INTERNET-DRAFT Local DNS Names
March 1998
Expires September 1998
Local Domain (DNS) Names
----- ------ ----- -----
Donald E. Eastlake 3rd
Status of This Document
This draft, file name draft-ietf-dnsind-local-names-05.txt, is
intended to be become an Experimental RFC. Distribution of this
document is unlimited. Comments should be sent to the DNS mailing
list <namedroppers@internic.net> or to the author.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months. Internet-Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet-
Drafts as reference material or to cite them other than as a
``working draft'' or ``work in progress.''
To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net (East USA), ftp.isi.edu (West USA),
ftp.nordu.net (North Europe), ftp.nis.garr.it (South Europe),
munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa).
Abstract
A new top level domain (TLD) name is defined such that local private
DNS zones can easily be maintained similar to the private IP
addresses reserved in [RFC 1918]. These zones locally appear to be
part of the global DNS name tree and can be locally resolved, even by
"out of the box" resolvers starting at the global root zone, but are
inaccessible outside their enclave. Additional second level domain
names are reserved under this TLD for IPv6 link and site local
addresses and loopback addresses. User confusion is reduced by
grouping all non-global names under this new TLD so they are more
easily recognizable.
Donald E. Eastlake 3rd [Page 1]
INTERNET-DRAFT Local DNS Names
Acknowledgments
The valuable contributions of the following persons are gratefully
acknowledged:
Dan Harrington
Michael A. Patton
Table of Contents
Status of This Document....................................1
Abstract...................................................1
Acknowledgments............................................2
Table of Contents..........................................2
1. Introduction............................................3
2. Local Names Via The .local Top Level Domain.............4
2.1 Local DNS Server Specifics.............................6
2.2 Local in-addr.arpa Zones...............................6
2.3 Name Conflicts.........................................7
2.4 Nested Enclaves........................................8
3. Other Names in .local...................................8
4. Analysis of Alternatives................................8
4.1 Locally Configured .local..............................8
4.2 Local Delegations Anywhere.............................9
4.3 No Change..............................................9
5. Security Considerations.................................9
5.1 Strength of Privacy Offered............................9
5.2 Interaction with DNSSEC...............................10
5.3 Network Abuse.........................................10
References................................................11
Author's Address..........................................11
Expiration and File Name..................................11
Appendix A: the .local zone...............................12
Appendix B: the .in-addr.arpa zone.......................14
Donald E. Eastlake 3rd [Page 2]
INTERNET-DRAFT Local DNS Names
1. Introduction
The global Internet Domain Name System (DNS) is documented in [RFC
1034, 1035, 1591] and numerous additional Requests for Comment. It
defines a tree of names starting with root, ".", immediately below
which are top level domain names such as .com and .us. Below top
level domain names there are normally additional levels of names.
Generally the information in the DNS is public and intended to be
globally accessible. Certainly, in the past, the model of the
Internet was one of end-to-end openness [RFC 1958]. However, with
increasing security threats and privacy concerns, firewalls and
enclaves have appeared. In many cases, organizations have hosts or
resources that they specifically want to reference with DNS names but
which they also want to be walled off from global access and even
from global knowledge of their DNS name.
In the realm of IPv4 addresses, this has been accomplished by
reserving three blocks of addresses as documented in [RFC 1918].
This designation of private IP addresses also helps conserve global
IP addresses. Familiarity with the contents of [RFC 1918] is
assumed.
In the DNS area, [RFC 1918] recommends "splitting" DNS at the enclave
boundary, giving different answers to resolvers depending or whether
they are inside or outside of the enclave, using different servers
for inside and outside, etc. Such relatively complex configuration
diddling is at variance with the simple global tree structure
envisaged in the original DNS design. It can cause the local names
to be invisible to "out of the box" resolvers within the enclave if
they start at a global root zone. Furthermore, because local DNS
names created in accordance with [RFC 1918] can be entirely arbitrary
and unrecognizable as local, user confusion is increased.
This document specifies an alternative approach to achieving the
effect of local names that is more in tune with the concept of a
single global DNS tree and reduces user confusion by making local
names easily recognizable. Use of this approach by local DNS
administrators is not required and older techniques will continue to
work as well as they have in the past.
