Network Working Group                            M. Konstantynowicz, Ed.
Internet-Draft                                             G. Heron, Ed.
Intended status: Informational                             Cisco Systems
Expires: October 5, 2014                                   R. Schatzmayr
                                                     Deutsche Telekom AG
                                                           W. Henderickx
                                                    Alcatel-Lucent, Inc.
                                                           April 3, 2014

                           Keyed IPv6 Tunnel


   This document describes a simple L2 Ethernet over IPv6 tunnel
   encapsulation with mandatory 64-bit key for connecting L2 Ethernet
   attachment circuits identified by IPv6 addresses.  The encapsulation
   is based on L2TPv3 over IP.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119 [RFC2119].

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
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   This Internet-Draft will expire on October 5, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Static 1:1 Mapping Without a Control Plane  . . . . . . . . .   3
   3.  64-bit Cookie . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Encapsulation . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Fragmentation and Reassembly  . . . . . . . . . . . . . . . .   7
   6.  OAM Considerations  . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .   9
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   L2TPv3, as defined in RFC3931 [RFC3931], provides a dynamic mechanism
   for tunneling Layer 2 (L2) "circuits" across a packet-oriented data
   network (e.g., over IP), with multiple attachment circuits
   multiplexed over a single pair of IP address endpoints (i.e. a
   tunnel) using the L2TPv3 session ID as a circuit discriminator.

   Implementing L2TPv3 over IPv6 provides the opportunity to utilize
   unique IPv6 addresses to identify Ethernet attachment circuits
   directly, leveraging the key property that IPv6 offers, a vast number
   of unique IP addresses.  In this case, processing of the L2TPv3
   Session ID may be bypassed upon receipt as each tunnel has one and
   only one associated session.  This local optimization does not hinder
   the ability to continue supporting the multiplexing of circuits via
   the Session ID on the same router for other L2TPv3 tunnels.

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2.  Static 1:1 Mapping Without a Control Plane

   Static local configuration creates a one-to-one mapping between the
   access-side L2 attachment circuit and the IP address used in the
   network-side IPv6 encapsulation.  The L2TPv3 Control Plane defined in
   RFC3931 [RFC3931] is not used.

   The IPv6 L2TPv3 tunnel encapsulating device uniquely identifies each
   Ethernet L2 attachment connection by a port ID or a combination of
   port ID and VLAN ID(s) on the access side, and by an IPv6 address on
   the network side.

   Any VLAN identifiers, S-VID, C-VID or tuple ( S-VID, C-VID ) are
   treated with local significance within the Ethernet L2 port and are
   not forwarded over the IPv6 L2TPv3 tunnel.  IPv6 address is treated
   as the IPv6 L2TPv3 tunnel endpoint.

   Certain deployment scenarios may require using a single IPv6 address
   to identify a tunnel endpoint for many IPv6 L2TPv3 tunnels.  For such
   cases the tunnel encapsulating device identifies each tunnel by a
   unique combination of tunnel source and destination IPv6 addresses.

   As mentioned above Session ID processing is not required as each
   keyed IPv6 tunnel has one and only one associated session.  However
   for compatibility with existing RFC3931 [RFC3931] implementations,
   the packets need to be sent with Session ID.  The router implementing
   L2TPv3 according to RFC3931 [RFC3931] can be configured with multiple
   L2TPv3 tunnels, with one session per tunnel, to interoperate with the
   router implementing the keyed IPv6 tunnel as specified by this

   Note that a previous IETF draft [I.D.ietf-pppext-l2tphc] introduces
   the concept of an L2TP tunnel carrying a single session and hence not
   requiring session ID processing.

3.  64-bit Cookie

   In line with RFC3931 [RFC3931], the key in the cookie field is used
   for additional tunnel endpoint context check.  All packets MUST carry
   a 64-bit key in the L2TPv3 cookie field.  The cookie MUST be 64-bits
   long in order to provide sufficient protection against spoofing and
   brute force blind insertion attacks.

   In the absence of the L2TPv3 Control Plane, the L2TPv3 encapsulating
   router must be provided with local configuration of the 64-bit cookie
   for each local and remote IPv6 endpoint - note that cookies are
   asymmetric, so local and remote endpoints may send different cookie
   values.  The value of the cookie must be able to be changed at any

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   time in a manner that does not drop any legitimate tunneled packets -
   i.e. the receiver must be willing to accept both "old" and "new"
   cookie values during a change of cookie value.

4.  Encapsulation

   RFC4719 [RFC4719] describes encapsulation of Ethernet over L2TPv3.
   Paraphrasing from this document, the Ethernet frame, without the
   preamble or frame check sequence (FCS), is encapsulated in L2TPv3 and
   is sent as a single packet by the ingress router.

