DHCPv4 over DHCPv6 with Relay Agent Support
draft-porfiri-dhc-dhcpv4-over-dhcpv6-ra-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Claudio Porfiri , Suresh Krishnan , Jari Arkko , Mirja Kühlewind | ||
| Last updated | 2024-02-01 | ||
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draft-porfiri-dhc-dhcpv4-over-dhcpv6-ra-00
Dynamic Host Configuration C. Porfiri
Internet-Draft Ericsson
Intended status: Standards Track S. Krishnan
Expires: 4 August 2024 Cisco
J. Arkko
M. Kühlewind
Ericsson
1 February 2024
DHCPv4 over DHCPv6 with Relay Agent Support
draft-porfiri-dhc-dhcpv4-over-dhcpv6-ra-00
Abstract
This document describes a general mechanism for networks with legacy
IPv4 only clients to use DHCPv4-over-DHCPv6 (DHCP 4o6) for
discovering information about network Topology. To address this
scenario, this document specifies an amendment to RFC7341 that allows
a new 4o6 Relay Agent (4o6RA) to perform the 4o6 DHCP en- and
decapsultion instead of the client.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-porfiri-dhc-dhcpv4-over-
dhcpv6-ra/.
Source for this draft and an issue tracker can be found at
https://github.com/mirjak/dhc-dhcpv4-over-dhcpv6-ra.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 4 August 2024.
Copyright Notice
Copyright (c) 2024 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Example Use Case: Switched Fronthaul . . . . . . . . . . . . 4
4. Existing DHCP-based Solutions for Topology Discovery . . . . 5
4.1. IPv6 Clients using DHCPv6 . . . . . . . . . . . . . . . . 5
4.2. Clients with Dual Connectivity and 4o6 DHCP support . . . 5
5. Layer 2 Topogoy Discovery using 4o6 DHCP with legacy IPv4
clients . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
In some networks the configuration of a client host may depend on the
Topology. However, when a new client host gets connected to the
network, it may be unaware of the Topology and respectively how it
has to be configured.
In IPv6 networks, Topology discover can be realized using DHCPv6
Relay Agents [RFC6221] that insert relay agent options in DHCPv6
message exchanges in order to identify the client-facing interfaces,
e.g. using the Serial Number or other hardcoded information. Then, a
reference host that is responsible for providing configuration to the
client host can obtain Topology information from the DHCP server.
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In DHCPv6, a Relay Agent can encapsulate the DHCP message from the
client in a new DHCP message along with any options it chooses to add
to provide information to the DHCP server. This mode of operation
also supports networks that include a hierarchy of switches.
However, if the client only supports IPv4 and cannot easily be
replaced or updated, this approach does not work, as DHCPv4 support
for relays is much more limited. For instance, there is no support
in DHCPv4 for hierarchical modes of deployment, as the specifications
prohibit chaining of Relay Agent Information Options (RAIOs)
[RFC3046].
A typical example where Topology Discovery is needed for host
configuration is the switched fronthaul in the Radio Access Network
(see Section 3). However, the specified approach in this document is
not limited to that example.
This document specifies how to provide Topology Discover using Relay
Agent functionality for legacy IPv4 clients using DHCPv4-over-DHCPv6
(DHCP 4o6) [RFC7341]. No new protocols or extensions are needed,
instead this document specifies an amendment to [RFC7341] that allows
a Relay Agent to perform the 4o6 DHCP en- and decapsultion instead of
the client in order to address the specific scenario that is detailed
in Section 4.2.
2. Conventions and Definitions
The following terms and acronyms are used in this document:
* 4o6 The architecture, the procedures and the protocols described
in the DHCPv4-over-DHCPv6 document [RFC7341].
* 4o6RA The 4o6 Relay Agent is the part of an LDRA implementing 4o6
* DHCP Relay Agent
This is a concept in all of the protocols, BOOTP [RFC0951]
[RFC1542], DHCPv4 [RFC2131] [RFC2132], and DHCPv6 [RFC8415],
although the details differ between the protocols.
* Lightweight DHCPv6 Relay Agent (LDRA)
This is an extension of the original DHCPv6 Relay Agent mechanism,
to support also Layer 2 devices performing a Relay Agent function
[RFC6221].
* Relay Agent Information Option (RAIO)
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This is a DHCP option defined in [RFC3046]. Also commonly
referred to as "Option 82". RAIO options were later extended to
be able to carry suboptions [RFC6925].
