+
DNS Operations WG A. Durand
Internet-Draft SUN Microsystems, Inc.
-Expires: May 1, 2004 J. Ihren
+Expires: July 1, 2004 J. Ihren
Autonomica
P. Savola
CSC/FUNET
- Nov 2003
+ Jan 2004
Operational Considerations and Issues with IPv6 DNS
- draft-ietf-dnsop-ipv6-dns-issues-03.txt
+ draft-ietf-dnsop-ipv6-dns-issues-04.txt
Status of this Memo
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
- This Internet-Draft will expire on May 1, 2004.
+ This Internet-Draft will expire on July 1, 2004.
Copyright Notice
- Copyright (C) The Internet Society (2003). All Rights Reserved.
+ Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Representing IPv6 Addresses in DNS Records . . . . . . . . . . 3
- 1.2 Difference of DNS Transport and DNS Records . . . . . . . . . 3
+ 1.2 Independence of DNS Transport and DNS Records . . . . . . . . 3
1.3 Avoiding IPv4/IPv6 Name Space Fragmentation . . . . . . . . . 4
2. DNS Considerations about Special IPv6 Addresses . . . . . . . 4
2.1 Limited-scope Addresses . . . . . . . . . . . . . . . . . . . 4
2.2 Privacy (RFC3041) Address . . . . . . . . . . . . . . . . . . 4
- 2.3 6to4 Addresses . . . . . . . . . . . . . . . . . . . . . . . . 4
+ 2.3 6to4 Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Observed DNS Implementation Misbehaviour . . . . . . . . . . . 5
3.1 Misbehaviour of DNS Servers and Load-balancers . . . . . . . . 5
3.2 Misbehaviour of DNS Resolvers . . . . . . . . . . . . . . . . 6
4.1 Use of Service Names instead of Node Names . . . . . . . . . . 6
4.2 Separate vs the Same Service Names for IPv4 and IPv6 . . . . . 7
4.3 Adding the Records Only when Fully IPv6-enabled . . . . . . . 7
- 4.4 IPv6 Transport Guidelines for DNS Servers . . . . . . . . . . 8
- 5. Recommendations for DNS Resolver IPv6 Support . . . . . . . . 8
- 5.1 DNS Lookups May Query IPv6 Records Prematurely . . . . . . . . 8
- 5.2 Recursive DNS Server Discovery . . . . . . . . . . . . . . . . 10
- 5.3 IPv6 Transport Guidelines for Resolvers . . . . . . . . . . . 10
- 6. Considerations about Forward DNS Updating . . . . . . . . . . 10
- 6.1 Manual or Custom DNS Updates . . . . . . . . . . . . . . . . . 10
- 6.2 Dynamic DNS . . . . . . . . . . . . . . . . . . . . . . . . . 11
- 7. Considerations about Reverse DNS Updating . . . . . . . . . . 11
- 7.1 Applicability of Reverse DNS . . . . . . . . . . . . . . . . . 11
- 7.2 Manual or Custom DNS Updates . . . . . . . . . . . . . . . . . 12
- 7.3 DDNS with Stateless Address Autoconfiguration . . . . . . . . 12
- 7.4 DDNS With DHCP . . . . . . . . . . . . . . . . . . . . . . . . 12
- 7.5 DDNS with Dynamic Prefix Delegation . . . . . . . . . . . . . 13
- 8. Miscellaneous DNS Considerations . . . . . . . . . . . . . . . 13
- 8.1 NAT-PT with DNS-ALG . . . . . . . . . . . . . . . . . . . . . 13
- 8.2 Renumbering Procedures and Applications' Use of DNS . . . . . 13
- 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
- 10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
- Normative References . . . . . . . . . . . . . . . . . . . . . 14
- Informative References . . . . . . . . . . . . . . . . . . . . 14
- Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
- A. Site-local Addressing Considerations for DNS . . . . . . . . . 17
- Intellectual Property and Copyright Statements . . . . . . . . 18
-
-
+ 4.4 The Use of TTL for IPv4 and IPv6 RRs . . . . . . . . . . . . . 8
+ 4.5 Behaviour of Glue in Mixed IPv4/IPv6 Environments . . . . . . 8
+ 4.6 IPv6 Transport Guidelines for DNS Servers . . . . . . . . . . 9
+ 5. Recommendations for DNS Resolver IPv6 Support . . . . . . . . 9
+ 5.1 DNS Lookups May Query IPv6 Records Prematurely . . . . . . . . 9
+ 5.2 Recursive DNS Resolver Discovery . . . . . . . . . . . . . . . 11
+ 5.3 IPv6 Transport Guidelines for Resolvers . . . . . . . . . . . 11
+ 6. Considerations about Forward DNS Updating . . . . . . . . . . 11
+ 6.1 Manual or Custom DNS Updates . . . . . . . . . . . . . . . . . 12
+ 6.2 Dynamic DNS . . . . . . . . . . . . . . . . . . . . . . . . . 12
+ 7. Considerations about Reverse DNS Updating . . . . . . . . . . 13
+ 7.1 Applicability of Reverse DNS . . . . . . . . . . . . . . . . . 13
+ 7.2 Manual or Custom DNS Updates . . . . . . . . . . . . . . . . . 14
+ 7.3 DDNS with Stateless Address Autoconfiguration . . . . . . . . 14
+ 7.4 DDNS with DHCP . . . . . . . . . . . . . . . . . . . . . . . . 14
+ 7.5 DDNS with Dynamic Prefix Delegation . . . . . . . . . . . . . 15
+ 8. Miscellaneous DNS Considerations . . . . . . . . . . . . . . . 15
+ 8.1 NAT-PT with DNS-ALG . . . . . . . . . . . . . . . . . . . . . 15
+ 8.2 Renumbering Procedures and Applications' Use of DNS . . . . . 15
+ 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
+ 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
+ Normative References . . . . . . . . . . . . . . . . . . . . . 16
+ Informative References . . . . . . . . . . . . . . . . . . . . 16
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19
+ A. Site-local Addressing Considerations for DNS . . . . . . . . . 19
+ Intellectual Property and Copyright Statements . . . . . . . . 21
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1. Introduction
This memo presents operational considerations and issues with IPv6
DNS; it is meant to be an extensive summary and a list of pointers
for more information about IPv6 DNS considerations for those with
- experience of IPv4 DNS.