   The s-tag (or in the multi-stack access case the s-tag and c-tag)
   SHOULD be removed before the packet is encapsulated.

   The full encapsulation is as follows:

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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |  Ver  | Traffic Class |             Flow Label                |
      |        Payload Length         |  Next Header  |   Hop Limit   |
      |                    Source address (0:31)                      |
      |                    Source address (32:63)                     |
      |                    Source address (64:95)                     |
      |                    Source address (96:127)                    |
      |                  Destination address (0:31)                   |
      |                  Destination address (32:63)                  |
      |                  Destination address (64:95)                  |
      |                  Destination address (96:127)                 |
      |                    Session ID (32 bits)                       |
      |                        Cookie (0:31)                          |
      |                        Cookie (32:63)                         |
      |                      Payload (variable)                       |
      |                              ?                                |
      |                              ?                                |
      |                              ?                                |
      |                              ?                                |

   The combined IPv6 and L2TPv3 header contains the following fields:

   o  Ver. Set to 0x6 to indicate IPv6.

   o  Traffic Class.  May be set by the ingress router to ensure correct
      PHB treatment by transit routers between the ingress and egress,
      and correct QoS disposition at the egress router.

   o  Flow Label.  May be set by the ingress router to indicate a flow
      of packets from the client which may not be reordered by the

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      network (if there is a requirement for finer grained ECMP load
      balancing than per-circuit load balancing).

   o  Payload Length.  Set to the length of the packet, excluding the
      IPv6 header (i.e. the length from the Session ID to the end of the

   o  Next Header.  Set to 0x73 to indicate that the next header is

   o  Hop Limit.  Set to 0xFF, and decremented by one by each router in
      the path to the egress router.

   o  Source Address.  IPv6 source address for the tunnel.  In the
      "Static 1:1" case the IPv6 source address may correspond to a port
      or VLAN being transported as an L2 circuit, or may be a loopback
      address terminating inside the router (e.g. if L2 circuits are
      being used within a multipoint VPN) or may be an anycast address
      terminating on a data center virtual machine.

   o  Destination Address.  IPv6 destination address for the tunnel.  As
      with the source address this may correspond to a port or VLAN
      being transported as an L2 circuit or may be a loopback or anycast

   o  Session ID.  In the "Static 1:1 mapping" case described in
      Section 2, the IPv6 address resolves to an L2TPv3 session
      immediately, thus the Session ID may be ignored upon receipt.  For
      compatibility with other tunnel termination platforms supporting
      only 2-stage resolution (IPv6 Address + Session ID), this
      specification recommends supporting explicit configuration of
      Session ID to any value other than zero.  For cases where both
      tunnel endpoints support one-stage resolution (IPv6 Address only),
      this specification recommends setting the Session ID to all ones
      for easy identification in case of troubleshooting.  The Session
      ID of zero MUST NOT be used, as it is reserved for use by L2TP
      control messages RFC3931 [RFC3931].

   o  Cookie. 64 bits, configured and described as in Section 3.  All
      packets for a destined L2 Circuit (or L2TPv3 Session) must match
      the configured Cookie value or be discarded (see RFC3931 [RFC3931]
      for more details).

   o  Payload.  The customer data, with s-tag or s-tag/c-tag removed.
      As noted above preamble and FCS are stripped before encapsulation.
      A new FCS will be added at each hop when the IP packet is

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5.  Fragmentation and Reassembly

   Using tunnel encapsulation, Ethernet L2 datagrams in IPv6 in this
   case, will reduce the effective MTU of the Ethernet L2 datagram.

   The recommended solution to deal with this problem is for the network
   operator to increase the MTU size of all the links between the
   devices acting as IPv6 L2TPv3 tunnel endpoints to accommodate both
   the IPv6 L2TPv3 encapsulation header and the Ethernet L2 datagram
   without fragmenting the IPv6 packet.

   If it is impossible to increase the link MTU across the network, the
   IPv6 L2TPv3 encapsulating device MUST perform fragmentation and
   reassembly if the outgoing link MTU cannot accommodate the extra IPv6
   L2TPv3 header for specific Ethernet L2 payload.  Fragmentation MUST
   happen after the encapsulation of the IPv6 L2TPv3 packet.  Reassembly
   MUST happen before the decapsulation of the IPv6 L2TPv3 packet.

   The proposed approach is in line with the DS-Lite specification
   RFC6333 [RFC6333].

6.  OAM Considerations

   OAM is an important consideration when providing circuit-oriented
   services such as those described in this document, and all the more
   so in the absence of a dedicated tunnel control plane, as OAM becomes
   the only way to detect failures in the tunnel overlay.

   Note that in the context of keyed IP tunnels, failures in the IPv6
   underlay network can be detected using the usual methods such as
   through the routing protocol.

