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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: September 5, 2009                                          UC3M
                                                           March 4, 2009


    First-Come First-Serve Source-Address Validation Implementation
                        draft-ietf-savi-fcfs-01

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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



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   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 . . . . . . . . . . . . . . . . . 3
     2.3.  Address ownership proof . . . . . . . . . . . . . . . . . . 4
     2.4.  Special cases . . . . . . . . . . . . . . . . . . . . . . . 5
   3.  FCFS SAVI specification . . . . . . . . . . . . . . . . . . . . 5
     3.1.  FCFS SAVI Data structures . . . . . . . . . . . . . . . . . 5
     3.2.  FCFS SAVI algorithm . . . . . . . . . . . . . . . . . . . . 6
       3.2.1.  Processing of data packets  . . . . . . . . . . . . . . 6
       3.2.2.  Processing of control packets . . . . . . . . . . . . . 7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 9
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9





























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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.

2.2.  Constraints for FCFS SAVI

   FCFS SAVI is designed to be susceptible of deployment 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 to define any new message on existing protocols
   nor to 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



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   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
   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 hast 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 uses 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 MAC address in a LAN, or
   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, FCFS SAVI performs an active check to
   verify if the host is still reachable using the previous layer-2
   information.  In order to do that FCFS SAVI uses ARP protocol in IPv4
   and ND in IPv6.  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 (see some caveats described in the following section).

   Note that this only applies to local traffic.  Transit traffic
   generated by a router would be verified using alternative techniques,
   such as ingress filtering.  ND checks would not be fulfilled by the



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   transit traffic, since the router is not the owner of the source
   address contained in the packets.

   Layer-2 considerations:TBD

2.4.  Special cases

   The following special cases that need to be considered
   o  Hosts with multiple physical interfaces, potentially connected to
      different networks.
   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.  FCFS SAVI specification

3.1.  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

   Finally, FCFS SAVI keep a list of the routers that are directly
   connected, since the FCFS SAVI checks will not directly apply to
   them.  In the FCFS SAVI Router List, the following information is
   stored:
   o  Router IP address (of the directly connected interface)
   o  Router Layer-2 information such as layer-2 address or port which
      the router is connected to




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3.2.  FCFS SAVI algorithm

3.2.1.  Processing of data packets

   The FCFS SAVI function is located in a forwarding device, such as a
   router or a layer-2 bridge.  Upon the reception of a data packet, the
   packet will be passed to the FCFS SAVI function which will perform
   the processing detailed in this section.  The outcome of such
   processing can be that the packet is discarded or that is forwarded
   as usual.

   After a data packet is received, the FCFS 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.
   o  If the IP source address belongs to one of the local prefixes of
      the receiving interface, the data packet is local traffic and the
      FCFS SAVI algorithm is executed as described next.
   o  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.  The FCFS SAVI SHOULD verify if the
      layer-2 information of the packet corresponds to one of the
      routers available in the receiving interface, by using the
      information available in the FCFS SAVI router list.  If the packet
      comes from one of the know routers for that interface, then the
      packet is passed so additional checks such as ingress filtering
      can be performed.  If the packet does not comes from one of the
      known routers, then 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) (Note; we
      could skip this verification altogether and simply pass it to the
      ingress filters, but it think this could be useful, especially if
      used along with SeND)

   After checking that the data packet is local traffic, the FCFS SAVI
   function will verify the source address used in the packet.  In order
   to do so, it searches the FCFS SAVI DB using the IP source address as
   a key.
   o  If no valid entry is found, then a new entry is created, using the
      information of the data packet, including all the related layer-2
      information of where the packet was received from and the lifetime
      of the entry is set to LIFETIME.  The status is set to valid.  The
      packet is forwarded as usual.  (NOTE: AS defined FCFS SAVI treats
      tentative entries as if they did not existed i.e. a data packet
      preempts the DAD procedure, this probably requires more
      discussion)



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   o  If a valid entry is found and the layer-2 information of the
      received data packet matches to the information contained in the
      existing entry, then the lifetime is set of LIFETIME and the
      packet is forwarded as usual.
   o  If a valid entry is found and the layer-2 information of the
      received data packet does not match the information contained in
      the existing matching entry, then the FCFS SAVI performs a
      Neighbor Unreachability Detection procedure as described in
      [RFC4861].  It uses the IP source address and Layer-2 information
      available in the FCFS SAVI DB entry.
      *  If the procedure determines that the neighbor is no longer
         reachable using the information available in the FCFS SAVI DB
         entry, then the entry information is modified to include the
         new information about the data packet received (in particular
         the new layer-2 information) and lifetime of the entry is
         updated to LIFETIME.  The packet is forwarded as usual.
      *  If the procedure determines that the neighbor is still
         reachable using the information available in the FCFS SAVI DB,
         then the data packet is discarded and the lifetime of the entry
         is set to LIFETIME.  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)

3.2.2.  Processing of control packets

   Processing of IPv6 ND packets

   The FCFS SAVI function will also create state based on control
   packets.  In particular, when a host configures an address, it
   performs the Duplicate Address Detection (DAD) procedure, to verify
   that the address is unique in the link.  FCFS SAVI keeps track of the
   DAD procedure and creates modify the FCFS SAVI DB state accordingly.

   Upon the reception of a Neighbor Solicitation message containing the
   unspecified source address FCFS SAVI retrieves the address contained
   in the Target Address filed of the NSOL message and performs the
   following actions:
   o  If no valid entry is found in the FCFS SAVI DB for that address,
      then it creates a new entry, includes the Target Address and the
      link layer information contained in the NSOL message and sets the
      status to tentative.  At that point FCFS SAVI will keep track of
      the Neighbor Advertisement messages.
      *  If a NADV message containing the address in the NADV Target
         Address field is received before DADTimeout then the entry is
         deleted.





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      *  If no NADV message for that Target Address is received in
         DADTimeout, then the status of the entry is change to valid and
         the lifetime of the entry is set to LIFETIME.  In addition, if
         the address contained in the newly created entry is a link
         local address, FCFS SAVI MAY as well create entries for the
         global addresses resulting from concatenating the Interface
         Identifier of the link local address and the global prefixes
         contained in the Prefix List for the Interface through which
         the NSOL message was received.
   o  If a valid entry is found in the FCFS SAVI DB for that address, no
      additional processing is performed.  (Note: there is no point of
      tracking the NADV at this point.  Either the SAVI DB is updated
      and there is no new information or it is not, which we will find
      out when we receive a data packet.  Moreover, tracking NADV
      messages could enable an attacker to overwrite an existing entry.)


4.  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
   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



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   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


5.  Acknowledgments

   This draft benefited from the input from: Christian Vogt, Fred Baker,
   Guang Yao, Dong Zhang, Frank Xia and Lin Tao. In particular the usage
   of ARP and ND packet to create SAVI DB state was suggested by Guang
   Yao in response to an attack described by Fred Baker.

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


6.  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.












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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


   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






























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