draft-ietf-dnsext-rfc2672bis-dname-02.txt   draft-ietf-dnsext-rfc2672bis-dname-03.txt 
DNS Extensions Working Group S. Rose DNS Extensions Working Group S. Rose
Internet-Draft NIST Internet-Draft NIST
Intended status: Standards Track W. Wijngaards Intended status: Standards Track W. Wijngaards
Expires: October 26, 2007 NLnet Labs Expires: December 6, 2007 NLnet Labs
April 24, 2007 June 4, 2007
Update to DNAME Redirection in the DNS Update to DNAME Redirection in the DNS
draft-ietf-dnsext-rfc2672bis-dname-02 draft-ietf-dnsext-rfc2672bis-dname-03
Status of This Memo Status of This Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on October 26, 2007. This Internet-Draft will expire on December 6, 2007.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The DNAME record provides redirection for a sub-tree of the domain The DNAME record provides redirection for a sub-tree of the domain
name tree in the DNS system. That is, all names that end with a name tree in the DNS system. That is, all names that end with a
particular suffix are redirected to another part of the DNS. This is particular suffix are redirected to another part of the DNS. This is
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3.1. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. CNAME synthesis . . . . . . . . . . . . . . . . . . . . . 6 3.2. CNAME synthesis . . . . . . . . . . . . . . . . . . . . . 6
3.3. Acceptance and Intermediate Storage . . . . . . . . . . . 7 3.3. Acceptance and Intermediate Storage . . . . . . . . . . . 7
3.4. Server algorithm . . . . . . . . . . . . . . . . . . . . . 7 3.4. Server algorithm . . . . . . . . . . . . . . . . . . . . . 7
4. DNAME Discussions in Other Documents . . . . . . . . . . . . . 9 4. DNAME Discussions in Other Documents . . . . . . . . . . . . . 9
5. Other Issues with DNAME . . . . . . . . . . . . . . . . . . . 10 5. Other Issues with DNAME . . . . . . . . . . . . . . . . . . . 10
5.1. MX, NS and PTR Records Must Point to Target of DNAME . . . 10 5.1. MX, NS and PTR Records Must Point to Target of DNAME . . . 10
5.2. Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 10 5.2. Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 10
5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 11 5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 10
5.3.1. DNAME bit in NSEC/NSEC3 type map . . . . . . . . . . . 11 5.3.1. DNAME bit in NSEC/NSEC3 type map . . . . . . . . . . . 10
5.3.2. Other issues with NSEC3 and DNAME . . . . . . . . . . 11 5.3.2. Other issues with NSEC3 and DNAME . . . . . . . . . . 11
5.3.3. Validators Must Understand DNAME . . . . . . . . . . . 11 5.3.3. Validators Must Understand DNAME . . . . . . . . . . . 11
5.3.3.1. DNAME in Bitmap Causes Invalid Name Error . . . . 11 5.3.3.1. DNAME in Bitmap Causes Invalid Name Error . . . . 11
5.3.3.2. Valid Name Error Response Involving DNAME in 5.3.3.2. Valid Name Error Response Involving DNAME in
Bitmap . . . . . . . . . . . . . . . . . . . . . . 12 Bitmap . . . . . . . . . . . . . . . . . . . . . . 11
5.3.3.3. Response With Synthesized CNAME . . . . . . . . . 12 5.3.3.3. Response With Synthesized CNAME . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. Normative References . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
DNAME is a DNS Resource Record type. DNAME provides redirection from DNAME is a DNS Resource Record type. DNAME provides redirection from
a part of the DNS name tree to another part of the DNS name tree. a part of the DNS name tree to another part of the DNS name tree.
For example, given a query for foo.example.com and a DNAME from For example, given a query for foo.example.com and a DNAME from
example.com to example.net, the query would be redirected to example.com to example.net, the query would be redirected to
foo.example.net. With the same DNAME a query for foo.bar.example.com foo.example.net. With the same DNAME a query for foo.bar.example.com
would be redirected to foo.bar.example.net. would be redirected to foo.bar.example.net.
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renumbering. So that with a careful set-up a renumbering event in renumbering. So that with a careful set-up a renumbering event in
the network causes no change to the authoritative server that has the the network causes no change to the authoritative server that has the
address-to-name mappings. Examples in practice are classless reverse address-to-name mappings. Examples in practice are classless reverse
address space delegations and punycode alternates for domain spaces. address space delegations and punycode alternates for domain spaces.
Other usage of DNAME lies in redirection of name spaces. For Other usage of DNAME lies in redirection of name spaces. For
example, a zone administrator may want subtrees of the DNS to contain example, a zone administrator may want subtrees of the DNS to contain
the same information. DNAME is also used for redirection of ENUM the same information. DNAME is also used for redirection of ENUM
domains to another maintaining party. domains to another maintaining party.
