Re: 11.2 client and DNS

From: Yong Huang <>
Date: Thu, 24 May 2012 13:29:59 -0700 (PDT)
Message-ID: <>


I think you're talking about several issues at the same time:

(1) A RAC SCAN is not resolved to 3 IP's. Verify with nslookup.

(2) `nslookup <SCAN>' on the client side multiple times does not rotate the IP's. Verify with nslookup.

(3) Pre-11gR2 Oracle client does not round-robin. See section "Problem with pre-11gR2 clients" at

(4) SCAN VIP and its SCAN listener are on different nodes of a RAC database.

The last issue is the most complicated and I was not able to reproduce. See,3
(ignore the issue of netstat showing a "ghost" local address)

Yong Huang

-----Original Message-----

of the 3 DNS servers for this client databases. This caused very long wait times where some people thought the listener was hung and or the databases were down. Listener and databases never were down. They said they were using 3 servers in a round-robin fashion.

They replaced the server and things were fine again. Someone asked what "oracle" did when there was an issue with DNS and all I found so far was this RAC pdf It stated:
Note: If your DNS server does not return a set of 3 IPs as shown in figure 3 or does not round-robin, ask your network administrator to enable such a setup. DNS using a round-robin algorithm on its own does not ensure failover of connections. However, the Oracle Client typically handles this. It is therefore recommended that the minimum version of the client used is the Oracle Database 11g Release 2 client.

It seems to me this should work the same way RAC or not. But some other DBAs said it only works that way for RAC.

Can someone clarify this and can anyone point me to a better document?

Did I miss this in
Oracle(r) Database
Net Services Administrator's Guide
11g Release 2 (11.2)


Received on Thu May 24 2012 - 15:29:59 CDT

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