Internet DRAFT - draft-massar-dnsop-service
draft-massar-dnsop-service
Domain Name System Operations J. Massar
(dnsop) Unfix / SixXS
Internet-Draft July 9, 2005
Expires: January 10, 2006
The _service domain and prefix
draft-massar-dnsop-service-00
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines a new domain, _service., which can be used for
automatic service configuration and discovery. The associated
anycast prefixes can be used to configure a default DNS server, which
provides lookups for a local _service. domain but also acts as a
(caching) recursive DNS server, thus allowing DNS clients to use this
well-known address as their default DNS server as well as to use it
to find various well known services, thus avoiding manual
configuration.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The _service domain . . . . . . . . . . . . . . . . . . . . . 3
3.1 DNS Search Path . . . . . . . . . . . . . . . . . . . . . 5
3.2 Browsing for services . . . . . . . . . . . . . . . . . . 5
4. The _service anycast address . . . . . . . . . . . . . . . . . 5
4.1 The _service prefix . . . . . . . . . . . . . . . . . . . 5
4.2 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3 Discovery and failover . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1 Normative References . . . . . . . . . . . . . . . . . . . 7
7.2 Informative References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Requirements notation
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].
2. Introduction
Currently there are a number of methods of configuring a (caching)
recursive DNS server into the resolver code of various clients.
Amongst these methods are static configuration, DHCP, IPv6 Router
Advertisement options, PPP configuration and a multitude of others.
Next to the configuration of a DNS server, the user of the client
will also have to configure various other services, eg Outgoing SMTP
server, incoming POP3 or IMAP4 server, HTTP proxy server, FTP proxy
server or with the advent of IPv6, one of the various IPv6 tunneling
techiques and one day one of the various IPv4 tunneling techniques,
to allow IPv6 hosts to contact IPv4 hosts.
All these services now have to be manually configured or using some
kind of automation, which is likely to be different for each type of
service.
SRV records [RFC2782] defines a method of defining services, it does
not however define where these records are located nor handles the
case when a service has multiple protocols.
This document specifies a method, which allows vendors to hardcode a
well known anycast prefix into their resolving clients. This anycast
prefix contains a single well known IP address that runs a (caching)
recursive DNS server. [RFC1034] [RFC1035]. This server thus allows
looking up of all available domains (example.com, example.org etc).
Additionally it is provides lookups for the _service. domain which
contains the in this document described domain to be used for
autoconfiguration.
3. The _service domain
The _service domain contains PTR records to their respective SRV
records. Service names should abide SRV naming rules, they are
protocol independent though.
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Typical contents of a _service domain.
$ORIGIN _service.
@ TXT "Example Networks"
@ RP helpdesk.example.net. helpdesk.people.example.net.
_website PTR _https._tcp.example.net.
PTR _http._tcp.example.net.
_pgpkey PTR _pgpkey-https._tcp.example.net.
PTR _pgpkey-http._tcp.example.net.
_imap PTR _imap._tcp.example.net.
_mailsubmit PTR _submission._tcp.example.net.
_ntp PTR _ntp._tcp.example.net.
PTR _ntp._udp.example.net.
The TXT record specifies which organisation is announcing this
prefix. This record can be shown in browser functions or to the
enduser. The RP record specifies a contact for this service zone.
The above defines a website, available over HTTP and HTTPS, based on
the priority and weights given by their SRV records. This allows one
to specify that a client must first try the HTTPS variant, if it does
not work, or the client does not understand this protocol it can try
the HTTP variant. Due to the nature of SRV, these services might be
located on different hosts. The NTP service is defined to use either
UDP or NTP.
The actual _service. Top Level Domain (TLD) can actually also be a
DNAME to the organisations domain, this way the organisation only has
to maintain one .service domain.
_service. DNAME _service.example.net.
