|Robert Penz||Aug 18, 2009 11:34 am|
|Sam Varshavchik||Aug 18, 2009 4:29 pm|
|Robert Penz||Aug 19, 2009 12:58 am|
|Sam Varshavchik||Aug 19, 2009 4:02 am|
|Robert Penz||Aug 19, 2009 8:08 am|
|Aidas Kasparas||Aug 19, 2009 11:05 am|
|Malcolm Weir||Aug 19, 2009 12:15 pm|
|Sam Varshavchik||Aug 19, 2009 2:59 pm|
|Alessandro Vesely||Aug 20, 2009 9:45 pm|
|Subject:||Re: [courier-users] Courier-MTA reacts badly if own DNS server goes down|
|From:||Aidas Kasparas (a.ka...@gmc.lt)|
|Date:||Aug 19, 2009 11:05:44 am|
Robert Penz wrote:
I think you misunderstand me. dns using is ok, but it should use also hosts entries for A and PTR records, specially for its own hostname. To be specific I don't care about anything else accept its own hostname. Why does every Linux system have a /etc/hosts? because of the entry for loopback and its own hostname. If you use "ping" or any other program it checks the hosts file before it does a dns query.
I understand your wish, but there are some technical difficulties to fulfill it.
There are two sets of functions for name resolution: (a) gethostbyname(3) / getnameinfo(3) & Co (b) res_query(3) & Co
(a) is simpler to use, takes info account nsswitch.conf and asks all the name services that are configured there -- /etc/hosts, ldap, DNS, etc -- in order they are configured there. But they allow just simple questions: I have host name, what is IP address (and vice versa).
(b) only asks DNS, but allows to ask more complex questions, like what is MX record for name example.com.
ping, telnet and "any other program" have luxury to use (a) set of functions. Therefore, they "consult" /etc/hosts file. Courier, and any other MTA, have to find MX records for other mail servers, TXT records for SPF, and therefore they have to go for (b) set of functions. Code using these functions is already complex. You ask to complicate it further. Using two sets of resolving functions would complicate even more.
All problems, what could be solved by "consulting /etc/hosts", could be solved by configuring DNS servers. And it is you, who is guilty for putting all the eggs into single basket, and as consequence loosing DNS service.
I have not checked other MTAs, if they check /etc/hosts, but I would bet they don't. Most of single threaded IRC servers do not check /etc/hosts too. The reason -- everything is doable using DNS. And DNS service absolutely MUST WORK.
-- Aidas Kasparas IT administrator GM Consult Group, UAB
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