                          +--+   +--+
      |H1|   |H2|                          |H3|   |R1|
      +--+   +--+                          +--+   +--+
        |     |                              |     |
   +-------------SAVI-ENFORCEMENT-PERIMETER--------------+
   |    |     |                              |     |     |
   |  +-1-----2-+                          +-1-----2-+   |
   |  |  SAVI1  |                          |  SAVI2  |   |
   |  +-3--4----+                          +--3------+   |
   |    |  |          +--------------+        |          |
   |    |  +----------|              |--------+          |
   |    |             |   SWITCH-A   |                   |
   |    |  +----------|              |--------+          |
   |    |  |          +--------------+        |          |
   |  +-1--2----+                          +--1------+   |
   |  |  SAVI3  |                          |  SAVI4  |   |
   |  +-3---4---+                          +----4----+   |
   |    |   |                                   |        |
   +-------------SAVI-ENFORCEMENT-PERIMETER--------------+
        |   |                                   |
      +--+ +--+                            +---------+
      |R2| |H4|                            |SWICTH-B |
      +--+ +--+                            +---------+
                                                 |    |
                                           +--+  +--+
                                           |H5|  |H6|
                                           +--+  +--+


   In the figure above, the SAVI enforcement perimeter is provided by 4
   SAVI devices, namely SAVI1, SAVI2, SAVI3 and SAVI4.  These devices
   verify information related to the source address both in data and in
   ND packets and filter packets accordingly.

   SAVI devices then have two types of ports: trusted ports and
   validating ports.
   o  Validating ports (VPs) are those in which SAVI processing is
      performed.  This means that when a packet is received through one
      of the validating ports, the SAVI processing and filtering will be
      executed.
   o  Trusted ports (TPs) are those in which SAVI processing is not
      performed.  So, packets received through trusted ports are not
      validated and no SAVI processing is performed in them.

   Trusted ports are used for connections with trusted infrastructure,
   including the communication between SAVI devices, the communication



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   with routers and the communication of other switches that while they
   are not SAVI devices, they only connect to trusted infrastructure
   (i.e. other SAVI devices, routers or other trusted nodes).  So, in
   the figure above, Port 3 of SAVI1 and port 1 of SAVI3 are trusted
   because the connect two SAVI devices.  Port 4 of SAVI1, port 3 of
   SAVI2, port 2 of SAVI3 and port 1 of SAVI4 are trusted because the
   connect to SWITCH-A to which only trusted nodes are connected.  In
   the figure above, port 2 of SAVI2 and port 3 of SAVI3 are trusted
   ports because they connect to routers.

   Validating ports are used for connection with non-trusted
   infrastructure.  In particular, hosts are normally connected to
   validating ports.  Non-SAVI switches that are outside of the SAVI
   enforcement perimeter also are connected through validating port.  In
   particular, non-SAVI devices that connect directly to hosts or that
   have no SAVI capable device between themselves and the hosts are
   connected through a validating port.  So, in the figure above, ports
   1 and 2 of SAVI1, port 1 of SAVI2, port 4 of SAVI 3 are validating
   ports because they connect to hosts.  Port 4 of SAVI4 is also a
   validating port because it is connected to SWITCH-B which is a non-
   SAVI capable switch which is connected to hosts H5 and H6.

3.2.  SAVI port configuration guidelines

   The guidelines for port configuration in SAVI devices are:
   o  Ports that are connected to another SAVI device SHOULD be
      configured as Trusted ports.  Not doing so will at least
      significantly increase the memory consumption in the SAVI devices.
   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 Trusted ports.
      Configuring them as Validating ports would increase the signaling
      due to SAVI.  The implication is that a router can generate
      traffic with any source address as they are assumed to be part of
      the trusted infrastructure.
   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 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 SAVI devices and increase the signaling traffic due to SAVI
      validation.





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   o  Ports connected to a chain of one or more legacy switches that
      have a mix of 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.  Nevertheless, this topology will result in increased
      SAVI signaling and memory consumption compared to a topology where
      SAVI-hosts communications and inter SAVI communications are kept
      through different legacy switches.

