Internet DRAFT - draft-ietf-l2tpext-keyed-ipv6-tunnel
draft-ietf-l2tpext-keyed-ipv6-tunnel
L2TPEXT Working Group M. Konstantynowicz, Ed.
Internet-Draft G. Heron, Ed.
Intended status: Standards Track Cisco Systems
Expires: April 17, 2017 R. Schatzmayr
Deutsche Telekom AG
W. Henderickx
Alcatel-Lucent, Inc.
October 14, 2016
Keyed IPv6 Tunnel
draft-ietf-l2tpext-keyed-ipv6-tunnel-07
Abstract
This document describes an Ethernet over IPv6 tunnel encapsulation
with mandatory 64-bit cookie for connecting L2 Ethernet attachment
circuits identified by IPv6 addresses. The encapsulation is based on
L2TPv3 over IP and does not use the L2TPv3 control plane.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this 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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2017.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
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 . . . . . . . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
L2TPv3, as defined in [RFC3931], provides a 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 [RFC2460] 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
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circuits via the Session ID on the same router for other L2TPv3
tunnels.
There are various advantages to this approach when compared to the
"traditional" L2TPv3 approach of using a loopback address to
terminate the tunnel and then carrying multiple sessions over the
tunnel. These include better ECMP load-balancing (since each tunnel
has a unique source/destination IPv6 address pair), and finer-grained
control when advertising tunnel endpoints using a routing protocol.
2. Static 1:1 Mapping Without a Control Plane
The L2TPv3 Control Plane defined in RFC3931 is not used for this
encapsulation. The management plane is used to create, and to
maintain, matching configurations at either end of each tunnel.
Local configuration by the management plane 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 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 a local IPv6
address on the network side. The local IPv6 address also identifies
the tunnel endpoint. The local IPv6 addresses identifying L2TPv3
tunnels SHOULD NOT be assigned from connected IPv6 subnets facing
towards remote tunnel endpoints, since that approach would result in
an IPv6 Neighbor Discovery cache entry per tunnel on the next hop
router towards the remote tunnel endpoint. It is RECOMMENDED that
local IPv6 addresses identifying L2TPv3 tunnels are assigned from
dedicated subnets used only for such tunnel endpoints.
Certain deployment scenarios may require using a single IPv6 address
(such as a unicast or anycast address assigned to a specific service
instance, for example a virtual switch) to identify a tunnel endpoint
for multiple IPv6 L2TPv3 tunnels. For such cases the tunnel
decapsulating device uses the local IPv6 address to identify the
service instance, and the remote IPv6 address to identify the
individual tunnel within that service instance.
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 implementations, the packets
need to be sent with Session ID. Routers implementing L2TPv3
according to RFC3931 can be configured with multiple L2TPv3 tunnels,
with one session per tunnel, to interoperate with routers
implementing the keyed IPv6 tunnel as specified by this document.
Note that as Session ID processing is not enabled for keyed IPv6
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tunnels that there can only be a single keyed IPv6 tunnel between two
IPv6 addresses.
3. 64-bit Cookie
In line with RFC3931, the 64-bit cookie is used for an additional
tunnel endpoint context check. This is the largest cookie size
permitted in RFC3931. All packets MUST carry the 64-bit L2TPv3
cookie field. The cookie MUST be 64 bits long in order to provide
sufficient protection against spoofing and brute force blind
insertion attacks. The cookie values SHOULD be randomly selected.
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, and in fact SHOULD do so. The value of the cookie MUST be
able to be changed at any time in a manner that does not drop any
legitimate tunneled packets, i.e. the receiver MUST be configurable
to accept two discrete cookies for a single tunnel simultaneously.
This enables the receiver to hold both the 'old' and 'new' cookie
values during a change of cookie value. Cookie values SHOULD be
changed periodically by the management plane.
Note that mandating a 64-bit cookie is a change from the optional
variable-length cookie of RFC3931, and that this requirement
constrains interoperability with existing RFC3931 implementations to
those supporting a 64-bit cookie. The management plane MUST NOT
configure a keyed IP tunnel unless both endpoints support the 64-bit
cookie.
4. Encapsulation
The ingress router encapsulates the entire Ethernet frame, without
the preamble and frame check sequence (FCS) in L2TPv3 as per RFC4719
[RFC4719]. The L2-specific sublayer MAY be carried if Virtual
Circuit Connectivity Verification ( VCCV ) [RFC5085] and/or frame
sequencing is required, but SHOULD NOT be carried otherwise. The
L2TPv3 packet is encapsulated directly over IPv6 (i.e. no UDP header
is carried).
