computer to "smart device" - subnet question

[Jim Cornette]

Lai Zit Seng wrote:
> On Sat, 28 May 2005, Jim Cornette wrote:
> 
>> Setting the netmask for the computer to 255.255.0.0 allows 
>> communication between a computer with addresses in the 192.168.127.x 
>> and with devices in the 192.168.2xx.x range. The problem I am 
>> experiencing is intermittent dropout of "smart devices" that also have 
>> settings for masking and are set to 192.168.127.xx with a mask of 
>> 255.255.255.0. The computer ethernet address is set to 192.168.217.14.
> 
> 
> If the netmask is wrong on those smart devices, they will need to route 
> through their default gateway to return traffic to you.
> 
> That said, I've seen (and it is possible for these smart devices you're 
> referring to) to cache the IP/ARP mapping seen from the first packets 
> that your computer sends to the smart devices. That would explain why 
> this appears to work. But ARP cache entries will expire. When they are 
> gone, the smart devices will try to send the packet according to normal 
> IP routing rules: i.e. if not in the same subnet, must route through 
> default gateway. If you do not have a default gateway for them, the 
> packet is lost.


This seems to describe the problem encountered. I believe a default 
gateway is specified, but there is no gateway available with these smart 
devices.

> 
>> Anyway, could the intermittent dropout with communication be caused by 
>> the masking on the smart device not ranging with the IP of the 
>> computer or would the broader setting for the computer be enough to 
>> not cause a loss of connectivity.
> 
> 
> You should really try to get the netmask set correctly. You cannot 
> depend on a "netmask trick" done on just one end to make it work 
> reliably for both ends of a communication.


I'll see what setting the smart device masking to the wider setting to 
see if the dropouts cease.

Thanks for the answer and Scott for his answer as well.

Jim

> 
> Regards,
> 
> .lzs
> -- 
> http://zitseng.com/
> 


-- 
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