[RFC 1918] requires that private IP addresses not be indirectly
exposed to the general Internet via DNS records or otherwise. This
RFC provides a recommended way to accomplish such private IP address
hiding and carves out an exception thereto for the addresses of the
servers for some zones which are children of the ".local" top level
domain name.
Donald E. Eastlake 3rd [Page 3]
INTERNET-DRAFT Local DNS Names
2. Local Names Via The .local Top Level Domain
The fundamental idea for providing local names, as described in more
detail below, is to define second level domains under ".local" which
are served by domain name system (DNS) name servers that have private
IP addresses. These server's addresses would only be routed within
the enclave to which the names are local. Thus the servers, and the
names and resource records inside them, would, if the guidelines in
this document are followed, be inaccessible outside the enclave.
The following figure shows a highly simplified overview of an example
configuration:
+----------------------------+
| domain/enclave A |
| |
| #====================# |
| H private IP addrs A H |
| H H |
+-----------------------O privhost1 H |
| | H H |
+-----+-----------------O privhost2 H |
| | | H H |
| | | #====================# |
| | a | |
| +--------------------O pubhost3 |
.local | | | | |
+----+ | | +----------------------------+
| | | |
| | | | +----------------------------+
| | | | | domain/enclave B |
(root) | | | | | |
. ----+ | | | | #====================# |
| | | | | H private IP addrs B H |
| | | | | H H |
| +--|--------------------O privhost2 H |
| | | | H H |
+-------+ +-----------------O privhost3 H |
.com | | H : H |
| | #====:===============# |
| | : |
| b +-------------O pubhost4 |
+------+ | |
| +-------------O pubhost5 |
| | |
| +----------------------------+
|
| example
+---------------------O pubhost6
Donald E. Eastlake 3rd [Page 4]
INTERNET-DRAFT Local DNS Names
Starting at the bottom, pubhost6 is intended to illustrate an
ordinary host connected to the Internet with domain name
pubhost6.example.com. Though not indicated in the above diagram,
every DNS zone is in fact served by at least two hosts and some by
substantially more than two. The addresses of the servers for the
root ("."), ".com", and example.com zones would all be in the public
portion of the IP address space, i.e., in the space of unicast IP
addresses not reserved for private use so these servers are
accessible to all.
Moving to the top of the figure, enclave A represents some
organization that wishes to have some hosts with publicly visible
names and some with hidden names that are only visible locally.
pubhost3.a.com is an example of a publicly visible host which would
probably have a public IP address (although access to pubhost3 from
outside the enclave might be filtered or even blocked by a firewall
or the like). privhost1 and privhost2 are examples of hidden names.
If a zone with privhost1 and privhost2 in it is served by DNS servers
with private IP addresses ("private IP addresses A") such that the
servers are accessible within enclave A but not from outside enclave
A, then the information is that zone will only be locally visible.
As show in the above figure, privhost1 and privhost2 have addresses
that are also private IP addresses, making those hosts inaccessible
outside enclave A, but it is the private addresses of the DNS
servers, not of the hosts pointed to from within the private DNS
zone, that provides the protection for the DNS names and other
private DNS information. (From the above simplified diagram, it
might appear that fully qualified domain names of these hosts would
be privhost1.local and privhost2.local but the names are actually a
little more complex as explained in Section 2.1.)
Finally, in the middle, another enclave is shown with two hosts with
visible names and public IP addresses, pubhost4.b.com and
pubhost5.b.com. In addition, there are two private host names
privhost2 and privhost3. The duplication of privhost2 between
enclaves A and B would not be a problem as only DNS resolvers in
enclave A can access the DNS servers with the zone having the enclave
A version of privhost2 and only DNS resolvers in enclave B can access
the DNS servers with the zone having the enclave B version of
privhost2.
Publicly visible host names are required by [RFC 1918] to have public
(i.e., globally unique) IP addresses. Private DNS names would
normally have private IP addresses, and all do in the figure above,
but this is not required. A public IP address could be stored under
a private name. And, of course, it is possible for the same physical
host to have multiple IP addresses, including a mix of public and
private addresses. The dotted line in the figure above is intended
to indicate that privhost3 and pubhost4 are actually the same
physical machine. The could also be accomplished by storing a single
Donald E. Eastlake 3rd [Page 5]
INTERNET-DRAFT Local DNS Names
public address for that host under both the public and private names
or by having the host answer to both a public IP address stored under
the public name and a private IP address stored under the private
name. In the later case you could even also store the public address
along with the private address under the private name.
