DOCUMENT:Q159302  12-APR-1999  [exchange]
TITLE   :XCLN: Exchange Server Push Notifications Generate ICMP Messages
PRODUCT :Microsoft Exchange
PROD/VER:WINDOWS:4.0
OPER/SYS:
KEYWORDS:kbnetwork

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Exchange MS-DOS client, version 4.0 
 - Microsoft Exchange Windows 3.x client, version 4.0 
 - Microsoft Exchange Windows NT client, version 4.0 
 - Microsoft Exchange Windows 95/98 client, version 4.0 
 - Microsoft Exchange Macintosh client, version 4.0 
-------------------------------------------------------------------------------

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:

   Q102973 REG: TCP/IP Transport Entries, PART 1


Additional query words:

======================================================================
Keywords          : kbnetwork 
Technology        : kbHWMAC kbOSMAC kbExchangeSearch kbExchange400 kbExchangeClientSearch kbZNotKeyword kbZNotKeyword2 kbZNotKeyword3 kbExchange400DOS kbExchange400Mac kbExchange400NT kbExchange400Win95
Version           : WINDOWS:4.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1999.