Bug in Patch MS05-019
From: Brian G. (bgis_at_YAHOO.COM)
Date: Wed, 20 Apr 2005 13:31:44 -0700 To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM
"The issue is a patched server sends out a packet and receives an ICMP Destination Unreachable. Normally the packet would be resent using a smaller size, but the bug causes the ICMP to be ignored and usually the same packet is sent again. The result is that the packet never reaches the destination, and the result of this could cause any number of problems. This caused replication Active Directory replication issues for us as well as Exchange 2003 connectivity issues over the VPN. You will see Event ID's 1232 and 1188 on your domain controllers from source NTDS Replication. You will also see 1726 and 1818 failure codes in Replmon. Article 830746 discusses Event ID's 1232 and 1188 but increasing the replication RPC timeout may not help.
The workaround is to either uninstall the patch or set the MTU size to match your environment. I saw the issue is a total meshed VPN network. All sites are connected via Checkpoint VPN's so we set the MTU size to 1430 so the packets will not get fragmented. 1430 allows enough space for encryption of about 60 bytes so the packet does not go over 1500 and need to be fragmented.
To set MTU size:
Put a registry value HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\(Interface Guid)
Creat DWORD value: MTU with a decimal value of the maximum workable MTU size.
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