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.
3. Example Use Case: Switched Fronthaul
In Radio Access Networks (RANs) the Fronthaul is the network segment
that connects Radio Units, the distributed radio elements in a mobile
network, to other network elements. The aggregation of Radio Unit
devices (also known as Switched Fronthaul) hides the relationship
between the Radio Units themselves and the physical ports where they
are connected. The Radio Units are the client hosts in the switched
Fronthaul network and need to be configured based on their Topology.
+--------+
| RU1 | P1 +-+------+ | |
| +--------| | L2RA | | +----+------+ |
+--------+ | +------+ | | | L3RA | |
| L2 | +--| +------+ |
+--------+ P2 | switch | | | | |
| RU2 +--------| #1 +-----| | Router +----|
| | +--------+ | +-----------+ | +---------+
+--------+ | | | |
| +--| DHCP |
+--------+ | | | Server |
| RU3 | P1 +-+------+ | | | #1 |
| +--------| | L2RA | | +-----------+ | +---------+
+--------+ | +------+ | | | |
| L2 | +--| Baseband | |
+--------+ P2 | switch | | | Unit | |
| RU4 +--------| #2 +-----| | +----|
| | +--------+ | +-----------+ |
+--------+ | |
Figure 1: Layer 2 Switched Fronthaul Example
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Figure 1 shows multiple Radio Units that are connected to one
Baseband Unit by means of a Layer 2 switched network. The Baseband
Unit is the central processing unit that handles baseband
information. A Baseband Unit is often placed rather centrally, while
the Radio Units need to be distributed to be co-located with or near
the antennas. Traffic between Radio Units and Bandband Units is both
IP-based and Layer-2-based and may pass a hierarchy of L2 switches.
In order to properly address the Radio Unit, the Baseband Unit needs
to associate the Radio Unit's MAC address to the L2 switch and
respective port where the Radio Unit is connected. To realize this
device configuration in the Switched Fronthaul network, DHCP can be
used to discover the network Topology.
4. Existing DHCP-based Solutions for Topology Discovery
4.1. IPv6 Clients using DHCPv6
If the network is fully IPv6 enabled, DHCPv6 [RFC8415] can be used
for Topology Discovery. This solution exploits DHCPv6 Relay Agent
support in the server, whilst Lightweight DHCPv6 Relay Agents (LDRA)
[RFC6221] are implemented in the L2 switches to inform DHCPv6 server
about the L2 Topology.
4.2. Clients with Dual Connectivity and 4o6 DHCP support
When the client needs an IPv4 address but is dual connected and can
support DHCPv4-over-DHCPv6 [RFC7341], DHCPv6 [RFC8415] with a DHCPv4-
over-DHCPv6 compliant DHCP server can be used for Topology Discovery
whereas DHCP is used still for IP address assignment.
An example network with 4o6 compliant clients can be sketched as
follows:
+---------+
| 4o6 | P1 +-+------+ | | +---------+
| Client +-------| | LDRA | | +----+------+ | | 4o6 |
+---------+ | +------+ | | | L3RA | +--| DHCP |
| L2 | +--| +------+ | | Server |
+---------+ P2 | switch | | | | | | |
| 4o6 +-------| +-----| | Router +----| +---------+
| Client | +--------+ | +-----------+ |
+---------+ | |
Figure 2: Layer 2 Topology discover with 4o6
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In Figure 2 the client supports [RFC7341] by implementing the 4o6
encapsulation whereas the intermediate nodes implement LDRA [RFC6221]
or L3RA [RFC8415] and finally the DHCP server is 4o6 DHCP capable
[RFC7341].
Still, [RFC7341] does not provide a solution for legacy IPv4 clients
that respectively do not support 4o6 encapsulation.
5. Layer 2 Topogoy Discovery using 4o6 DHCP with legacy IPv4 clients
This document extends [RFC7341] to enable a deployment scenario where
the 4o6 encapsulation is implemented at the Relay Agent instead of
the DHCP client. This makes it possible to enable Topology Discovery
for legacy IPv4 DHCP clients through a 4o6-DHCP-enabled network.
