Does SCAN redirect to node-IP or node-VIP?

Question

I have a 2 node 11gR2 RAC cluster with both SCAN and node VIPs configured. Users connect to the SCAN address. The SCAN listener then redirects connections to the node listener. Does it redirect to the node listener via the node's address or the node's VIP address?
Here's why I'm asking. I'm trying to troubleshoot a recurring problem where node2's VIPs (scan and node-vip) keep failing over to node1 every few weeks. CRS logs on node1 say that it thinks (incorrectly) that node2 is inaccesible so it failed over both VIPs (scan and node-vip). Within a minute or so however, node1 can see node2 again without anyone intervening.
Node2 however remains up the entire time and is running normally. Neither the node listener, database instance, or ASM instance show any indication of a problem in their logs.
On node2's database instance however, all sessions have dropped even though the instance remained up. If the SCAN listeners redirect directly to node2, I would not expect this to happen and I can pin the problem down to some network component (switch, NIC, etc). If SCAN redirects to the node-VIP then I would expect this and need to troubleshoot why node1 is incorrectly thinking node2 went down.

Answer 1

Chuck1958 wrote:
Users connect to the SCAN address. The SCAN listener then redirects connections to the node listener. Does it redirect to the node listener via the node's address or the node's VIP address?That depends on
a) the service the user requests to be connected to
b) the registered hostnames of that service in the Listener
The SCAN listener is a remote listener, with which local listeners, register. The SCAN listener hands off/redirects connections based on what has been registered with it.
Also, a redirect is done using hostname and not dotted IP. Which means in exceptional circumstances, the client can use a hosts file with all static and virtual hostnames, referring to the same single (static or virtual) IP address.
Irrespective of what the SCAN Listener provides as hostname for the redirect, will in such a case be resolved, by the client, to the same IP address. Useful when troubleshooting, or when dealing with NAT firewalls.