Network Working Group T. Lemon
Internet-Draft Nominum, Inc.
Intended status: Informational T. Mrugalski
Expires: November 7, 2016 ISC
May 6, 2016
Customizing DHCP Configuration on the Basis of Network Topology
draft-ietf-dhc-topo-conf-08
Abstract
DHCP servers have evolved over the years to provide significant
functionality beyond that which is described in the DHCP base
specifications. One aspect of this functionality is support for
context-specific configuration information. This memo describes some
such features and explains their operation.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on November 7, 2016.
Copyright Notice
Copyright (c) 2016 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
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Identifying Client's Location by DHCP Servers . . . . . . . . 3
3.1. DHCPv4 Specific Behavior . . . . . . . . . . . . . . . . 7
3.2. DHCPv6 Specific Behavior . . . . . . . . . . . . . . . . 7
4. Simple Subnetted Network . . . . . . . . . . . . . . . . . . 9
5. Relay Agent Running on a Host . . . . . . . . . . . . . . . . 11
6. Cascaded Relays . . . . . . . . . . . . . . . . . . . . . . . 11
7. Regional Configuration Example . . . . . . . . . . . . . . . 12
8. Multiple subnets on the same link . . . . . . . . . . . . . . 14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The DHCPv4 [RFC2131] and DHCPv6 [RFC3315] protocol specifications
describe how addresses can be allocated to clients based on network
topology information provided by the DHCP relay infrastructure.
Address allocation decisions are integral to the allocation of
addresses and prefixes in DHCP.
The DHCP protocol also describes mechanisms for provisioning devices
with additional configuration information; for example, DNS [RFC1034]
server addresses, default DNS search domains, and similar
information.
Although it was the intent of the authors of these specifications
that DHCP servers would provision devices with configuration
information appropriate to each device's location on the network,
this practice was never documented, much less described in detail.
Existing DHCP server implementations do in fact provide such
capabilities; the goal of this document is to describe those
capabilities for the benefit both of operators and of protocol
designers who may wish to use DHCP as a means for configuring their
own services, but may not be aware of the capabilities provided by
most modern DHCP servers.
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2. Terminology
o CPE device: Customer Premise Equipment device. Typically a router
belonging to the customer that connects directly to the provider
link.
o DHCP, DHCPv4, and DHCPv6. DHCP refers to the Dynamic Host
Configuration Protocol in general and applies to both DHCPv4 and
DHCPv6. The terms DHCPv4 and DHCPv6 are used in contexts where it
is necessary to avoid ambiguity and explain differences.
o PE router: Provider Edge router. The provider router closest to
the customer.
o Routable IP address: an IP address with a scope of use wider than
the local link.
o Shared subnet: a case where two or more subnets of the same
protocol family are available on the same link. 'Shared subnet'
terminology is typically used in Unix environments. It is
typically called 'multinet' in Windows environment. The
administrative configuration inside a Microsoft DHCP server is
called 'DHCP Superscope'.
3. Identifying Client's Location by DHCP Servers
Figure 1 illustrates a small hierarchy of network links with Link D
serving as a backbone to which the DHCP server is attached.
Figure 2 illustrates a more complex case. Although some of its
aspects are unlikely to be seen in actual production networks, they
are beneficial for explaining finer aspects of the DHCP protocols.
Note that some nodes act as routers (which forward all IPv6 traffic)
and some are relay agents (i.e. run DHCPv6 specific software that
forwards only DHCPv6 traffic).