+---------+
| 4o6 | P1 +-+------+ | | +---------+
| Client +-------| | LDRA | | +----+------+ | | 4o6 |
+---------+ | +------+ | | | L3RA | +--| DHCP |
| L2 | +--| +------+ | | Server |
+---------+ | switch | | | | | +---------+
| Legacy | P2 +------+ +-----| | Router +----|
| Client +-------+ 4o6 | | | +-----------+ | +---------+
+---------+ +------+-+ | | | Legacy |
+--| DHCP |
| | Server |
| +---------+
Figure 3: Layer 2 architecture with 4o6 and legacy client
The new scenario, not described in [RFC7341], is shown in Figure 3.
In such a scenario, the 4o6 encapsulation is implemented in the Relay
Agent deployed in the edge L2 switch, or in general in the edge
device providing connectivity to the legacy client. In this case it
is up to the Relay Agent to provide the full 4o6 DHCP set of
functionality whereas the legacy client is not aware of being served
via a 4o6 DHCP service.
This new 4o6 Relay Agent (4o6RA), as specified in this document,
exchanges DHCP messages between clients and servers using the message
formats established in [RFC8415]. To maintain interoperability with
existing DHCP relays and servers, the message format is unchanged
from [RFC8415]. The 4o6RA implements the same message types as a
normal DHCPv6 Relay Agent Section 6 of [RFC7341]. They are: - Relay-
Forward Messages - Relay-Reply Messages
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In this specification, the 4o6RA creates the DHCPV4-QUERY Message and
encapsulates the DHCP request message received from the legacy DHCPv4
client.
When DHCPV4-RESPONSE Message is received by the 4o6 Relay Agent, it
looks for the DHCPv4 Message option within this message. If this
option is not found, the DHCPv4-response message MUST be discarded.
If the DHCPv4 Message option is present, the 4o6RA MUST extract the
DHCPv4 message and forward the encapsulated DHCPv4-response to the
legacy DHCPv4 client.
An Layer 2 Relay Agent receiving DHCPV4-QUERY or DHCPV4-RESPONSE
messages will handle them as specified in Section 6 of [RFC6221].
6. Security Considerations
This documents applies 4o6 DHCP in a scenario where legacy IPv4
clients are connected to 4o6 DHCP Relay Agent that performs the en-
and decapsulation. This document does not change anything else in
the 4o6 DHCP speacification and therefore the security consideration
of [RFC7341] still apply.
The legacy IPv4 client is not aware of this mechanism, however, even
when 4o6 DHCP is used, the client does not have any control about the
information provided by the Relay agent. As such this change does
not provide any additional secruity concerns.
7. IANA Considerations
This document has no IANA actions.
8. References
8.1. 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,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, DOI 10.17487/RFC3046, January 2001,
<https://www.rfc-editor.org/rfc/rfc3046>.
[RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
DOI 10.17487/RFC6221, May 2011,
<https://www.rfc-editor.org/rfc/rfc6221>.
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[RFC6925] Joshi, B., Desetti, R., and M. Stapp, "The DHCPv4 Relay
Agent Identifier Sub-Option", RFC 6925,
DOI 10.17487/RFC6925, April 2013,
<https://www.rfc-editor.org/rfc/rfc6925>.
[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
RFC 7341, DOI 10.17487/RFC7341, August 2014,
<https://www.rfc-editor.org/rfc/rfc7341>.
[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/rfc/rfc8174>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/rfc/rfc8415>.
8.2. Informative References
[RFC0951] Croft, W. and J. Gilmore, "Bootstrap Protocol", RFC 951,
DOI 10.17487/RFC0951, September 1985,
<https://www.rfc-editor.org/rfc/rfc951>.
[RFC1542] Wimer, W., "Clarifications and Extensions for the
Bootstrap Protocol", RFC 1542, DOI 10.17487/RFC1542,
October 1993, <https://www.rfc-editor.org/rfc/rfc1542>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/rfc/rfc2131>.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
<https://www.rfc-editor.org/rfc/rfc2132>.
Acknowledgments
The authors would also like to acknowledge interesting discussions in
this problem space with Sarah Gannon, Ines Ramadza and Siddharth
Sharma.
Authors' Addresses
Claudio Porfiri
Ericsson
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Email: claudio.porfiri@ericsson.com
Suresh Krishnan
Cisco
Email: suresh.krishnan@gmail.com
Jari Arkko
Ericsson
Email: jari.arkko@ericsson.com
Mirja Kühlewind
Ericsson
Email: mirja.kuhlewind@ericsson.com
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