Zero Configuration Networking A. Williams
Internet-Draft Motorola
Expires: March 20, 2003 September 19, 2002
Requirements for Automatic Configuration of IP Hosts
draft-ietf-zeroconf-reqts-12.txt
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Many common TCP/IP protocols such as DHCP [RFC2131], DNS
[RFC1034][RFC1035], MADCAP [RFC2730], and LDAP [RFC2251] must be
configured and maintained by an administrative staff. This is
unacceptable for emerging networks such as home networks, automobile
networks, airplane networks, or ad hoc networks at conferences,
emergency relief stations, and many others. Such networks may be
nothing more than two isolated laptop PCs connected via a wireless
LAN. For all these networks, an administrative staff will not exist
and the users of these networks neither have the time nor inclination
to learn network administration skills. Instead, these networks need
protocols that require zero user configuration and administration.
This document is part of an effort to define such zero configuration
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(zeroconf) protocols.
Before embarking on defining zeroconf protocols, protocol
requirements are needed. This document states the zeroconf protocol
requirements for four protocol areas; they are: IP interface
configuration, translation between host name and IP address, IP
multicast address allocation, and service discovery. This document
does not define specific protocols, just requirements. The
requirements for these four areas result from examining everyday use
or scenarios of these protocols.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Key Words . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Reading This Document . . . . . . . . . . . . . . . . . . 4
1.3 Zeroconf Coexistence . . . . . . . . . . . . . . . . . . . 5
1.4 Scalability . . . . . . . . . . . . . . . . . . . . . . . 5
1.5 Routable Protocol Requirement . . . . . . . . . . . . . . 5
1.6 Maintaining Consistent Network State . . . . . . . . . . . 6
2. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Addition and Removal of Devices . . . . . . . . . . . . . 6
2.2 Network Coalescing and Partitioning . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 IP Interface Configuration . . . . . . . . . . . . . . . . 8
3.1.1 IPv6 Considerations . . . . . . . . . . . . . . . . . . . 10
3.2 Translation between Host name and IP Address . . . . . . . 10
3.2.1 IPv6 Considerations . . . . . . . . . . . . . . . . . . . 11
3.2.2 Relationship to the DNS . . . . . . . . . . . . . . . . . 11
3.2.2.1 Close coupling . . . . . . . . . . . . . . . . . . . . . . 12
3.2.2.2 Completely orthogonal . . . . . . . . . . . . . . . . . . 12
3.2.2.3 API compatible . . . . . . . . . . . . . . . . . . . . . . 12
3.3 IP Multicast Address Allocation Scenarios . . . . . . . . 13
3.3.1 Scope Enumeration . . . . . . . . . . . . . . . . . . . . 14
3.3.2 Address Allocation . . . . . . . . . . . . . . . . . . . . 14
3.3.3 Multiple Sources . . . . . . . . . . . . . . . . . . . . . 15
3.3.4 IPv6 Considerations . . . . . . . . . . . . . . . . . . . 15
3.4 Service Discovery Scenarios . . . . . . . . . . . . . . . 15
3.4.1 Printer Service . . . . . . . . . . . . . . . . . . . . . 16
3.4.2 IPv6 Considerations . . . . . . . . . . . . . . . . . . . 16
4. Security Considerations . . . . . . . . . . . . . . . . . 16
4.1 The Basic in/out Security Policy . . . . . . . . . . . . . 17
4.2 Security Scenarios . . . . . . . . . . . . . . . . . . . . 18
4.2.1 Use on an isolated, secure network link . . . . . . . . . 18
4.2.2 Use on a shared (insecure) link . . . . . . . . . . . . . 18
4.2.3 Use in conjunction with configured protocols . . . . . . . 18
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 19
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 19
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Normative References . . . . . . . . . . . . . . . . . . . 19
Informative References . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . 21
Full Copyright Statement . . . . . . . . . . . . . . . . . 22
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1. Introduction
A zeroconf protocol is able to operate correctly in the absence of
configured information from either a user or infrastructure services
such as conventional DHCP [RFC2131] or DNS [RFC1034][RFC1035]
servers. Zeroconf protocols may use configured information, when it
is available, but do not rely on it being present. For example, the
use of MAC addresses (i.e. layer two addresses) as parameters in
zeroconf protocols is generally acceptable because they are globally
unique and readily available on most devices of interest.