+ experience with IPv4 DNS.
The first section gives a brief overview of how IPv6 addresses and
names are represented in the DNS, how transport protocols and
The second section summarizes the special IPv6 address types and how
they relate to DNS. The third section describes observed DNS
- implementation misbehaviour which have a varying effect on the use of
- IPv6 records with DNS. The fourth section lists recommendations and
- considerations for provisioning services with DNS. The fifth section
- in turn looks at recommendations and considerations about providing
- IPv6 support in the resolvers. The sixth and seveth sections
- describe considerations with forward and reverse DNS updates,
- respectively. The eighth section introduces several miscellaneous
- IPv6 issues relating to DNS for which no better place has been found
- in this memo. Appendix A looks briefly at the requirements for
- site-local addressing.
+ implementation misbehaviours which have a varying effect on the use
+ of IPv6 records with DNS. The fourth section lists recommendations
+ and considerations for provisioning services with DNS. The fifth
+ section in turn looks at recommendations and considerations about
+ providing IPv6 support in the resolvers. The sixth and seventh
+ sections describe considerations with forward and reverse DNS
+ updates, respectively. The eighth section introduces several
+ miscellaneous IPv6 issues relating to DNS for which no better place
+ has been found in this memo. Appendix A looks briefly at the
+ requirements for site-local addressing.
1.1 Representing IPv6 Addresses in DNS Records
records in the reverse tree, or Bitlabels in the reverse tree is not
recommended [2].
-1.2 Difference of DNS Transport and DNS Records
+1.2 Independence of DNS Transport and DNS Records
+
+ DNS has been designed to present a single, globally unique name space
+ [6]. This property should be maintained, as described here and in
+ Section 1.3.
In DNS, the IP version used to transport the queries and responses is
independent of the records being queried: AAAA records can be queried
over IPv4, and A records over IPv6. The DNS servers must not make any
assumptions about what data to return for Answer and Authority
- sections.
-
- However, there is some debate whether the addresses in Additional
- section could be selected or filtered using hints obtained from which
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+ sections.
+ However, there is some debate whether the addresses in Additional
+ section could be selected or filtered using hints obtained from which
transport was being used; this has some obvious problems because in
many cases the transport protocol does not correlate with the
requests, and because a "bad" answer is in a way worse than no answer
The IPv6 addressing architecture [5] includes two kinds of local-use
addresses: link-local (fe80::/10) and site-local (fec0::/10). The
- site-local addresses are being deprecated [6], and are only discussed
+ site-local addresses are being deprecated [7], and are only discussed
in Appendix A.
Link-local addresses should never be published in DNS, because they
- have only local (to the connected link) significance [7].
+ have only local (to the connected link) significance [8].
2.2 Privacy (RFC3041) Address
- Privacy addresses (RFC3041 [8]) use a random number as the interface
+ Privacy addresses (RFC3041 [9]) use a random number as the interface
identifier. Publishing DNS records relating to such addresses would
defeat the purpose of the mechanism and is not recommended. If
absolutely necessary, a mapping could be made to some
- non-identifiable name, as described in [8].
-
-2.3 6to4 Addresses
-
- 6to4 [9] specifies an automatic tunneling mechanism which maps a
+ non-identifiable name, as described in [9].
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+2.3 6to4 Addresses
+
+ 6to4 [10] specifies an automatic tunneling mechanism which maps a
public IPv4 address V4ADDR to an IPv6 prefix 2002:V4ADDR::/48.
Providing reverse DNS delegation path for such addresses is a
challenge. Note that similar difficulties don't surface with the
- other automatic tunneling mechanisms (in parcicular, providing
- reverse DNS information for Teredo hosts whose address includes the
- UDP port of the NAT binding does not seem reasonable).
+ other automatic tunneling mechanisms (in particular, providing
+ reverse DNS information for Teredo [11] hosts whose address includes
+ the UDP port of the NAT binding does not seem reasonable).
