draft-ietf-ntp-dhcpv6-ntp-opt-03.txt   draft-ietf-ntp-dhcpv6-ntp-opt-04.txt 
Network Working Group R. Gayraud Network Working Group R. Gayraud
Internet-Draft None Internet-Draft None
Intended status: Standards Track B. Lourdelet Obsoletes: RFC 4075 B. Lourdelet
Expires: September 7, 2009 Cisco Systems, Inc. (if approved) Cisco Systems, Inc.
March 6, 2009 Intended status: Standards Track July 28, 2009
Expires: January 29, 2010
Network Time Protocol (NTP) Server Option for DHCPv6 Network Time Protocol (NTP) Server Option for DHCPv6
draft-ietf-ntp-dhcpv6-ntp-opt-03.txt draft-ietf-ntp-dhcpv6-ntp-opt-04.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
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Abstract Abstract
The NTP Server Option for DHCPv6 provides NTP (Network Time Protocol The NTP Server Option for DHCPv6 provides NTP (Network Time Protocol
version 4) configuration information to DHCPv6 hosts. version 4) configuration information to DHCPv6 hosts.
Table of Contents Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 1. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Related Work and Usage Model . . . . . . . . . . . . . . . 3 2.1. Related Work and Usage Model . . . . . . . . . . . . . . . 3
3. NTP Server Option for DHCPv6 . . . . . . . . . . . . . . . . . 4 3. NTP Server Option for DHCPv6 . . . . . . . . . . . . . . . . . 3
3.1. NTP Server Address Suboption . . . . . . . . . . . . . . . 5 3.1. NTP Server Address Suboption . . . . . . . . . . . . . . . 5
3.2. NTP Multicast Address Suboption . . . . . . . . . . . . . 5 3.2. NTP Multicast Address Suboption . . . . . . . . . . . . . . 5
3.3. NTP Server FQDN Suboption . . . . . . . . . . . . . . . . 6 3.3. NTP Server FQDN Suboption . . . . . . . . . . . . . . . . . 6
4. Examples of use . . . . . . . . . . . . . . . . . . . . . . . 6 4. Examples of use . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Appearance of this Option . . . . . . . . . . . . . . . . . . 8 5. Appearance of this Option . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Requirements notation 1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Introduction 2. Introduction
This document defines a DHCPv6 option and associated suboptions to This document defines a DHCPv6 option and associated suboptions to
provide Network Time Protocol version 4 [draft-ntpv4] or greater provide Network Time Protocol version 4 [draft-ntpv4] or greater
configuration information to DHCPv6 hosts. configuration information to DHCPv6 hosts.
2.1. Related Work and Usage Model 2.1. Related Work and Usage Model
[RFC4075] (SNTP Configuration Option for DHCPv6) provides some degree
of automatic time server configuration for IPv6, as it specifies how
to transmit SNTP [RFC4330] servers addresses through DHCPv6. However
this approach is not suitable for all NTP deployments. It is not an
extensible mechanism and introduces some semantic confusion throught
the use of the "SNTP" acronym. Additionally the approach of only
offering IPv6 addresses to specify server location does not meet NTP
requirements that make use of a FQDN (Fully Qualified Domain Name) as
well.
The NTP service is publicly offered on the Internet by a number of The NTP service is publicly offered on the Internet by a number of
organizations. Those servers can be used but not abused, so any organizations. Those servers can be used but not abused, so any
method which is tasked to disseminate locations of NTP servers must method which is tasked to disseminate locations of NTP Servers must
act responsibly in a manner that does not lead to public server act responsibly in a manner that does not lead to public server
overloading. When using DHCPv6 to offer NTP server location, and if overloading. When using DHCPv6 to offer NTP Server location, and if
there is a need to distribute a device with a hardcoded there is a need to distribute a device with a hardcoded
configuration, this configuration MUST NOT include server location configuration, this configuration MUST NOT include server location
that is not part of the organization that distribute this device. that is not part of the organization that distribute this device.
Typical usage of this option is to specify an NTP server that is part Typical usage of this option is to specify an NTP Server that is part
of the organization that operates the DHCPv6 server. of the organization that operates the DHCPv6 server.
