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Date:      Thu, 19 Jan 2012 15:36:10 +0100
From:      Damien Fleuriot <ml@my.gd>
To:        freebsd-questions@freebsd.org
Subject:   Re: changed ip-adress, DNS lookups don't work anymore
Message-ID:  <4F182A5A.30202@my.gd>
In-Reply-To: <CAEFCw4u4_ZYX4ekHx_Gm0pxj5M+8jQHjesdd0FoGxNhPRgOp5w@mail.gmail.com>
References:  <CAEFCw4u4_ZYX4ekHx_Gm0pxj5M+8jQHjesdd0FoGxNhPRgOp5w@mail.gmail.com>

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On 1/19/12 3:32 PM, n dhert wrote:
> FreeBSD 8.2. system.
> Gets is TCP/IP parameters (and DNS name-servers IPs) from a DHCP server,
> with a fixed IP address
> (the system always gets the same IP, based on its MAC address as specified
> in the DHCP config file)
> 
> Now I wanted the system to have a different IP address.
> Changed the DHCP server config accordingly.
> Reboot. OK, from  $ ifconfig -a I can see it received the new IP.
> 
> But DNS lookups don't work any longer ..
> $ host xxx.yyy.zzz.com
> ;; connection timed out; no servers could be reached
> 
> The system is behind a firewall, but there are NO errors logged relating
> to the (new) IP address.
> Other FreeBSD-8.2 systems using the same DHCP server, configured in exactly
> the same way, work perfectly well.
> 
> I can SSH to the sytem, but it takes 20 or 30 seconds before the Password:
> prompt appears (normally should
> be immediate)
> Once in the system, starting my alpine mail-client, it takes a minute or so
> to display the messages (normally this should be immediate)
> Also at boot of the system there is wait for a 2,5 minutes somewhere in the
> series of Starting <deamon>.
> Probably these three phenomena have the same cause: DNS lookups don't work
> 
> any idea what can be wrong ??
> I've looked and compared with other systems, can't find it ...
>


First, add "UseDNS no" to either /etc/ssh/sshd_config or
/usr/local/etc/ssh/sshd_config

That'll allow you to log in via SSH without the server performing DNS
lookups, which are rather useless anyway.

Second, you should run "tcpdump" on your DNS host to check if you're
actually receiving requests from your freebsd box.


Also, post your /etc/resolv.conf , "netstat -rn" and "ifconfig"

I'd also be interested in the relevant parts of your firewalling config



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