在两节点rac中，见到一些环境中会使用交叉线直连两数据库节点作为心跳线，oracle 对此解释为：

s crossover cable supported as an interconnect with RAC on any platform ?

NO. CROSS OVER CABLES ARE NOT SUPPORTED. The requirement is to use a switch: 

Detailed Reasons:

1) cross-cabling limits the expansion of RAC to two nodes 

2) cross-cabling is unstable:

a) Some NIC cards do not work properly with it. They are not able to negotiate the DTE/DCE clocking, and will thus not function. These NICS were made cheaper by assuming that the switch was going to have the clock. Unfortunately there is no way to know which NICs do not have that clock.

b) Media sense behaviour on various OS's (most notably Windows) will bring a NIC down when a cable is disconnected. Either of these issues can lead to cluster instability and lead to ORA-29740 errors (node evictions).

Due to the benefits and stability provided by a switch, and their afforability ($200 for a simple 16 port GigE switch), and the expense and time related to dealing with issues when one does not exist, this is the only supported configuration.

From a purely technology point of view Oracle does not care if the customer uses cross over cable or router or switches to deliver a message. However, we know from experience that a lot of adapters misbehave when used in a crossover configuration and cause a lot of problems for RAC. Hence we have stated on certify that we do not support crossover cables to avoid false bugs and finger pointing amongst the various parties: Oracle, Hardware vendors, Os vendors etc...


由此可见，oracle并不支持使用交叉线，必须使用交换机，否则极有可能引发rac的不稳定。