This also allows an organisation have multiple domain names or
clients domains, simply adding the DNAME to the service domain allows
the users to pick any of the domains and the configuration
information is already available to the user. This is naturally only
required when the user is not inside the anycast range of the
organisation.
A _service domain SHOULD be AXFR'able [RFC1995] this to facilitate
browsing of the service zone. An organisation MAY opt to decline
AXFR's based on their policy.
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3.1 DNS Search Path
Lookups in the _service domain should be done according to the DNS
search path. Thus if the DNS search path of host is: example.com
example.net then the resolver should try the items in:
_service.
_service.example.com.
_service.example.net.
This allows the _service domain to be located anywhere in the search
path of the client. Additionally this also allows one to specify a
remote domain and thus having components be configured based on the
service values given for that domain.
3.2 Browsing for services
In case the user wants to know what kind of services are available
for her, as provided by the local organisation, an application could
try to AXFR the _service zones of the domains in the search path and
then displaying the available services.
4. The _service anycast address
x.x.x.1 and xxxx::1 (*IANA UPDATE!*) can be hardcoded into any client
resolver. These addresses point to the IPv4 and IPv6 variant of a
resolver which also provides access to the _service prefix.
On the _service anycast address a full recursive DNS server is
responding. It must also provide the lookup facility for the
_service. domain. This domain might reside on another DNS server.
This address can be passed to the client using DHCP [RFC2131], other
automatic configuration methods or manual configuration.
4.1 The _service prefix
x.x.x.1 is part of x.x.x.1/32 and xxxx::1 is part of xxxx::/64.
The prefix SHOULD only be announced in the local IGP of the
organisation. The prefix MAY be announced to other organisations
when the two parties agree on this setup. The prefix MUST not be
seen globally around the world. Though it is of course possible,
having the prefix available to the global internet would not have
much of a function as the services are most likely only provided for
users of the organisation.
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4.2 Monitoring
Any organisation corresponding to this specification must include a
monitoring function, to check that the _service is operational. The
router must stop injecting the route leading to the server
immediately if it detects that the DNS function is not operational.
A remote host should try to query either the TXT or RP record of the
to be monitored service zone to see if the DNS server still answers
queries. Other methods can of course also be used.
4.3 Discovery and failover
The DNS client resolver send packets to the DNS service by sending
them to the anycast address. These packets will reach the closest
service provided by their organisation or by another organisation.
When a client does not have connectivity to this prefix, there will
be no routing entry for the anycast prefix and thus a destinatation
unreachable will be sent to the host. The resolver then learns that
the DNS service in question is not available.
When a _service server somehow breaks it should stop announcing the
anycast prefix to the local network. At that point, the local IGP
will automatically compute a route towards the "next best" _service
server. We expect that adequate monitoring tools will be used to
guarantee timely discovery of connectivity losses and should allow
seamless functionality for the endusers.
5. Security Considerations
This anycast technique introduces an risk, that a rogue router or a
rogue AS could introduce a bogus route to their own resolver setup
providing rogue _service entries, thereby diverting the traffic to
the service they want. Any service using cleartext passwords and
having no additional security, eg TLS/SSL, can thus be easily
transformed into password collection setups. Care must be taken that
nobody can insert a faked _service server into a network.
6. IANA Considerations
IANA will need to mark the _service. domain and the _service sub
domain as reserved to be used solely for this purpose.
IANA will need to allocate a IPv6 /64 and a IPv4 /32 for the purposes
of having a well known anycast address in which the (caching)
recursive DNS server can operate.
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The prefix is only required in the organisation itself and should not
be carried in intra-domain routing tables. A global prefix is
required so that the prefix can be shared between organisations. eg
an organisation providing this service to other autonomous systems.
7. References
7.1 Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
7.2 Informative References
[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
August 1996.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
Author's Address
Jeroen Massar
Unfix / SixXS
Hofpoldersingel 45
Gouda 2807 LW
NL
Email: jeroen@unfix.org
URI: http://unfix.org/~jeroen/
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