3.3.  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 the nodes attached to that particular VLAN.


4.  FCFS SAVI specification

4.1.  FCFS SAVI Data structures

   FCFS SAVI function relies on state information binding the source
   address used in data packets to the layer-2 information that
   contained the first packet that used that source IP address.  Such
   information is stored in FCFS SAVI Data Base (DB).  The FCFS SAVI DB
   will contain a set of entries about the currently used IP source
   addresses.  So each entry will contain the following information:
   o  IP source address
   o  Layer-2 information, such as Layer-2 address, port through which
      the packet was received, etc
   o  Lifetime
   o  Status:either tentative or valid
   o  Creation time: the value of the local clock when the entry was
      firstly created

   In addition to this, FCFS SAVI need to know what are the prefixes
   that are directly connected, so it maintains a data structure called
   the the FCFS SAVI prefix list, which contains:
   o  Prefix
   o  Interface where prefix is directly connected

4.2.  FCFS SAVI algorithm

4.2.1.  Processing of transit traffic

   The FCFS SAVI function is located in a forwarding device, such as a
   router or a layer-2 bridge.  The following processing is performed
   depending on the type of port the packet has been received through:



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   o  If the data packet is received through a Trusted port, the data
      packet is forwarded and no SAVI processing performed to the
      packet.
   o  If the data packet is received through a Validating port, then the
      SAVI function checks whether the received data packet is local
      traffic or transit traffic.  It does so by verifying if the source
      address of the packet belongs to one of the directly connected
      prefixes available in the receiving interface.  It does so by
      searching the FCFS SAVI Prefix List.
      *  If the IP source address does not belong to one of the local
         prefixes of the receiving interface, this means that the dat
         packet is transit traffic and the packet SHOULD be discarded.
         The FCFS SAVI function MAY send an ICMP Destination Unreachable
         Error back to the source address of the data packet.  (ICMPv6,
         code 5 (Source address failed ingress/egress policy) should be
         used).
      *  If the source address of the packet does belong to one of the
         prefixes available in the the receiving port, then the SAVI
         local traffic validation processes is executed as described
         below.

4.2.2.  Processing of local traffic.

   We describe next how the local traffic, including both control and
   data packets are processed by the SAVI device using a state machine
   approach.

   The state machine described is for the binding of a given source IP
   address in a given SAVI device.  So this means that all the packets
   described as inputs in the state machine above refer to that given IP
   address.  The key attribute is the IP address.  The full state
   information is:
   o  IP ADDRESS: IPAddr
   o  LAYER_2 ANCHOR: P
   o  LIFETIME: LT

   The possible states are:
   o  NO_BIND
   o  TENTATIVE
   o  VALID
   o  TESTING_TP
   o  TESTING_VP
   o  TESTING_LIFETIME

   We will use VP for Validating Port and TP for Trusted Port.

   After bootstrapping (when no binding exists), the state for all
   source IP address is NO-BIND i.e. there is no binding for the IP



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   address to any Layer-2 anchor.

   NO_BIND: The binding for a source IP address entry is in this state
   when it does not have any binding to a Layer 2 anchor.  All addresses
   are in this state by default after bootstrapping, unless bindings
   were created for it.

   TENTATIVE: The binding for a source address is in this state during
   the waiting period during which the DAD procedure is being executed
   (either directly by the host itself or by the SAVI device on its
   behalf).

   VALID: The binding for the source address has been verified, it is
   valid and usable for filtering traffic.

   TESTING_TP: A binding for a source address enters in this sate when a
   DAD_NSOL has been received through a Trusted port. this implies that
   another host is performing the DAD procedure for that source address
   in another switch. this may due to an attack or to the fact that the
   host may have moved.  The binding in this state is then being tested
   to determine which is the situation.

   TESTING_TP: A binding for a source address enters in this sate when a
   DAD_NSOL or a data packet has been received through a Validating
   port. this implies that another host is performing the DAD procedure
   for that source address in another switch. this may due to an attack
   or to the fact that the host may have moved.  The binding in this
   state is then being tested to determine which is the situation.