If the reverse DNS population would be desirable (see Section 7.1 for
applicability), there are a number of ways to tackle the delegation
- path problem [10], some more applicable than the others.
+ path problem [12], some more applicable than the others.
- The main proposal [11] has been to allocate 2.0.0.2.ip6.arpa. to RIRs
+ The main proposal [13] has been to allocate 2.0.0.2.ip6.arpa. to RIRs
and let them do subdelegations in accordance to the delegations of
the respective IPv4 address space. This has a major practical
drawback: those ISPs and IPv4 address space holders where 6to4 is
being used do not, in general, provide any IPv6 services -- as
- otherwise, most people would not use 6to4 to begin with -- and it is
- improbable that the reverse delegation chain would be completed
- either. In most cases, creating such delegation chains might just
- lead to latencies caused by lookups for (almost always) non-existant
- DNS records.
+ otherwise, most people would not have to use 6to4 to begin with --
+ and it is improbable that the reverse delegation chain would be
+ completed either. In most cases, creating such delegation chains
+ might just lead to latencies caused by lookups for (almost always)
+ non-existent DNS records.
3. Observed DNS Implementation Misbehaviour
Several classes of misbehaviour in DNS servers, load-balancers and
- resolvers has been observed. Most of these are rather generic, not
+ resolvers have been observed. Most of these are rather generic, not
only applicable to IPv6 -- but in some cases, the consequences of
this misbehaviour are extremely severe in IPv6 environments and
deserve to be mentioned.
3.1 Misbehaviour of DNS Servers and Load-balancers
There are several classes of misbehaviour in certain DNS servers and
- load-balancers which have been noticed and documented [12]: some
+ load-balancers which have been noticed and documented [14]: some
implementations silently drop queries for unimplemented DNS records
types, or provide wrong answers to such queries (instead of a proper
negative reply). While typically these issues are not limited to
getaddrinfo() implementations, with AF_UNSPEC hint given, first try
to query the AAAA records of the name, and after receiving a
response, query the A records. This is done in a serial fashion -- if
- the first query is never responded (instead of properly returning a
- negative answer), significant timeouts will occur.
-
- In consequence, this is an enermous problem for IPv6 deployments, and
+ the first query is never responded to (instead of properly returning
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+ a negative answer), significant timeouts will occur.
+
+ In consequence, this is an enormous problem for IPv6 deployments, and
in some cases, IPv6 support in the software has even been disabled
due to these problems.
possible ways to mitigate the problem, e.g. by performing the lookups
somewhat in parallel and reducing the timeout as long as at least one
answer has been received; but such methods remain to be investigated;
- slightly more on this in Section 5.
+ slightly more on this is included in Section 5.
3.2 Misbehaviour of DNS Resolvers
Several classes of misbehaviour have also been noticed in DNS
- resolvers [13]. However, these do not seem to directly impair IPv6
+ resolvers [15]. However, these do not seem to directly impair IPv6
use, and are only referred to for completeness.
4. Recommendations for Service Provisioning using DNS
look up the mail via IMAP from "pobox.example.com", one should use
e.g. "smtp.example.com" for SMTP (for both message submission and
mail relaying between SMTP servers) and "imap.example.com" for IMAP.
- Note that in the specific case of STMP relaying, the server itself
+ Note that in the specific case of SMTP relaying, the server itself
must typically also be configured to know all its names to ensure
loops do not occur. DNS can provide a layer of indirection between
service names and where the service actually is, and using which
another. A specific reason why this is relevant for IPv6 is that the
different services may have a different level of IPv6 support -- that
is, one node providing multiple services might want to enable just
- one service to be IPv6-visible while keeping some others as
- IPv4-only. Using service names enables more flexibility with
- different IP versions as well.
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+ one service to be IPv6-visible while keeping some others as
+ IPv4-only. Using service names enables more flexibility with
+ different IP versions as well.
4.2 Separate vs the Same Service Names for IPv4 and IPv6
separately to a sub-domain, like, "service.ipv6.example.com".
Both methods have different characteristics. Using a sub-domain
- allows for easier service piloting, probably not disturbing the
+ allows for easier service piloting, minimizing the disturbance to the
"regular" users of IPv4 service; however, the service would not be
used without explicitly asking for it (or, within a restricted
network, modifying the DNS search path) -- so it will not actually be
In addition, if the AAAA record is added for the node, instead of
service as recommended, all the services of the node should be
- IPv6-enabled prior to adding the AAAA record.
+ IPv6-enabled prior to adding the resource record.
For example, if an IPv6 node is isolated from an IPv6 perspective
(e.g., it is not connected to IPv6 Internet) constraint #3 would mean
Consider the case of two dual-stack nodes, which both have IPv6
enabled, but the server does not have (global) IPv6 connectivity. As
- the client looks up the server's name, only A records are returned
- (if the recommendations above are followed), and no IPv6
- communication, which would be unsuccessful, is even attempted.
-
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+ the client looks up the server's name, only A records are returned
+ (if the recommendations above are followed), and no IPv6
+ communication, which would have been unsuccessful, is even attempted.