The benefits of zeroconf protocols over existing configured protocols
are an increase in the ease-of-use for end-users and a simplification
of the infrastructure necessary to operate protocols.
This document discusses requirements for zeroconf protocols in four
areas:
o IP interface configuration
o Translation between host name and IP address
o IP multicast address allocation
o Service discovery
Security considerations are also discussed.
1.1 Key Words
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].
1.2 Reading This Document
Introduction, Scenarios, Requirements, and Security Considerations
are the major sections of this document.
The Scenarios & Requirements sections walk through protocol scenarios
and then lists the requirements of the protocol needed to accomplish
the scenario.
The Security Consideration section lists security issues with
zeroconf protocols.
Requirements dispersed throughout this document begin with the text
"Requirements:" or "Requirement:" on a single line, which is followed
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by a bulleted list of requirements.
1.3 Zeroconf Coexistence
It is not necessary to simultaneously use zeroconf protocols in all
four areas (i.e. IP interface configuration, translation between
host name and IP address, IP multicast address allocation, service
discovery). For example, it may make sense on some networks to
provide a DHCP server for configured IP interface configuration, but
perform translation between host name and IP address using a zeroconf
protocol.
Given that zeroconf protocols may be deployed on existing configured
networks, care must be taken in their design to ensure minimum
disruption to existing networks and applications. Particular
consideration should be given to the security implications of
deploying zeroconf protocols in conjunction with standard configured
network protocols.
Requirements:
o Zeroconf protocols MUST minimise their impact on existing
networks.
o Zeroconf protocols SHOULD minimise their impact on existing
applications.
o Zeroconf protocols MUST NOT be any less secure than related
current IETF-Standard protocols.
1.4 Scalability
The primary reasons to deploy Zeroconf protocols are simplicity and
ease-of-use. Scalability is important but it is a secondary goal.
Thus, scalability should not detract from the primary goals of
simplicity and ease-of-use.
1.5 Routable Protocol Requirement
Zeroconf protocols are not inherently limited to a single IP subnet.
If a protocol is intended to span multiple IP subnets it MUST NOT use
broadcasts or link-local addressing.
Requirement:
o Protocols intended to span multiple IP subnets MUST NOT use
broadcasts or link-local addressing.
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1.6 Maintaining Consistent Network State
Many networks undergo change during their lifetime. For example,
hosts may be added and removed, network segments may be re-arranged,
and devices may change names or run different services. In a
configured network an administrator ensures that protocol parameters
are updated to reflect these changes and is responsible for ensuring
network consistency.
In contrast, zeroconf protocols must adapt to changing network
conditions. Zeroconf protocols must be able to resolve conflicts and
return the network to a consistent state after changes in network
topology or other events.
Requirement:
o Zeroconf protocols MUST restore the network to a consistent state
in a timely fashion when changes in network topology or other
events occur.
This is a general requirement applicable to all zeroconf protocols.
It should be kept in mind when considering the scenarios in Section 2
and will be applied to derive requirements for each zeroconf protocol
area considered in Section 3.
2. Scenarios
The scenarios described in the next few sections highlight the
general characteristics of the zeroconf protocol environment. Each
zeroconf protocol needs to deal with the following aspects of the
zeroconf environment.
2.1 Addition and Removal of Devices
Zeroconf protocols are expected to be useful in networks where hosts
come and go. Hosts using zeroconf protocols must not assume that
network resources assigned to them (e.g. address assignments, names,
etc) will be appropriate for networks they subsequently join. In
addition, network resources allocated to a host should be reclaimed
once it leaves the network.
