DOCUMENT:Q99932  30-JUL-2001  [lanman]
TITLE   :IP Fragment Reassembly Bug Identified and Corrected
PRODUCT :Microsoft LAN Manager
PROD/VER:
OPER/SYS:
KEYWORDS:

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SYMPTOMS
========


Dropped connections over wide-area networks that do information packet (IP)
fragmentation using Microsoft TCP/IP for OS/2 or MS-DOS.

CAUSE
=====

Many wide-area networks such as the Internet have links that don't support
full-sized Ethernet or token ring frames. Routers that send packets over these
links are forced to break them up into fragments at the IP layer. Each fragment
of a given packet is labeled with a fragment ID# so that they can be reassembled
into one packet by the IP layer of the destination machine.

LAN Manager TCP/IP machines reassemble packets into control blocks (CBs). Once
the first fragment of a packet is received, a control block is allocated for
reassembling that packet. If all the fragments composing that packet are not
received within a time-out period, the fragments in the CB should be discarded,
and the CB returned to the free list for future use. LAN Manager versions up to
and including 2.2 had problems:

 - allocating CBs at system initialization

 - timing out CBs

 - sending ICMP "time exceeded" messages back to the originating host

RESOLUTION
==========

Microsoft has confirmed this to be a problem in LAN Manager version 2.1, 2.1a
and 2.2. This problem was corrected in patch 2.2B for LAN Manager. For
information on obtaining this update, query on the following word in the
Microsoft Knowledge Base:

   " LMPATCH" (without the quotation marks)

STATUS
======

Resolved.

Additional query words: 2.20 2.2 re-assembly Internet

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Keywords          :  

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