Welcome back to our videocasts — this is the last video in the series about Oracle RAC Virtual IP’s. I strongly suggest to watch the two previous videos:
I’m writing this post sitting in Vancouver airport but I won’t get into details of my travel complications here, I think it deserves a separate post as it makes a good point for DR plans. :)
What we are looking at during this videocast is how to troubleshoot the connectivity issues that can be caused by VIP’s in Oracle RAC environment and how to diagnose cryptic Oracle error messages using SQL*Net tracing facility on the client side.
We first look at the typical error message “
ORA-12545: Connect failed because target host or object does not exist” and how it leads to the IP alias resolution problem that, at first, seems to be easily fixed by changing IP aliases in the connection descriptor to the numerical IP addresses. Then we find out that it’s not enough with Oracle RAC and server-side connection load balancing can still cause you some grief.
Next, we use SQL*Net client tracing facility and find out where the IP alias resolution happens for addresses in case of connections redirected by a listener to a remote instance — it’s on the client side! Finally, we see how to fix intermittent ORA-12545 errors and understand why Oracle keeps insisting on adding VIP aliases in your DNS and also find out the reliable method of avoiding IP aliases resolution all together by changing server-side listener configuration to use numeric IP addresses instead of VIP aliases.
As usual all comments are welcome.