The network tiebreaker provides an alternative to the disk and operator-based tie breakers. It uses an external IP (network instance) to resolve a tie situation.
- A shared disk to be used as a disk tiebreaker is not available.
- The ability to communicate with instances outside the cluster has the highest priority.
Use the network tiebreaker only for domains where all nodes are in the same IP sub net. Having the nodes in different IP sub nets makes it more likely that both nodes can ping the network tiebreaker, while they cannot communicate with each other. Additionally, the default gateway IP address must not be used if it is virtualized by the network infrastructure. Choose an IP address, which can be reached only through a single path from each node in the domain.
In the default setting, the network tiebreaker makes two attempts to ping the network tie breaker IP address. This default number of pings can be too low in virtualized environments or environments with a slow or unreliable network connection. For those environments, you can increase the number of pings that are executed by the network tie breaker up to a maximum of nine. Then, you can ensure a correct result of the tie breaker reserve operation.
Requirements for the network tiebreaker
To ensure the network tiebreaker function, the external IP instance must be reachable from all nodes within the highly available cluster. Also, the external IP instance must be able to reply to ICMP echo requests (ping). If you install a firewall rule, which blocks ICMP traffic between the cluster nodes and the external IP instance, the network tiebreaker does not work. In this situation, the cluster nodes might not communicate to their peers (cluster split), but both sub clusters are able to reach the external IP instance. Usually, IP ensures that if both sub clusters can reach the external gateway, they are also able to communicate with their peers. If this rule cannot be ensured, for example due to firewall settings, you cannot use the network tiebreaker.
|Network-based tiebreaker||Disk-based tiebreaker|