The issues are not always so black-and-white. Usually it's important
if the service offered using both protocols is of roughly equal
this is typically very important especially for interactive or
real-time services. In many cases, the quality of IPv6 connectivity
is not yet equal to that of IPv4, at least globally -- this has to be
- taken into consideration when enabling services [14].
+ taken into consideration when enabling services [16].
+
+4.4 The Use of TTL for IPv4 and IPv6 RRs
+
+ The behaviour of DNS caching when different TTL values are used for
+ different records of the same name requires explicit discussion. For
+ example, let's consider a part of a zone:
+
+ example.com. 300 IN MX foo.example.com.
+ foo.example.com. 300 IN A 192.0.2.1
+ foo.example.com. 100 IN AAAA 2001:db8::1
+
+ Now, when a caching resolver asks for the MX record of example.com,
+ it gets both A and AAAA records of foo.example.com. Then, after 100
+ seconds, the AAAA record is removed from the cache because its TTL
+ expired. Now, subsequent queries only result in the cache returning
+ the A record; after 200 seconds the A record is purged as well. So,
+ in this particular case, there is a window of 200 seconds when
+ incomplete information is returned from the cache.
-4.4 IPv6 Transport Guidelines for DNS Servers
+ Therefore, when the same name refers to both A and AAAA records,
+ these records should have the same TTL. Otherwise, the caches may
+ return incomplete information about the queried names. More issues
+ with caching and A/AAAA records is presented in the next section.
+
+4.5 Behaviour of Glue in Mixed IPv4/IPv6 Environments
+
+ In the previous section, we discussed the effect of impartial data
+ returned from the caches when the TTLs are not kept the same. Now,
+ we present another problem highlighted in the mixed IPv4/IPv6
+ environments.
+
+ Consider the case where the query is so long or the number of the
+ additional ("glue") records is so high that the response must either
+ be truncated (leading to a retry with TCP) or some of the additional
+ data removed from the reply. Further, resource record sets are never
+ "broken up", so if a name has 4 A records and 5 AAAA records, you can
+
+
+
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+
+ either return all 9, all 4 A records, all 5 AAAA records or nothing.
+
+ In the case of too much additional data, it might be tempting to not
+ return the AAAA records if the transport for DNS query was IPv4, or
+ not return the A records, if the transport was IPv6. However, this
+ breaks the model of independence of DNS transport and resource
+ records, as noted in Section 1.2.
+
+ This temptation would have significant problems in multiple areas.
+ Remember that often the end-node, which will be using the records, is
+ not the same one as the node requesting them from the authorative DNS
+ server (or even a caching resolver). So, whichever version the
+ requestor ("the middleman") uses makes no difference to the ultimate
+ user of the records. This might result in e.g., inappropriately
+ returning A records to an IPv6-only node, going through a
+ translation, or opening up another IP-level session (e.g., a PDP
+ context [31]).
+
+ The problem of too much additional data seems to be an operational
+ one: the zone administrator entering too many records which will be
+ returned either truncated or impartial to the users. A protocol fix
+ for this is using EDNS0 [32] to signal the capacity for larger UDP
+ packet sizes, pushing up the relevant threshold. The operational fix
+ for this is having the DNS server implementations return a warning
+ when the administrators create the zones which would result in too
+ much additional data being returned.
+
+4.6 IPv6 Transport Guidelines for DNS Servers
As described in Section 1.3 and [3], there should continue to be at
least one authorative IPv4 DNS server for every zone, even if the
zone has only IPv6 records. (Note that obviously, having more servers
- with robust connectivity would be preferably, but this is the
- recommendation.)
+ with robust connectivity would be preferable, but this is the minimum
+ recommendation; also see [17].)
5. Recommendations for DNS Resolver IPv6 Support
1. The system library does not know whether IPv6 has been enabled in
the kernel of the operating system: it may start looking up AAAA
+
+
+
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records with getaddrinfo() and AF_UNSPEC hint when the system is
upgraded to a system library version which supports IPv6.
3. The system library might implement a toggle which would apply
some heuristics to the "IPv6-readiness" of the node before
- starting to perform queries; for example, it could check that a
- link-local IPv6 address exists, or a global IPv6 address exists.
+ starting to perform queries; for example, it could check whether
+ only link-local IPv6 address(es) exists, or if at least one
+ global IPv6 address exists.
First, let us consider generic implications of unnecessary queries
for AAAA records: when looking up all the records in the DNS, AAAA
records are typically tried first, and then A records. These are
done in serial, and the A query is not performed until a response is
-
-
-
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-
received to the AAAA query. Considering the misbehaviour of DNS
servers and load-balancers, as described in Section 3.1, the look-up
delay for AAAA may incur additional unnecessary latency, and
An additional concern is the address selection, which may, in some
circumstances, prefer AAAA records over A records, even when the node
- does not have any IPv6 connectivity [15]. In some cases, the
+ does not have any IPv6 connectivity [18]. In some cases, the
implementation may attempt to connect or send a datagram on a
- physical link [16], incurring very long protocol timeouts, instead of
+ physical link [19], incurring very long protocol timeouts, instead of
quickly failing back to IPv4.