2.1 Local DNS Server Specifics
A variety of second level names are provided in the ".local" zone
each of which is a delegation point to a zone with some number of
name servers in one of the private IP address space blocks. The
multiple second level names permit choice between the different
private IP blocks and different numbers of servers. Thus the actual
fully qualified name for the private host examples in the figure
above would be more like privhost1.a2.local, privhost2.a2.local, etc.
(but see Section 2.3 below).
Glue records are provided to give private IP addresses for initial
name servers; however, it should be noted that the NS and A records
in the local zones will dominate the information stored in the
".local" zone. This means that once a resolver has contacted a local
server, the list of NS RRs in the local zone on that server will
control and could contain more or different servers than were given
at the chosen ".local" delegation point. Nevertheless, the glue A
records in the global ".local" zone do place some constraints of the
private IP address of the local DNS servers implementing zones which
are children of ".local".
It is only necessary for the local DNS servers to have private IP
addresses to achieve the effect of local names. However, care MUST be
taken that none of the local DNS servers or any server that might
cache their output is accessible by any globally accessible network
interface. Otherwise confusion could result if local names are
resolved by a resolver outside a local enclave to private IP
addresses which are meaningless or have a different meaning for that
resolver.
The Appendix A to this document gives an initial content of the
".local" zone.
2.2 Local in-addr.arpa Zones
Inverse look up of local names corresponding to private IP addresses
needs to be provided via the in-addr.arpa zone. Appendix B contains
recommended additions to the in-addr.arpa domain to accomplish this.
Because of the fixed naming within this zone, different names with
Donald E. Eastlake 3rd [Page 6]
INTERNET-DRAFT Local DNS Names
different numbers of servers or different addresses can not be
provided. As with the forward ".local" entries, the actual NS RRs in
the servers serving the private portions of the inverse in-addr.arpa
will dominate. When one of these is queried by a resolver, it can
provide information on additional servers for that particular subzone
in the private IP address portion of the in-addr.arpa tree.
2.3 Name Conflicts
The intention is that local names would only be used in the enclave
where the entities they refer to exist, and these names would not be
exported. However, experience indicates that, despite best efforts
to avoid it, some such names will occasionally leak out via email
cc's, URL's in HTML, etc. This occurs currently with local names not
following the design in this document. These leaked private names
can cause confusion if they can conflict with global names or names
local to other enclaves. Use of the ".local" top level domain
assures no conflict with global names. To assure no conflict with
different local fully qualified names, the domain name of the enclave
SHOULD always be included in ".local" names.
For example, a company might have
host1.company.co.xy
as a globally accessible host and
host2.company.co.xy.b3.local
as a host for internal use only. The global name could normally be
resolvable anywhere on the Internet while the local name would be
undefined anywhere except within the company.co.xy enclave.
Note that different names were chosen for the initial label in the
two names above, i.e., host1 and host2. The reason for this is that,
in some environments, local hosts are referred to by an unqualified
names, such as host3. For DNS look up purposes, such a name must be
expanded into a fully qualified domain name and a "search list" of
possible suffix qualifications is tried. If, for example, both
host4.school.ac.xy and host4.school.ac.xy.b3.local existed, then a
local reference to "host4" would be ambiguous and could lead to
either machine depending on the order of qualifications tried. This
order could even be different in different pieces of local software
or on different local hosts, resulting in local confusion. For this
reason, it is strongly recommended that fully qualified domain names
be used wherever practical and that disjoint name sets be used for
global and local entity unqualified domain names.
Donald E. Eastlake 3rd [Page 7]
INTERNET-DRAFT Local DNS Names
2.4 Nested Enclaves
It is possible to have enclaves within enclaves. The best way to
accomplish this is to use a different portion of the private IP
address space at each nesting level of enclave. (Private IP address
space can be reused in enclaves that are siblings or the like.) Then
similar entries to those proposed here for ".local" can be made in
the private zone referring to name servers with addresses in the next
lower level nested enclave's private IP address space.
