You can reduce the network traffic caused by replication by configuring the ReplicationGovernor on each BDC (Backup Domain Controller) if the PDC (Primary Domain Controller) is running NT 3.5 or later.

The ReplicationGovernor defines the size of the data transferred on each call to the PDC and the frequency of the calls. When you adjusting the ReplicationGovernor:

It reduces the size of the buffer used on each call from the BDC to the PDC,
so that a single call does not occupy the WAN link for too long.

It causes NetLogon to hibernate between calls, so other applications can access the WAN link.

Edit:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters

From the Edit menu, Add Value as a type REG_DWORD. ReplicationGovernor is a percentage (0 - 100) of the 128KB buffer size and that same percentage of WAN usage. The deafult is 100%.

If you set ReplicationGovernor to 50, synchronization will use a 64KB buffer (128 x 0.50) and will only have an call on the net for a maximum of 50 percent of the time.

If you set ReplicationGovernor too low, synchronization may never complete.