The ingress router MAY retain the FCS as per section 4.7 of
[RFC4720]. Support for retaining the FCS and for receiving packets
with a retained FCS is OPTIONAL, and if present MUST be configurable.
In the absence of the L2TPv3 control plane such configuration MUST be
consistent for the two endpoints of any given tunnel, i.e. if one
router is configured to retain the FCS then the other router MUST be
configured to receive packets with the retained FCS. Any router
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configured to retain FCS for a tunnel MUST retain FCS for all frames
sent over that tunnel. All routers implementing this specification
MUST support the ability to send frames without retaining the FCS and
to receive such frames.
Any service-delimiting IEEE 802.1Q [IEEE802.1Q] or IEEE 802.1ad
[IEEE802.1ad] VLAN IDs - S-tag, C-tag or tuple (S-tag, C-tag) - are
treated with local significance within the Ethernet L2 port and MUST
NOT be forwarded over the IPv6 L2TPv3 tunnel.
Note that the same approach may be used to transport protocols other
than Ethernet, though this is outside the scope of this
specification.
The full encapsulation is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ IPv6 Header (320 bits) +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cookie (0:31) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cookie (32:63) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Optional) L2-specific Sublayer (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload (variable) |
| ? |
| ? |
| ? |
| ? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The combined IPv6 and Keyed IP Tunnel header contains the following
fields:
o IPv6 Header. Note that:
* The 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.
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* The flow label, as defined in [RFC6437] may be set by the
ingress router to indicate a flow of packets from the client
which may not be reordered by the network (if there is a
requirement for finer grained ECMP load balancing than per-
circuit load balancing).
* The next header will be set to 0x73 to indicate that the next
header is L2TPv3.
* In the "Static 1:1" case the IPv6 source address may correspond
to a port or port/VLAN being transported as an L2 circuit, or
may correspond to a virtual interface terminating inside the
router (e.g. if L2 circuits are being used within a multipoint
VPN, or if an anycast address is being terminated on a set of
data center virtual machines.)
* As with the source address the IPv6 destination address may
correspond to a port or port/VLAN being transported as an L2
circuit, or to a virtual interface.
o Session ID. In the "Static 1:1 mapping" case described in
Section 2, the IPv6 address identifies an L2TPv3 session directly,
thus at endpoints supporting one-stage resolution (IPv6 Address
only) the Session ID SHOULD be ignored upon receipt. It is
RECOMMENDED that the remote endpoint is configured to set the
Session ID to all ones (0xFFFFFFFF) for easy identification in
case of troubleshooting. For compatibility with other tunnel
termination platforms supporting only two-stage resolution (IPv6
Address + Session ID), this specification recommends supporting
explicit configuration of Session ID to any value other than zero
(including all ones). The Session ID of zero MUST NOT be used, as
it is reserved for use by L2TP control messages as specified in
RFC3931. Note that the Session ID is unidirectional, the sent and
received Session IDs at an endpoint may be different.
o Cookie. 64-bit cookie, configured and described as in Section 3.
All packets for a destined L2 circuit (or L2TPv3 Session) MUST
match one of the cookie values configured for that circuit. Any
packets that do not contain a valid cookie value MUST be discarded
(see RFC3931 for more details).
o L2-specific sublayer (optional). As noted above this will be
present if VCCV and/or frame sequencing is required. If VCCV is
required then any frames with bit 0 (the "V-bit") set are VCCV
messages. If frame sequencing is required then any frames with
bit 1 (the "S-bit") set have a valid frame sequence number in bits
8 - 31.
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o Payload (variable length). As noted above the preamble and any
service-delimiting tags MUST be stripped before encapsulation and
the FCS MUST be stripped unless FCS retention is configured at
both ingress and egress routers. Since a new FCS is added at each
hop when the encapsulating IP packet is transmitted the payload is
protected against bit errors.
5. Fragmentation and Reassembly
Using tunnel encapsulation of Ethernet L2 datagrams in IPv6 will
reduce the effective MTU allowed for the encapsulated traffic.
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 requiring fragmentation of the IPv6 packet.
It is RECOMMENDED that routers implementing this specification
implement IPv6 PMTU discovery as defined in [RFC1981] to confirm that
the path over which packets are sent has sufficient MTU to transport
a maximum length Ethernet frame plus encapsulation overhead.
Routers implementing this specification MAY implement L2TPv3
fragmentation (as defined in section 5 of [RFC4623]). In the absence
of the L2TPv3 control plane, it is RECOMMENDED that fragmentation (if
implemented) is locally configured on a per-tunnel basis.
