Bug#414569: [Pkg-utopia-maintainers] Bug#414569: Reverse lookup for said host is not set up

[Sjoerd Simons]

reassign 414569 nss-mdns
thanks,

On Tue, Mar 13, 2007 at 09:59:31AM +0100, Martin Steigerwald wrote:
> 
> Hello!
> 
> Reverse lookup for said the host in the strace - our ldap server - is not set 
> up.
> 
> ms at mango:~> host 172.21.242.9
> Host 9.242.21.172.in-addr.arpa not found: 3(NXDOMAIN)
> 
> It tells so immediately. 
> 
> To my knowledge there is no strict requirement that an LDAP or any other
> hosts in a local network needs a reverse lookup set up.
> 
> I imagine there may be lots of networks where reverse lookup is not defined 
> for some hosts, my network at home doesn't even have a DNS server.
> 
> At least I do not get whether avahi tries to find out about the same IP 
> address again and again. Since the workstation uses LDAP I think that IP 
> reverse lookup for that IP address is queried for very often. The "strace 
> ssh" case was repeatable after a second. It shouldn't try to find out about 
> that IP address that often IMHO. If it isn't known it should wait some time 
> before it tries again. That would be an avahi-daemon issue.
> 
> Added to that I would be more reluctant to add an option to nsswitch that 
> delays reverse lookups where the DNS server returns not found in a fraction 
> of a second by 5 seconds or more. 

Avahi doesn't query the dns server for the reverse lookup, but uses Multicast
DNS.. Because that's what avahi is, a multicast dns daemon :)..  I'll ask
upstream why avahi doesn't cache negative lookups for some time.. But even if
it did it wouldn't really solve your problem, as the timeout will keep occuring
from time to time.

> Its the postinst script of the package libnss-mdns that does it:

> I cannot remember that it asked me whether I like to do these changes. It 
> maybe tries to do these changes again when the package is updated.

Correct, it configures the system automatically for mdns to work..  

> I recommend that "mdns4_minimal" is added by default - I doesn't create the 
> timeout as I tested today -, but "mdns4" after dns lookup is not without 
> asking the user first. That would be a libnss-mdns issue.

Right, mdns4_minimal only does actual checking for certain names, that's why it
doesn't time-out for you.. It's not actually doing anything.

I'm reassigning this bug to nss-mdns.. I need to discuss with some others what
to do about this.. Your suggestion of not adding the final mdns fallback does
make sense for your network, but it will break some functionality on others..
(Where mdns can actually rev. resolv the ip because the other machine also uses
mdns..)


  Sjoerd
-- 
The truth is rarely pure, and never simple.
		-- Oscar Wilde