> Source: [sk143932](https://support.checkpoint.com/results/sk/sk143932)

# sk143932 - ClusterXL flapping due to "Interface Active Check" problem on the Sync interface

| Property | Value |
|----------|-------|
| Solution ID | sk143932 |
| Date Created | 2019-01-06 |
| Last Modified | 2020-02-03 |
| Technical Level | Advanced |
| Products | Security Gateway, Cloud Firewall |
| Versions | R82.10, R82, R81.20, R82.10, R81.20, R82 |
| OS | Gaia |

## Symptoms

- * ClusterXL is flapping and SNMP alert is showing: cluster member down, Sync interface is down every 'X' amount of times.
* 'kernel: neighbour table overflow' appears repeatedly in /var/log/messages files (as shown in [sk43772](https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solutionid=sk43772))
* Sync interfaces flapping cause all the hosts in the Vlans that configured on this Cluster to re-transmit ARP requests
* Uncheck "cluster synchronization" for services that are not critical (like http, https dns) upon failover in order to reduce the load - doesn't resolve the issue
* Changing CCP mode to broadcast or multicast - doesn't resolve the issue.
* Increasing the size of the RX and TX ring buffer on the sync interface (per [sk42181](https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solutionid=sk42181)) - doesn't resolve the issue

## Cause

A Port Scanner Server that is located in the internal network scans the network from time to time for available IP's, causing ARP flood on the Security Gateway/s.

## Solution

This solution requires authentication. Please log in to view the full solution.

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