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Connectivity issues after the installation of MS05-019 or Server 2003 SP1


Network connectivity between clients and servers may fail after the installation of either security update MS05-019 or Microsoft Windows Server 2003 Service Pack 1 (SP1). Any one or more of the following symptoms may occur:

1. Inability to connect to terminal servers or to file share access.

2. Failure of domain controller replication across WAN links.

3. Microsoft Exchange servers cannot connect to domain controllers.


These issues typically exist where routers and data-link level protocols that have different Maximum Transmission Units (MTUs) are used across the network. This problem occurs because the code incorrectly increments the number of host routes on the computer when the code modifies the MTU size of a host route. The maximum number of host routes is controlled by the Registry Value in MaxIcmpHostRoutes. The default number of host routes is 1,000. Because of the incorrect increment, the number of host routes eventually reaches the maximum value. After the maximum value is reached, the ICMP packets are ignored.


1. Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem.

2. Workground

To work around this problem set the default MTU size to the largest size that the routers can process. The actual MTU value that is required to work around this problem depends on the network configuration. However, an MTU value of 576 should help reduce the effect of the problem because routers on the Internet should be able to handle such packets without fragmentation.

Note: Setting a low default MTU value can slow down the network performance.

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Related Topics

Modify MTU

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