On 06/15/2010 05:06 PM, Dag Wieers wrote:
Hi,
We have a strange problem that I never experienced before and cannot
explain, but doesn't seem to be the right behavior nevertheless.
When you resolve a hostname on RHEL5 (RHEL4 is affected too) that is
in /etc/hosts, libresolv performs a DNS lookup. If your DNS is
unavailable for whatever reason, it takes a long timeout for DNS
before it returns the answer from /etc/hosts...
Interesting!
I have found a few things:
0. This is obviously caused by gethostbyname2() call
1. The DNS queries are IPv6 (AAAA record) queries only.
2. 'ping <hostname-that-is-in-/etc/hosts>' doesn't trigger a DNS query,
while 'getent hosts' does.
3. If /etc/hosts has both IPv4 and IPv6 addresses, no DNS queries are
sent by 'getent hosts'
This led me to the conclusion, that libc/libnss tries to get both IPv4
and IPv6 addresses.
Ping command probably tells gethostbyname2() that it wants only IPv4
command, getent doesn't.
I hope it helps :)
Oren
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