[HPADM] Re:(SUMMARY): new DNS server - entry on resolv.conf - any services needs to be stopped and restarted???
From: Balaji Nathan (balajinathan2003_at_yahoo.com)
Date: 09/11/03
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Date: Thu, 11 Sep 2003 12:53:25 -0700 (PDT) To: hpux-admin@dutchworks.nl
Thanks for all who replied. Sundar, Tom,Bill and Stuart gave some valid information.
As soon as my old dns server was out of production, I deleted the entry in the /etc/resolv.conf file, (the old dns ip address).
As Sundar and Tom mentioned, you HAVE to remove the old dns entry or move the new dns server entry above the old dns server entry, in the resolv.conf file, otherwise you will have problem.
Reply from Sundar:
The resolver (DNS client) doesnt use any daemons. So you can just update the /etc/resolv.conf file. Dont follow what has Stuart mentioned :-), DONT add both the IP addresses to ur /etc/resolv.conf, since most likely your old DNS server will no longer be available in the network and thus if u have entry for the older server in the /etc/resolv.conf, then you may face delay while name resolution and thus ur clients telnet/ftp session may take longer to connect to ur server.
Thanks, Sundar.
Reply from Tom Myers:
The /etc/resolv.conf file is dynamic. You can update it at any time and the changes will be recognized the next time a DNS query is made. I know this sound inefficient but if the file is being read often, it will tend to stay in the filesystem cache in RAM so accessing it stays pretty fast. One thing to remember when the "old" DNS server is shutdown. There is a timeout associated with attempting to access each "nameserver" entry in the /etc/resolv.conf file. If the first one is down, you will suffer that timeout on *EVERY* new DNS query. This means that you will want to remove that nameserver entry from your files as soon as the server is shutdown. In fact, you probably want to move the "new" server to the top of the list as soon as your DNS admins say it's stable and ready for production. Then you can delete the old server at your leisure.
Cheers, Tom
Reply from Bill Hassel:
No. /etc/resolv.conf is a realtime file that is consulted for every DNS server query.
However, do not change /etc/resolv/conf until you have tested the new server with
nslookup. To do this, use:
nslookup some-name new-DNS-server
This tells nslookup to NOT use resolv.conf but to query the new-DNS-server. You should use
the new-DNS-server's IP address since nslookup will convert the new-DNS-server from a name
to an IP address based on resolv.conf and the old DNS server may not have an entry for the
new DNS server (a common mistake).
Also, read the man page for switch (man switch) that describes the /etc/nsswitch.conf file.
This is a critical file and if it is missing, then your DNS server must *never* go down or your
HP-UX box will be unable to connect to any machines by name. There aer sample nsswitch
files in /etc/nsswitch.* but I prefer keeping a small /etc/hosts file with the most important
machine names and setup nsswitch.conf with a DNS rule that says: look in /etc/hosts first,
then query the nameserver. That way, loss of the nameserver (a real possibility when using
a PC as a nameserver) will not cripple your HP-UX box. The entry would look like:
hosts: files [NOTFOUND=continue UNAVAIL=continue TRYAGAIN=continue] dns
and the above entry is all one line. /etc/hosts is an excellent way to get a new hostname
working before the DNS admins can add it to your new DNS server. Once it is working in
the DNS server, you can remove it from /etc/hosts. But I would always leave critical production
hostnames in /etc/hosts just in case your DNS server stops responding.
Bill
Original Question:
Do I need to restart any services /daemons after adding the new dnsserver.
(I am going to add the new dns server as a second dns entry in the resolv.conf file)
Balaji Nathan <balajinathan2003@yahoo.com> wrote:
Hi admins,
All my UNIX servers (K,D, L & N) are configured to use NT DNS server as the primary DNS server.
On each servers, in the /etc/resolv.conf file, I have an entry for the domain name and the
DNS (NT) server name and ip address.
Now the issue is,
my NT admins are going to replace the the old DNS server with the new server.
(with different name and ip address).
Can I jut go ahead and replace the resolv.conf with the new DNS name and ip address, or is anything more I have to do?
Please help.
Regards,
Balaji.
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