New Windows NT TCP/IP Registry Parameter: ArpTRSingleRoute

• Microsoft Windows NT Workstation version 3.51
• Microsoft Windows NT Server version 3.51

SUMMARY

A new, configurable TCP/IP parameter has been added to the Windows NT Registry. In order to use the new parameter, you must obtain a new Tcpip.sys driver. This driver will be released in Service Pack 5, but can be obtained in the meantime by contacting Microsoft Product Support.

The parameter is described below:

   ArpTRSingleRoute
   Key: Tcpip\Parameters
   Value Type: REG_DWORD - Boolean
   Valid Range: 0,1 (False or True)
   Default: 0 (False)
   Description: Setting this parameter to 1 causes ARP broadcasts that are
   source-routed (Token Ring) to be sent as single-route broadcasts instead
   of all-routes broadcasts.

MORE INFORMATION

In a Token Ring network, when an all-routes broadcast is sent, a copy of the broadcast will be delivered to each of the other rings by each available path. This will generally result in multiple copies being delivered to a given ring. A system responding to the broadcast will respond to each of the packets it receives, and the routing information added to each response will cause it to follow the same route back to the original broadcaster, who will receive multiple responses, each via a different route. The broadcaster is then free to choose which route to use for future communications. Most implementations choose the first response.

When a single-route broadcast is sent, the source routing bridges will only deliver one copy of the broadcast to each of the other rings. The broadcaster will only receive a single response, and it will use the route contained in the response for future communications.

ARP is the protocol used by TCP/IP to map an IP address to a hardware address.

By default, Windows NT TCP/IP tries ARPs in the following sequence when attempting to locate an IP address on a Token Ring network:

1. Broadcast ARP, not source routed.

Adding the ArpTRSingleRoute Registry parameter and setting it to "1" will cause the second and fourth ARPs to be single-route broadcasts, instead of all-routes broadcasts.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.51. This problem was corrected in the latest Windows NT 3.51 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K