   TESTING_LIFETIME: A binding for a source address is in this state
   cause the lifetime of the entry is about to expire. this is due to
   the fact that no packets has been seen by the SAVI device for the
   LIFETIME period. this may be due to the host simply being silent or
   because the host has left the location.  In order to determine which
   is the case, a test is performed, in order to determine if the
   binding information should be discarded.

   We describe next how the different inputs are processed depending on
   the state of the binding of the IP address.

   A simplified figure of the state machine can be found at
   http://www.it.uc3m.es/~marcelo/SAVI_state_machine.pdf

   NO_BIND

   o  Upon the reception through a Validating Port (VP) of a Neighbour
      Solicitation (NSOL) generated by the Duplicate Address Detection
      (DAD) procedure (hereafter named DAD_NSOL) containing Target



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      Address IPAddr, or after the reception of a DATA packet containing
      IPAddr as the source address, the SAVI device will execute the
      process of sending Neighbour Solicitation (NSOL) messages of the
      Duplicate Address Detection process as described in section 5.4.2
      of [RFC4862] for the IPAddr using the following default
      parameters: DupAddrDetectTransmits set to 2 (i.e. 2 Neighbour
      Solicitation messages for that address will be sent by the SAVI
      device) and RetransTimer set to 500 milliseconds (i.e. the time
      between two Neighbour Solicitation messages is 500 millisecs and
      also the wait time for replies in the form of Neighbour
      Advertisement for the queried address).  The NSOL messages are not
      sent through any of the ports configured as Validating Ports.  The
      NSOL messages are sent through the proper Trusted Ports (as
      defined by the switch behaviour that will depend on whether it
      performs MLD snooping or not) The SAVI device MAY discard the data
      packet while the DAD procedure is being executed.
      *  EDITOR NOTE: We need to rate limit the emission of NSOL of the
         SAVI device as a whole.
      *  EDITOR NOTE 2: should we send the NSOL through the port the
         packet was received through?
      The state is moved to TENTATIVE.  The LIFETIME is set to TENT_LT
      (i.e.  LT==TENT_LT) and the LAYER_2 ANCHOR is set to VP (i.e.
      P==VP)
   o  Data packets containing IPAddr as the source address received
      through Trusted ports are processed and forwarded as usual (i.e.
      no special SAVI processing)
   o  DAD_NSOL packets 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 behaviour that will depend on
      whether it performs MLD snooping or not)
   o  Neighbor Advertisement packets sent to all nodes as a reply to the
      DAD_NSOL (hereafter called DAD_NADV) containing IPAddr as the
      target address coming through a Validating port are discarded.
   o  Other signaling packets are processed and forwarded as usual (i.e.
      no SAVI processing)

   TENTATIVE

   o  If the LIFETIME times out, the state is moved to VALID.  The
      LIFETIME is set to DEFAULT_LT (i.e.  LT== DEFAULT_LT).  Stored
      data packets are forwarded (if any).
   o  If a Neighbour Advertisement (NADV) is received through a Trusted
      Port with Target Address set to IPAddr, then state is set to
      NO_BIND and the LAYER_2 ANCHOR and the LIFETIME are cleared.  Data
      packets stored corresponding to this binding are discarded.





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   o  If a NADV is received through a Validating Port with Target
      Address set to IPAddr, the NADV packet is discarded
   o  If a data packet with source address IPAddr is received with
      Layer_2 anchor equal to P, then the packet is either stored or
      discarded.
      *  EDITOR NOTE: we need to define a maximum storage space for the
         data packets.  Having a single default value may be hard since
         it will heavily depend on the capability of the device.  Maybe
         it would be enough that the device has a maximum and that the
         value can be configured?
   o  If a data packet with source address IPAddr is received through a
      Trusted port, the data packet is forwarded. the state is
      unchanged. ( waiting for the NADV?)
   o  If a data packet with source address IPAddr is received through a
      Validating port other than P, the data packet is discarded.
   o  Other signaling packets are processed and forwarded as usual (i.e.
      no SAVI processing)
      *  EDITOR NOTE: this may need more thought

