Sounds like its the layer 2 switch problem that is well known. Its a replacement MXE needed as there is no cure for it permanently. There is a command you can run that will overcome it for a temp fix. You can issue the command "period 900,mips_reset" without quotations into vxworks and this will reset the L2 switch every 900 secs. However this interrupts the LAN whilst the reset occours for a couple of seconds. You may have to adjust the timer if its too long.
