| >>
>>Visit your registry...
>>
>>HKEY_LOCAL_MACHINE\SYSTEM\Current\Services\<devicename>\Parameters\TCPIP\MTU
That registry keyword is only useful in lowering the MTU for TCP/IP. If you
want to lower the MTU size for the entire FDDI interface (regardless of
protocol), you need to add the MaxFrameSize keyword in
...\Services\Defpa?\Parameters\MaxFrameSize
Go under Control Panel\Network Settings, highlight the FDDI adapter, then
select Configure. Once the dialog box pops up, select Help which will bring up
the Help screens for the driver which documents this and other keywords.
- Larry
|
| I looked in the registry and saw that these keys (MTU and MaxFrameSize)
do not exist and if I wish to set them I assume I would need to create
the key.
Is MaxFrameSize the same as MTU? Is the registry keyword case
sensitive I decide to add it?
I am investigating the reason my customer wants to do this. I think
they want to set it to 1500 because that is the Ethernet size and they
exchange some data between FDDI rings using Ethernet. Assuming this is
so, should this be a problem for the customer?
Thanks,
Dick
|
| >> I looked in the registry and saw that these keys (MTU and MaxFrameSize)
>> do not exist and if I wish to set them I assume I would need to create
>> the key.
Yes, that's true. You select Add Value, enter the name, type, and the initial
value in decimal or hex.
>> Is MaxFrameSize the same as MTU?
No. MaxFrameSize is a DEFEA/DEFPA driver-specific key which directly impacts
the maximum frame size value that the driver presents to NDIS during driver
initialization. That's why I mentioned that MaxFrameSize impacts ALL network
protocols running on that driver since it's setting the maximum frame size for
the interface at the NDIS layer.
MTU is a TCP/IP-specific key which is LAN driver independent. It sets the MTU
size at the protocol layer, not the NDIS layer, so you could lower the MTU for
TCP/IP yet allow a different MTU size for NetBEUI, IPX, etc.
>> Is the registry keyword case sensitive I decide to add it?
I believe the answer is yes. I would certainly add the keyword as written.
>> I am investigating the reason my customer wants to do this. I think
>> they want to set it to 1500 because that is the Ethernet size and they
>> exchange some data between FDDI rings using Ethernet. Assuming this is
>> so, should this be a problem for the customer?
Again, if the customer is only using TCP/IP, or only worried about the MTU size
over TCP/IP, use the MTU setting. If they want to lower the MTU size for the
entire FDDI interface, use the MaxFrameSize setting.
To be honest, only in rare cases does the MaxFrameSize or MTU setting need to
be used. Most FDDI-Ethernet bridges support IP fragmentation, so larger than
Ethernet-sized packets destined to the Ethernet network is not a problem. As
for the other protocols, they usually negotiate packet sizes across an
FDDI-Ethernet bridged network so that lowering the packet size at the FDDI
interface is not necessary.
Above all, get your customer configuration working, but let them know the
consequences of these Registry additions.
- Larry
|