The location of the NTP service, like any other Internet service, can The location of the NTP service, like any other Internet service, can
be specified by an IP address or an FQDN. By design, DHCP offers be specified by an IP address or an FQDN. By design, DHCP offers
information to multiple devices and is prone to amplification of information to multiple devices and is prone to amplification of
mistakes, so great care must be taken to define its configuration. mistakes, so great care must be taken to define its configuration.
Specification of the NTP service by FQDN offers a level of Specification of the NTP service by FQDN offers a level of
indirection that works as a possible mitigation tool in case of indirection that works as a possible mitigation tool in case of
misconfiguration. DNS can be used to redirect misconfigured clients misconfiguration. DNS can be used to redirect misconfigured clients
to an unexisting IPv6 address instead of having to change the address to an unexisting IPv6 address instead of having to change the address
of the NTP Server itself. of the NTP server itself.
While the NTP specification defines a comprehensive set of While the NTP specification defines a comprehensive set of
configuration parameters, modification of those parameters is best configuration parameters, modification of those parameters is best
left to the decision of the client itself. The DHCPv6 option for NTP left to the decision of the client itself. The DHCPv6 option for NTP
is then restricted to server location. is then restricted to server location.
3. NTP Server Option for DHCPv6 3. NTP Server Option for DHCPv6
This option serves as a container for all the information related to This option serves as a container for all the information related to
one NTP server. This option can appear multiple times in a DHCPv6 one NTP server or SNTP server. This option can appear multiple times
message. Each instance of this option is to be considered by the NTP in a DHCPv6 message. Each instance of this option is to be
client as a server to include in its configuration. considered by the NTP client or SNTP client as a server to include in
its configuration.
The option itself does not contain any value. Instead, it contains The option itself does not contain any value. Instead, it contains
one or several suboptions that carry NTP server configuration one or several suboptions that carry NTP server or SNTP server
information. This option MUST include one, and only one, time source configuration information. This option MUST include one, and only
suboption. The currently defined time source suboptions are: one, time source suboption. The currently defined time source
NTP_OPTION_SRV_ADDR, NTP_OPTION_SRV_MC_ADDR, NTP_OPTION_SRV_FQDN. It suboptions are: NTP_OPTION_SRV_ADDR, NTP_OPTION_SRV_MC_ADDR,
carries the NTP server location, as a unicast or multicast IPv6 NTP_OPTION_SRV_FQDN. It carries the NTP server or SNTP server
address or as an NTP server FQDN. More time source suboptions may be location, as a unicast or multicast IPv6 address or as an NTP server
defined in the future. While the FQDN option offers the most or SNTP server FQDN. More time source suboptions may be defined in
deployment flexibility, resiliency as well as security, the IP the future. While the FQDN option offers the most deployment
address options are defined to cover cases where a dependancy to DNS flexibility, resiliency as well as security, the IP address options
is not desirable. are defined to cover cases where a dependancy to DNS is not
desirable.
If the NTP server location is an IPv6 multicast address, the client If the NTP server or SNTP server location is an IPv6 multicast
SHOULD use this address as an NTP multicast group address and listen address, the client SHOULD use this address as an NTP multicast group
to messages sent to this group in order to synchronize its clock. address and listen to messages sent to this group in order to
synchronize its clock.
The format of the NTP Server Option is: The format of the NTP Server Option is:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_NTP_SERVER | option-len | | OPTION_NTP_SERVER | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboption-1 | | suboption-1 |
: : : :
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| suboption-2 | | suboption-2 |
: : : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: : : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboption-n | | suboption-n |
: : : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_NTP_SERVER (TBD_IANA), option-code: OPTION_NTP_SERVER (TBD_IANA),
option-len: Total length of the included suboptions. option-len: Total length of the included suboptions.
This document does not define any priority between the client's This document does not define any priority between the client's
embedded configuration and the NTP servers discovered via this embedded configuration and the NTP servers or SNTP servers discovered
option. In particular, the client is allowed to simultaneously use via this option. In particular, the client is allowed to
its own configured NTP servers and the servers discovered via DHCP. simultaneously use its own configured NTP servers or SNTP servers and
the servers discovered via DHCP.
