DHC M. Stapp
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track July 7, 2009
Expires: January 8, 2010
The DHCPv4 Relay Agent Identifier Suboption
draft-ietf-dhc-relay-id-suboption-07.txt
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Abstract
This memo 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
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relay agent device. The value may be administratively-configured or
may be generated by the relay agent. The suboption allows a DHCP
relay agent to include the identifier in the DHCP messages it sends.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Example Use-Cases . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Industrial Ethernet . . . . . . . . . . . . . . . . . . . . 3
3.2. Bulk Leasequery . . . . . . . . . . . . . . . . . . . . . . 4
4. Suboption Format . . . . . . . . . . . . . . . . . . . . . . . 4
5. Relay Identifier Types . . . . . . . . . . . . . . . . . . . . 5
6. Generating a Relay Identifier . . . . . . . . . . . . . . . . . 5
7. Identifier Stability . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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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 information option echo it back in their replies.
This specification introduces a Relay Agent Identifier suboption for
the Relay Information option. The Relay-Id suboption carries a
sequence of octets that is intended to identify the relay agent
uniquely within the administrative domain. The identifier may be
administratively configured: in some networks it may be adequate to
assign ASCII strings such as "switch1" and "switch2". Alternatively,
the identifier may be generated by the relay agent itself, and we
specify use of DUIDs [RFC3315] for this purpose.
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]. DUID terminology is in
[RFC3315].
3. Example Use-Cases
3.1. 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 -
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
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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.
3.2. 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 draft ([draft-kinnear]) proposing a
variety of enhancements to the existing Leasequery protocol. The
draft describes a use-case where a relay agent queries DHCP servers
using the Relay Identifier to retrieve all the leases allocated
through the relay device.
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 | type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. 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 two.
type a single octet describing the type of
identifier that is present.
identifier the identifying data.
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5. Relay Identifier Types
For clarity, the suboption specified here includes a type octet that
describes the data used in the identifier field. The type value zero
is reserved and MUST NOT be used. Two type values are defined here:
RELAY_IDENTIFIER_DUID and RELAY_IDENTIFIER_ASCII.
RELAY_IDENTIFIER_DUID is used when the identifier field contains a
DUID [RFC3315]. Administrators may want to assign human-friendly
ASCII identifiers: RELAY_IDENTIFIER_ASCII is used when the identifier
field contains an ASCII string.
6. Generating a Relay Identifier
As described in Section 1, in some situations it may be useful for
network devices to generate identifiers themselves. Relay agents who
send the Relay Agent Identifier suboption using identifiers that are
not administratively-configured MUST be generated following the
procedures in the DUID section of [RFC3315]. Relay agents who use
generated identifiers SHOULD make the generated value visible to
their administrators via their user interface, through a log entry,
or through some other mechanism.
7. Identifier Stability
If the relay identifier is to be meaningful it has to be stable. A
relay agent SHOULD use a single identifier type and value
consistently. The identifier used by a relay device SHOULD be
committed to stable storage, unless the relay device can regenerate
the value upon reboot.
Implementors 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 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
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for the new device to continue to provide the same relay identifier
as the old device. Implementors should be aware of this possibility,
and consider making it possible for administrators to configure the
identifier.
8. Security Considerations
Security issues with the Relay Agent Information option and its use
by servers in address assignment are discussed in [RFC3046] and
[RFC4030]. Relay agents who send the Relay Agent Identifier
suboption SHOULD use the Relay Agent Authentication suboption
[RFC4030] to provide integrity protection.
9. 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]
We request that IANA establish a new registry of DHCP Relay Agent
Identifier Sub-Option Types, to be maintained in
http://www.iana.org/assignments/bootp-dhcp-parameters. The
Identifier Type is a single octet. The initial values assigned in
this document are:
Reserved 0
RELAY_IDENTIFIER_DUID 1
RELAY_IDENTIFIER_ASCII 2
Additional Identifier Type values will be allocated and assigned
through IETF Review, as defined in [RFC5226].
10. References
10.1. 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.
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[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for
the Dynamic Host Configuration Protocol (DHCP) Relay Agent
Option", RFC 4030, March 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
10.2. Informative References
[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.
[draft-kinnear]
Kinnear, K., Volz, B., Russell, N., and M. Stapp, "Bulk
DHCPv4 Lease Query
(draft-kinnear-dhc-dhcpv4-bulk-leasequery-*)", July 2008.
Author's Address
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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