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Link A Link B
|===+===========| |===========+======|
| |
| |
+---+---+ +---+---+
| relay | | relay |
| A | | B |
+---+---+ +---+---+
| |
| Link C |
|===+==========+=================+======|
|
|
+----+---+ +--------+
| router | | DHCP |
| A | | Server |
+----+---+ +----+---+
| |
| |
| Link D |
|==============+=================+======|
|
|
+----+---+
| router |
| B |
+----+---+
|
|
|===+==========+=================+======|
| Link E |
| |
+---+---+ +---+---+
| relay | | relay |
| C | | D |
+---+---+ +---+---+
| |
| |
|===+===========| |===========+======|
Link F Link G
Figure 1: A simple network with a small hierarchy of links
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Link A Link B Link H
|===+==========| |=========+======| |======+======|
| | |
| | |
+---+---+ +---+---+ +---+---+
| relay | | relay | | relay |
| A | | B | | G |
+---+---+ +---+---+ +---+---+
| | |
| Link C | | Link J
|===+==========+==============+======| |======+======|
| |
| |
+----+---+ +--------+ +---+---+
| router | | DHCP | | relay |
| A | | Server | | F |
+----+---+ +----+---+ +---+---+
| | |
| | |
| Link D | |
|==============+=========+=======+=============+======|
| |
| |
+----+---+ +---+---+
| router | | relay |
| B | | E |
+----+---+ +---+---+
| |
| |
|===+==========+=========+=======+======|
| Link E |
| |
+---+---+ +---+---+
| relay | | relay |
| C | | D |
+---+---+ +---+---+
| |
| |
|===+===========| |===========+======|
Link F Link G
Figure 2: Complex network
Those diagrams allow us to represent a variety of different network
configurations and illustrate how existing DHCP servers can provide
configuration information customized to the particular location from
which a client is making its request.
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It is important to understand the background of how DHCP works when
considering those diagrams. It is assumed that the DHCP clients may
not have routable IP addresses when they are attempting to obtain
configuration information.
The reason for making this assumption is that one of the functions of
DHCP is to bootstrap the DHCP client's IP address configuration; if
the client does not yet have an IP address configured, it cannot
route packets to an off-link DHCP server, therefore some kind of
relay mechanism is required.
The details of how packet delivery between clients and servers works
are different between DHCPv4 and DHCPv6, but the essence is the same:
whether or not the client actually has an IP configuration, it
generally communicates with the DHCP server by sending its requests
to a DHCP relay agent on the local link; this relay agent, which has
a routable IP address, then forwards the DHCP requests to the DHCP
server (directly or via other relays). In later stages of the
configuration when the client has acquired an address and certain
conditions are met, it is possible for the client to send packets
directly to the server, thus bypassing the relays. The conditions
for such behavior are different for DHCPv4 and DHCPv6 and are
discussed in sections Section 3.1 and Section 3.2.
To determine the client's point of attachment and link specific
configuration, the server typically uses the client facing IP address
of the relay agent. In some cases the server may use the routable IP
address of the client, if the client has the routable IP address
assigned to its interface and it is transmitted in the DHCP message.
The server is then able to determine the client's point of attachment
and select appropriate subnet- or link-specific configuration.
Sometimes it is useful for the relay agents to provide additional
information about the topology. A number of extensions have been
defined for this purpose. The specifics are different, but the core
principle remains the same: the relay agent knows exactly where the
original request came from, so it provides an identifier that will
help the server to choose appropriate address pool and configuration
parameters. Examples of such options are mentioned in the following
sections.
Finally, clients may be connected to the same link as the server, so
no relay agents are required. In such cases, the DHCPv4 server
typically uses the IPv4 address assigned to the network interface
over which the transmission was received to select an appropriate
subnet. This is more complicated for DHCPv6, as the DHCPv6 server is
not required to have any globally unique addresses. In such cases,
additional configuration information may need to be required. Some
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servers allow indicating that a given subnet is directly reachable
over a specific local network interface.
3.1. DHCPv4 Specific Behavior
In some cases in DHCPv4, when a DHCPv4 client has a routable IPv4
address, the message is unicast to the DHCPv4 server rather than
going through a relay agent. Examples of such transmissions are
renewal (DHCPREQUEST) and address release (DHCPRELEASE).
The relay agent that receives client's message sets giaddr field to
the address of the network interface the message was received on.
The relay agent may insert a relay agent option [RFC3046].
There are several options defined that are useful for subnet
selection in DHCPv4. [RFC3527] defines the Link Selection sub-option
that is inserted by a relay agent. This option is particularly
useful when the relay agent needs to specify the subnet/link on which
a DHCPv4 client resides, which is different from an IP address that
can be used to communicate with the relay agent. The Virtual Subnet
Selection sub-option, specified in [RFC6607], can also be added by a
relay agent to specify information in a VPN environment. In certain
cases, it is useful for the client itself to specify the Virtual
Subnet Selection option, e.g. when there are no relay agents involved
during the VPN set up process.