Requirements:
o Zeroconf protocols MUST support mechanisms to probe whether a
network resource is currently in use.
o Hosts using zeroconf protocols MUST validate allocated network
resources when moving to a new network or powering up.
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o Zeroconf protocols MUST support timely reclamation of any network
resources they allocate.
Implication:
o The information needed to allocate network resources must arrive
in the network along with the host.
2.2 Network Coalescing and Partitioning
Inevitably, two or more operational networks using zeroconf protocols
will be connected together, creating a single merged network. Prior
to the merge, each zeroconf network has independently allocated
resources (e.g. addresses, names, etc). After merging, two hosts in
the merged network may end up using the same network resource, thus
potentially creating conflicts.
In general a network merge "event" cannot be detected. For example,
the installation of a layer-2 bridge between two zeroconf networks
does not result in network interfaces going up and down on the hosts,
which would be an indication that they should re-validate or
reconfigure the network resources they are using.
Implication:
o It is not sufficient to rely on hosts detecting conflicts during
power on or movement from network to network. Rather, detection
and resolution of network conflicts is an ongoing part of zeroconf
protocol operation.
Requirement:
o Zeroconf protocols MUST resolve network resource conflicts in a
timely manner and on an ongoing basis.
Zeroconf protocols that detect and resolve network resource conflicts
on an ongoing basis will benefit from increased robustness in the
face of poor implementation, and varying network conditions.
A zeroconf network may also be split into two or more smaller
independent networks. The requirement from Section 2.1 that network
resources be reclaimed in a timely fashion also applies in this case.
Since network merging increases the potential for network conflicts,
it may be prudent to ensure that network resources associated with
hosts are not immediately re-claimed for re-use. Any network which
periodically joins and partitions with another zeroconf network will
benefit from this behaviour. An example is an IP network in a car
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joining with the home network whilst the car is parked in the garage
and partitioning when it is driven away.
Requirement:
o Zeroconf protocols SHOULD NOT immediately reuse network resources
as soon as they become available.
o Network resources SHOULD be allocated in a way that minimises the
probability that two hosts will be allocated the same resource.
o Network resources SHOULD be allocated in a way that increases the
chances of a particular host being allocated the same resource
should it leave and rejoin the network.
3. Requirements
This section contains a subsection for each of the four protocol
areas. Within each subsection, terms and assumptions are followed by
specific zeroconf protocol requirements in that area. Each
subsection ends with IPv6 considerations.
3.1 IP Interface Configuration
In this document, IP interface configuration always includes the
configuration of an IP address and netmask; it may include some
routing information (such as default route). IP interface
configuration is needed before almost any IP communication can take
place.
Terms:
IP subnet: A single logical IP network that may span multiple link
layer networks. All IP hosts on the IP subnet communicate without
any layer 3 forwarding device (e.g. router).
internetwork: Multiple IP subnets connected by routers.
network: a context sensitive term that may apply to one or more of
the terms: a link layer network, an IP subnet, or an internetwork.
bridge: a networking device that connects two link layer networks by
using only link-layer protocols (e.g. Ethernet).
IP interface configuration must take place before an IP packet can be
sent from one host to another. This section requires that sufficient
information be provided by a zeroconf interface configuration
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protocol to allow IP packets to be sent to a unicast destination IP
address on the same subnet as the sender, and on a different subnet
to the sender.
Requirements: A zeroconf IP interface configuration protocol
o MUST configure an appropriate netmask.
o MUST allocate unique IP addresses within an IP subnet.
o MUST allow configuration of zero or more gateways (for the
internetwork scenario).
o MUST have unique IP subnets within an internetwork (This is only
for the case when there is one or more router attached in the
network where autoconfigured hosts. How routers obtain their
configuration is beyond of the scope of this document.)