   Since keyed IP tunnels always carry an Ethernet payload, and since
   OAM at the tunnel layer is unable to detect failures in the Ethernet
   service processing at the ingress or egress router, or on the
   Ethernet attachment circuit between the router and the Ethernet
   client, this document recommends that Ethernet OAM as defined in IEEE
   802.1ag [IEEE802.1ag] and/or ITU Y.1731 [Y.1731] is enabled for keyed
   IP tunnels.  More specifically the following Connecitivity Fault
   Management ( CFM ) and/or Ethernet continuity check ( ETH-CC )
   configurations are to be used in conjunction with keyed IPv6 tunnels:

   o  Connectivity verification between the tunnel endpoints across the
      tunnel - use an Up MEP located at the tunnel endpoint for
      transmitting the CFM PDUs towards, and receiving them from the
      direction of the tunnel.

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   o  Connectivity verification from the tunnel endpoint across the
      local attachment circuit - use a Down MEP located at the tunnel
      endpoint for transmitting the CFM PDUs towards, and receiving them
      from the direction of the local attachment circuit.

   o  Intermediate connectivity verifcation - use a MIP located at the
      tunnel endpoint to generate CFM PDUs in response to received CFM

   In addition the Pseudowire Virtual Circuit Connectivity Verfiication
   ( VCCV ) RFC5085 [RFC5085] MAY be used.

7.  IANA Considerations


8.  Security Considerations

   Packet spoofing for any type of Virtual Private Network (VPN)
   tunneling protocol is of particular concern as insertion of carefully
   constructed rogue packets into the VPN transit network could result
   in a violation of VPN traffic separation, leaking data into a
   customer VPN.  This is complicated by the fact that it may be
   particularly difficult for the operator of the VPN to even be aware
   that it has become a point of transit into or between customer VPNs.

   Keyed IPv6 encapsulation provides traffic separation for its VPNs via
   use of separate 128-bit IPv6 addresses to identify the endpoints.
   The mandatory authentication key carried in the L2TPv3 cookie field,
   provides an additional check to ensure that an arriving packet is
   intended for the identified tunnel.

   In the presence of a blind packet spoofing attack, the authentication
   key provides security against inadvertent leaking of frames into a
   customer VPN, like in case of L2TPv3 RFC3931 [RFC3931].  To
   illustrate the type of security that it is provided in this case,
   consider comparing the validation of a 64-bit Cookie in the L2TPv3
   header to the admission of packets that match a given source and
   destination IP address pair.  Both the source and destination IP
   address pair validation and Cookie validation consist of a fast check
   on cleartext header information on all arriving packets.  However,
   since L2TPv3 uses its own value, it removes the requirement for one
   to maintain a list of (potentially several) permitted or denied IP
   addresses, and moreover, to guard knowledge of the permitted IP
   addresses from hackers who may obtain and spoof them.  Further, it is
   far easier to change a compromised L2TPv3 Cookie than a compromised
   IP address," and a cryptographically random RFC4086 [RFC4086] value

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   is far less likely to be discovered by brute-force attacks compared
   to an IP address.

   For protection against brute-force, blind, insertion attacks, a 64-
   bit Cookie MUST be used with all tunnels.

   Note that the Cookie provides no protection against a sophisticated
   man-in-the-middle attacker who can sniff and correlate captured data
   between nodes for use in a coordinated attack.

   The L2TPv3 64-bit cookie must not be regarded as a substitute for
   security such as that provided by IPsec when operating over an open
   or untrusted network where packets may be sniffed, decoded, and
   correlated for use in a coordinated attack.

9.  Contributing Authors

   Peter Weinberger
   Cisco Systems


   Michael Lipman
   Cisco Systems


   Mark Townsley
   Cisco Systems


10.  Acknowledgements

   The authors would like to thank Carlos Pignataro for his suggestions
   and review.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3931]  Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
              Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.

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   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4719]  Aggarwal, R., Townsley, M., and M. Dos Santos, "Transport
              of Ethernet Frames over Layer 2 Tunneling Protocol Version
              3 (L2TPv3)", RFC 4719, November 2006.

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007.

11.2.  Informative References

              Valencia, A., "L2TP Header Compression", December 1997.

              IEEE, "IEEE Standard for Local and metropolitan area
              networks - Virtual Bridged Local Area Networks, Amendment
              5: Connectivity Fault Managements", 2007.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [Y.1731]   ITU, "ITU-T Recommendation G.8013/Y.1731 - OAM functions
              and mechanisms for Ethernet based networks", 2011.

Authors' Addresses

   Maciek Konstantynowicz (editor)
   Cisco Systems


   Giles Heron (editor)
   Cisco Systems


   Rainer Schatzmayr
   Deutsche Telekom AG


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   Wim Henderickx
   Alcatel-Lucent, Inc.


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