Communicating over TCP/IP May Fail Due to 802.3 Frame Type (140913)
The information in this article applies to:
- Microsoft Windows NT Workstation 3.5
- Microsoft Windows NT Workstation 3.51
- Microsoft Windows NT Workstation 4.0
- Microsoft Windows NT Server 3.5
- Microsoft Windows NT Server 3.51
- Microsoft Windows NT Server 4.0
This article was previously published under Q140913 SYMPTOMS
A Windows NT TCP/IP node is not be able to communicate to a non Microsoft
based TCP/IP node.
CAUSE
The non Microsoft TCP/IP node is configured to use 802.3 SNAP encoding.
Some devices can be configured to use 802.3 SNAP encoding. By default, the
Microsoft TCP/IP stack transmits packets in DIX Ethernet format.
RESOLUTION
If the node device is using 802.3 SNAP encoding, modify the Windows NT
registry and change the ArpUseEtherSNAP setting to 1 on the Windows NT
system to match the 802.3 SNAP encoding.
Registry path:
This parameter is under the subtree HKEY_LOCAL_MACHINE under the following
subkey:
\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Value (Parameter) Name: ArpUseEtherSNAP
Data Type: REG_DWORD - Boolean
Data Range: 0 or 1 (False or True)
Default: 0 (False)
Description: Setting this parameter to 1 will force TCP/IP to transmit
Ethernet packets using 802.3 SNAP encoding. By default, the stack transmits
packets in DIX Ethernet format. Windows NT always receives both formats.
MORE INFORMATION
In Windows NT 3.1, when TCP/IP is used on an Ethernet network, it will use
only the Ethernet II frame format. It will recognize a SNAP formatted ARP
request, but will respond with an Ethernet II formatted ARP reply in the
hopes that the remote station TCP/IP stack will recognize the frame type
and switch to the Ethernet II frame format.
In Windows NT 3.5, 3.51, and 4.0, there is a registry parameter
(ArpUseEtherSNAP) that instructs TCP/IP to use SNAP on an Ethernet (802.3)
network. With this parameter set, TCP/IP uses SNAP to encapsulate IP, ICMP,
and ARP frames in 802.3 frames. If, however, a SNAP-encapsulated ARP
request is responded to with an Ethernet II format ARP reply, or if a
Ethernet II format ARP request is received, TCP/IP will automatically
switch to using Ethernet II frames on that link.
Modification Type: | Major | Last Reviewed: | 12/5/2003 |
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Keywords: | kbnetwork kbprb KB140913 |
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