The following requirements are derived from applying Section 2.1 and
Section 2.2 to IP interface configuration.
Requirements: A zeroconf IP interface configuration protocol
o MUST be capable of discovering whether an IP address is currently
in use.
o Hosts using a zeroconf interface configuration protocol MUST
validate allocated IP addresses when moving to a new network or
powering up.
o MUST support timely reclamation of allocated IP addresses.
o MUST resolve IP address conflicts in a timely manner and on an
ongoing basis.
o SHOULD NOT immediately reuse IP addresses as soon as they become
available.
o IP addresses SHOULD be allocated in a way that minimises the
probability that two hosts will be allocated the same address.
o IP addresses SHOULD be allocated in a way that increases the
chances of a particular host being allocated the same address
should it leave and rejoin the network.
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3.1.1 IPv6 Considerations
IPv6 provides a mechanism that allows a host to generate a link-local
IP address Autoconfiguration[RFC2462]. Thus a zeroconf IP interface
configuration solution for generating link-local addresses already
exists for hosts using IPv6.
3.2 Translation between Host name and IP Address
A zeroconf name resolution protocol allows users to refer to their
devices by name rather than IP address. Host names are more user
friendly than IP addresses and host names have a greater chance of
remaining unchanged over time. A zeroconf device connected to
different networks is quite likely to use different IP addresses,
however a host name may stay the same. For applications like web
browsers which store bookmarks and histories, use of names rather
than IP addresses is beneficial.
In a zeroconf network, the information required to construct a host
name must enter the network with the device. It is expected that
users will configure names into devices, or that devices will come
with a pre-configured name. Devices may also construct a name from a
MAC address or serial number. How this is to be achieved is outside
the scope of this document.
Terms:
host name: A textual name that allows a user to refer to a host by
name rather than IP address.
Requirements:
o A zeroconf name resolution protocol MUST allow host names to be
mapped into IP addresses.
o A zeroconf name resolution protocol SHOULD allow IP addresses to
be mapped back to names.
o Because hosts can connect and disconnect from a network at any
time, the failure to resolve a name at some time MUST NOT be taken
as an indication that the name will remain invalid for any length
of time.
o A zeroconf name resolution protocol SHOULD support resolution of
names on multiple IP subnets connected by a router.
The following requirements are derived from applying Section 2.1 and
Section 2.2 to zeroconf name resolution.
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Requirements:
o A zeroconf name resolution protocol MUST support mechanisms to
probe whether a host name is currently in use.
o A host moving to a new network or powering up MUST ensure that all
names it will respond to do not conflict with names already in
use.
o Zeroconf name resolution protocols MUST allow timely re-use of
hostnames.
o Zeroconf name resolution protocols MUST resolve host name
conflicts in a timely manner and on an ongoing basis.
o Conflict detection procedures (such as probing for the existence
of a desired host name) MUST NOT prevent valid hostnames from
being resolved.
o Zeroconf name resolution protocols SHOULD NOT immediately reuse
host names as soon as they become available.
o Host names SHOULD be chosen in a way that minimises the
probability that two hosts will use the same name. Note that this
is out of scope of the name resolution protocol itself.
3.2.1 IPv6 Considerations
Protocols to perform translation between host name and IP address
have no known zeroconf-related differences for IPv4 and IPv6.
3.2.2 Relationship to the DNS
Zeroconf name resolution protocols cannot be directly equated with
the DNS even though they may have a number of similarities. For
example, the DNS protocols as deployed today rely on a server
infrastructure that may not be present in a zeroconf environment.
Host names used in zeroconf networks are inherently locally scoped
whereas DNS names are global and unique by design.
At the time of writing, consensus on how zeroconf name resolution
protocols should interact with the DNS has not been reached. The
next sections will attempt to capture the flavour of the different
approaches that have proposed.
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3.2.2.1 Close coupling
In this approach an application may look up a DNS name (e.g.