Another option that may influence the subnet selection is the IPv4
Subnet Selection Option, defined in [RFC3011], which allows the
client to explicitly request allocation from a given subnet.
3.2. DHCPv6 Specific Behavior
In DHCPv6 unicast communication is possible in case where the server
is configured with a Server Unicast option (see Section 22.12 in
[RFC3315]) and clients are able to take advantage of it. In such
cases, once a client is assigned a, presumably global, address, it is
able to contact the server directly, bypassing any relays. It should
be noted that such a mode is completely controllable by
administrators in DHCPv6. (They may simply choose to not configure
server unicast option, thus forcing clients to send their messages
always via relay agents in every case).
In the DHCPv6 protocol, there are two core mechanisms defined in
[RFC3315] that allow a server to distinguish which link the relay
agent is connected to. The first mechanism is the link-address field
in the Relay-forward and Relay-reply messages. Somewhat contrary to
its name, relay agents insert in the link-address field an address
that is typically global and can be used to uniquely identify the
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link on which the client is located. In normal circumstances this is
the solution that is easiest to maintain, as existing address
assignments can be used and no additional administrative actions
(like assigning dedicated identifiers for each relay agent, making
sure they are unique and maintaining a list of such identifiers) are
needed. It requires, however, for the relay agent to have an address
with a scope larger than link-local configured on its client-facing
interface.
The second mechanism uses Interface-Id option (see Section 22.18 of
[RFC3315]) inserted by the relay agent, which identifies the link
that the client is connected to. This mechanism may be used when the
relay agent does not have a globally unique address or ULA [RFC4193]
configured on its client-facing interface, thus making the first
mechanism not feasible. If the interface-id is unique within an
administrative domain, the interface-id value may be used to select
the appropriate subnet. As there is no guarantee for the uniqueness
([RFC3315] only mandates the interface-id to be unique within a
single relay agent context), it is up to the administrator to check
whether the relay agents deployed use unique interface-id values. If
the interface-id values are not unique, the Interface-id option
cannot be used to determine the client's point of attachment.
It should be noted that Relay-forward and Relay-reply messages are
exchanged between relays and servers only. Clients are never exposed
to those messages. Also, servers never receive Relay-reply messages.
Relay agents must be able to process both Relay-forward (sending
already relayed message further towards the server, when there is
more than one relay agent in a chain) and Relay-reply (when sending
back the response towards the client, when there is more than one
relay agent in a chain).
For completeness, we also mention an uncommon, but valid case, where
relay agents use a link-local address in the link-address field in
relayed Relay-forward messages. This may happen if the relay agent
doesn't have any address with a larger scope on the interface
connected to that specific link. Even though link-local addresses
cannot be automatically used to associate relay agent with a given
link, with additional configuration information the server may still
be able to select the proper link. That requires the DHCP server
software to be able to specify relay agent link-address associated
with each link or a feature similar to 'shared subnets' (see
Section 8). Both may or may not be supported by the server software.
Network administrator has to manually configure additional
information that a given subnet uses a relay agent with link-address
X. Alternatively, if the relay agent uses link address X and relays
messages from a subnet A, an administrator can configure that subnet
A is a shared subnet with a very small X/128 subnet. That is not a
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recommended configuration, but in cases where it is impossible for
relay agents to get an address from the subnet they are relaying
from, it may be a viable solution.
DHCPv6 also has support for more finely grained link identification,
using Lightweight DHCPv6 Relay Agents [RFC6221] (LDRA). In this
case, the link-address field is set to unspecified address (::), but
the DHCPv6 server also receives an Interface-Id option from the relay
agent that can be used to more precisely identify the client's
location on the network. It is possible to mix LDRA and regular
relay agents in the same network. See Sections 7.2 and 7.3 in
[RFC6221] for detailed examples.
What this means in practice is that the DHCP server in all cases has
sufficient information to pinpoint, at the very least, the layer 3
link to which the client is connected, and in some cases which layer
2 link the client is connected to, when the layer 3 link is
aggregated out of multiple layer 2 links.