3. Other Names in .local
Three additional second level domain names are assigned in the
".local" top level domain for other types of local names.
In particular, link.local and site.local are reserved for use in
qualifying IPv6 link local names and site local names and
loopback.local is assigned and given the loopback address.
4. Analysis of Alternatives
Possible alternatives to the scheme described in this document are
(1) recommend that DNS administrators locally configure a ".local",
(2) recommend that DNS administrators do a similar thing to ".local"
somewhere in their current domain name tree, and (3) take no action
leaving [RFC 1918] fully in effect. These alternatives are examined
below.
Only the scheme recommended in the sections of this document above
always permit generic resolvers running within a enclave and starting
at a global root zone to find private names and minimize user
confusion.
4.1 Locally Configured .local
It is possible for an enclave to locally configure its own version of
the ".local" zone. This version could have whatever private
addresses were desired for the name servers involved. However this
generally requires that all of the resolvers within the enclave be
configured to go through DNS servers that have this local variant of
".local" configured. Thus "out of the box" resolvers starting at a
true root zone will not find the information. Furthermore, the
probability is increased that some administrators will use a variant
name increasing confusion.
Donald E. Eastlake 3rd [Page 8]
INTERNET-DRAFT Local DNS Names
4.2 Local Delegations Anywhere
It would be possible to just recommend putting hidden names in a
branch of the enclave's domain, like put them for the example company
under local.example.com. If all these apexes of hidden name subtrees
are visible in this way, then there would be a large number of
different looking local domain names that could confuse users by not
being globally resolvable. There would be a much greater chance of
completely different names (private.example.com, hidden.example.com,
net10.example.com, ...) being used increasing confusion.. However,
generic resolvers starting from a global root inside an enclave would
find private names configured in this way.
4.3 No Change
Just banishing private IP addresses from the global DNS by fiat and
having everyone who wants to use them run split DNS is the
recommendation of RFC 1918. But as private IP addresses become more
and more common, this restriction is increasingly overlooked. The
private names leak out anyway. Browsers inside a enclave that
started at a global root server are unable to find such hidden names.
And there is be much less uniformity of naming resulting in more user
confusion.
5. Security Considerations
This section discusses the strength of the privacy offered by using
subzones of ".local", interactions with DNS security, and possible
interaction with network abuse.
5.1 Strength of Privacy Offered
It should be noted that the privacy of the DNS information protected
by storing it in servers with private IP addresses is relatively
weak. It is dependent on the integrity of enclave perimeter routing
to make these servers inaccessible. And the names may leak out in
any case due to inclusion in email address fields, web pages, and the
like; however, such leakage will be no worse than current split DNS
implementations of DNS data hiding.
Software should not depend on local names only existing within a
particular enclave as someone could deliberately create the same
names within a different enclave even if the names incorporate the
name of the original enclave in an attempt to avoid such conflicts.
Donald E. Eastlake 3rd [Page 9]
INTERNET-DRAFT Local DNS Names
5.2 Interaction with DNSSEC
Although an enclave may derive some amount of security by virtue of
its isolation, it will normally be desirable to implement DNS
security [RFC 2065, draft-ietf-dnssec-secext-*.txt] within the
enclave. The enclave owner should generate their own keys and sign
their subzone of ".local". However, a signed copy of their public
key can not be included in the ".local" zone as it is different for
every enclave. Thus, to authenticate the ".local" subzone contents,
it will be necessary to staticly configure the public key for the
".local" subzone in local resolvers or sign the KEY RR at the apex of
the local subzone of ".local" with another key that is trusted by
local resolvers such as the enclave domain name zone key or the
".local" zone key.
5.3 Network Abuse
The existence of local IP addresses as provided in [RFC 1918]
provides another way for network abusers to create confusion to cover
their tracks and make abuse hard to trace. Use of ".local" does not
change this but will reduce confusion by providing clearer notice
that an address is not globally meaningful.
Donald E. Eastlake 3rd [Page 10]
INTERNET-DRAFT Local DNS Names
References
RFC 1033 - M. Lottor, "Domain Administrators Operations Guide",
November 1987.
RFC 1034 - P. Mockapetris, "Domain Names - Concepts and Facilities",
STD 13, November 1987.
RFC 1035 - P. Mockapetris, "Domain Names - Implementation and
Specifications", STD 13, November 1987.
