I have a straaaaange problem that I'm stuck with for a while now.
I'm running Red Hat ELS 5.6 and have four network interfaces configured on this machine.
All are using privet IP addresses but only one (eth0) has a NATed firewall in front of it that is begin used to access the "outside" others are used for access privet vlans.

99% of time everything is working well, but sometimes randomly I get a situation when UDP traffic is hitting the server from the outside (let say from 88.88.88.88) and server should respond to it, but instead it is sending ARP broadcast from eth3 asking who is 88.88.88.88 with source IP of eth0. That's how UDP communication fails.
eth3 has access only to one non-routable vlan that should never see anything other than it's privet /24.

The strange thing is that all TCP traffic is working fine and only UDP communication is broken..

I can fix it by simply restarting networks interfaces.

Does anyone has any idea what is going on?
Have anyone see something like that before?

This has happened to me before on a Linux RH box before.

Hi..

Can you explain little more about which application is running on this box & from outside IP address what it trying to access.Please also share the logs if possibel.