In all cases, then, the DHCPv6 server will have a link-identifying IP
address, and in some cases it may also have a link-specific
identifier (e.g. Interface-Id Option or Link Address Option defined
in Section 5 of [RFC6977]). It should be noted that the link-
specific identifier is unique only within the scope of the link-
identifying IP address. For example, link-specific identifier of
"eth0" assigned to a relay agent using IPv6 address 2001:db8::1 is
distinct from a "eth0" identifier used by a different relay agent
with address 2001:db8::2.
It is also possible for link-specific identifiers to be nested, so
that the actual identifier that identifies the link is an aggregate
of two or more link-specific identifiers sent by a set of LDRAs in a
chain; in general this functions exactly as if a single identifier
were received from a single LDRA, so we do not treat it specially in
the discussion below, but sites that use chained LDRA configurations
will need to be aware of this when configuring their DHCPv6 servers.
The Virtual Subnet Selection Options, present in DHCPv4, are also
defined for DHCPv6. The use case is the same as in DHCPv4: the relay
agent inserts VSS options that can help the server to select the
appropriate subnet with its address pool and associated configuration
options. See [RFC6607] for details.
4. Simple Subnetted Network
Consider Figure 1 in the context of a simple subnetted network. In
this network, there are four leaf subnets: links A, B, F and G, on
which DHCP clients will be configured. Relays A, B, C and D in this
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example are represented in the diagram as IP routers with an embedded
relay function, because this is a very typical configuration, but the
relay function can also be provided in a separate node on each link.
In a simple network like this, there may be no need for link-specific
configuration in DHCPv6, since local routing information is delivered
through router advertisements. However, in IPv4, it is very typical
to configure the default route using DHCP; in this case, the default
route will be different on each link. In order to accomplish this,
the DHCP server will need link-specific configuration for the default
route.
To illustrate, we will use an example from a hypothetical DHCP server
that uses a simple JSON notation [RFC7159] for configuration.
Although we know of no DHCP server that uses this specific syntax,
most modern DHCP server provides similar functionality.
{
"prefixes": {
"192.0.2.0/26": {
"options": {
"routers": ["192.0.2.1"]
},
"on-link": ["A"]
},
"192.0.2.64/26": {
"options": {
"routers": ["192.0.2.65"]
},
"on-link": ["B"]
},
"192.0.2.128/26": {
"options": {
"routers": ["192.0.2.129"]
},
"on-link": ["F"]
},
"192.0.2.192/26": {
"options": {
"routers": ["192.0.2.193"]
},
"on-link": ["G"]
}
}
}
Figure 3: Configuration Example
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In Figure 3, we see a configuration example for this scenario: a set
of prefixes, each of which has a set of options and a list of links
for which it is on-link. We have defined one option for each prefix:
a routers option. This option contains a list of values; each list
only has one value, and that value is the IP address of the router
specific to the prefix.
When the DHCP server receives a request, it searches the list of
prefixes for one that encloses the link-identifying IP address
provided by the client or relay agent. The DHCP server then examines
the options list associated with that prefix and returns those
options to the client.
So for example a client connected to link A in the example would have
a link-identifying IP address within the 192.0.2.0/26 prefix, so the
DHCP server would match it to that prefix. Based on the
configuration, the DHCP server would then return a routers option
containing a single IP address: 192.0.2.1. A client on link F would
have a link-identifying address in the 192.0.2.128/26 prefix, and
would receive a routers option containing the IP address 192.0.2.129.
5. Relay Agent Running on a Host
A relay agent is DHCP software that may be run on any IP node.
Although it is typically run on a router, this is by no means
required by the DHCP protocol. The relay agent is simply a service
that operates on a link, receiving link-local multicasts (IPv6) or
broadcasts (IPv4) and relaying them, using IP routing, to a DHCP
server. As long as the relay has an IP address on the link, and a
default route or more specific route through which it can reach a
DHCP server, it need not be a router, or even have multiple
interfaces.
A relay agent can be run on a host connected to two links. That case
is presented in Figure 2. There is router B that is connected to
links D and E. At the same time there is also a host that is
connected to the same links. The relay agent software is running on
that host. That is uncommon, but a valid configuration.
6. Cascaded Relays
Let's observe another case, shown in Figure 2. Note that in this
configuration, the clients connected to link G will send their
requests to relay D which will forward its packets directly to the
DHCP server. That is typical, but not the only possible
configuration. It is possible to configure relay agent D to forward
client messages to relay E which in turn will send it to the DHCP
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server. This configuration is sometimes referred to as cascaded
relay agents.
