XCLN: Exchange Server Push Notifications Generate ICMP Messages (159302)

SUMMARY

Microsoft Exchange clients that use TCP/IP may generate ICMP "Destination Unreachable, Port Unreachable" error messages in response to push notifications from the Exchange Server computer. These messages are considered normal. A network analyzer tool, such as Microsoft's Network Monitor or Network General's Sniffer, is required to see these errors.

MORE INFORMATION

The Exchange Server computer sends push notifications using datagrams (UDP) to notify Exchange clients of changes in the Inbox, such as the arrival of new mail. After a change occurs in the Inbox, the Exchange Server computer sends the datagrams every 60 seconds. The Exchange Server computer stops sending the push notifications when the Exchange client retrieves the new mail.

If the Exchange client is rebooted without logging out of Exchange, The Exchange Server computer continues sending push notifications because it has no immediate way of knowing that the TCP/IP session is broken and that the client is no longer online. These push notifications are sent to a port where the Exchange client is no longer connected, and in turn generate ICMP "Destination Unreachable, Port Unreachable" responses from the Exchange client. The push notifications continue until the TCP/IP session on the Exchange Server computer terminates due to no response. The push notifications do not affect the notification of new mail for subsequent Exchange logons by the same client.

TCP/IP uses some registry entries to define how long to allow an inactive session to continue. Default time is two hours, which is configurable. Modifying the KeepAlive time is not recommended.

For more information on how the TCP/IP KeepAlive registry entry works, please see the following Microsoft Knowledge Base article:

102973 REG: TCP/IP Transport Entries, PART 1