This update to DNAME does not change the wire format or the handling This update to DNAME does not change the wire format or the server
of DNAME Resource Records by existing software. Discussion is added processing of DNAME Resource Records. Resolvers now have to be able
on problems that may be encountered when using DNAME. to accept synthesized CNAME records both with zero and nonzero TTLs,
and resolvers now have to accept a reply without synthesized CNAME
records on queries with DO-bit enabled. Discussion is added on
problems that may be encountered when using DNAME.
2. The DNAME Resource Record 2. The DNAME Resource Record
2.1. Format 2.1. Format
The DNAME RR has mnemonic DNAME and type code 39 (decimal). The DNAME RR has mnemonic DNAME and type code 39 (decimal).
The format of the DNAME record has not changed from the original The format of the DNAME record has not changed from the original
specification in RFC 2672. DNAME has the following format: specification in RFC 2672. DNAME has the following format:
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The DNAME owner name can be compressed like any other owner name. The DNAME owner name can be compressed like any other owner name.
The DNAME RDATA target name MUST NOT be sent out in compressed form, The DNAME RDATA target name MUST NOT be sent out in compressed form,
so that a DNAME RR can be treated as an unknown type. so that a DNAME RR can be treated as an unknown type.
Although the previous specification [RFC2672] talked about signaling Although the previous specification [RFC2672] talked about signaling
to allow compression of the target name, no such signaling is to allow compression of the target name, no such signaling is
explicitly specified. explicitly specified.
RFC2672 stated that the EDNS version had a meaning for understanding RFC2672 stated that the EDNS version had a meaning for understanding
of DNAME and DNAME target name compression. This document updates of DNAME and DNAME target name compression. This document updates
RFC2672, in that there is no EDNS version signaling for DNAME. RFC2672, in that there is no EDNS version signaling for DNAME as of
yet.
3. Processing 3. Processing
3.1. Wildcards 3.1. Wildcards
The use of DNAME in conjunction with wildcards is discouraged The use of DNAME in conjunction with wildcards is discouraged
[RFC4592]. Thus records of the form "*.example.com DNAME [RFC4592]. Thus records of the form "*.example.com DNAME
example.net" SHOULD NOT be used. example.net" SHOULD NOT be used.
The interaction between the expansion of the wildcard and the The interaction between the expansion of the wildcard and the
redirection of the DNAME is non-deterministic. Because the redirection of the DNAME is non-deterministic. Because the
processing is non-deterministic, DNSSEC validating resolvers may not processing is non-deterministic, DNSSEC validating resolvers may not
be able to validate a wildcarded DNAME. be able to validate a wildcarded DNAME.
A server MAY give a warning that the behaviour is unspecified if such A server MAY give a warning that the behavior is unspecified if such
a wildcarded DNAME is loaded. a wildcarded DNAME is loaded.
3.2. CNAME synthesis 3.2. CNAME synthesis
On the server side, the DNAME RR record is always included in the On the server side, the DNAME RR record is always included in the
answer section of a query. A CNAME RR record with TTL 0 is answer section of a query. A CNAME RR record with TTL 0 is
synthesized for old resolvers, specifically for the QNAME in the synthesized for old resolvers, specifically for the QNAME in the
query. DNSSEC [RFC4033], [RFC4034], [RFC4035] says that the query. DNSSEC [RFC4033], [RFC4034], [RFC4035] says that the
synthesized CNAME does not have to be signed. The DNAME has an RRSIG synthesized CNAME does not have to be signed. The DNAME has an RRSIG
and a validating resolver can check the CNAME against the DNAME and a validating resolver can check the CNAME against the DNAME
record and validate the DNAME record. record and validate the DNAME record.
It does not make sense for the authoritative server to follow the It does not make sense for the authoritative server to follow the
chain of DNAMEs, CNAMEs and wildcards outside of the zone of the chain of DNAMEs, CNAMEs and wildcards outside of the zone of the
query, as modern resolvers will remove out-of-zone information from query, as modern resolvers will remove out-of-zone information from
the answer. the answer.
The EDNS DNSSEC-OK bit signals understanding of the DNAME record
[RFC4034]. If set, the synthesized CNAME MAY be omitted, since it is
not signed and therefore not useful for validation and consumes
bandwidth. This is a change from RFC2672, which specified CNAMEs had
to be synthesized for all EDNS0, or non-extended queries.