Note that the relaying mechanism works differently in DHCPv4 and in
DHCPv6. In DHCPv4 only the first relay is able to set the giaddr
field in the DHCPv4 packet. Any following relays that receive that
packet will not change it as the server needs giaddr information from
the first relay (i.e. the closest to the client). The server will
send the response back to the giaddr address, which is the address of
the first relay agent that saw the client's message. That means that
the client messages travel on a different path than the server's
responses. A message from client connected to link G will travel via
relay D, relay E and to the server. A response message will be sent
from the server to relay D via router B, and relay D will send it to
the client on link G.
Relaying in DHCPv6 is more structured. Each relay agent encapsulates
a packet that is destined to the server and sends it towards the
server. Depending on the configuration, that can be a server's
unicast address, a multicast address or next relay agent address.
The next relay repeats the encapsulation process. Although the
resulting packet is more complex (may have up to 32 levels of
encapsulation if the packet traveled through 32 relays), every relay
may insert its own options and it is clear which relay agent inserted
which option.
7. Regional Configuration Example
In the Figure 2 example, link C is a regional backbone for an ISP.
Link E is also a regional backbone for that ISP. Relays A, B, C and
D are PE routers, and Links A, B, F and G are actually link
aggregators with individual layer 2 circuits to each customer--for
example, the relays might be DSLAMs or cable head-end systems. At
each customer site we assume there is a single CPE device attached to
the link.
We further assume that links A, B, F and G are each addressed by a
single prefix, although it would be equally valid for each CPE device
to be numbered on a separate prefix.
In a real-world deployment, there would likely be many more than two
PE routers connected to each regional backbone; we have kept the
number small for simplicity.
In the example presented in Figure 4, the goal is to configure all
the devices within a region with server addresses local to that
region, so that service traffic does not have to be routed between
regions unnecessarily.
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{
"prefixes": {
"2001:db8::/40": {
"on-link": ["A"]
},
"2001:db8:100::/40": {
"on-link": ["B"]
},
"2001:db8:200::/40": {
"on-link": ["F"]
},
"2001:db8:300::/40": {
"on-link": ["G"]
}
},
"links": {
"A": {"region": "omashu"},
"B": {"region": "omashu"},
"F": {"region": "gaoling"},
"G": {"region": "gaoling"}
},
"regions": {
"omashu": {
"options": {
"sip-servers": ["sip.omashu.example.org"],
"dns-servers": ["dns1.omashu.example.org",
"dns2.omashu.example.org"]
}
},
"gaoling": {
"options": {
"sip-servers": ["sip.gaoling.example.org"],
"dns-servers": ["dns1.gaoling.example.org",
"dns2.gaoling.example.org"]
}
}
}
}
Figure 4: Regional Configuration Example
In this example, when a request comes in to the DHCPv6 server with a
link-identifying IP address in the 2001:db8::/40 prefix, it is
identified as being on link A. The DHCPv6 server then looks on the
list of links to see what region the client is in. Link A is
identified as being in omashu. The DHCPv6 server then looks up
omashu in the set of regions, and discovers a list of region-specific
options.
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The DHCPv6 server then resolves the domain names listed in the
options and sends a sip-server option containing the IP addresses
that the resolver returned for sip.omashu.example.org, and a dns-
server option containing the IP addresses returned by the resolver
for dns1.omashu.example.org and dns2.omashu.example.org. Depending
on the server capability and configuration, it may cache resolved
responses for specific period of time, repeat queries every time or
even keep the response until reconfiguration or shutdown. For more
detailed discussion see Section 7 of [RFC7227].
Similarly, if the DHCPv6 server receives a request from a DHCPv6
client where the link-identifying IP address is contained by the
prefix 2001:db8:300::/40, then the DHCPv6 server identifies the
client as being connected to link G. The DHCPv6 server then
identifies link G as being in the gaoling region, and returns the
sip-servers and dns-servers options specific to that region.
As with the previous example, the exact configuration syntax and
structure shown above does not precisely match what existing DHCPv6
servers do, but the behavior illustrated in this example can be
accomplished with most existing modern DHCPv6 servers.
