Public bug reported:
When attempting to resolve a DNS name abstracted via a DNAME record (see
RFC 2672), glibc's stub resolver:
(1) logs, via syslog, a debug message:
$ grep DNAME /var/log/auth.log
Apr 20 12:43:38 callisto alpine: gethostby*.getanswer: asked for
"1.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.2.0.0.0.d.1.1.0.8.4.3.0.1.0.a.2.ip6.arpa IN
PTR", got type "DNAME"
(2) ignores the DNAME record;
(3) falls back to the synthesised CNAME record inserted by my BIND 9
recursive resolver.
RFC 2672 states that a DNS server SHOULD synthesise CNAME records where
a DNAME exists in response to "DNS clients sending Extended DNS [EDNS0]
queries with Version 0 or non-extended queries", which "are presumed not
to understand the semantics of the DNAME record", so step (3) above is
valid in the interim until full DNAME support is implemented in glibc.
However in this case the debug message is irrelevant, and as DNAME
records become more widespread will result in needless log spam (e.g.
Cambridge University is soon to roll out DNAME records for reverse DNS).
Suggestion: only log a debug message if the answer contains a DNAME
record but no CNAME record (i.e. the DNS server has not synthesised a
CNAME record). Alternatively, skip the debug message entirely for DNAME
records.
The relevant code is around glibc-2.9/resolv/gethnamaddr.c:342 and
glibc-2.9/resolv/nss_dns/dns-host.c (2.9-4ubuntu6).
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
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glibc does not understand DNAME (RFC 2672) DNS records
https://bugs.launchpad.net/bugs/364094
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