"www.someco.com") using an existing API and receive and answer from a
zeroconf name resolution protocol. The zeroconf name resolution
protocol makes use of existing on-the-wire DNS formats, resource
record definitions, and namespace. Some names may have a DNS suffix
that identifies them as being local in scope.
Issues yet to be resolved with this approach relate to security and
consistency. If the zeroconf name resolution involves multicasting
the request on a local network then the risk of spoofed responses to
global DNS names like "www.someco.com" is increased. If the
namespace is the same, then doing a zeroconf name lookup should
return results consistent with DNS lookup for the same name. What is
meant by this consistency is not agreed. Should the zeroconf lookup
only be used when the DNS lookup has failed? Should that lookup
reflect what would have been returned by the DNS? How should the
probing for uniqueness of a zeroconf name relate to updating of a DNS
record?
3.2.2.2 Completely orthogonal
Another approach is to ensure that the zeroconf namespace and the DNS
namespace are completely orthogonal. There is therefore no
possibility of any application using the DNS via existing APIs
behaving differently after a zeroconf name resolution protocol is
deployed. Applications would need to explicitly use a zeroconf name
lookup API in order to resolve names using a zeroconf lookup
protocol. Conversely, existing applications will derive no benefit
from zeroconf protocols unless they are re-written. Deployment of a
zeroconf name resolution protocol would necessitate application
upgrade.
3.2.2.3 API compatible
In this approach the zeroconf namespace is distinct from the DNS
namespace however zeroconf names may be resolved using an existing
API. A number of operating systems use generalised name service
interfaces that transparently allow a variety of name lookup
protocols to be used when resolving hostnames for applications. A
zeroconf name resolution protocol could be incorporated into such a
system in a straightforward manner as just one more namespace and
lookup protocol.
Again, there is increased risk of spoofed responses if the multicast
zeroconf name resolution protocol is used to resolve
"www.someco.com". One possible way of minimising the security risk
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is to ensure that locally scoped names are distinguishable from DNS
names, perhaps via a known reserved DNS suffix or by virtue of not
containing a dot. A multicast zeroconf resolution protocol could
then avoid making requests for names which look like global DNS
names. Alternatively, we could require that zeroconf name lookups
only be performed when the equivalent DNS lookup has failed.
3.3 IP Multicast Address Allocation Scenarios
IP Multicast is used to conserve bandwidth for multi-receiver bulk-
delivery applications, such as audio, video, or news.
IP Multicast is also used to perform a logical addressing function.
For example, when a host needs to communicate with local routers, it
can send packets to the all-routers multicast address without having
to know in advance the IP address(es) of the router(s).
IPv4 multicast addresses range from 224.0.0.0 to 239.255.255.255.
[RFC2365] defined multicast scopes are:
node-local (unspecified for IPv4)
link-local (224.0.0.0/24)
local (239.255.0.0/16)
site-local (unspecified for IPv4)
organizational-local (239.192.0.0/14)
global (224.0.1.0-238.255.255.255)
A relative assignment is an integer offset from the highest address
in the scope and represents a 32-bit address. For example, within
the local scope, 239.255.255.0/24 is reserved for relative
allocations.
Source-Specific Multicast addresses are 232.0.0.0 to 232.255.255.255
[I-D.ietf-ssm-arch].
Unicast-prefix-based IPv6 multicast addresses are defined, as well as
source-specific multicast addresses for IPv6[RFC3306].
Assumptions:
o The node-local and SSM addresses require no protocol or
interaction between multiple hosts, thus are not mentioned further
in this document.
o Global and organizational scoped addresses are meant for networks
of a greater scale than zeroconf protocols, thus are not mentioned
further in this document.
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o Only local, link-local and site-local scopes are considered
further in this document.
o If it is desirable to restrict multicast packets from entering and
leaving a multicast scope boundary, it is assumed that the router
at the boundary is a "boundary router" as described in [RFC2365].
