How do I add DHCP Option 35 to an XP workstation?

[wchull]

It has been suggested that we set Option 35 (ARP Cache Timeout) in DHCP for all clients to reduce unnecessary network traffic. Although we set the option to 8 hours, the clients don't automatically get this option. From what I have been able to get off of Microsoft to get the client to accept the option I must add a new option key to the XP registry in HKLM\SYSTEM\CurrentControlSet\Services\Dhcp\Parameters\Options\Option#
Where Option# is the number of option you wish to add. Although Microsoft's KB312468 does a good job of explaining how this key is setup one of the values in the key (i.e. RegLocation) is suppose to reference where in another key, the actual data is to be stored. This is where I'm having trouble. Does anyone know where this Arp Cache timeout value is supposed to be stored and what the value name is?

 

[brianinms]

Are you experiencing some sort of network issue and you are trying to use this to correct it?

 

[wchull]

We are not trying to solve a specific issue. What we have been told is that, by default, XP workstations send out ARP requests every few minites and in a stable environment where the client has a long DHCP lease, ARP'ing that frequently is a waste of network resources. What we were told is that we should set the ARP Cache Timeout to 8 hours. Although you can set the option in DHCP, we noticed that the client was not getting the Option 35 record from DHCP.

 

[brianinms]

I disagree with whoever told you that. In a well designed network, arp traffic will be so minimal that you wont even notice it.

 

[chipk]

Ditto. If you have a slow networks, the reason is not ARP traffic.

 

[Hondy]

You could use Wireshark to view the amount of ARP traffic.

Do a capture, then got to "Statistics" then "Protocol Heirarchy" and you can see the percentage of ARP traffic amongst other things.

Obviously the capture needs to be in an area that sees all the traffic so a switch is no good unless you mirror the ports.

 

[wchull]

Interestingly enough, the reason why we were considering an implementation of Option 35 was a class we had on WireShark. The instructor that was teaching the class was an expert on WireShark and he suggested the change. Apparently, what he didn't know was that Windows XP workstations, by default, won't automatically get option 35 records, you have to configure the machine to do so. So far, however, nobody has been able to explain exactly what to do to configure XP correctly so it will work. In the end I think that we came to the conclusion that we weren't experiencing a problem to begin with and even if we could configure XP for option 35 the benefit wasn't worth the effort.