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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: July 26, 2009                                              UC3M
                                                        January 22, 2009


    First-Come First-Serve Source-Address Validation Implementation
                        draft-ietf-savi-fcfs-00

Status of this Memo

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Abstract

   This memo describes FCFS SAVI a mechanism to provide source address



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   validation for IPv4 and 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  . . . . . . . . . . . . . . . .  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
     3.3.  IPv4 Neighbor Unreachability Detection Procedure . . . . .  7
       3.3.1.  ARP-based Neighbor Unreachability Detection
               procedure  . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.2.  ICMP-based Neighbor Unreachability Detection
               procedure  . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

























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1.  Introduction

   This memo describes FCFS SAVI, a mechanism to provide source address
   validation for IPv4 and 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.  FCFS SAVI can be used in IPv4 and in
   IPv6 networks.

   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.




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   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
   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 sends a packet
   with 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 consideration 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,



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   such as ingress filtering.  ARP or ND checks would not be fulfilled
   by the 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 ARP/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

   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

   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.  (In ICMPv4, code 0 (net
      unreachable) should be used and in 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 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 packet is forwarded as
      usual.
   o  If an 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.



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   o  If an 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] for
      IPv4 and in Section 3.3 for IPv4.  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.  (In ICMPv4, code 0 (net unreachable) should be
         used and in ICMPv6, code 5 (Source address failed ingress/
         egress policy) should be used)

3.3.  IPv4 Neighbor Unreachability Detection Procedure

   As opposed to IPv6, there is no general Neighbor Unreachability
   Detection procedure defined for IPv4.  Since this is needed in order
   to verify if the original node is still using the IP address it once
   used, in this section, we define the procedure to perform such
   verification.  However, unlike IPv6 Neighbor discovery, the IPv4 ARP
   protocol [RFC0826] cannot be assumed to be available in all link
   layers.  So, we will define a ARP based procedure to be used in
   layers 2 that the ARP protocol is available and an ICMP based
   [RFC0792] procedure for the cases where the ARP protocols is not
   available.  The ARP based procedure is used whenever it is possible
   and when ARP is not available, the ICMP based procedure is used.

3.3.1.  ARP-based Neighbor Unreachability Detection procedure

   Consider two nodes, S and T, directly connected through a layer 2
   where the ARP protocol is available.  Node S has with IP address IPS
   and layer 2 address MACS and Node T has IP address IPT and layer 2
   address MACT.

   Node S wants to perform the ARP based Neighbor Unreachability
   Detection Procedure for node T. Node S has both IPT and MACT
   available.  So, node S generates an ARP REQUEST packet, containing
   the following information:





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      Ethernet transmission layer:
         Ethernet address of destination: MACT
         Ethernet address of sender: MACS
         Protocol type = ether_type$ADDRESS_RESOLUTION
      Ethernet packet data:
         (ar$hrd) Hardware address space (e.g., Ethernet, Packet Radio
         Net.)
         (ar$pro) Protocol address space:0x0800 Internet Protocol
         Version 4 (IPv4)
         (ar$hln) byte length of each hardware address
         (ar$pln) byte length of each protocol address: 4
         (ar$op) opcode (ares_op$REQUEST)
         (ar$sha) Hardware address of sender of this packet: MACS
         (ar$spa) Protocol address of sender of this packet: IPS
         (ar$tha) Hardware address of target of this packet: MACT
         (ar$tpa) Protocol address of target: IPT

   Upon the reception of the ARP REQUEST, if node T follows current ARP
   specification [RFC0826], it will reply with an ARP REPLY packet with
   the following information:
      Ethernet transmission layer:
         Ethernet address of destination: MACS
         Ethernet address of sender: MACT
         Protocol type = ether_type$ADDRESS_RESOLUTION
      Ethernet packet data:
         (ar$hrd) Hardware address space (e.g., Ethernet, Packet Radio
         Net.)
         (ar$pro) Protocol address space:0x0800 Internet Protocol
         Version 4 (IPv4)
         (ar$hln) byte length of each hardware address
         (ar$pln) byte length of each protocol address: 4
         (ar$op) opcode (ares_op$REPLY)
         (ar$sha) Hardware address of sender of this packet: MACT
         (ar$spa) Protocol address of sender of this packet: IPT
         (ar$tha) Hardware address of target of this packet: MACS
         (ar$tpa) Protocol address of target: IPS

   If node S receives the ARP REPLY message, the Neighbor Unreachability
   procedure was successful and the neighbor T is still reachable with
   the available information.  If node S does not receives the ARP REPLY
   message after ARPTIMEOUT, then the Neighbor Unreachability procedure
   has failed and the neighbor T is no longer reachable with the current
   information.

3.3.2.  ICMP-based Neighbor Unreachability Detection procedure

   Consider two nodes, S and T, directly connected through a layer 2.
   Node S has with IP address IPS and layer 2 address LLAS and Node T



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   has IP address IPT and layer 2 address LLAT.

   Node S wants to perform the ICMP based Neighbor Unreachability
   Detection Procedure for node T. Node S has both IPT and LLAT
   available.  So, node S generates an ICMP ECHO packet [RFC0792] ,
   containing the following information:
      Link Layer fields:
         Source address: LLAS
         Destination address: LLAT
      IP header fields:
         IP Source Address: IPS
         IP Destination Address: IPT
      ICMP fields
         Type: 8
         Identifier: set to random number by S

   Upon the reception of the ICMP ECHO message, if node T follows
   current ICMP specification [RFC0792], it will reply with an ECHO
   REPLY packet with the following information:
      Link Layer fields:
         Source address: LLAT
         Destination address: LLAS
      IP header fields:
         IP Source Address: IPT
         IP Destination Address: IPS
      ICMP fields
         Type: 0
         Identifier: copied from the ECHO message received

   If node S receives a ECHO REPLY message, it will verify that the
   source IP address and the source link layer address match to the
   original ones used in the ECHO message.  Besides, it will check that
   the identifier matches to the one contained in the original ECHO
   message.  If these checks are successful the Neighbor Unreachability
   procedure was successful and the neighbor T is still reachable with
   the available information.  If node S does not receives the ECHO
   REPLY message after ICMPTIMEOUT, then the Neighbor Unreachability
   procedure has failed and the neighbor T is no longer reachable with
   the current information.


4.  Security Considerations

   Compare with Threat analysis and identify residual threats: TBD







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5.  Acknowledgments

   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.

   [RFC0826]  Plummer, D., "Ethernet Address Resolution Protocol: Or
              converting network protocol addresses to 48.bit Ethernet
              address for transmission on Ethernet hardware", STD 37,
              RFC 826, November 1982.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.


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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