Scenarios are scope enumeration, address allocation, and multiple
sources.
3.3.1 Scope Enumeration
Applications that leave the choice of scope up to the user require
the ability to enumerate what scopes the host is operating within.
In addition, services that are assigned relative addresses require
the ability to enumerate what scopes the host is within; only then
will a host be able to apply the relative address to a scope.
Requirements: Application support software used to autoconfigure
multicast addresses
o MUST list which of the scopes (local, link-local, or site-local)
are available for hosts.
o MUST list per-scope address ranges that may be allocated.
3.3.2 Address Allocation
IP multicast address allocation (local, link-local and site-local
scopes only) requires an application to be able to request the use of
a suitable multicast address. Coordination among applications must
occur to avoid conflicting allocations of the same address. This
coordination must span the entire scope respective to the address.
When an allocated address is no longer required, that address MUST
become available for use again.
Requirements: A zeroconf multicast address allocation protocol
o MUST select a multicast address.
o MUST prevent conflicting allocations of the same address.
o MUST allow the multicast address to become available after the
address is no longer in use.
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3.3.3 Multiple Sources
An intercom system inside a home is an example of a multiple source
IP multicast application. In this type of application, several
sources may be sending packets destined to the same IP multicast
address.
This multiple source example illustrates the problem that a
particular address may continue to be valid, even after the host that
initially allocated the address is no longer present; the zeroconf
multicast address allocation must correctly support this type of
operation. In other words, if a host allocates a multicast address,
then leaves the multicast group, some other host must defend the
address.
Requirements:
o A host other than the allocating host MUST be able to defend or
otherwise maintain the allocation of a multicast address.
3.3.4 IPv6 Considerations
To date, no range has been reserved for dynamic allocation of Link-
scoped addresses in IPv4. Hence, unless such a range is reserved,
dynamic allocation of link-scoped addresses applies only to IPv6.
3.4 Service Discovery Scenarios
Service discovery protocols allow users or software to discover and
select among available services. This removes the requirement that
the user or client software know a server's location in advance in
order for the client to communicate with the server.
Terms:
service: a particular logical function that may be invoked via some
network protocol, such as printing, storing a file on a remote
disk, or even perhaps requesting delivery of a pizza.
service characteristics: Characteristics provide a finer granularity
of description to differentiate services beyond just the service
type. For example if the service type is printer, the
characteristics may be color, pages printed per second, location,
etc.
service discovery protocol: A service discovery protocol enables
clients to discover servers (or peers to find other peers) of a
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particular service. A service discovery protocol is an
application layer protocol that relies on network and transport
protocol layers.
service protocol: A service protocol is used between the client and
the server after service discovery is complete.
The scenarios are the discovery of a simple printer service.
3.4.1 Printer Service
Network-enabled printers allow various network clients to submit
print jobs. A service discovery protocol MUST allow a printer
service to be discovered by devices needing to print. This requires
a service type as well as a service identifier to distinguish
instances of a single service type. Service discovery MUST be
independent from any particular printing protocol such as lpd, raw-
tcp, ipp.
Printers vary in their characteristics such as location, status, dots
per inch, etc. Discovering a service based on these characteristics
SHOULD be part of the service discovery protocol.
Service discovery MUST complete in a timely (10s of seconds) manner.
Requirements:
o MUST allow a service to be discovered.
o MUST discover via service identifier and/or service type.
o MUST discover services without use of a service-specific protocol.
o SHOULD discover via service characteristics.
o MUST complete in a timely (10s of seconds) manner.
3.4.2 IPv6 Considerations
Service discovery protocols have no zeroconf related differences for
IPv4 and IPv6.
4. Security Considerations
Zeroconf protocols are intended to operate in a local scope, in
networks containing one or more IP subnets, and potentially in
parallel with standard configured network protocols.