8. Multiple subnets on the same link
There are scenarios where there is more than one subnet from the same
protocol family (i.e. two or more IPv4 subnets or two or more IPv6
subnets) configured on the same link. Such a configuration is often
referred to as 'shared subnets' in Unix environments or 'multinet' in
Microsoft terminology.
The most frequently mentioned use case is a network renumbering where
some services are migrated to the new addressing scheme, but some
aren't yet.
Second example is expanding the allocation space. In DHCPv4 and for
DHCPv6 Prefix Delegation, there could be cases where multiple subnets
are needed, because a single subnet may be too small to accommodate
the client population.
The third use case covers allocating addresses (or delegation
prefixes) that are not the same as topological information. For
example, the link-address is on prefix X and the addresses to be
assigned are on prefix Y. This could be based on differentiating
information (i.e., whether device is CPE or CM in DOCSIS) or just
because the link-address/giaddr is different from the actual
allocation space.
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The fourth use case is a cable network, where cable modems and the
devices connected behind them are connected to the same layer 2 link.
However, operators want the cable modems and user devices to get
addresses from distinct address spaces, so users couldn't easily
access their modems management interfaces.
To support such a configuration, additional differentiating
information is required. Many DHCP server implementations offer a
feature that is typically called client classification. The server
segregates incoming packets into one or more classes based on certain
packet characteristics, e.g. presence or value of certain options or
even a match between existing options. Servers require additional
information to handle such configuration, as they cannot use the
topographical property of the relay addresses alone to properly
choose a subnet. Exact details of such operation is not part of the
DHCPv4 or DHCPv6 protocols and is implementation dependent.
9. Acknowledgments
Thanks to Dave Thaler for suggesting that even though "everybody
knows" how DHCP servers are deployed in the real world, it might be
worthwhile to have an IETF document that explains what everybody
knows, because in reality not everybody is an expert in how DHCP
servers are administered. Thanks to Andre Kostur, Carsten Strotmann,
Simon Perreault, Jinmei Tatuya, Suresh Krishnan, Qi Sun, Jean-
Francois Tremblay, Marcin Siodelski and Bernie Volz for their
reviews, comments and feedback.
10. Security Considerations
This document explains existing practice with respect to the use of
Dynamic Host Configuration Protocol [RFC2131] and Dynamic Host
Configuration Protocol Version 6 [RFC3315]. The security
considerations for these protocols are described in their
specifications and in related documents that extend these protocols.
This document introduces no new functionality, and hence no new
security considerations.
11. IANA Considerations
The IANA is hereby absolved of any requirement to take any action in
relation to this document.
12. References
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12.1. Normative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
12.2. Informative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC3011] Waters, G., "The IPv4 Subnet Selection Option for DHCP",
RFC 3011, DOI 10.17487/RFC3011, November 2000,
<http://www.rfc-editor.org/info/rfc3011>.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, DOI 10.17487/RFC3046, January 2001,
<http://www.rfc-editor.org/info/rfc3046>.
[RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy,
"Link Selection sub-option for the Relay Agent Information
Option for DHCPv4", RFC 3527, DOI 10.17487/RFC3527, April
2003, <http://www.rfc-editor.org/info/rfc3527>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<http://www.rfc-editor.org/info/rfc4193>.
[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,
<http://www.rfc-editor.org/info/rfc6221>.
[RFC6607] Kinnear, K., Johnson, R., and M. Stapp, "Virtual Subnet
Selection Options for DHCPv4 and DHCPv6", RFC 6607,
DOI 10.17487/RFC6607, April 2012,
<http://www.rfc-editor.org/info/rfc6607>.
[RFC6977] Boucadair, M. and X. Pougnard, "Triggering DHCPv6
Reconfiguration from Relay Agents", RFC 6977,
DOI 10.17487/RFC6977, July 2013,
<http://www.rfc-editor.org/info/rfc6977>.
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[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<http://www.rfc-editor.org/info/rfc7227>.
Authors' Addresses
Ted Lemon
Nominum, Inc.
2000 Seaport Blvd
Redwood City, CA 94063
USA
Phone: +1-650-381-6000
Email: Ted.Lemon@nominum.com
Tomek Mrugalski
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
USA
Phone: +1 650 423 1345
Email: tomasz.mrugalski@gmail.com
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