Resolvers MUST be able to handle a synthesized CNAME TTL of zero or Resolvers MUST be able to handle a synthesized CNAME TTL of zero or
equal to the TTL of the corresponding DNAME record. The TTL of zero equal to the TTL of the corresponding DNAME record. The TTL of zero
means that the CNAME can be discarded immediately after processing means that the CNAME can be discarded immediately after processing
the answer. DNSSEC aware resolvers (setting the DNSSEC-OK bit) MUST the answer. DNSSEC aware resolvers (setting the DNSSEC-OK bit) MUST
be able to handle responses with only the DNAME RR and no synthesized be able to handle responses with only the DNAME RR and no synthesized
CNAMEs. CNAMEs.
Servers MUST be able to answer a query for a synthesized CNAME. An Servers MUST be able to answer a query for a synthesized CNAME. An
answer containing the synthesized CNAME cannot contain an error answer containing the synthesized CNAME cannot contain an error
(since a CNAME has been followed), as per RFC 1034 CNAME rules. (since a CNAME has been followed), as per RFC 1034 CNAME rules.
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DNS Caches MUST NOT allow data to be cached below the owner of a DNS Caches MUST NOT allow data to be cached below the owner of a
DNAME RR, except CNAME records or perhaps NSEC3 records and their DNAME RR, except CNAME records or perhaps NSEC3 records and their
signatures. CNAME records below the owner of a DNAME MUST be re- signatures. CNAME records below the owner of a DNAME MUST be re-
synthesized from the DNAME, or checked against the DNAME record synthesized from the DNAME, or checked against the DNAME record
before sending them out. This improves consistency of the DNAME and before sending them out. This improves consistency of the DNAME and
CNAME records below the owner of the DNAME. CNAME records below the owner of the DNAME.
3.4. Server algorithm 3.4. Server algorithm
Below the server algorithm, which appeared in RFC 2672 Section 4.1, Below the server algorithm, which appeared in RFC 2672 Section 4.1,
is expanded to handle the DO bit. is displayed. It includes DNAME substitution and CNAME synthesis.
1. Set or clear the value of recursion available in the response 1. Set or clear the value of recursion available in the response
depending on whether the name server is willing to provide depending on whether the name server is willing to provide
recursive service. If recursive service is available and recursive service. If recursive service is available and
requested via the RD bit in the query, go to step 5, otherwise requested via the RD bit in the query, go to step 5, otherwise
step 2. step 2.
2. Search the available zones for the zone which is the nearest 2. Search the available zones for the zone which is the nearest
ancestor to QNAME. If such a zone is found, go to step 3, ancestor to QNAME. If such a zone is found, go to step 3,
otherwise step 4. otherwise step 4.
3. Start matching down, label by label, in the zone. The matching 3. Start matching down, label by label, in the zone. The matching
process can terminate several ways: process can terminate several ways:
A. If the whole of QNAME is matched, we have found the node. A. If the whole of QNAME is matched, we have found the node.
If the data at the node is a CNAME, and QTYPE doesn't match If the data at the node is a CNAME, and QTYPE does not match
CNAME, copy the CNAME RR into the answer section of the CNAME, copy the CNAME RR into the answer section of the
response, change QNAME to the canonical name in the CNAME RR, response, change QNAME to the canonical name in the CNAME RR,
and go back to step 1. and go back to step 1.
Otherwise, copy all RRs which match QTYPE into the answer Otherwise, copy all RRs which match QTYPE into the answer
section and go to step 6. section and go to step 6.
B. If a match would take us out of the authoritative data, we B. If a match would take us out of the authoritative data, we
have a referral. This happens when we encounter a node with have a referral. This happens when we encounter a node with
NS RRs marking cuts along the bottom of a zone. NS RRs marking cuts along the bottom of a zone.
Copy the NS RRs for the subzone into the authority section of Copy the NS RRs for the subzone into the authority section of
the reply. Put whatever addresses are available into the the reply. Put whatever addresses are available into the
additional section, using glue RRs if the addresses are not additional section, using glue RRs if the addresses are not
available from authoritative data or the cache. Go to step available from authoritative data or the cache. Go to step
4. 4.
C. If at some label, a match is impossible (i.e., the C. If at some label, a match is impossible (i.e., the
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available from authoritative data or the cache. Go to step available from authoritative data or the cache. Go to step
4. 4.
C. If at some label, a match is impossible (i.e., the C. If at some label, a match is impossible (i.e., the
corresponding label does not exist), look to see whether the corresponding label does not exist), look to see whether the
last label matched has a DNAME record. last label matched has a DNAME record.