Now, we can consider the issues specific to each of the three
should be able to disable these unnecessary queries, for both latency
and reliability reasons. However, as IPv6 has not been enabled, the
connections to IPv6 addresses fail immediately, and if the
+
+
+
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+
application is programmed properly, the application can fall
- gracefully back to IPv4 [17].
+ gracefully back to IPv4 [20].
The second case is similar to the first, except it happens to a
smaller set of nodes when IPv6 has been enabled but connectivity has
an indication that either the address has been configured either from
a router advertisement, DHCPv6, or manually. Each would indicate at
least some form of IPv6 connectivity, even though there would not be
-
-
-
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guarantees of it.
- XXXX: are there any actual recommendations in here?!? :-)
+ These issues should be analyzed at more depth, and the fixes found
+ consensus on, perhaps in a separate document.
-5.2 Recursive DNS Server Discovery
+5.2 Recursive DNS Resolver Discovery
- Recursive IPv6 DNS server discovery is a subject of active debate at
- the moment: the main proposed mechanisms include the use of
- well-known addresses [18], the use of Router Advertisements to convey
- the information [19], and using DHCPv6 (or the stateless subset of it
- [20]) for DNS server configuration. No consensus has been reached
+ Recursive IPv6 DNS resolver discovery is a subject of active debate
+ at the moment: the main proposed mechanisms include the use of
+ well-known addresses [21], the use of Router Advertisements to convey
+ the information [22], and using DHCPv6 (or the stateless subset of it
+ [23]) for DNS resolver configuration. No consensus has been reached
yet.
- Note that IPv6 DNS server discovery, while an important topic, is not
- required for dual-stack nodes with dual-stack networks: IPv6 DNS
- records can very well be queried over IPv4.
+ Note that IPv6 DNS resolver discovery, while an important topic, is
+ not required for dual-stack nodes in dual-stack networks: IPv6 DNS
+ records can very well be queried over IPv4 as well.
5.3 IPv6 Transport Guidelines for Resolvers
While the topic how to enable updating the forward DNS, i.e., the
mapping from names to the correct new addresses, is not specific to
+
+
+
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+
IPv6, it bears thinking about especially due to adding Stateless
- Address Autoconfiguration [21] to the mix.
+ Address Autoconfiguration [24] to the mix.
Typically forward DNS updates are more manageable than doing them in
the reverse DNS, because the updater can, typically, be assumed to
point to a new address.
A more complex form of DNS updates -- adding a whole new name to a
- DNS zone, instead of updating an existing one -- is considered
- out-of-scope (XXX: at least for now, send text/feedback!).
+ DNS zone, instead of updating an existing name -- is considered
+ out-of-scope: this is not an IPv6-specific problem, and one still
+ being explored.
6.1 Manual or Custom DNS Updates
fashion or by running non-standardized protocols. These are not
considered at more length in this memo.
-
-
-
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6.2 Dynamic DNS
- Dynamic DNS updates (DDNS) [22][23] is a standardized mechanism for
+ Dynamic DNS updates (DDNS) [25][26] is a standardized mechanism for
dynamically updating the DNS. It works equally well with stateless
address autoconfiguration (SLAAC), DHCPv6 or manual address
- configuration. The only (minor) twist that with SLAAC, the DNS
+ configuration. The only (minor) twist is that with SLAAC, the DNS
server cannot tie the authentication of the user to the IP address,
and stronger mechanisms must be used. Actually, relying on IP
addresses for Dynamic DNS is rather insecure at best, so this is
probably not a significant problem (but requires that the
authorization keying will be explicitly configured).
- Note that the nodes must somehow be configured with the information
- about the servers where they will attempt to update their addresses,
- sufficient security material for authenticating themselves to the
- server, and the hostname they will be updating. Unless otherwise
- configured, the first could be obtained by looking up the authorative
- name servers for the hostname; the second must be configured
- explicitly unless one chooses to trust the IP address -based
- authentication (not a good idea); and lastly, the nodename is
- typically pre-configured somehow on the node, e.g. at install time.
+ Note that with DHCP, it is also possible that the DHCP server updates
+ the DNS, not the host. The host might only indicate in the DHCP
+ exchange which hostname it would prefer, and the DHCP server would
+ make the appropriate updates. Nonetheless, while this makes setting
+ up a secure channel between the updater and the DNS server easier, it
+ does not help much with "content" security, i.e., whether the
+ hostname was acceptable -- if the DNS server does not include
+ policies, they must be included in the DHCP server (e.g., a regular
+ host should not be able to state that its name is "www.example.com").
+
+ The nodes must somehow be configured with the information about the
+ servers where they will attempt to update their addresses, sufficient
+ security material for authenticating themselves to the server, and
+ the hostname they will be updating. Unless otherwise configured, the
+ first could be obtained by looking up the authorative name servers
+ for the hostname; the second must be configured explicitly unless one
+
+
+
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+
+
+ chooses to trust the IP address -based authentication (not a good
+ idea); and lastly, the nodename is typically pre-configured somehow
+ on the node, e.g. at install time.