Fragmentation configuration MUST be consistent between the two ends
of a tunnel.
It is NOT RECOMMENDED for routers implementing this specification to
enable IPv6 fragmentation (as defined in section 4.5 of RFC2460) for
keyed IP tunnels. IP fragmentation issues for L2TPv3 are discussed
in section 4.1.4 of RFC3931.
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, including the use of single-hop
Bidirectional Forwarding Detection ( BFD ) [RFC5881] to rapidly
detect link failures. Multi-Hop BFD MAY also be enabled between
tunnel endpoints as per [RFC5883].
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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, it is RECOMMENDED that Ethernet OAM as defined in
[IEEE802.1ag] and/or [Y.1731] is enabled for keyed IP tunnels. As
defined in those specifications, the following Connectivity 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.
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 verification - use a MIP located at the
tunnel endpoint to relay CFM PDUs.
In addition Pseudowire Virtual Circuit Connectivity Verification (
VCCV ) [RFC5085] MAY be used. Furthermore BFD MAY be enabled over
the VCCV channel [RFC5885].
Note that since there is no control plane it is RECOMMENDED that the
management plane take action when attachment circuit failure is
detected, for example by dropping the remote attachment circuit.
7. IANA Considerations
None.
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 use of the 64 bit L2TPv3 cookie provides an additional
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check to ensure that an arriving packet is intended for the
identified tunnel.
In the presence of a blind packet spoofing attack, the 64-bit L2TPv3
cookie provides security against inadvertent leaking of frames into a
customer VPN, as documented in section 8.2 of RFC3931.
For protection against brute-force, blind, insertion attacks, the 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
Email: peweinbe@cisco.com
Michael Lipman
Cisco Systems
Email: mlipman@cisco.com
Mark Townsley
Cisco Systems
Email: townsley@cisco.com
10. Acknowledgements
The authors would like to thank Carlos Pignataro, Stewart Bryant,
Karsten Thomann, Qi Sun and Ian Farrer for their insightful
suggestions and review.
11. References
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11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, DOI 10.17487/RFC3931, March 2005,
<http://www.rfc-editor.org/info/rfc3931>.
[RFC4719] Aggarwal, R., Ed., Townsley, M., Ed., and M. Dos Santos,
Ed., "Transport of Ethernet Frames over Layer 2 Tunneling
Protocol Version 3 (L2TPv3)", RFC 4719,
DOI 10.17487/RFC4719, November 2006,
<http://www.rfc-editor.org/info/rfc4719>.
11.2. Informative References
[IEEE802.1ad]
IEEE, "802.1ad-2005 - IEEE Standard for Local and
Metropolitan Area Networks - Virtual Bridged Local Area
Networks - Amendment 4: Provider Bridges", 2005.
[IEEE802.1ag]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Virtual Bridged Local Area Networks, Amendment
5: Connectivity Fault Managements", 2007.
[IEEE802.1Q]
IEEE, "802.1Q-2014 - IEEE Standard for Local and
metropolitan area networks - Bridges and Bridged
Networks", 2014.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
1996, <http://www.rfc-editor.org/info/rfc1981>.
[RFC4623] Malis, A. and M. Townsley, "Pseudowire Emulation Edge-to-
Edge (PWE3) Fragmentation and Reassembly", RFC 4623,
DOI 10.17487/RFC4623, August 2006,
<http://www.rfc-editor.org/info/rfc4623>.
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[RFC4720] Malis, A., Allan, D., and N. Del Regno, "Pseudowire
Emulation Edge-to-Edge (PWE3) Frame Check Sequence
Retention", RFC 4720, DOI 10.17487/RFC4720, November 2006,
<http://www.rfc-editor.org/info/rfc4720>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
December 2007, <http://www.rfc-editor.org/info/rfc5085>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<http://www.rfc-editor.org/info/rfc5881>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
June 2010, <http://www.rfc-editor.org/info/rfc5883>.
[RFC5885] Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
Forwarding Detection (BFD) for the Pseudowire Virtual
Circuit Connectivity Verification (VCCV)", RFC 5885,
DOI 10.17487/RFC5885, June 2010,
<http://www.rfc-editor.org/info/rfc5885>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<http://www.rfc-editor.org/info/rfc6437>.
[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
Email: maciek@cisco.com
Giles Heron (editor)
Cisco Systems
Email: giheron@cisco.com
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Rainer Schatzmayr
Deutsche Telekom AG
Email: rainer.schatzmayr@telekom.de
Wim Henderickx
Alcatel-Lucent, Inc.
Email: wim.henderickx@alcatel-lucent.com
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