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Application protocols running on networks employing zeroconf
protocols will be subject to the same sets of security issues
identified for standard configured networks. Examples are: denial of
service due to the unauthenticated nature of IPv4 ARP and lack of
confidentiality unless IPSec-ESP, TLS, or similar is used. However,
networks employing zeroconf protocols do have different security
characteristics and the subsequent sections attempt to draw out some
of the implications.
Security schemes usually rely on some sort of configuration.
Security mechanisms for zeroconf network protocols should be designed
in keeping with the spirit of zeroconf, thus making it easy for the
user to exchange keys, set policy, etc. It is preferable that a
single security mechanism be employed that will allow simple
configuration of all the various security parameters that may be
required.
Generally speaking, security mechanisms in IETF protocols are
mandatory to implement. A particular implementation might permit a
network administrator to turn off a particular security mechanism
operationally. However, implementations should be "secure out of the
box" and have a safe default configuration.
Zeroconf protocols MUST NOT be any less secure than related current
IETF-Standard protocols. This consideration overrides the goal of
allowing systems to obtain configuration automatically. Security
threats to be considered include both active attacks (e.g. denial of
service) and passive attacks (e.g. eavesdropping). Protocols that
require confidentiality and/or integrity should include integrated
confidentiality and/or integrity mechanisms or should specify the use
of existing standards-track security mechanisms (e.g. TLS [RFC2246],
ESP [RFC1827], AH [RFC2402]) appropriate to the threat.
4.1 The Basic in/out Security Policy
The claim/collide approach to resource allocation is attractive in
the zeroconf environment. To operate securely, hosts allocating
resources need to ensure that messages indicating that a network
resource is in use are authenticated. Hosts soliciting for a name or
service must also be able to authenticate the responses they receive.
A message is considered "authenticated" if it can be proved to have
been sent by a member of a group of devices running zeroconf
protocols. Note that in general, devices running zeroconf protocols
must trust the other devices in the group because any device may
claim to be using an address or name, or advertising a service.
Zeroconf security mechanisms must at a minimum be able to distinguish
between messages originating from a device "inside" the group or a
device "outside" the group.
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Requirement:
o Security schemes for zeroconf protocols MUST be able to implement
a basic "inside/outside" security policy.
Access control mechanisms within a zeroconf network are beyond the
scope of this document.
4.2 Security Scenarios
In the next few sections, several scenarios are examined to highlight
the security implications of employing zeroconf protocols in various
environments.
4.2.1 Use on an isolated, secure network link
In this scenario all the devices in the network are connected to a
secure link (e.g. a control network in a car, or a private network
between two devices used for configuration). The link might be a
separate physical wire or shared media with layer-2 security enabled
(e.g. wireless or power-line networks). Any host that has access to
the link is trusted and any packet received from the secure link is
considered to be authenticated. In this case, the inside/outside
policy is implemented by controlling access to the link itself.
4.2.2 Use on a shared (insecure) link
In this scenario, a group of devices use zeroconf protocols on
link(s) they share with other devices who are NOT part of the group.
Various pieces of network configuration MUST be consistent across all
hosts sharing the link (e.g. addresses, netmask, routing
information) in order for communication to occur at all.
Consequently, hosts inside the group are potentially at risk from
hosts outside their group when they try to configure such information
(e.g. via ARP insecurity). Host names and service identifiers MUST
be unique within a group, but with authentication may not need to be
unique across the link. Assuming that requests and responses can be
associated with a group and authenticated, solicitations and
responses for host names and services that are not located inside the
group can be ignored.
4.2.3 Use in conjunction with configured protocols
Zeroconf protocols are likely to be used in conjunction with
configured network protocols. In general, zeroconf protocols must
not allocate resources from the same address or name spaces used by
configured network protocols. Locally allocated zeroconf network
resources must not mask global assigned resources.
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5. IANA Considerations
No known IANA considerations arise from this document.