Care should be observed when updating the addresses not to use longer
TTLs for addresses than are preferred lifetimes for the
- autoconfigured addresses, so that if the node is renumberedin a
+ autoconfigured addresses, so that if the node is renumbered in a
managed fashion, the amount of stale DNS information is kept to the
- minimum.
+ minimum. Actually, the DNS TTL should be much shorter (e.g., a half
+ or a third) than the lifetime of an address; that way, the node can
+ start lowering the DNS TTL if it seems like the address has not be
+ renewed/refreshed in a while. Some discussion on how to manage the
+ DNS TTL is included in [28].
7. Considerations about Reverse DNS Updating
- Forward DNS updating was rather straightforward; reverse DNS is
+ Forward DNS updating is rather straightforward; reverse DNS is
significantly trickier especially with certain mechanisms. However,
first it makes sense to look at the applicability of reverse DNS in
the first place.
reverse record for an address would signal some form of
authorization).
- One additional, maybe slightly more useful applicability is ensuring
- the reverse and forward DNS contents match and correspond to a
- configured name or domain. As a security check, it is typically
-
-
-
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-
- accompanied by other mechanisms, such as a user/password login; the
- main purpose of the DNS check is to weed out the majority of
- unauthorized users, and if someone managed to bypass the checks, he
- would still need to authenticate "properly".
+ One additional, maybe slightly more useful usage is ensuring the
+ reverse and forward DNS contents match and correspond to a configured
+ name or domain. As a security check, it is typically accompanied by
+ other mechanisms, such as a user/password login; the main purpose of
+ the DNS check is to weed out the majority of unauthorized users, and
+ if someone managed to bypass the checks, he would still need to
+ authenticate "properly".
It is not clear whether it makes sense to require or recommend that
reverse DNS records be updated. In many cases, it would just make
exists at all) should be modified as soon as possible to avoid such
lookups completely.
+ The applicability is discussed at more length in [29].
+
+
+
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+
+
7.2 Manual or Custom DNS Updates
- Reverse DNS can be updated using manual or custom methods, naturally.
+ Reverse DNS can of course be updated using manual or custom methods.
These are not further described here, except for one special case.
One way to deploy reverse DNS would be to use wildcard records, for
but would at least provide some form of "topological information" or
"weak authorization" if that is really considered to be useful. Note
that this is not actually updating the DNS as such, as the whole
- point is to avoid DNS updates completely by manual configuration of a
+ point is to avoid DNS updates completely by manually configuring a
generic name.
7.3 DDNS with Stateless Address Autoconfiguration
disconnected, and cannot send a DNS update using the correct source
address to remove a record.
-7.4 DDNS With DHCP
+ To insert or update the record, the node must discover the DNS server
+ to send the update to somehow, similar to as discussed in Section
+ 6.2. One way to automate this is looking up the DNS server
+ authoritative for the IP address being updated, but the security
+ material (unless the IP address -based authorization is trusted) must
+ also be established by some other means.
+
+7.4 DDNS with DHCP
With DHCP, the reverse DNS name is typically already inserted to the
- DNS that reflects to the name (e.g., "dhcp-67.example.com").
+ DNS that reflects to the name (e.g., "dhcp-67.example.com"). This is
+ pre-configured, and requires no updating.
+
+ If a more explicit control is required, similar considerations as
+ with SLAAC apply, except for the fact that typically one must update
+ a reverse DNS record instead of inserting one -- due to a denser
+ address assignment policy -- and updating a record seems like a
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- If a more explicit control is required, similar considerations as
- with SLAAC apply, except for the fact that typically one must update
- a reverse DNS record instead of inserting one -- due to a denser
- address assignment policy -- and updating a record seems like a
slightly more difficult thing to secure.
+ Note that when using DHCP, either the host or the DHCP server could
+ perform the DNS updates; see the implications in Section 6.2.
+
7.5 DDNS with Dynamic Prefix Delegation
In cases where more than one address is being used and updated, one
8.1 NAT-PT with DNS-ALG
- NAT-PT [24] DNS-ALG is a critical component (unless something
+ NAT-PT [27] DNS-ALG is a critical component (unless something
replacing that functionality is specified) which mangles A records to
look like AAAA records to the IPv6-only nodes. Numerous problems have
- been identified with DNS-ALG [25].
+ been identified with DNS-ALG [30].
8.2 Renumbering Procedures and Applications' Use of DNS
- One of the most difficult problems of renumbering procedures [26] is
- that an application which gets a DNS name disregards information such
- as TTL, and uses the result obtained from DNS as long as it happens
- to be stored in the memory of the application. For applications
- which run for a long time, this could be days, weeks or even months;
- some applications may be clever enough to organize the data
- structures and functions in such a manner that look-ups get refreshed
- now and then. This is an issue with no clear solution.
+ One of the most difficult problems of systematic IP address
+ renumbering procedures [28] is that an application which looks up a
+ DNS name disregards information such as TTL, and uses the result
+ obtained from DNS as long as it happens to be stored in the memory of
+ the application. For applications which run for a long time, this
+ could be days, weeks or even months; some applications may be clever
+ enough to organize the data structures and functions in such a manner
+ that look-ups get refreshed now and then.
