156-315.81.20 ClusterXL and VRRP High Availability Practice Question
A security administrator is troubleshooting a ClusterXL High Availability cluster where the standby member repeatedly fails to synchronize its kernel tables. The administrator suspects that the synchronization network is being blocked. Which interface type must be allowed to pass ClusterXL synchronization traffic for the cluster to function correctly?
⚠ Common exam trap
Test-takers frequently confuse the management interface with the synchronization interface, since both are used for inter-member communication but only one carries kernel table updates.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The dedicated synchronization interface configured in the cluster topology.
ClusterXL synchronization traffic must flow over the dedicated synchronization interface that is configured in the cluster topology. This interface is used exclusively for state updates between members. If a rule or routing issue blocks this interface, the standby member cannot stay synchronized. The other interfaces serve different purposes and do not carry sync traffic, so they are not the required path.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The external interface facing the Internet.
Why it's wrong here
The external interface handles production traffic entering and leaving the security gateway. It is not used for ClusterXL synchronization. Allowing sync traffic on the external interface would be a security risk and is not how the cluster is designed. Blocking it would not cause sync failures because synchronization does not traverse that interface.
- ✗
The loopback interface of each cluster member.
Why it's wrong here
The loopback interface is a logical interface used for internal communication on the same member. It does not carry traffic between cluster members. ClusterXL synchronization requires a physical or VLAN interface that connects the members. Therefore, the loopback interface is irrelevant to synchronization and cannot be the cause of the described problem.
- ✗
The management interface used for SmartConsole connections.
Why it's wrong here
The management interface carries administrative traffic such as SmartConsole sessions, policy installation, and logging. ClusterXL synchronization uses a dedicated sync interface, not the management interface. Blocking or allowing management traffic has no effect on kernel table synchronization. Therefore, this interface is not the one that must be permitted for sync traffic.
- ✓
The dedicated synchronization interface configured in the cluster topology.
Why this is correct
ClusterXL synchronization relies on a dedicated sync interface to exchange kernel table updates between members. This interface is defined in the cluster object topology and must be reachable and permitted by the security policy. If it is blocked or misconfigured, the standby member cannot receive state updates, leading to synchronization failures and an out-of-sync state.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
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