Internet DRAFT - draft-ietf-dhc-relay-id-suboption
draft-ietf-dhc-relay-id-suboption
DHC B. Joshi
Internet-Draft D. Ramakrishna Rao
Intended status: Standards Track Infosys Ltd.
Expires: August 23, 2013 M. Stapp
Cisco Systems, Inc.
February 19, 2013
The DHCPv4 Relay Agent Identifier Suboption
draft-ietf-dhc-relay-id-suboption-13.txt
Abstract
This document defines a new Relay Agent Identifier suboption for the
Dynamic Host Configuration Protocol's (DHCP) Relay Agent Information
option. The suboption carries a value that uniquely identifies the
relay agent device within the administrative domain. The value is
normally administratively-configured in the relay agent. The
suboption allows a DHCP relay agent to include the identifier in the
DHCP messages it sends.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 23, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Example Use-Cases . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Bulk Leasequery . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Industrial Ethernet . . . . . . . . . . . . . . . . . . . . 3
4. Suboption Format . . . . . . . . . . . . . . . . . . . . . . . 4
5. Identifier Stability . . . . . . . . . . . . . . . . . . . . . 4
5.1. Identifier Uniqueness . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6.1. Forged Relay ID attacks . . . . . . . . . . . . . . . . . . 6
6.2. Factory Floor Scenario . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) [RFC2131]
provides IP addresses and configuration information for IPv4 clients.
It includes a relay agent capability, in which network elements
receive broadcast messages from clients and forward them to DHCP
servers as unicast messages. In many network environments, relay
agents add information to the DHCP messages before forwarding them,
using the Relay Agent Information option [RFC3046]. Servers that
recognize the relay agent information option echo it back in their
replies.
This specification introduces a Relay Agent Identifier (Relay-Id)
suboption for the Relay Agent Information option. The Relay-Id
suboption carries a sequence of octets that is intended to uniquely
identify the relay agent within the administrative domain. In this
document, an administrative domain consist of all DHCP servers and
relay agents that communicate with each other.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
DHCPv4 terminology is defined in [RFC2131], and the DHCPv4 Relay
Agent Information Option in [RFC3046].
3. Example Use-Cases
3.1. Bulk Leasequery
There has been quite a bit of recent interest in extending the DHCP
Leasequery protocol [RFC4388] to accommodate some additional
situations. There is a recent document
[I-D.ietf-dhc-dhcpv4-bulk-leasequery] proposing a variety of
enhancements to the existing Leasequery protocol. The document
describes a use-case where a relay agent queries DHCP servers using
the Relay Identifier to retrieve all the leases allocated through the
relay agent.
3.2. Industrial Ethernet
DHCP typically identifies clients based on information in their DHCP
messages - such as the Client-Identifier option, or the value of the
chaddr field. In some networks, however, the location of a client -
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its point of attachment to the network - is a more useful identifier.
In factory-floor networks (commonly called 'Industrial' networks),
for example, the role a device plays is often fixed and based on its
location. Using manual address configuration is possible (and is
common) but it would be beneficial if DHCP configuration could be
applied to these networks.
One way to provide connection-based identifiers for industrial
networks is to have the network elements acting as DHCP relay agents
supply information that a DHCP server could use as a client
identifier. A straightforward way to form identifier information is
to combine something that is unique within the scope of the network
element, such as a port/slot value, with something that uniquely
identifies that network element, such as a Relay Agent Identifier.
4. Suboption Format
Format of the Relay Agent Identifier suboption:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SUBOPT_RELAY_ID| length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. identifier (variable) .
. .
+---------------------------------------------------------------+
Where:
SUBOPT_RELAY_ID [TBA]
length the number of octets in the suboption
(excluding the suboption ID and length fields);
the minimum length is one.
identifier the identifying data.
5. Identifier Stability
If the relay identifier is to be meaningful it has to be stable. A
relay agent SHOULD use a single identifier value consistently. The
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identifier used by a relay device SHOULD be committed to stable
storage, unless the relay device can regenerate the value upon
reboot.
If the relay-id configured in a relay agent is not unique within its
administrative domain, resource allocation problems may occur as the
DHCP server attempts to allocate the same resource to devices behind
two different relay agents. Therefore, relay-id configured in a
relay agent MUST be unique within its administrative domain. To aid
in ensuring uniqueness of relay-ids, relay agents SHOULD make their
relay identifiers visible to their administrators via their user
interface, through a log entry, through a MIB field, or through some
other mechanism.
Implementors of relay agents should note that the identifier needs to
be present in all DHCP message types where its value is being used by
the DHCP server. The relay agent may not be able to add the Relay
Agent Information option to all messages - such as RENEW messages
sent as IP unicasts. In some deployments that might mean that the
server has to be willing to continue to associate the relay
identifier it has last seen with a lease that is being RENEWed.
Other deployments may prefer to use the Server Identifier Override
suboption [RFC5107] to permit the relay device to insert the Relay
Agent Information option into all relayed messages.
