anima Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track L. Xia
Expires: October 9, 2020 Huawei
April 07, 2020
IPv6 over Link-Local Discovery Protocol
draft-richardson-anima-ipv6-lldp-04
Abstract
This document describes a mechanism to encapsulate IPv6 packets over
the Link Layer Discovery Protocol (LLDP). The LLDP is a single
layer-two protocol with its own ethertype. It is never forwarded,
which is a desireable property when building the IPv6-over-IPsec-
over-IPv6-Link-Local tunnels that make up the ANIMA Autonomic Control
Plane (ACP).
This unorthodox encapsulation avoids unwanted interactions between
the ACP packets and native packet forwarding engines, as well as
being safe for layer-2 switches which might otherwise have no IPv6
capabilities.
Status of This Memo
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This Internet-Draft will expire on October 9, 2020.
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. LLDP Encapsulation . . . . . . . . . . . . . . . . . . . 3
2.2. Content of Payload - option 1 - entire IPv6 packet . . . 4
2.3. Content of Payload - option 2 - elided IPv6 packet . . . 5
2.4. Content of Payload - option 3 - RFC8138 compressed packet 5
3. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The IEEE802.1AB Link Layer Discovery Protocol (LLDP) is a one-hop,
vendor-neutral link-layer protocol used by network devices or Things
for advertising their identity, capabilities, and neighbors on an
IEEE 802 local area network.
The LLDP uses its own ethertype (0x88cc), and so is distinct from
production IPv4 or IPv6 traffic that might appear on a network.
Switching equipment is usually configured such that it does not
forward LLDP packets.
Its Type-Length-Value (TLV) design allows for "vendor-specific"
extensions to be defined. IANA has a registered IEEE 802
organizationally unique identifier (OUI) defined as documented in
[RFC7042].
The creation and maintenance of the Autonomic Control Plane described
in [I-D.ietf-anima-autonomic-control-plane] requires creation of hop-
by-hop discovery of adjacent systems. There are Campus L2 systems
that are not broadcast safe until they have been connected to their
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Software Defined Networking (SDN) controller. The use of the stable
connectivity provided by [RFC8368] can provide the SDN connectivity
required.
There is a bootstrap interlocking problem: the network may be unsafe
for ACP discovery broadcasts without the support of Spanning Tree
Protocol (STP) or similar mechanisms until configured, yet it can not
be automatically configured until the ACP discovery (and onboarding
process) is done.
LLDP provides a way for the above problem, as it is never forwarded
to other ports, and it discovers all compliant layer-2 devices in a
network, even if they do not normally do layer-3 forwarding.
Additionally, LLDP has the advantage that received LLDP frames are
already configured in routing fabrics to be send up to the control
plane processor, with information identifying which physical port
they were received on. This is exactly the desired data flow for the
[I-D.ietf-anima-autonomic-control-plane]: all traffic goes to the
control plane processor.
This document provides a way to transmit the IPv6 Link-Layer packets
that are needed for formation of the
[I-D.ietf-anima-autonomic-control-plane] over the LLDP. Those
packets types include: IPv6 Neighbor Discovery, GRASP DULL over IPv6
Link-Local, IPsec ESP and IKEv2 packets.
1.1. Terminology
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The term "octet" is used as a synonym for byte. As the IEEE prefers
the term octet, it is used whenever speaking of LLDP specific things.
2. Protocol
2.1. LLDP Encapsulation
The LLDP vendor-specific frame has the following format:
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+--------+--------+----------+---------+--------------
|TLV Type| len | OUI |subtype | IPv6 fragment
| =127 | |= 00 00 5E| = TBD |
|(7 bits)|(9 bits)|(3 octets)|(1 octet)|(0-507 octets)
+--------+--------+----------+---------+--------------
where:
o TLV Type = 127 indicates a vendor-specific TLV
o len = indicates the TLV string length
o OUI = 00 00 5E is the organizationally unique identifier of IANA
o subtype = TBD (as assigned by IANA for this document)
o IPv6 fragment, up to 508 octets of packet.
The vendor-specific frame has a limit of 508 octets, while IPv6 has a
minimum MTU of 1280 bytes. An LLDP frame can contain more than one
TLV, and ethernet accomodates up to 1500 bytes (often larger), so it
should all fit. Two possible solutions are discussed here:
1. use three subtype TLV values. The first 508 octets go into the
first TLV, the second 508 octets go into the second TLV, etc.
three TLVs of 508 octets payload each results in a maximum
payload size of 1524, which exceeds the IPv6 minimum MTU of 1280
bytes. Given the overhead of 6 octets per TLV, the result is
that a maximum IPv6 MTU of 1464 bytes will fit within a standard
1500 octet ethernet payload space.
2. use the same subtype TLV value, repeated three times.
The second method seems more obvious but it is unclear if all LLDP
subsystems would permit TLVs to be repeated, or if they would keep
the TLVs in the correct order. While the IANA has only 253 available
TLVs, and perhaps a request for three values might seem excessive, if
this resource was depleted, a new OUI could be used.
Alternatively, an OUI specific to this effort could be allocated. A
vendor OUI could be used during prototyping.
2.2. Content of Payload - option 1 - entire IPv6 packet
The simplest encapsulation would put the entire IPv6 packet,
including the IPv6 header in. This takes a bit more space, but
provides the maximum flexibility.
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This flexibility may come at a cost of creating a new attack surface
for devices. Any L2 connected device may not inject IPv6 frames into
the control plane of the adjacent devices.
2.3. Content of Payload - option 2 - elided IPv6 packet
The [I-D.ietf-anima-autonomic-control-plane] use case only sends IPv6
Link-Local packets. The IPv6 source and destination address are
always directly related to the L2 Ethernet headers, with the use of
SLAAC derived IIDs, and the prefix "fe80".
This proposal is to include only the fields:
1. Payload Length
2. Next Header
The Hop Limit is always 1 for Link-Local packets. The Flow Label is
always 0.
Note that in the [I-D.ietf-anima-autonomic-control-plane] a mesh of
IPsec tunnels is created on top of ESP packets over IPv6 Link-Local,
and within that tunnel all of IPv6 packets can be sent.
The use of hard coding of so many values significantly limits the
attack surface possible.
2.4. Content of Payload - option 3 - RFC8138 compressed packet
An option similar to above, yet providing a bit more flexibility is
to use [RFC8138] compression of packets as it done on low powered
802.15.4 networks.
This results in compression that is close to what option 2 provides,
yet providing a lot of flexibility.
This option requires more code, may be subject to new attacks on the
decompression code, and expands the attack surface to all of IPv6, as
well as the [RFC8138] compression code.
3. Privacy Considerations
YYY
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4. Security Considerations
LLDP is relatively simple and does not provide any protections to the
traffic over it. The IPv6 packets over the LLDP SHOULD be protected
by all the existing best current practices.
The device control plane processor will be subject to the Deny of
Service (DoS) attack if excessive IPv6 packets over LLDP frames are
send up. Certain protecting mechanisms like rate limit and filtering
can be considered.
5. IANA Considerations
6. Acknowledgements
Hello.
7. Changelog
8. References
8.1. Normative References
[I-D.ietf-anima-autonomic-control-plane]
Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", draft-ietf-anima-autonomic-control-
plane-24 (work in progress), March 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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8.2. Informative References
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
Authors' Addresses
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Liang Xia (Frank)
Huawei
Email: frank.xialiang@huawei.com
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