-9. Acknowledgements
+ While the issue appears to have a clear solution, "fix the
+ applications", practically this is not reasonable immediate advice;
+ the TTL information is not typically available in the APIs and
+ libraries (so, the advice becomes "fix the applications, APIs and
+ libraries"), and a lot more analysis is needed on how to practically
+ go about to achieve the ultimate goal of avoiding using the names
+ longer than expected.
- Some recommendations (Section 4.3, Section 5.1) about IPv6 service
- provisioning were moved here from [27] by Erik Nordmark and Bob
- Gilligan. Havard Eidnes provided useful feedback and improvements.
+Durand, et al. Expires July 1, 2004 [Page 15]
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+9. Acknowledgements
+ Some recommendations (Section 4.3, Section 5.1) about IPv6 service
+ provisioning were moved here from [33] by Erik Nordmark and Bob
+ Gilligan. Havard Eidnes and Michael Patton provided useful feedback
+ and improvements. Scott Rose, Rob Austein, Masataka Ohta, and Mark
+ Andrews helped in clarifying the issues regarding additional data and
+ the use of TTL.
10. Security Considerations
This document reviews the operational procedures for IPv6 DNS
operations and does not have security considerations in itself.
- However, it is worth nothing that in particular with Dynamic DNS
+ However, it is worth noting that in particular with Dynamic DNS
Updates, security models based on the source address validation are
very weak and cannot be recommended. On the other hand, it should be
noted that setting up an authorization mechanism (e.g., a shared
[5] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
- [6] Huitema, C. and B. Carpenter, "Deprecating Site Local
- Addresses", draft-ietf-ipv6-deprecate-site-local-02 (work in
- progress), November 2003.
- [7] Hazel, P., "IP Addresses that should never appear in the public
- DNS", draft-ietf-dnsop-dontpublish-unreachable-03 (work in
- progress), February 2002.
- [8] Narten, T. and R. Draves, "Privacy Extensions for Stateless
+Durand, et al. Expires July 1, 2004 [Page 16]
+\f
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-\f
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+ [6] Internet Architecture Board, "IAB Technical Comment on the
+ Unique DNS Root", RFC 2826, May 2000.
+
+ [7] Huitema, C. and B. Carpenter, "Deprecating Site Local
+ Addresses", draft-ietf-ipv6-deprecate-site-local-02 (work in
+ progress), November 2003.
+ [8] Hazel, P., "IP Addresses that should never appear in the public
+ DNS", draft-ietf-dnsop-dontpublish-unreachable-03 (work in
+ progress), February 2002.
+ [9] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
- [9] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
+ [10] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
- [10] Moore, K., "6to4 and DNS", draft-moore-6to4-dns-03 (work in
+ [11] Huitema, C., "Teredo: Tunneling IPv6 over UDP through NATs",
+ draft-huitema-v6ops-teredo-00 (work in progress), June 2003.
+
+ [12] Moore, K., "6to4 and DNS", draft-moore-6to4-dns-03 (work in
progress), October 2002.
- [11] Bush, R. and J. Damas, "Delegation of 2.0.0.2.ip6.arpa",
+ [13] Bush, R. and J. Damas, "Delegation of 2.0.0.2.ip6.arpa",
draft-ymbk-6to4-arpa-delegation-00 (work in progress), February
2003.
- [12] Morishita, Y. and T. Jinmei, "Common Misbehavior against DNS
+ [14] Morishita, Y. and T. Jinmei, "Common Misbehavior against DNS
Queries for IPv6 Addresses",
draft-morishita-dnsop-misbehavior-against-aaaa-00 (work in
progress), June 2003.
- [13] Larson, M. and P. Barber, "Observed DNS Resolution
+ [15] Larson, M. and P. Barber, "Observed DNS Resolution
Misbehavior", draft-ietf-dnsop-bad-dns-res-01 (work in
progress), June 2003.
- [14] Savola, P., "Moving from 6bone to IPv6 Internet",
+ [16] Savola, P., "Moving from 6bone to IPv6 Internet",
draft-savola-v6ops-6bone-mess-01 (work in progress), November
2002.
- [15] Roy, S., "Dual Stack IPv6 on by Default",
+ [17] Elz, R., Bush, R., Bradner, S. and M. Patton, "Selection and
+ Operation of Secondary DNS Servers", BCP 16, RFC 2182, July
+ 1997.
+
+ [18] Roy, S., "Dual Stack IPv6 on by Default",
draft-ietf-v6ops-v6onbydefault-00 (work in progress), October
2003.
- [16] Roy, S., "IPv6 Neighbor Discovery On-Link Assumption Considered
- Harmful", draft-ietf-v6ops-onlinkassumption-00 (work in
- progress), October 2003.
- [17] Shin, M., "Application Aspects of IPv6 Transition",
- draft-shin-v6ops-application-transition-02 (work in progress),
- October 2003.
- [18] Ohta, M., "Preconfigured DNS Server Addresses",
- draft-ohta-preconfigured-dns-00 (work in progress), July 2003.