   VALID

   o  If a data packet containing IPAddr as a source address arrives
      from Validating port P, then the LIFETIME is set to DEFAULT_LT and
      the packet is forwarded as usual.
      *  EDITOR NOTE: Is this feasible? i.e. to reset a timer each time
         a data packet arrives?  We could just have a long lifetime and
         actively check for the host when the lifetime is about to
         expire.
   o  If a DAD_NSOL is received from a Trusted port, then the DAD_NSOL
      message is forwarded to port P and it is also forwarded to the
      proper Trusted Ports (as defined by the switch behaviour that will
      depend on whether it performs MLD snooping or not).  The state is
      changed to TESTING_TP.  The LIFETIME is set to TENT_LT.
   o  If a data packet containing source address IPAddr or a DAD_NSOL
      packet with target address set to IPAddr is received through a
      Validating port P' other than P, then the SAVI device will execute
      the process of sending DAD_NSOL messages as described in section
      5.4.2 of [RFC4862] for the IPAddr using the following default
      parameters: DupAddrDetectTransmits set to 2 (i.e. 2 NSOL messages
      for that address will be sent by the SAVI device) and RetransTimer
      set to 500 milliseconds (i.e. the time between two NSOL messages
      is 500 millisecs and also the wait time for replies in the form of
      Neighbour Advertisement for the queried address).  The DAD_NSOL
      message will be forwarded to the port P.
      *  EDITOR NOTE: should we also forward it though the TP?
         Theoretically, there shouldn't be another binding in any other
         SAVI device, so there should not be a need for this.
      The state is moved to TESTING_VP.  The LIFETIME is set to TENT_LT.



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      The SAVI device MAY discard the data packet while the DAD
      procedure is being executed.
   o  If the LIFETIME expires, then the SAVI device will execute the
      process of sending DAD_NSOL messages as described in section 5.4.2
      of [RFC4862] for the IPAddr using the following default
      parameters: DupAddrDetectTransmits set to 2 (i.e. 2 NSOL messages
      for that address will be sent by the SAVI device) and RetransTimer
      set to 500 milliseconds (i.e. the time between two NSOL messages
      is 500 millisecs and also the wait time for replies in the form of
      Neighbour Advertisement for the queried address).  The DAD_NSOL
      messages will be forwarded to the port P. The state is changed to
      TESTING_LIFETIME and the LIFETIME is set to TENT_LT.
   o  If a data packet containing IPAddr as a source address arrives
      from Trusted port, the packet is discarded.
      *  EDITOR NOTE: receiving such a packet means that another SAVI
         device has created a binding for this address, or that the
         perimeter has been breached.  This should be logged?
   o  Other signaling packets are processed and forwarded as usual (i.e.
      no SAVI processing).  In particular DAD_NADV containing IPAddr as
      the target address are forwarded as usual.

   TESTING_TP

   o  If the LIFETIME expires, the LAYER_2 ANCHOR is cleared and the
      state is changed to NO_BIND
   o  If a NADV message containing the IPAddr as target address is
      received through the Validating port P as a reply to the DAD_NSOL
      message, then the NADV is forwarded as usual and the state is
      changed to VALID.  The LIFETIME is set to DEFAULT_LT
   o  If a data packet containing IPAddr as the source address is
      received through port P, then the packet is forwarded.
      *  EDITOR NOTE: should we move back to VALID?
   o  If a data packet is received through a port that is other than
      port P, then the packet is discarded.

   TESTING_VP

   o  If the LIFETIME expires, the LAYER_2 ANCHOR set to P' (i.e.
      P==P'), the LIFETIME is set to DEFAULT_LT and the state is changed
      to VALID.  Data packet stored coming from P' are forwarded.
   o  If a NADV message containing the IPAddr as target address is
      received through the Validating port P as a reply to the DAD_NSOL
      message, then the NADV is forwarded as usual and the state is
      changed to VALID.  The LIFETIME is set to DEFAULT_LT
   o  If a data packet containing IPAddr as the source address is
      received through port P, then the packet is forwarded.





