topic Re: DNS issue in Operating System - Linux

DNS issue

iinfi1 — Sun, 22 May 2011 06:27:28 GMT

hi all,

I have a sles 10 system and Oracle BI is installed on the same.
Authentication for Oracle BI users is through windows AD.
when i do a nslookup to the windows AD in our network, this is what I get:
nslookup mic.com

Server: 10.1.1.100
Address: 10.1.1.100#53

Name: mic.com
Address: 10.1.1.110
Name: mic.com
Address: 10.25.100.2
Name: mic.com
Address: 10.1.1.100

one is primary and other two are backup domain controllers:

out of the three, one domain controller is at a remote site and is not accessible from the Oracle BI server.
when i ping mic.com from the Linux BI server I am taken to one of the three Windows DCs alternatively in a round-robin fashion.
i.e
if I ping mic.com I am taken to 10.1.1.110
few seconds later
if I ping mic.com I am taken to 10.25.100.2
few seconds later
if I ping mic.com I am taken to 10.1.1.100

this doesn't happen on windows clients.
so every time a user authenticates he is either taken either of the three IPs. As I said earlier the third backup DC is not accessible from the Oracle BI server resulting in users complaining about failed windows authentication off and on.

Re: DNS issue

Matti_Kurkela — Sun, 22 May 2011 09:24:30 GMT

Please run "man resolv.conf" and look for the "sortlist" option. If it's not supported in SLES 10, too bad.

If Oracle BI uses the standard system library functions for DNS queries (like almost all programs do), adding "sortlist 10.1.0.0/255.255.0.0" to /etc/resolv.conf might help. It should cause the 10.1.*.* addresses to always be given to applications before 10.25.*.* (or any other) addresses associated with the same hostname.

This is just a workaround, though: the real fix would be to make Oracle BI use a smarter DNS lookup algorithm when looking for AD. Unfortunately, this is probably something only Oracle (the company) can do.

MK

Re: DNS issue

iinfi1 — Mon, 23 May 2011 09:37:23 GMT

thank you Matti. i will check this.

Re: DNS issue

Wilfred Chau_1 — Mon, 23 May 2011 17:45:08 GMT

try add this to resolv.conf too
options timeout:1
options attempts:1

The first option tells the resolver to timeout for 1 sec before switching to the second DNS server listed. The second options said only query the same DNS once.

This does not solve your issue but will help you shorten the DNS failover time.