Conference 7.286::fddi

We've been shipping NT 4.0 supported drivers for DEFPA for at 
least six months now.  Can you try using the NDIS3 driver found 
on our v2.81 DEFPA driver kit? You can find it at:

	ftp://ftp.digital.com/pub/DEC/adapters/fddi/defpa/interim
or
	netcad::pcdrivers:[fddi.defpa.interim]


The file you're looking for is FPKIT281.ZIP.

As for your performance problems, could you provide a little more
information? What is the customer using for a bridge? Is is possible
to put an FDDI analyzer on the ring to see if there are packets which
aren't getting through to the ethernet side of the network?

I ask that because it's possible that NDIS isn't properly
negociating a maximum frame size between the server and each client.
While TCP/IP packets can be fragmented, Netbeui packets cannot. Thus
any Netbeui packet greater than the ethernet max of 1500 bytes will
not get sent from the FDDI server, through the bridge, to the other
side.

If this is the case, one solution is to set the maximum frame size
handled by the DEFPA in the server to 1500. This would force the
DEFPA to transmit packets no greater than 1500 bytes. While this 
might help your ethernet clients, it would handcuff the DEFPA when
talking to other FDDI nodes as it would not be able to take
advantage of FDDI's 4500 byte maximum frame size.

As for swapping the DEFPAs with ethernet adapters, that's not a
completely valid test as the customer has removed the FDDI component.
Now if they had swapped the DEFPAs for someone else's FDDI adapters 
and the problem disappeared, that would be another story.


-Devon

    Hi Devon,
    
    Thanks for your quick response. 
    I have already copied the 2.81 kit and will test it at the customers
    site. As for the bridges, they are all DECswitch 900EFs with FW 1.6 or
    1.7. I have already checked the IP Fragmentation switch on them but i
    cannot verify the correct function since i dont have an FDDI analyzer.
    I want to cross check this by disabling large packet sizes in NT.
    i assume this is a registry setting, so do you know where it is or how
    it should look like?
    
    and finally jfyi,
    As for the FDDI to Ethernet swap, since these servers are "production"
    machines the customer HAD to swap them back to ethernet to get them up
    and running for the next day.
    
    cheers
    Robert

The parameter you want to modify is MaxFrameSize. Use the registry
editor to add the parameter to the following subtree:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Defpa?\Parameters

where ? is the instance of the DEFPA adapter in question.

Value Name:  MaxFrameSize
Date Type:   REG_DWORD
Values:      3-4478
Default:     4478

The max FDDI frame size (not including the FDDI frame header or 4-byte
CRC) is 4478 bytes. You'll probably want to lower this to 1500 bytes 
for your experiment.

BTW, should you ever need to do this again and you lose this note, 
simply click on the network icon on the NT Control Panel, then select
Adapters>Properties>Help and you'll get a narrative much like the one 
I've written here.

-Devon

Thanks,

I will check this out at the customer site.

rgds
robert
[Posted by WWW Notes gateway]