- [19] Jeong, J., "IPv6 DNS Discovery based on Router Advertisement",
- draft-jeong-dnsop-ipv6-dns-discovery-00 (work in progress),
- July 2003.
+Durand, et al. Expires July 1, 2004 [Page 17]
+\f
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- [20] Droms, R., "A Guide to Implementing Stateless DHCPv6 Service",
- draft-ietf-dhc-dhcpv6-stateless-01 (work in progress), October
- 2003.
+ [19] Roy, S., "IPv6 Neighbor Discovery On-Link Assumption Considered
+ Harmful", draft-ietf-v6ops-onlinkassumption-00 (work in
+ progress), October 2003.
+ [20] Shin, M., "Application Aspects of IPv6 Transition",
+ draft-ietf-v6ops-application-transition-00 (work in progress),
+ December 2003.
+ [21] Ohta, M., "Preconfigured DNS Server Addresses",
+ draft-ohta-preconfigured-dns-00 (work in progress), July 2003.
-Durand, et al. Expires May 1, 2004 [Page 15]
-\f
-Internet-Draft Considerations and Issues with IPv6 DNS Nov 2003
+ [22] Jeong, J., "IPv6 DNS Discovery based on Router Advertisement",
+ draft-jeong-dnsop-ipv6-dns-discovery-00 (work in progress),
+ July 2003.
+ [23] Droms, R., "Stateless DHCP Service for IPv6",
+ draft-ietf-dhc-dhcpv6-stateless-04 (work in progress), January
+ 2004.
- [21] Thomson, S. and T. Narten, "IPv6 Stateless Address
+ [24] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
- [22] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
+ [25] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
April 1997.
- [23] Wellington, B., "Secure Domain Name System (DNS) Dynamic
+ [26] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000.
- [24] Tsirtsis, G. and P. Srisuresh, "Network Address Translation -
+ [27] Tsirtsis, G. and P. Srisuresh, "Network Address Translation -
Protocol Translation (NAT-PT)", RFC 2766, February 2000.
- [25] Durand, A., "Issues with NAT-PT DNS ALG in RFC2766",
+ [28] Baker, F., "Procedures for Renumbering an IPv6 Network without
+ a Flag Day", draft-baker-ipv6-renumber-procedure-01 (work in
+ progress), October 2003.
+
+ [29] Senie, D., "Requiring DNS IN-ADDR Mapping",
+ draft-ietf-dnsop-inaddr-required-03 (work in progress), March
+ 2002.
+
+ [30] Durand, A., "Issues with NAT-PT DNS ALG in RFC2766",
draft-durand-v6ops-natpt-dns-alg-issues-00 (work in progress),
February 2003.
- [26] Baker, F., "Procedures for Renumbering an IPv6 Network without
- a Flag Day", draft-baker-ipv6-renumber-procedure-01 (work in
- progress), October 2003.
+ [31] Wiljakka, J., "Analysis on IPv6 Transition in 3GPP Networks",
+ draft-ietf-v6ops-3gpp-analysis-07 (work in progress), October
+ 2003.
+
+
+
+
+Durand, et al. Expires July 1, 2004 [Page 18]
+\f
+Internet-Draft Considerations and Issues with IPv6 DNS Jan 2004
- [27] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for
+
+ [32] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
+ August 1999.
+
+ [33] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for
IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2-01 (work in
progress), October 2003.
EMail: johani@autonomica.se
-
-
-
-
-
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-
-
Pekka Savola
CSC/FUNET
As site-local addressing is being deprecated, and it is not yet clear
whether an addressing-based replacement (and which kind) is devised,
- the considerations for site-local addressing are introduced here.
+ the considerations for site-local addressing are discussed briefly
+ here.
The interactions with DNS come in two flavors: forward and reverse
DNS.
To actually use site-local addresses within a site, this implies the
deployment of a "split-faced" or a fragmented DNS name space, for the
+
+
+
+Durand, et al. Expires July 1, 2004 [Page 19]
+\f
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+
+
zones internal to the site, and the outsiders' view to it. The
procedures to achieve this are not elaborated here. The implication
is that site-local addresses must not be published in the public DNS.
servers, not e.g. starting from the root servers, so that the
site-local information may be provided locally. Note that the
experience private addresses in IPv4 has shown that the root servers
- get loaded for requests for private address lookups in any case.
+ get loaded for requests for private address lookups in any.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
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+Internet-Draft Considerations and Issues with IPv6 DNS Jan 2004
Intellectual Property Statement
Full Copyright Statement
- Copyright (C) The Internet Society (2003). All Rights Reserved.
+ Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
-Durand, et al. Expires May 1, 2004 [Page 18]
+Durand, et al. Expires July 1, 2004 [Page 21]
\f
-Internet-Draft Considerations and Issues with IPv6 DNS Nov 2003
+Internet-Draft Considerations and Issues with IPv6 DNS Jan 2004
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
-Durand, et al. Expires May 1, 2004 [Page 19]
+Durand, et al. Expires July 1, 2004 [Page 22]
\f
projects / thirdparty / bind9.git / commitdiff