Handling situations where a relay agent device is replaced is another
aspect of stability. One of the use-cases for the relay identifier
is to permit a server to associate clients' lease bindings with the
relay device connected to the clients. If the relay device is
replaced, because it has failed or been upgraded, it may be desirable
for the new device to continue to provide the same relay identifier
as the old device. Therefore if a relay agent supports relay-id, the
relay-id should be administratively configurable.
5.1. Identifier Uniqueness
Administrators should take special care to ensure that relay-ids
configured in their relay agents are not duplicated. There are a
number of strategies that may be used to achieve this.
Administrators may use a strategy to configure unique relay-ids. One
such strategy is that a relay-id on a relay agent may re-use an
existing identifier or set of identifiers that are already guaranteed
to be unique (e.g., UUID [RFC4122]).
For administrators who are already using a provisioning system to
manage their networking infrastructure, it may work to enumerate
relay agents on the basis of roles, and then as a second step, assign
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those roles to specific relay agents or groups of relay agents. In
such a scenario, when a replacement relay agent is first seen by the
DHCP server, this could trigger a configuration event on the
provisioning system, and the new relay agent could be assigned to the
role of the relay agent it is replacing.
In some cases it may be that the DHCP server has configurable event
notification, and that a duplicate relay-id would cause some event
that could trigger a notification, and that would never happen in any
other case. In this scenario, administrators should take advantage
of this feature. This is not a perfect solution, because it will not
work until such an event occurs.
A network management/provisioning system may also be able to collect
a full list of all relay agents on the network. It may then notice
that more than one device reports the same relay-id. In such a case,
the provisioning system could notify the administrator of the fault,
which could then be corrected.
This is not an exhaustive list of strategies. We suggest an
additional strategy in the security considerations section;
administrators are also encouraged to consider the specifics of their
own network configuration to see if there is some way to detect
duplicate relay-ids other than the ones listed here, if none of these
will work.
6. Security Considerations
6.1. Forged Relay ID attacks
Security issues with the Relay Agent Information option and its use
by servers in address assignment are discussed in [RFC3046] and
[RFC4030]. The DHCP Relay Agent Information option depends on a
trusted relationship between the DHCP relay agent and the DHCP
server, as described in Section 5 of RFC 3046. While the
introduction of fraudulent DHCP relay agent information options can
be prevented by a perimeter defense that blocks these options unless
the DHCP relay agent is trusted, a deeper defense using the
authentication suboption for DHCP relay agent information option
[RFC4030] SHOULD be deployed as well. It also helps in avoiding
duplication of relay identifiers by malicious entities. However,
implementation of authentication suboption for DHCP relay agent
information option [RFC4030] is not a must to support relay-id
suboption.
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6.2. Factory Floor Scenario
One possible use case for the relay-id suboption is the automated
configuration of machines on a factory floor. In this situation,
various sections of the factory floor might be on their own network
links, with a relay agent interposed between those links and the DHCP
server. The relay-id of each relay agent might cause special
configurations to be downloaded to those devices to control their
behavior.
If a relay agent was deployed on the factory floor in such a
situation, with an incorrect relay-id, there is the potential that
devices could be misconfigured in a way that could produce incorrect
results, cause physical damage, or even create hazardous conditions
for workers.
In deployment scenarios like this one, administrators must use some
dependable technique to ensure that such misconfigurations do not
occur. It is beyond the scope of this document to provide a complete
list of such techniques.
However, as an example, a relay agent device intended for use in such
a scenario could require the use of a hardware token that contains
the relay-id, that is physically attached to the installation
location of the relay agent device, and that can be connected to and
disconnected from the relay agent device without the use of special
tools. Such a relay agent device should not be operable when this
hardware token is not connected to it: either it should fail because
it presents an unknown identifier to the DHCP server, or it should
simply refuse to relay DHCP packets until the token is connected to
it.
A relay agent device that does not provide a clear mitigation
strategy for a scenario where misconfiguration could have damaging or
hazardous consequences should not be deployed in such a scenario.
7. IANA Considerations
We request that IANA assign a new suboption code from the registry of
DHCP Agent Sub-Option Codes maintained in
http://www.iana.org/assignments/bootp-dhcp-parameters.
Relay Agent Identifier Suboption [TBA]
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8. Acknowledgments
Thanks to Bernie Volz, David W. Hankins, Pavan Kurapati and Ted Lemon
for providing valuable suggestions.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
[RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for
the Dynamic Host Configuration Protocol (DHCP) Relay Agent
Option", RFC 4030, March 2005.
9.2. Informative References
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006.
[RFC5107] Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,
"DHCP Server Identifier Override Suboption", RFC 5107,
February 2008.
[I-D.ietf-dhc-dhcpv4-bulk-leasequery]
Kinnear, K., Stapp, M., Joshi, B., and N. Russell, "Bulk
DHCPv4 Lease Query",
draft-ietf-dhc-dhcpv4-bulk-leasequery-07 (work in
progress), October 2012.
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Authors' Addresses
Bharat Joshi
Infosys Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
Email: bharat_joshi@infosys.com
URI: http://www.infosys.com/
D.T.V Ramakrishna Rao
Infosys Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
Email: ramakrishnadtv@infosys.com
URI: http://www.infosys.com/
Mark Stapp
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: +1 978 936 0000
Email: mjs@cisco.com
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