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      *  EDITOR NOTE: should we move back to VALID?
   o  If a data packet is received through a port that is other than
      port P, then the packet is discarded.

   TESTING_LIFETIME

   o  If the LIFETIME expires, the LAYER_2 ANCHOR is cleared and the
      state is changed to NO_BIND
   o  If a NADV message containing the IPAddr as target address is
      received through the Validating port P as a reply to the DAD_NSOL
      message, then the NADV is forwarded as usual and the state is
      changed to VALID.  The LIFETIME is set to DEFAULT_LT
   o  If a data packet containing IPAddr as the source address is
      received through port P, then the packet is forwarded and the
      state is changed to VALID.  The LIFETIME is set to DEFAULT_LT

   Rate limiting of messages: TBD

   MLD considerations

   The 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 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 SAVI device.  So,
   the SAVI device SHOULD join the solicited node multicast groups for
   all the addresses that are in a state other than NO_BIND


5.  Security Considerations

   First of all, it should be noted that any SAVI solution will be 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 anchors (and there is only one host connected to each
   port) it is likely that the resulting SAVI solution will be
   considerably more secure.

   Denial of service attacks

   There are two types of DoS attacks that can be envisaged in a SAVI
   environment.  On one hand, we can envision attacks against the SAVI
   device resources.  On the other hand, we can envision DoS attacks



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   against the hosts connected to the network where SAVI is running.

   The attacks against the SAVI device basically consist on making the
   SAVI device to consume its resource until it runs out of them.  For
   instance, a possible attack would be to send packets with different
   source addresses, making the SAVI device to create state for each of
   the addresses and waste memory.  At some point the SAVI device runs
   out of memory and it needs to decide how to react in this situation.
   The result is that some form of garbage collection is needed to prune
   the entries.  It is recommended that when the SAVI device runs out of
   the memory allocated for the SAVI DB, it creates new entries by
   deleting the entries which Creation Time is higher.  This implies
   that older entries are preserved and newer entries overwrite each
   other.  In an attack scenario where the attacker sends a batch of
   data packets with different source address, each new source address
   is likely to rewrite another source address created by the attack
   itself.  It should be noted that entries are also garbage collected
   using the LIFETIME, which is updated using data packets.  The result
   is that in order for an attacker to actually fill the SAVI DB with
   false source addresses, it needs to continuously send data packets
   for all the different source addresses, in order for the entries to
   grow old and compete with the legitimate entries.  The result is that
   the cost of the attack for the attacker is highly increased.

   The other type of attack is when an attacker manages to create state
   in the SAVI device that will result in blocking the data packets sent
   by the legitimate owner of the address.  In IPv6 these attacks are
   not an issue thanks to the 2^64 addresses available in each link.

   Compare with Threat analysis and identify residual threats: TBD


6.  Contributors

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

      Guang Yao
      CERNET
      Network Research Center, Tsinghua University
      Beijing 100084
      China





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      Email: yaog@netarchlab.tsinghua.edu.cn

      Fred Baker
      Cisco Systems
      Email: fred@cisco.com

      Alberto Garcia Martinez
      University Carlos III of Madrid
      Email: alberto@it.uc3m.es


7.  Acknowledgments

   This draft benefited from the input from: Christian Vogt, Dong Zhang,
   Frank Xia and Lin Tao.

   Marcelo Bagnulo is partly funded by Trilogy, a research project
   supported by the European Commission under its Seventh Framework
   Program.


8.  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.

   [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.


Authors' Addresses

   Erik Nordmark
   Sun Microsystems, Inc.
   17 Network Circle
   Menlo Park, CA  94025
   USA

   Phone: +1 650 786 2921
   Email: Erik.Nordmark@Sun.COM






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   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


   Eric Levy-Abegnoli
   Cisco Systems
   Village d'Entreprises Green Side - 400, Avenue Roumanille
   Biot-Sophia Antipolis - 06410
   France

   Email: elevyabe@cisco.com

































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