6. Acknowledgments
Thanks to Peter Ford and Stuart Cheshire for hosting the NITS
(Networking In The Small) BOF that was the catalyst to forming the
Zeroconf Working Group.
Thanks to Erik Guttman and Stuart Cheshire for forming and chairing
the Zeroconf Working Group, which is responsible for this document.
Thanks to Erik Guttman for providing key input to the service
discovery and the security sections.
Thanks to Dave Thaler for providing key input to the IP multicast
address allocation sections.
Thanks to Stuart Cheshire for providing key input to the introduction
and IP interface configuration sections.
Thanks to Myron Hattig for acting as editor for previous versions of
this document.
Additional recognition goes the following people for their
influential contributions to this document and its predecessors:
Brent Miller, Thomas Narten, Marcia Peters, Bill Woodcock, Bob Quinn,
John Tavs, Matt Squire, Daniel Senie, Cuneyt Akinlar, Karl Auerbach,
Kanchei Loa, Dongyan Wang, James Kempf, Yaron Goland, and Bernard
Aboba, Ran Atkinson.
Normative References
Informative References
[I-D.ietf-ssm-arch] Cain, B. and H. Holbrook, "Source-Specific
Multicast for IP", draft-ietf-ssm-arch-00 (work
in progress), February 2002.
[RFC0826] Plummer, D., "Ethernet Address Resolution
Protocol: Or converting network protocol
addresses to 48.bit Ethernet address for
transmission on Ethernet hardware", STD 37, RFC
826, November 1982.
[RFC1034] Mockapetris, P., "Domain names - concepts and
facilities", STD 13, RFC 1034, November 1987.
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[RFC1035] Mockapetris, P., "Domain names - implementation
and specification", STD 13, RFC 1035, November
1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
October 1989.
[RFC1827] Atkinson, R., "IP Encapsulating Security Payload
(ESP)", RFC 1827, August 1995.
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[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.
[RFC2246] Dierks, T., Allen, C., Treese, W., Karlton, P.,
Freier, A. and P. Kocher, "The TLS Protocol
Version 1.0", RFC 2246, January 1999.
[RFC2251] Wahl, M., Howes, T. and S. Kille, "Lightweight
Directory Access Protocol (v3)", RFC 2251,
December 1997.
[RFC2365] Meyer, D., "Administratively Scoped IP
Multicast", BCP 23, RFC 2365, July 1998.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture
for the Internet Protocol", RFC 2401, November
1998.
[RFC2402] Kent, S. and R. Atkinson, "IP Authentication
Header", RFC 2402, November 1998.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson,
"Neighbor Discovery for IP Version 6 (IPv6)",
RFC 2461, December 1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless
Address Autoconfiguration", RFC 2462, December
1998.
[RFC2535] Eastlake, D., "Domain Name System Security
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Extensions", RFC 2535, March 1999.
[RFC2541] Eastlake, D., "DNS Security Operational
Considerations", RFC 2541, March 1999.
[RFC2608] Guttman, E., Perkins, C., Veizades, J. and M.
Day, "Service Location Protocol, Version 2", RFC
2608, June 1999.
[RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast
Address Dynamic Client Allocation Protocol
(MADCAP)", RFC 2730, December 1999.
[RFC2931] Eastlake, D., "DNS Request and Transaction
Signatures ( SIG(0)s)", RFC 2931, September
2000.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-
based IPv6 Multicast Addresses", RFC 3306,
August 2002.
Author's Address
Aidan Williams
Motorola Australian Research Centre
Locked Bag 5028
Botany, NSW 1455
Australia
Phone: +61 2 9666 0500
EMail: Aidan.Williams@motorola.com
URI: http://www.motorola.com.au/marc/
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Full Copyright Statement
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or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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included on all such copies and derivative works. However, this
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the copyright notice or references to the Internet Society or other
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The limited permissions granted above are perpetual and will not be
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Williams Expires March 20, 2003 [Page 22]
