reverse DNS resolution...

Oliver Fromme olli at
Tue Oct 23 10:02:48 PDT 2007

Eric F Crist wrote:
 > As I already stated, if I do a host 172.30.x.x, I get a the correct  
 > reverse resolution.  dig works as well.  What isn't working is the  
 > reverse resolution in certain command outputs, etc.

Note that the DNS tools (host, nslookup, dig) use their
own resolver code, not the one from FreeBSD's libc, like
all other tools.  That might explain the difference.

Make sure that you have configured /etc/nsswitch.conf
and /etc/resolv.conf correctly.  Also note that /etc/hosts
overrides DNS by default.

You can use tcpdump to check if a reverse lookup request
is sent to the DNS server when the failure occurs, and
what the reply looks like.  E.g. let this command run in
one terminal:

# tcpdump -i tun0 -s 1500 -l -n -vvv udp port domain

Add an -i option to specify the interface to listen on,
if you have multiple interfaces (e.g. -i fxp0).

Then run the command (w, irc client, whatever) in another
terminal and watch the tcpdump output.  Oh by the way,
I think the addresses in IRC are resolved by the servers,
not by the clients, so you would have to run the tcpdump
command on the IRC server (if it's an internal one to
which you can login and have root access).

Best regards

Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart

FreeBSD-Dienstleistungen, -Produkte und mehr:

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