DNS Server Change

[Chad Brindley]

Hi,

We have 5 HPUX boxes running 11.23 hosting Oracle 9.2 and SAP R3 4.7

I need to change the servers to point at new DNS servers, everything should be configured on the DNS side and I know how to change through SAM to point at different DNS servers but is there anything I should watch out for?

Do I need to shutdown oracle or anything?

Two servers are part of a serviceguard cluster so is there anything I need to be wary of here.

Can the change be made on the fly?

Chad

[Fedon Kadifeli]

Assuming that the new DNS server(s) will respond to the queries with the same information as the old one(s) you need not worry.

Actually you can just edit /etc/resolv.conf using vi.

I always advise you to put very crucial information (such as the names of the servers in the cluster) to the /etc/hosts files, just in case the DNS server(s) become unavailable.

[Peter Godron]

Chad,
ideally I'd shut down any external connections and then change the order of DNS servers via SAM. But it should work on the fly.
Oracle would not have to be shut down.
After a while you can then remove your current active server entry.

[Jannik]

Change the order in the resolv.conf file:
nameserver
nameserver

SG does use it - and the recommended way for SG is to have files first. So change nsswitch.conf:
hosts: files [NOTFOUND=return] dns

And make sure you have all hosts in your /etc/hosts file.

10.0.0.2 server1.company.com server1
10.0.0.3 server2.company.com server2
...

Hope it helps!

[Chad Brindley]

Hi,

I shutdown all external connections and have added the two new DNS servers into /etc/resolv.conf commenting out the old ones for now.

I can no longer use X-windows to logon but can telnet through command prompt. Does it mess up the display variable? if so how to fix?

Chad

[Peter Godron]

Chad,
is your terminal ip known to the DNSs?
nslookup youripaddress

[Fedon Kadifeli]

For the XWindows logon problem. Check the following:

# grep ipnodes /etc/nsswitch.conf
ipnodes: files[NOTFOUND=continue UNAVAIL=continue TRYAGAIN=return] dns

[Chad Brindley]

Hi,

This was what I got.

grep ipnodes /etc/nsswitch.conf
ipnodes: files[NOTFOUND=return UNAVAIL=continue TRYAGAIN=return] files

Could this be a reverse DNS issue with our new DNS servers or is our switching wrong?

I guess it should look at host table first and then if not in there use DNS.

Chad

[Fedon Kadifeli]

I am not sure about this. But, once I had a similar problem and it was caused by a missing ipnodes entry in nsswitch.conf. You can try and see if fixes the problem.

Also, after telneting to the box, check to see if the IP you are trying to connect from can be resolved. Enter

# who am i -R

and look in the string within parentheses.

[rick jones]

Unless things have changed, a process only reads /etc/resolv.conf once - the first time it makes a call such as gethostbyname() or if it is properly up-to-date getaddrinfo(). So, long-lived processes need to be restarted to see changes in /etc/resolv.conf.

You can confirm or deny this with a small test program that makes gethostbyname() calls in a loop with some sleep() in between. Tusc that application, and IIRC you will see it open /etc/resolv.conf only once and not stat() or otherwise check for changes.

[Chad Brindley]

Hi,

I ahve made the DNS server changes direct in resolv.conf commenting out the old DNS servers.

I re-booted the server to make sure there were no processes using the old servers.

If I do an nslookup I get the errors;

*** Can't find server name for address 10.212.16.150: Non-existent domain
*** Can't find server name for address 10.212.16.152: Non-existent domain
*** Default servers are not available
Using /etc/hosts on: covbwdq

I can then not see certain systems for example vax.vaxes.

In nslookup if I then type server 10.212.16.150 to make sure it is using this server and type vax.vaxes it works fine.

Do I have some sort of reverse DNS issue going on here?

Chad

[rick jones]

Yes. While nslookup arguably should not care if there is a PTR record for the IP of the DNS server(s) it is using, it is equally true that any well-configured DNS servers will have PTR records for their IPs. If you get your new DNS servers fixed to have PTR records for their IPs then I suspect all will be well.

Actually, almost all may already be well - gethostbyname and the replacement call your apps should be making - getaddrinfo - do not IIRC care about PTR records for the server's they query. Neither do 'dig' nor 'host' one of which you might want to consider as a replacement for nslookup.