DOCUMENT:Q149270 09-AUG-2001 [winnt] TITLE :How Routers Handle IPX Type 20 NetBIOS Packets PRODUCT :Microsoft Windows NT PROD/VER:3.1 3.5 3.51 4.0 OPER/SYS: KEYWORDS:kbnetwork ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Server version 3.1 - Microsoft Windows NT Workstation version 3.1 - Microsoft Windows NT Advanced Server, version 3.1 - Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 - Microsoft Windows NT Server versions 3.5, 3.51, 4.0 - Microsoft Windows 95 ------------------------------------------------------------------------------- SUMMARY ======= NetBIOS provides session-layer services like packet assembly-disassembly and named addressing for Microsoft's NWLink protocol. NetBIOS, like SPX, also provides guaranteed packet delivery and packet sequencing on the Transport layer. For NetBIOS to operate within an NWLink environment, routers must be able to propagate NetBIOS packets across the network. This is done by defining a specific IPX packet for NetBIOS. Since IPX is a derivative of XNS's IDP protocol, it follows the assigned packet types given by Xerox as shown below: Protocol Packet type (hex) ------------------------------------------ Unknown 00 Routing information 01 Echo 02 Error 03 Packet exchange protocol (PEP) 04 Sequence packet exchange (SPX) 05 Experimental 10 NetWare core protocol 11 NetBIOS 14 Packet type 20 (0x14) identifies a NetBIOS packet and is designated as a propagated packet. The Destination Node field in the IPX header is set to 0xFFFFFFFFFFFF. When this packet is received by a router, the router checks the IPX header Packet Type field. If the Packet Type is 20 (0x14), the router examines the Transport Control field. If the Transport Control field is more than 8, the router will discard the packet. (A type 20 packet is propagated over a maximum of 8 networks.) The router then compares the value in the Network Number field with the network number of the segment it received the packet from. If these match, the router discards the packet to prevent it from being sent over the same segment twice. The router then puts the network number of the segment it received the packet from in the next available Network Number field and increments the Transport Control field before broadcasting the packet to all directly connected network segments not represented in the Network Number fields. Additional query words: IPX NWLINK TYPE 20 ROUTER ROUTING ntfaqmax ====================================================================== Keywords : kbnetwork Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTW310 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS310 kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNTS351search kbWinNTS350search kbWinNTS310search kbWin95search kbWinNT310Search kbWinNTW310Search kbZNotKeyword3 Version : 3.1 3.5 3.51 4.0 ============================================================================= 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 2001.