3.1. NTP Server Address Suboption 3.1. NTP Server Address Suboption
This suboption is intended to appear inside the OPTION_NTP_SERVER This suboption is intended to appear inside the OPTION_NTP_SERVER
option. It specifies the IPv6 unicast address of an NTP server option. It specifies the IPv6 unicast address of an NTP server or
available to the client. An example of use is present in Section 4. SNTP server available to the client. An example of use is present in
Section 4.
The format of the NTP Server Address Suboption is: The format of the NTP Server Address Suboption is:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NTP_SUBOPTION_SRV_ADDR | suboption-len = 16 | | NTP_SUBOPTION_SRV_ADDR | suboption-len = 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| | | |
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| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
suboption-code: NTP_SUBOPTION_MC_ADDR (2), suboption-code: NTP_SUBOPTION_MC_ADDR (2),
suboption-len: 16. suboption-len: 16.
3.3. NTP Server FQDN Suboption 3.3. NTP Server FQDN Suboption
This suboption is intended to appear inside the OPTION_NTP_SERVER This suboption is intended to appear inside the OPTION_NTP_SERVER
option. It specifies the FQDN of an NTP server available to the option. It specifies the FQDN of an NTP server or SNTP server
client. available to the client.
The format of the NTP Server FQDN Suboption is: The format of the NTP Server FQDN Suboption is:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NTP_SUBOPTION_SRV_FQDN | suboption-len | | NTP_SUBOPTION_SRV_FQDN | suboption-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| FQDN of NTP server | | FQDN of NTP server |
: : : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
suboption-code: NTP_SUBOPTION_SRV_FQDN (3), suboption-code: NTP_SUBOPTION_SRV_FQDN (3),
suboption-len: Length of the included FQDN field, suboption-len: Length of the included FQDN field,
FQDN: Fully Qualified Domain Name of the NTP server. This FQDN: Fully Qualified Domain Name of the NTP server or SNTP server.
field MUST be encoded as described in [RFC3315], This field MUST be encoded as described in [RFC3315],
section 8. section 8.
4. Examples of use 4. Examples of use
To instruct a client to use an NTP server located at address 2001: To instruct a client to use an NTP server or SNTP server located at
db8::1, a DHCP server shall use the following format: address 2001:db8::1, a DHCP server shall use the following format:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_NTP_SERVER | option-len = 20 | | OPTION_NTP_SERVER | option-len = 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NTP_SUBOPTION_SRV_ADDR | suboption-len = 16 | | NTP_SUBOPTION_SRV_ADDR | suboption-len = 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| IPv6 address = 2001:db8::1 | | IPv6 address = 2001:db8::1 |
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The option number for this option MAY appear in the "Option Request" The option number for this option MAY appear in the "Option Request"
option [RFC3315] in the following messages: Solicit, Request, Renew, option [RFC3315] in the following messages: Solicit, Request, Renew,
Rebind, Information-Request, and Reconfigure. If this option number Rebind, Information-Request, and Reconfigure. If this option number
appears in the "Option Request" option in messages other than those appears in the "Option Request" option in messages other than those
specified above, the receiver SHOULD ignore it. specified above, the receiver SHOULD ignore it.
6. Security Considerations 6. Security Considerations
This option could be used by an intruder to advertise the address of This option could be used by an intruder to advertise the address of
a malicious NTP server and adversely affect the clock of clients on a malicious NTP server or SNTP server and adversely affect the clock
the network. The consequences of such an attack can be critical, of clients on the network. The consequences of such an attack can be
because many security protocols depend on time synchronization to run critical, because many security protocols depend on time
their algorithms. As an example, an attacker could break synchronization to run their algorithms. As an example, an attacker
connectivity between SEND-enabled nodes [RFC3971], simply by could break connectivity between SEND-enabled nodes [RFC3971], simply
affecting the clock on these nodes. by affecting the clock on these nodes.
To prevent these attacks, it is strongly advisable to secure the use To prevent these attacks, it is strongly advisable to secure the use
of this option either by: of this option either by:
- using the NTPv4 Autokey public key authentication, as defined - using the NTPv4 Autokey public key authentication, as defined
in [draft-autokey] or, in [draft-autokey] or,
- using authenticated DHCP as described in [RFC3315] section 21. - using authenticated DHCP as described in [RFC3315] section 21.
7. IANA Considerations 7. IANA Considerations
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