If a DNAME record exists at that point, copy that record into If a DNAME record exists at that point, copy that record into
the answer section. If substitution of its <target> for its the answer section. If substitution of its <target> for its
<owner> in QNAME would overflow the legal size for a <domain- <owner> in QNAME would overflow the legal size for a <domain-
name>, set RCODE to YXDOMAIN [RFC2136] and exit; otherwise name>, set RCODE to YXDOMAIN [RFC2136] and exit; otherwise
perform the substitution and continue. The server SHOULD perform the substitution and continue. The server MUST
synthesize a CNAME record as described above and include it synthesize a CNAME record as described above and include it
in the answer section. The server MAY omit this CNAME in the answer section. Go back to step 1.
synthesis if the query has the EDNS DNSSEC-OK bit set. Go
back to step 1.
If there was no DNAME record, look to see if the "*" label If there was no DNAME record, look to see if the "*" label
exists. exists.
If the "*" label does not exist, check whether the name we If the "*" label does not exist, check whether the name we
are looking for is the original QNAME in the query or a name are looking for is the original QNAME in the query or a name
we have followed due to a CNAME or DNAME. If the name is we have followed due to a CNAME or DNAME. If the name is
original, set an authoritative name error in the response and original, set an authoritative name error in the response and
exit. Otherwise just exit. exit. Otherwise just exit.
If the "*" label does exist, match RRs at that node against If the "*" label does exist, match RRs at that node against
QTYPE. If any match, copy them into the answer section, but QTYPE. If any match, copy them into the answer section, but
set the owner of the RR to be QNAME, and not the node with set the owner of the RR to be QNAME, and not the node with
the "*" label. Go to step 6. the "*" label. If the data at the node with the "*" label is
a CNAME, and QTYPE doesn't match CNAME, copy the CNAME RR
into the answer section of the response changing the owner
name to the QNAME, change QNAME to the canonical name in the
CNAME RR, and go back to step 1. Otherwise, Go to step 6.
4. Start matching down in the cache. If QNAME is found in the 4. Start matching down in the cache. If QNAME is found in the
cache, copy all RRs attached to it that match QTYPE into the cache, copy all RRs attached to it that match QTYPE into the
answer section. If QNAME is not found in the cache but a DNAME answer section. If QNAME is not found in the cache but a DNAME
record is present at an ancestor of QNAME, copy that DNAME record record is present at an ancestor of QNAME, copy that DNAME record
into the answer section. If there was no delegation from into the answer section. If there was no delegation from
authoritative data, look for the best one from the cache, and put authoritative data, look for the best one from the cache, and put
it in the authority section. Go to step 6. it in the authority section. Go to step 6.
5. Use the local resolver or a copy of its algorithm to answer the 5. Use the local resolver or a copy of its algorithm to answer the
query. Store the results, including any intermediate CNAMEs and query. Store the results, including any intermediate CNAMEs and
DNAMEs, in the answer section of the response. DNAMEs, in the answer section of the response.
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In Section 5.3.3 examples are given that illustrate this need. These In Section 5.3.3 examples are given that illustrate this need. These
examples are shown with NSEC records, but similar cases exist for examples are shown with NSEC records, but similar cases exist for
NSEC3. NSEC3.
8. Acknowledgments 8. Acknowledgments
The authors of this draft would like to acknowledge Matt Larson for The authors of this draft would like to acknowledge Matt Larson for
beginning this effort to address the issues related to the DNAME RR beginning this effort to address the issues related to the DNAME RR
type. type.
9. Normative References 9. References
9.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[RFC1912] Barr, D., "Common DNS Operational and Configuration
Errors", RFC 1912, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", "Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997. RFC 2136, April 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997. Specification", RFC 2181, July 1997.
[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", [RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection",
RFC 2672, August 1999. RFC 2672, August 1999.
[RFC3363] Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
Hain, "Representing Internet Protocol version 6 (IPv6)
Addresses in the Domain Name System (DNS)", RFC 3363,
August 2002.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, September 2003. (RR) Types", RFC 3597, September 2003.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005. RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005. RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
skipping to change at page 14, line 16 skipping to change at page 14, line 6
RFC 4033, March 2005. RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005. RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
[RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294,
April 2006.
[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, July 2006. System", RFC 4592, July 2006.
9.2. Informative References
[RFC1912] Barr, D., "Common DNS Operational and Configuration
Errors", RFC 1912, February 1996.
[RFC3363] Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
Hain, "Representing Internet Protocol version 6 (IPv6)
Addresses in the Domain Name System (DNS)", RFC 3363,
August 2002.
[RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294,
April 2006.
Authors' Addresses Authors' Addresses
Scott Rose Scott Rose
NIST NIST
100 Bureau Dr. 100 Bureau Dr.
Gaithersburg, MD 20899 Gaithersburg, MD 20899
USA USA
Phone: +1-301-975-8439 Phone: +1-301-975-8439
Fax: +1-301-975-6238 Fax: +1-301-975-6238
 End of changes. 22 change blocks. 
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