kernel arp log message

[Muhammad Reza]

hi, i have a problem in a FreeBSD server,
Kernel message show this message;
arp: [ip redhat firewall gateway] moved from [1st nic redhat firewall gateway]  to [2nd redhat firewall gateway] on
fxp0
arp: [ip redhat firewall gateway] moved from [2nd nic redhat firewall gateway]  to [1st redhat firewall gateway] on
fxp0

message show, every 30 minutes, but varies...

any ideas???

regards,

reza