RFC 1591 - J. Postel, "Domain Name System Structure and Delegation",
03/03/1994.
RFC 1918 - Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de Groot, E.
Lear, "Address Allocation for Private Internets", 02/29/1996.
RFC 1958 - B. Carpenter, "Architectural Principles of the Internet",
06/06/1996.
RFC 2065 - D. Eastlake, C. Kaufman, "Domain Name System Security
Extensions", 01/03/1997.
draft-ietf-dnssec-secext2-*.txt -
Author's Address
Donald E. Eastlake 3rd
CyberCash, Inc.
318 Acton Street
Carlisle, MA 01741 USA
Telephone: +1 978 287 4877
+1 703 620-4200 (main office, Reston, VA)
FAX: +1 978 371 7148
EMail: dee@cybercash.com
Expiration and File Name
This draft expires September 1998.
Its file name is draft-ietf-dnsind-local-names-05.txt.
Donald E. Eastlake 3rd [Page 11]
INTERNET-DRAFT Local DNS Names
Appendix A: the .local zone
===== The .local zone suggested initial contents ====
local. IN SOA ... ... (
.... ; serial
..... ; refresh
..... ; retry
....... ; expiry
..... ) ; minimum
NS ... ; actual servers for .local zone
NS ...
...
loopback A 127.0.0.1
AAAA 0::1
MX 100 loopback.local.
link TXT "Reserved. See RFC xxxx." [the rfc this draft becomes]
site TXT "Reserved. See RFC xxxx." [the rfc this draft becomes]
a2.local. NS ns1.a2.local.
NS ns2.a2.local.
ns1.a2.local. A 10.1.1.2
ns2.a2.local. A 10.1.2.2
a3.local. NS ns1.a3.local.
NS ns2.a3.local.
NS ns3.a3.local.
ns1.a3.local. A 10.1.1.2
ns2.a3.local. A 10.1.2.2
ns3.a3.local. A 10.2.1.2
a4.local. NS ns1.a4.local.
NS ns2.a4.local.
NS ns3.a4.local.
NS ns4.a4.local.
ns1.a4.local. A 10.1.1.2
ns2.a4.local. A 10.1.2.2
ns3.a4.local. A 10.2.1.2
ns4.a4.local. A 10.128.1.2
b2.local. NS ns1.b2.local.
NS ns2.b2.local.
ns1.b2.local. A 172.16.1.2
ns2.b2.local. A 172.16.2.2
b3.local. NS ns1.b3.local.
NS ns2.b3.local.
Donald E. Eastlake 3rd [Page 12]
INTERNET-DRAFT Local DNS Names
NS ns3.b3.local.
ns1.b3.local. A 172.16.1.2
ns2.b3.local. A 172.16.2.2
ns3.b3.local. A 172.16.128.2
c2.local. NS ns1.c2.local.
NS ns2.c2.local.
ns1.c2.local. A 192.168.1.2
ns2.c2.local. A 192.168.2.2
c3.local. NS ns1.c3.local.
NS ns2.c3.local.
NS ns3.c3.local.
ns1.c3.local. A 192.168.1.2
ns2.c3.local. A 192.168.2.2
ns3.c3.local. A 192.168.128.2
Donald E. Eastlake 3rd [Page 13]
INTERNET-DRAFT Local DNS Names
Appendix B: the .in-addr.arpa zone
===== Suggested additional entries in the in-addr.arpa zone ====
10.in-addr.arpa. NS ns1.a2.local.
NS ns2.a2.local.
ns1.a2.local. A 10.1.1.2
ns2.a2.local. A 10.1.2.2
16.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
ns1.b2.local. A 172.16.1.2 ; one set of glue records
ns2.b2.local. A 172.16.2.2 ; for all the b2 cases
17.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
18.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
19.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
20.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
21.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
22.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
23.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
24.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
25.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
26.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
27.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
28.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
29.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
30.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
31.172.in-addr.arpa. NS ns1.b2.local.
NS ns2.b2.local.
168.192.in-addr.arpa. NS ns1.c2.local.
NS ns2.c2.local.
ns1.c2.local. A 192.168.1.2
ns2.c2.local. A 102.168.2.2
Donald E. Eastlake 3rd [Page 14]